Digitized  by  the  Internet  Archive 

in  2007  with  funding  from 

IVIicrosoft  Corporation 


http://www.archive.org/details/chemistryinorganOObloxiala 


i 


CHEMISTRY 


INORGANIC  AND   ORGANIC 


r- 


CHEMISTRY 


INORGANIC  AND  ORGANIC 


WITH  EXPEKIMENTS 


/ 


CHARLES  LOUDON  BLOXAM 

PKOFESSOB  OF  CHEMISTRY  IS  KING'S  COLLEGE,  LONDON  ;    IN  THE  DBPARTMENT  OP 

ARTILLERY  STDDIES,  WOOLWICH  ;   AND  FOKMEKLY  IN  THE 

ROYAL  MIUTARY  ACADEMY,  WOOLWICH 


Fl  FTH     EDITION 


LONDON 

J.   &  A.   CHURCHILL 

11    NEW    BURLINGTON    STREET 


1883 


EXTRACTS 


PKEFACE   TO   THE   FIRST   EDITION. 


This  work  is  designed  to  give  a  clear  and  simple  description  of 
the  elements  and  their  principal  compounds,  and  of  the  chemical 
principles  involved  in  some  of  the  most  important  branches  of 
manufacture.  Keeping  this  in  view,  I  have,  employed  as  few 
technical  terms  as  possible,  especially  at  the  commencement,  so 
that  the  student  may  glide  into  Chemistry  without  having  first 
to  toil  through  a  difficult  chapter  on  the  terminology  of  the 
science,  which  he  can  never  appreciate  until  he  has  become 
acquainted  with  the  examples  which  serve  to  illustrate  its  appli- 
cation. 

Convinced,  by  experience,  of  the  great  assistance  afforded  to 
the  learner  by  referring  him  to  a  simple  illustrative  experiment, 
I  have  introduced,  generally  in  smaller  type,  a  description,  and 
in  most  cases  a  wood  engraving,  of  the  experiments  which  I 
have  found  most  useful  in  illustrating  lectures,  hoping  that  these 
may  prove  of  service  in  fixing  the  attention  of  the  student,  and 
may  assist  those  who  are  desirous  of  performing  such  experiments 
for  their  own  instruction,  or  for  that  of  a  class. 

In  general,  English  weights  and  measures,  and  Fahrenheit  ther- 
inometric  degrees,  have  been  employed,  as  conveying  more  clearly 
to  the  beginner  the  absolute  values  expressed,  since  the  mental 
effort  of  converting  what  must  still  be  called  the  Continental 
systems,  slight  though  it  be,  might  have  the  effect  of  diverting 
the  attention  of  the  reader  from  the  chemical  question  under 
consideration.  The  various  calculations  have  been  conducted  in 
the  simplest   arithmetical   form,  because   the   more    compendious 


VI  PREFACE. 

algebraical  expressions  are  not  so  generally  intelligible,  and  when 
the  principle  is  once  understood,  a  general  algebraical  formula  for 
the  calculation  is  easily  constructed  by  the  learner. 

The  special  attention  devoted  to  Metallurgy  and  some  other 
branches  of  Applied  Chemistry,  will  render  the  work  useful  to 
those  who  are  being  educated  for  employment  in  manufacture. 

The  military  student  will  find  more  than  the  usual  space  allotted 
to  the  Chemistry  of  the  various  substances  employed  in  warlike 
stores. 

The  attention  of  the  student  is  called  to  the  Table  of  Contents, 
which  has  been  drawn  up  to  serve  the  purpose  of  an  abstract,  by 
which  he  may  examine  himself  upon  each  paragraph  of  the  book. 
The  Index  is  also  a  dictionary  of  the  most  important  formulse,  in 
which  either  the  name  of  a  compound  may  be  referred  to,  in  order 
to  find  its  formula,  or  the  formula  may  be  sought  when  it  is 
desired  to  ascertain  the  compound  to  which  it  belongs. 


The  Fifth  Edition  has  been  carefully  revised,  and  some  altera- 
tions have  been  made  in  the  theoretical  portion,  to  bring  it  into 
harmony  with  modern  views. 

The  Table  of  Atomic  Weights  (at  page  xxiv)  has  been  arranged 
so  as  to  indicate  the  quantivalence  of  the  elementary  bodies. 

King's  Collegk,  Lonoox, 
Afarch  1883. 

i 

*^*  In  the  following  pages,  the  smaller  type  contains  not  only 
the  descriptions  of  experiments,  but  all  such  matter  as  would  be 
of  less  importance  to  a  student  desiring  only  a  general  knowledge 
of  the  subject  without  going  into  details. 


TABLE    OF    CONTENTS. 


Paragraph 

Introduction. — Definitions,  Molecules,  Atoms,  Law  of  Avogadro,  Mole- 
cular and  atomic  weights,       ......  1 

Enumeration  and  classification  of  elements,  with  their  symbols,  use  of 
symbols  and  equations,   chemical  attraction,  combination,  and 
decomposition,        .......  2 

Classification  of  compounds  into  oi^anic  and  inorganic,  .  .  3 

Chemistry  of  the  Non-metallic  Elements  and  their  Compounds. 
Water — Analysis  of  water  by  the  galvanic   battery  ;  construction  of 

Grove's  battery,  .  .  .  .  .  .  .4 

Electrolysis y  electro-positive  and  electro-negative  elements,     .  .  5 

Relative  volumes  of  hydrogen  and  oxygen  in  water  ;  diff'erence  in 

application  of  electricity  according  to  quantity  and  tension,     .  6 

Decomposition  of  steam  into  detonating  gas  by  heat  and  electric 

sparks,      ........  7 

Disengagement  of  hydrogen  from  water  by  metals,  .  .  8 

Definition   of  an  alkali  ;    definition   of  chemical   equivalent  of  a 
metal  J-  action  of  potassium  and  sodium  on  water  ;  classification 
of  metals  according  to  their  action  upon  water,  .  .  9 

Hydrogen. — Preparation  of  hydrogen  by  action  of  red  hot  iron  upon 

steam;  by  action  of  zinc  or  iron  upon  diluted  sulphuric  acid,  .         10 

Physical  properties  of  hydrogen ;  its  value  as  a  tlieoretical   unit  of 

volume  ;  illustrations  of  its  extreme  lightness,       .  .  .  11-12 

Diffusihility  of  gases  defined  and  illustrated  ;  separation  of  hydrogen 

and  oxygen  by  atTnolysis ;  law  of  the  velocities  of  diffusion,  .         13 

Chemical  properties  of  hydrogen ;  character  of  its  flame,      .  .         14 

Explosive  mixtures  of  hydrogen  with  air  and  oxygen,  .  .         15 

Oxygen. — Its  occurrence  in  nature,  .....         16 

Physical  properties  of  oxygen.     Specific  gravity  of  gases  defined,     .         17 
Chemical  properties  of  oxygen.     Combustion,  .  .  .18 

Relations  of  oxygen  to  phosphorus  ;  effects  of  heat  and  minute  divi- 
sion upon  chemical  attraction  ;  nature  of  acids  ;  anhydrides,  19 
Relations  of  oxygen  to  sulphur,          .             .             .             .             .20 

Relations  of  oxygen  to  carbon,  .  .  .  .  .21 

Etymology  of  oxygen.     Definition  of  an  acid,  .  .  .22 

Relations  of  oxygen  to  the  metals  ;  sodium  and  oxygen,      .  .         23 

Relations  of  oxygen  to  zinc  ;  definition  of  base,  salt,  .  .         24 

Relations  of  oxygen  to  iron ;  naming  oxides  to  indicate  their  com- 
position ;  definition  of  a  metal,    .  .  .  .  .25 

Indifferent  oxides,       .......         26 

Preparation  of  oxygen  from  atmospheric  air,  .  .  .27 

„  „  manganese  dioxide,        .  .  .28 

Preparation  of  oxygen  from  potassium  chlorate  ;  calculation  of  the 

weight  of  a  given  volume  of  gas,    .  .  .  .  .29 


VIU 


CONTENTS. 


AVater. — Synthesis  of  water  from  its  elements,  . 

Explosion  of  hydrogen  and  oxygen  in  the  eudiometer, 
Eudiometric  analysis  of  air, 
Synthesis  of  vapour  of  water,     . 
Synthesis  of  water  by  weight,    . 
Reciprocal  character  of  combustion, 
Oxyhydrogen  blowpipe, 
Chemical  relations  of  hydrogen;  Hydrogenium ;  occlusion  of  hydrogen 
by  palladium,  ....... 

Chemical  relations  of  water  toother  substances;   hydrates;  nature  of 
simple  solution  ;   crystallisation    from  water ;    super-saturated 
solutions,     ........ 

Efflorescence  ;  water  of  crystallisation  and  water  of  constitution  of 
salts  ;  deliquescence,       ...... 

Hydrated  bases,  ....... 

Hydroxyle  the  radical  of  the  hydrates  or  hydroxides, 
Water  from  various  natural  sources  ;  air  dissolved  in  water,    . 
Saline  components  of  nattiral   waters ;  hardness  ;  boiler  incrusta- 
tions ;  petrifying  springs  ;  stalactites ;  processes  for  softening 
waters ;  temporary  and  permanent  hardness ;  organic  matter 
in  waters.     Tests  for  purity  of  water,      .... 

Action  of  water  upon  leaden  cisterns  and  pipes.     Testing  of  water  for 
lead.     Mineral  waters,    ...... 

Sea-water,       ........ 

Purification  of  water  by  distillation  ;  the  still  and  worm ;  Liebig's 
condenser,  ....... 

Physical  properties  of  water  ;  specific  gravity  of  liquids  and  solids 
defined  ;  definition  of  boiling-point,       .... 

Hydric  peroxide  ;   its   preparation  and  properties  ;  decomposition 

by  contact ;  positive  and  negative  oxygen, 
Ozone  :  its  constitution  and  production ;  ozonic  ether ;  Dr.  Day's 
test  for  blood,      ....... 

Atmospheric  air. — Its  composition  ;  rough  demonstration  of  the  pro- 
portions of  oxygen  and  nitrogen  by  phosphorus  ;  exact  analysis 
of  air  by  copper,     ....... 

Air  a  mixture,  not  a  chemical  compound ;  functions  of  the  nitrogen 

in  air  ;  uniform  composition  of  the  atmosphere  maintained  by 

diff'usion  ;  dialysis  of  air  ;  Sprengel's  air-pump  ;  dust  in  air,    . 

Carbon. — Its    natural    varieties;     demonstration    of    the    nature    of 

diamond ;    exact   synthesis   of    carbonic  acid  gas ;   graphite ;  its 

useful  applications,     ....... 

Artificial  varieties  of  carbon  ;  lamp-black,  wood-charcoal ;  destructive 
distillation  defined ;  charcoal-burning  ;  decolorisation  and   deo- 
dorisation    by  charcoal ;    animal    charcoal ;    calorific    value  of 
carbon,         ........ 

Coal. — Chemistry  of  its  formation ;  composition  and  special  uses  of 
lignite,  bituminous  coal  and  anthracite  ;  spontaneous  combustion 
of  coal,         ........ 

Oxides  of  carbon  ;  their  composition  by  weight, 
'  'urbonic  acid  gas. — Sources  of  atmospheric  carbonic  acid  gas  ;  respira- 
tion ;  fermentation  ;  decomposition  of  carbonic  acid  by  plants,    . 


ragraph 
30 
31 
32 
33 
34 
35 
36 

37 


38 

39 
40 
41 
42 


43 

44 

4.5 

46 
47 
48 
49 

50 

51 

52 

53 


54 
55 


56 


CONTENTS.  IX 

Paragraph 

Occurrence  of  carbon  dioxide  in  the  mineral  kingdom ;  preparation 

of  carbonic  acid  gas,         ......         57 

Properties  of  carbonic  acid  gas  ;  illustrations  of  its  high  specific 
gravity  and  power  of  extinguishing  flame;  limit  to  combustion 
of  a  taper  in  confined  air  ;  limit  to  respiration  of  animals  in 
confined  air  ;  noxious  efl"ect3  of  carbonic  acid  gas ;  principles  of 
ventilation ;  solubility  of  carbonic  acid  gas  in  water  ;  spark- 
ling drinks ;  importance  of  dissolved  carbonic  acid  to  plants,    .         58 
Liquefaction   of    carbonic  acid  gas    in   glass  tubes    and  in   iron 
cylinders  ;  continuity  of  the  gaseous  and  liquid  states  of  matter ; 
experiments  with  the  solidified  gas,        .  .  .  .59 

Separation  of  carbon  dioxide  from  other  gases,  .  .  .60 

Ultimate  analysis  of  organic  substances ;  calculation  of  formulae  exem- 
plified ;  empirical  and  rational  formulae,     .  .  .  .61 

Salts  formed  by  carbonic  acid.     Table  of  the  commonest  carbonates, 

with  their  common  names,  additive  and  substitutive  formulae,         62 
Analytical  proof  of  the  composition  of  carbon  dioxide,  .  .         63 

Carbonic  oxide. — Its  formation  in  fires  and  furnaces  ;    its  poisonous 

character,     ........         64 

Formation  of  carbonic  oxide  by  passing  steam  over  red-hot  carbon ; 

its  useful  application,       ......         65 

Carbonic  oxide  compared  with  carbonic  acid  gas,       .  .  .66 

Preparation  of  carbonic  oxide  ;  from  oxalic  acid ;  from  potassium 

ferrocyauide,        .......         67 

Reduction  of  metallic  oxides  by  carbonic   oxide ;    preparation  of 

pyrophoric  iron,  .......         68 

Composition  by  volume  of  carbonic  oxide  and  carbon  dioxide,       .         69 
Atomic  weight  of  carbon,        ......         70 

Compounds  of  carbon  and  hydrogen ;  formulae  of  acetylene,  marsh  gas, 

and  olefiant  gas,       .  .  .  .  .  .  .71 

Acetylene. — Its  production   by   direct   synthesis  ;   its  preparation  in 
quantity  by  the  imperfect  combustion  of  coal  gas  ;  new  radicals 
derived     from     acetylene ;     cupros-ethenyle,    argent-ethenyle  ; 
fulminating  argent-ethenyle   hydrate  ;  remarkable  properties  of 
acetylene;  formation  of  sty  role  by  action  of  heat  upon  acetylene; 
synthesis  of  prussic  acid  with  acetylene  and  nitrogen,       .  .         72 

Olefiant  gas. — Its   preparation   and  properties  ;  formation  of  Dutch 
liquid  ;  production  of  acetylene  from  olefiant  gas  by  the  spark- 
ling discharge,         .......         73 

Marsh  gas. — Its  occurrence  in  nature  ;   fire-damp  ;   preparation  and 
properties  of  marsh  gas  ;  chemistry  of  explosions  in  coal-mines  ; 
safety-lamps  ;  fire-damp  indicator,  .  .  .  .74 

Structure  of  flame;  cause  of  luminosity  in  ordinary  flames;  experiments 
illustrating  the  structure  of  flame  ;  influence  of  the  supply  of  air 
upon  the  character  of  flames  ;  smokeless  gas-biirners  ;  effect  of 
atmospheric    pressure   upon    the   luminosity   of  flames  ;    com- 
position of  illuminating  fuels,         .  .  .  .  .75 

The  blowpipe  flame. — Functions  of  its  different  parts  ;  reduction  of 

metals  by  the  blowpipe,  on  charcoal ;  hot-blast  blowpipe,  .         76 

Eudiometric  analysis  of  marsh  gas,    .  .  .  .  .77 

Goal  gas. — Products  of  the  distillation  of  coal,  .  .  .  .78 


CONTENTS. 


82 

83 

84 
85 

86 


Paragraph 
Silicon. — Its  occurrence  as  silica  in  nature  ;  conversion  of  silica  into  a 
soluble  form  ;  preparation  of  pure  silica  by  dialysis  ;  crystallised 
and  amorphous  silica,         .  .  .  .  .  .79 

Apparatus  for  effecting  fusions  in  the  laboratory,  .  .  .80 

Silicates  ;  tetra-basic  character  of  silicic  acid,    .  .  .  .81 

Preparation  and  properties  of  silicon ;   amorphous,   graphitoid,  and 
adamantine  silicon ;  comparison  of  silicon  with  carbon  ;  hydride 
and  nitride  of  silicon  ;  atomic  weight  of  silicon,    . 
Boron. — Boracic  acid;  its  extraction   from  the  soffioni ;  properties  of 
boracic  acid  ;  its  antiseptic  character  ;  borates. 
Extraction  of  boron  from  boracic  anhydride  ;  amorphous  and  diamond 
boron,  ...... 

Review  of  carbon,  boron,  and  silicon,   . 
Nitrogen. — Its  occurrence  in  nature  and  preparation  from  air  ;  inert 
character  of  the  element,  and  activity  of  its  compounds. 
Ammonia. — An    important    medium    of    circulation    for    nitrogen 
extraction  from  the  ammoniacal  liquor  of  the  gas-works  ;  sub- 
limation ;  preparation  of  ammonia  gas  ;   solution  of  ammonia 
mode   of  ascertaining  its   strength  ;   liquefaction  of  ammonia 
Carre's    refrigerator ;     conibination    of    ammonia    with    acids 
the  ammonium-theory  ;  formation  of  ammonium-amalgam, 
Atomic  weight  and  volume  of  nitrogen. 
Process  for  ascertaining  the  proportion  of  nitrogen  in  an  organic 

substance  ;  calculation  of  the  formula  of  urea,  . 
Formation  of  ammonia  in  the  rusting  of  iron  ;  nascent   state  of 

elements  ;  ammonia  from  atmospheric  nitrogen, 
Production  of  nitrous  and  nitric  acids  from  ammonia  ;  nitrification 

formation  of  nitrates  in  nature  ;  nitrifying  ferment. 
Compounds  of  nitrogen  and  oxygen. 
Nitric  acid. — Preparation  in  the  laboratory  and  on  the  lai^e  scale  ;  pro- 
perties of  nitric  acid  ;  its  action  upon  metals  and  organic  substances. 
Oxidising  effects  of  nitrates,   ...... 

Anhydrous    nitric   acid    or    nitric    anhydride.      Table   of    the  chief 

nitrates,  with  their  common  names  and  formulae,  . 
Nitrous  oxide ;  preparation  from  ammonium  nitrate,    . 
Nitric  oxide  ;  rough  analysis  of  air  by  nitric  oxide. 
Nitrous  acid ;  preparation  of  potassium  nitrite, 
Nitric  peroxide  ;  commercial  nitrous  acid. 

General  review  of  the  oxides  of  nitrogen  ;  combination  in  multiple 

proportions  ;  determination  of  the  composition  of  the  oxides  of 

nitrogen ;  tabular  review  of  their  composition, 

C'hlorine. — Its  occurrence  in  nature  and  extraction  from  common  salt ; 

Weldon's  and  Deacon's  chlorine  processes.     Striking  physical  and 

chemical  properties  of  chlorine  ;  powerful  attraction  for  non-metallic 

and  metallic  elements,  ...... 

Relations  of  chlorine  to  hydrogen  ;  synthesis  of  hydrochloric  acid 
effected  by  natural  and  artificial  light ;  displacement  of  oxygen 
from  water  by  chlorine  ;  action  of  chlorine  upon  other  hydrogen- 
compounds  ;  substitution  of  chlorine  for  hydrogen  in  organic 
substances  ;  oxidising  action  of  moist  chlorine, 
Pileacliing  properties  of  chlorine  ;  their  application. 


87 
88 

89 

90 

91 
92 

93 
94 

95 
96 
97 
98 
99 


100 


101 


102 
103 


CONTENTS. 


XI 


Paragraph 
Chloride  of  lime. — Mode  of  using  it  for  bleaching,  and  for  printing 
white  patterns  on  a  coloured  ground  ;  disinfecting  properties  of 
chlorine  ;  application  of  chloride  of  lime  for  disinfecting,  .       104 

History  of  the  discovery  of  chlorine ;  phlogiston,      .  .  .       105 

Hydrochloric  acid. — Preparation  and  properties  of  the  gas  ;  production 
of  solution  of  hydrochloric  acid  in  the  alkali  works.     Weak  acid 
properties  of  liquefied  hydrochloric  acid,   ....       106 

Action  of  hydrochloric  acid  upon  metals  ;    demonstration  of  its 

composition  by  volume,  ......       107 

Action  of  hydrochloric  acid  upon  basic  metallic  oxides  ;  formation 

of  chlorides,  .  .  .  .  .  .  108 

Action  of  hydrochloric  acid  on  indifferent  oxides  and  anhydrides,   .       109 
Compounds  of  chlorine  with  oxygen,  .  .  .  .110 

Hypochlorous   acid. — Its    use   for  erasing  ink ;    the    hypochlorites  ; 
preparation    of    oxygen    from    chloride    of    lime.     Chloride    of 
soda,  .  .  .  .  .  .  .  .111 

Chloride  of  lime,  its  relation  to  hypochlorous  acid,        .  .  .112 

Chloric  acid.      Chlorate  of  potash ;   preparation  ;  from  potassium  car- 
bonate ;  from  potassium  chloride.     Preparation  and  properties 
of  chloric  acid.    Useful  applications  of  potassium  chlorate.    Com- 
bustion of  potassium  chlorate  in  coal  gas.     Coloured  fire  com- 
positions.    Anomalous  evolution  of  heat  in  the  decomposition  of 
the  chlorates,  .  .  .  .  .  .  .113 

Perchloric  acid. — Explosive  properties,  .  .  .  .  .114 

Chloric  peroxide. — Its  unstable  character  and  powerful  oxidising  action. 

Euchlorine,    .  .  .  .  .  .  .115 

C/iZoroM5  anhydride  ;  chlorous  acid  ;  chlorites,  .  .  .  .116 

General  review  of  the  oxides  of  chlorine  ;  their  composition   by 

volume,    ........       117 

Chlorides  of  carbon. — Preparation  of  the  bichloride  or  tetrachloride. 
Composition  by  volume  of  the  chlorides  of  carbon.     Influence  of 
the  composition  by  volume  of  a  compound  upon  its  properties. 
Table  of  the  molecular  formulae,  weights  and  volumes  of  the 
chlorides  of  carbon,  .  .  .  .  .  .118 

Phosgene  gas  or  carbon  oxychloride,  .  .  .  .  .119 

Silicon  tetrachloride.     Boron  trichloride,  .  .  .  .120 

Chloride  of  nitrogen. — Processes  for  preparing  it  ;  violent  explosive 

character,     ........       121 

Aqua  regia.     Nitrosyle  chloride,  .  .  .  .  .122 

Bromine. —  Extraction  from  the  waters  of  mineral  springs ;  great  chemical 

resemblance  to  chlorine  ;  hypobromous  and  bromic  acids,    .  .123 

Hydrobromic  acid.     Bromide  of  nitrogen.     Chloride  of  bromine,         .       124 
Iodine. — Extraction  from  ashes  of  sea-weed.     Characteristic  properties 

of  iodine  and  the  iodides,        .     '        .  .  .  .  .       125 

Iodic  acid.     Periodic  acid,  ......       126 

Hydriodic  acid. — Its  powerful  reducing  properties  ;  carbon  tetra-iodide,      127 

Iodide  of  nitrogen. — Explosive  character  ;  iodammonium  iodide,  .       128 

Chlorides  and  bromides  of  iodine,      .  .  .  .  .129 

Potassium  iodide. — Its  preparation.     Ferrous  iodide,    .  .  .       130 

Fluorine. — Fluor  spar,     .......       131 

Hydrofluoric  acid ;  etching  on  glass.     Fluorides;  kryolite,       .  .       132 


Xll  CONTENTS. 

Paragraph 
Silicon  tetrafluoride  J-  its  decomposition  by  water,         .  .  133 

Hydrofluosilicic  acid ;  silico&noridee,      .  .  .  .  .134 

Boron  trifluoridej  fluoboric  and  hydrofluoboric  acids,  .  .       135 

General  review  of  chlorine,  bromine,  iodine,  and  fluorine,    .  .       136 

Sulphur, — Its  occurrence  in  nature  ;  composition  of  the  principal  sul- 
phides and  sulphates  found  in  the  mineral  kingdom.     Extraction 
of  sulphur  in  Sicily.     Eefining  of  sulphur.     Distillation  of  sulphur 
from  pyrites.     Commercial  varieties  of  sulphur,        .  .  .       137 

Properties  of  sulphur ;  remarkable  transformation  by  heat ;  electro- 
positive  and  electro-negative   sulphur ;   soluble  and    insoluble 
varieties ;  octahedral  and  prismatic  sulphur ;  table  of  the  chief 
allotropic  forms  of  sulphur,  .  .  .  .  .138 

Influence  of  temperature  upon  the  specific  gravity  of  gases  and 

vapours  ;  anomalous  expansion  of  sulphur  vapour,        .  .139 

Hydrosulphuric  acid. — Its  preparation  for  laboratory  use  ;  prepara- 
tion of  sulphide  of  iron.    Properties  of  sulphuretted  hydrogen  ; 
action    upon  metals  and    their  oxides ;    blackening    of    paint, 
pictures,  &c.,  by  impure  air  ;  use  of  hydric  sulphide  in  analysis  ; 
sulphur  acids,   bases,   and  salts ;    action  of  air  upon   metallic 
sulphides,     ........       140 

Hydric  persulphide,         .  .  .  .  .  .  .141 

Compounds  of  sulphur  with  oxygen,  .  .  .  .142 

Suljyhurous  acid. — Its  bleaching  and  antiseptic  properties.     Sulphites,       143 
iSulphuric  acid ;  Nordhausen  oil  of  vitriol ;  gradual  development  of 
the  English  manufacture  of  oil  of  vitriol ;  experiments  illustra- 
ting tlie  theory  of  the  process ;  preparation  of  oil  of  vitriol  in 
the  laboratory  and  on  the  large  scale  ;   plan  for  economising 
nitric  oxide  ;  commercial  varieties  of  sulphuric  acid.     Properties 
of  oil  of  vitriol;  its  action  upon  organic  substances  and  upon 
metals,         ........       144 

Sulphuric    anhydride  y    its    formation    from    sulphur    dioxide    and 

oxygen,        ...........       145 

Sulphates.       Action    of    sulphuric    acid    upon    metallic    oxides. 
Normal,  acid  and  double  sulphates.     Decomposition  of  sul- 
phates by  heat  and  bj'^  reducing  agents.     Table  of  the  chief 
sulphates,  with  their  common  names  and  formulae,       .  .       146 

Hyposidjyhurous   or    thiosulphuric    acid. — Hyposulphite    of    soda    or 
sodium  thiosulphate  ;  its  preparation  and  use  for  fixing  photo- 
graphic prints,  and  for  making  antimony  vermilion.     Hydrosul- 
phurous  acid,  .......       147 

Hyposulphuric  or  dithionic  acid,  .....       148 

Trithionic  or  sulphuretted  hyposulphuric  acid,     ....       149 

Tetrathionic  or  bisulphuretted  hyposulphuric  acid,  .  .  .       150 

Pentathionic  acid,  .  .  .  .  .  .  .151 

Bisulphide  of  carbon. — Its  use  in  spectrum  analysis  ;  its  diathermanous 
character  and  inflammability  ;  a  starting-point  for  the  synthesis 
of  organic  compounds.     Sulphocarbonates.     Removal  of  carbon 
disulphide  from  coal  gas.     Preparation  and  properties  of  carbon 
oxysulphide,  .  .  .  .  .  .  .152 

Silicon  disulphide,  .  .  .  .  .  .  .153 

Xitrogen  sulphide. — Its  explosive  character,      .  .  .  .154 


CONTENTS.  xiii 

Paragraph 

Chlorides  of  stdphur. — Preparation  of  the  subchloride  or  chloride  of 

sulphur.     Iodides  of  sulphur,  .  .  .  .  .       1.5.5 

Selenium. — Its  extraction  from   the  deposit  in  the  vitriol  chambers. 
Selenious  and  selenic  acids.     Selenietted  hydrogen.     Chlorides  and 
sulphides  of  selenium  ;  use  of  selenium  in .  the  photophone,  .       156 

Tellurium. — Tellurous    and    telluric   acids  ;    telluretted    hydrogen  ; 

chlorides  and  sulphides  of  tellurium,  .  .  .  .1.57 

Review  of  the  sulphur  group  of  elements,  comprising  sulphur,  sele- 
nium, and  tellurium,  .  .  .  .  .  .158 

Phosphorus. — Its  distribution  in  nature  ;  extraction  from  bones  on  the 
large  and  small  scales  ;  action  of  light  on  phosphorus.     Phosphor- 
escence.    Allotropic  modifications  of  phosphorus.     Preparation  of 
red  phosphorus.     Precipitation  of  metals  by  phosphorus,     .  .       159 

Lucifer  matches  ;  silent  matches  ;  safety  matches,        .  .  .160 

Armstrong  fuze  composition ;  amorces  fulminantes,       .  .  .       161 

Oxidfis  of  phosphorus. — Table  of  their  composition,         .  ...       162 

Phosphoric  acid. — Its  natural  sources  ;  preparation  from  bones.     Phos- 
phoric anhydride.     Metaphosphoric,  pyrophosphoric,  and  ortho- 
phosphoric  acids,     .  .  .  .  .  .  .163 

Phosplwrous  acid;  phosphites.     Hypophosj>lwric  acid,    .  .  .164 

Hypo2Jhosphorov^  acid,     .  .  .  .  .  .  .165 

Svhoxide  of  pliosphorm. — Combustion  of  phosphorus  under  water,        .       166 
Phosphides  of  hydrogen. — Preparation  and  properties  of  phosphuretted 

hydrogen  gas,  .......       167 

Chlorides  of  phosphorus. — Oxychloride   and   sulphochloride    of  phos- 
phorus ;  sodium  siUphoxyphosphate.     Action  of  iodine  on  phos- 
phorus,       ........       168 

Sulphides  of  phosphorus,        .  .  .  .  .  .169 

Action  of  ammonia  on  oxychloride  and  pentachloride  of  phosphorus. 

Amides  of  phosphoric  acid,  .  .  .  .  .170 

Arsenic. — Formulae  of  natural  arsenides  and  arseniosulphides.     Extrac- 
tion of  arsenic  from  mispickel.     Properties  and  chemical  relations 
ofar.senic,       ........       171 

Oxides   of  arsenic.     Arsenions  acid. — Composition   of  arsenious  and 

arsenic  acids.     Arsenites.     Scheele's  green,  .  .  .       1 72 

Arsenic  acid. — -Sodium  arseniate,  .  .  .  .  .173 

Arsenietted    hydrogen. — Marsh's    test  for    arsenic.     Composition  and 
molecular  formula  of  arsenietted  hydrogen.     General  review  of 
ammonia,  phosphuretted  and  arsenietted  hydrogen,  .  .       174 

Arsenic  trichloride  and  tribrnmide,  .  .  .  .  .175 

Arsenic  di-  and  tri-odides  and  trifltuyride,  .  .  .  .176 

Sulphides  of  arsenic.     Realgar.     King's  yellow,  .  .177 

General   review  of    the  non-metallic    elements. — Classification 
according  to  their  atomicities.     Elucidation  of  the  constitution  of 
compound  bodies  by  the  doctrine  of  atomicity.    Structural  formulae. 
Bonds,  ........       178 

Constitution  of  salts. — Haloid  and  oxy-acid  salts.  Difference 
between  neutral  and  normal  salts.  Criterion  of  normality.  Water - 
type  theory.  Constitution  of  polybasic  acids  and  their  salts. 
Hydroxyle  theory  of  acids,     ....  .179 


XIV  CONTENTS. 

Pai'agraph 

CHEMISTRY  OF  THE  METALS. 

Classification  of  metals. — Periodic  law   of  the  chemical  eleiiieuts, 
Potassium. — Its    occurrence    in     nature.      Potassium    carbonate, 
Potassium  hydrate.     Extraction  of  potassium.     Blowpipe  test  for 
potassium.     Potassium  cliloride.     Bicarbonate  of  potash,     . 
Sodium. — Extraction  of  .salt.     Salt  gardens  of  Marseilles, 

Manufacture  of  carbonate  of  soda  from  common  salt.     Soda  ash.      Soda 
crystals.     Soda-lye.     Alkali  waste.     Sodium  hydrate, 
Extraction  of  sodium  from  the  carbonate.     Uses  of  sodium, 
Borax.     Reftning  of  tineal.     Crystallisation  of  borax, 
Silicate  of  soda.     Soluble  glass.     Artificial  stone.     Sulphate  of  soda. 
Phosphate  of  soda,  ..... 

Salts  of  ammonium,         ...... 

Sulphate  of  ammonia  or  ammonium  sulphate, 
Sesquicapbonate  of  ammonia  or  ammonium  carljonate. 
Ammonium  chloride  ;  its  dissociation  by  heat, 
Ammonium  sulphide,     ...... 

Lithium. — Lepidolite,    petalite,    .spodumeue.      Lithia.    Lithium  car 
bonate.     Rubidium.     Casium,         .... 

Spectrum  analysis,      .  .  . 

General  review  of  the  group  of  alkali-metals, 
Bauium. — Preparation  of  barium-compounds  from  heavy  spai\     Barium 

nitmte  and  hydrate.     Barium  dioxide,  chloride  and  chlorate. 
Strontium. — Preparation  of  strontium  nitrate,    . 
Calcium. — Carbonate    of   lime;    its    various    mineral    forms.     Lime 
burning.     Sulphate    of    lime.     Preparation   of   plaster    of    Paris 
Calcium  chloride,  calcium  sulphide  ;  luminous  paint. 
General  review  of  the  metals  of  the  alkaline  earths,     . 
Relation  between  specific  heats  and  atomic  weights.     Atomic  heats. 
Magnesium. — Extraction  and  properties  of  the  metal.     Preparation  of 

magnesium  sulphate  and  carbonate.     Magnesium  chloride. 
Zinc. — Properties  upon  which  its  usefulness  depends.     Galvanized  iron. 
Ores  of  zinc.     Distillation  of  zinc.     English  method  of  extracting 
the  metal  from  its  ores.     Belgian  and  Silesian  processes.     Oxide, 
sulphate,  and  chloride  of  zinc,  .....       200 

Cadmium. — Sulphide  and  iodide  of  cadmium,       ....       201 

Glucinum,  ........       202 

Aluminium. — Minerals    containing    alumina.     Composition    of    clay. 

Manufacture  of  alum.     Alumina.     Aluminium  chloride,      .  .       203 

Extraction  of  aluminium  from  bauxite.     Sodium  aluminate.     Pro- 
perties and  uses  of  aluminium,   .  ....       204 

Mineral  .silicates  of  alumina.     Exchange  of  isomorphous  metals  in 

minerals.     Natural  and  artificial  ultramarine,       .  .  •       205 

Thorinum,  Yttrium,  Erbium,  Lanthanium,  Didymium,  Zirconium,  206-210 
Gallium,  Indium,  ......  211-212 

Cerium,  Uranium,  ......  213-214 

Iron. — Its  occurrence  in  nature.     Ores  of  iron.     Table  of  composition 

of  British  iron  ores,    .  .  .  .  .  •  .215 

Metallurgy  of  iron. — Its  physical  properties,     ....       216 


180 
181 

182 
183 
184 

185 
186 
187 
188 
189 
190 

191 
192 
193 

194 
195 


196 
197 
198 

199 


CONTENTS.  XV 

Paragraph 
English  process  of  smelting  clay  iron-stone. — Blast-furnace.     Chemical 
changes  in  the  blast-furnace.     Composition  of  gas  from  blast- 
furnace.    The  hot  blast.     Composition  of  slag  from  the  blast- 
furnace,       ........       217 

Cast-iron. — Composition  of    different  varieties  of    cast-iron.     Grey, 

mottled,  and  white  iron.     Chill  casting,     .  .  .  .218 

Conversion  of  cast-iron  into  bar-iron. — Refining.     Puddling.     Varieties 
of  bar-iron.     Chemical  efifect  of  puddling  and  forging  on  cast- 
iron.      Composition    of    tap-cinder.      Defects   of    the   puddling 
process.     Bessemer's  process.    Conditions  influencing  the  strength 
of  bar-iron,  .  .......       219 

Manufacture  of  steel. — The  cementation  process.     Shear  steel.     Pro- 
duction of  cast-steel.     Hardening   and  tempering  steel.     Case- 
hardening.     Malleable  cast-iron.     Bessemer  steel.     Spiegel-eisen. 
Ferromanganese.    Homogeneous  iron.   Puddled  steel.   Natural  or 
German  steel.     Siemens- Martin  steel.     Krupp's  cast-steel,  .       220 

Direct  extraction  of  tm-ou^ht-iron  from  the  ore. — The  Catalan  process,    .       221 
Extraction  of  iron  on  the  small  scale.     Sefstrom  furnace,     .  .       222 

Chemical  properties  of  iron.     Passive  state  of  iron,  .  .  .       223 

Oxides  of  iron.     Ferrous  oxide.     Ferric  oxide.     Magnetic  oxide  of 

iron.     Ferric  acid,  ......       224 

Ferrous  sulphate.     Ferric  sulphate,  ....       225 

Perchloride  of  iron  or  ferric  chloride,  ....       226 

Atomic  weight  of  iron.     Varying  atomicity  of  iron.    Ferrosum  and 

ferricum,  .......       227 

Cobalt. — Cobaltous  and  cobaltic  oxides,  ....       228 

Nickel. — Oxides,  sulphate,  and  sulphides  of  nickel,        .  .  .       229 

Manganese,  ........       230 

Oxides  of  manganese.     Manganous  and  manganic  oxides ;  manganese 
dioxide.        Manganic     acid.      Permanganic     acid.      Potassium 
permanganate,  .......       231 

Chlorides  of  manganese.     Recovery  of  waste  manganese,  .  .       232 

Chromium. — Preparation  of  bichromate  of  potash  from,  chrome-iron,  .       233 

Chromic  acid.       Potassium  chromate.      Chrome    yellow.     Oxides  of 

chromium.     Perchromic  acid,         .....       234 

Chromous  and  chromic  chlorides.      Chlorochromic  acid.      Fluoride 

and  sulphide  of  chromium.     Sulphochromites,      .  .  .       235 

General  review  of  zinc,  iron,  cobalt,  nickel,  manganese,  and  chromium,       236 

Molybdenum,  Vanadium  .....  237-239 

Bismuth. — Extraction  and  properties.     Fusible  alloy,     .  .  .       240 

Bismuthous  and  bismuthic  oxides.     Bismuthic  acid,     .  ,  .       241 

Trisnitrate  of  bismuth  or  flake-white.     Pearl-white.     Bismuth  tri- 
chloride.    Bismiithous  and  bismuthic  sulphides,  .  .  .       242 
Antimony. — Extraction  of  regulus  of  antimony.     Amorphous  antimony,       243 
Oxides  of  antimony.      Antimonic  acid.      Antimoniate,  metantimo- 

niate  and  bimetantimoniate  of  potassium,  .  .  .       244 

Antimonietted  hydrogen,  ......       245 

Antimony  trichloride  and  pentachloride,  ....       246 

Sulphides  of  antimony.     Mineral  kermes.     Schlippe's  salt,      .  .       247 

Tin. — Cornish  treatment  of  tin  ores.     Extraction  and  purification  of  tin,       248 


XVI 


CONTENTS. 


Physical  properties  of  tin.     Manufacture  of  tin-plate.     Tinning 
copper  vessels,         ...... 

Alloys  of  tin.     Solder.     Gun  metal.     Bronze.     Bell  metal, 

Oxides  of  tin.     Stannous  oxide.     Stannic  oxide.     Preparation 

stannate  of  soda.     Metastannic  acid,      .  .  . 

Stannous  chloride  or  tin-crystals.    Stannic  chloride  or  nitromuriate 
of  tin.     Pink  salt,  ..... 

Sulphides  of  tin.     Preparation  of  mosaic  gold. 
Titanium. — Titanic  acid  ;  its  extraction  from  iron-sand.      Other  com 
pounds  of  titanium,     ...... 

Tungsten. — Preparation  of  tungstate  of  soda  from  wolfram.     Dialysed 
tungstic    acid.      Oxides,    chlorides,    and    sulphides    of   tungsten 
Tungstoborates,  ...... 

Niobium,  Tantalum,        ...... 

Copper. — Its  occurrence  in  nature.     Ores  of  copper.     Copper  pyrites, 
Malachite.     Grey  copper  ore,  .... 

Smelting  of  copper  ores. — Calcining  the  ore.     Copper  smoke.     Fusion 
for  coarse  metal.     Calcining  the  coarse  metal.     Fusion  for  white 
metal.     Roasting  the  white  metal.    Refining  the  blister  copper. 
Toughening  or  poling.    Underpoled  and  overpoled  copper.    Table 
of  products  obtained  in  smelting  copper  ores, 
Extraction  of  copper  from  copper  pyrites  in  the  laboratory. 
Effect    of    impurities   upon    the    quality  of    copper.      Phosphor 
bronze,  ...... 

Properties  of  copper,  ...... 

Effect  of  sea  water  upon  copper.     Muntz  metal, 
Danger  attending  the  use  of  copper  vessels  in  cooking  food. 
Alloys  of  copper  with  other  metals. — Table  of  their  composition.     Brass, 
Bronzing.     Aich  metal.     Sterro  metal. 
Oxides  of  copper.     Cupric  and  cuprous  oxides.     Quadrantoxide 
Cupi'ic  acid,  ...... 

Sulphate  of  copper.     Carbonates  and  silicates  of  copper. 
Chlorides  of  copper.     Oxychloride  ;    Brunswick  green.     Cuprous 
chloride,  ....... 

Sulphides    of   copper.     Extraction  of  copper  by  kernel-roasting, 
Cuprous  sulphide.     Copper  pyrites.     Phosphide  of  copper. 
Lead. — Its  useful  qualities.     Ores  of  lead.      Galena, 
Smelting  of  galena.     Old  English  process.     Economico-fumace, 
Improving  process  for  hard  lead,  .... 

Extraction  of  silver  from  lead. — Pattinson's  process  for  concentrating 
silver  in  lead,  ...... 

Cupellation  of  argentiferous  lead.     Sprouting  of  .silver. 
Extraction  and  cupellation  of  lead  in  the  laboratory. 
Uses  of  lead.     Type  metal.     Shot.     Solder, 
Lead   pyrophorus.      Oxides   of  lead.     Lithai^e.     Minium.     Lead 
peroxide,  ...... 

Manufacture   of  white    lead. — Dutch    process.      Pattinson's  process. 
Carbonate,  sulphate,  and  phosphate  of  lead, 
Chloride  and  oxychloride  of  lead.     Turner's  yellow.     Lead  iodide. 
Sulphides,  chlorosulphide,  and  selenide  of  lead, 


Paragraph 
of 


CONTENTS.  xvii 

'  Paragraph 

Thallium. — Its  discovery  by  the  spectroscope.    It  position  among  the 

metals,  ........       280 

Silver. — Extraction  of  silver  from  copper  by  liquation.    Amalgamation 
of  silver  ores.      Standard  silver.  <    Plating    and    electro-plating. 
Silvering  glass.     Preparation  of  pure  silver,  .  .  .281 

Properties  of  silver,        .......       282 

Oxides  of  silver.    Preparation  and  uses  of  nitrate  of  silver.    Permanent 

ink,  ........       283 

Chloride    of  silver.     Recovery  of  silver  from  photographic   baths. 

Subchloride,  bromide,  iodide,  and  sulphide  of  silver,         .  .       284 

Mercury. — Extraction  from  cinnabar  at  Idria  and  Almaden.     Purifica- 
tion of  mercury,  .......       285 

Medicinal  preparations  of  metallic  mercury,      .  .  .  .       286 

Uses  of  mercury.     Silvering  looking-glasses.     Amalgams,       .  .       287 

Mercurous  and  mercuric  oxides.     Mercuramine,  .  .  .       288 

Mercurous  and  mercuric  nitrates  and  sulphates,  .  .  .       289 

Chlorides  of  mercury.     Corrosive  sublimate.     White  precipitate,        .      29() 
Calomel.     Its  preparation  and  properties.     Mercurous  and  mercuric 

iodides,        .  .  .  .  .  ...  .291 

Sulphides  of  mercury.     Preparation  of  vermilion,         .  .  .       292 

Platinum. — Treatment  of  platinum  ores  by  the  wet  and  dry  processes. 

Spongy  platinum.     Platinum  black,  ....       293 

Platinous  and  platinic  oxides.     Preparation  of  platinic  chloride.     Its 
double  salts  with  alkaline  chlorides.     Platinous  chloride.     Its 
behaviour  with  ammonia.     Platosamine  and  platinamine,  .       294 

Palladium. — Its  separation  from  platinum  ores, ....       295 

Rhodium. — Extraction  of  the  metal  from  rhodio-chloride  of  sodium,      .       296 
Osmium. — Osmic  acid.     Chlorides  of  osmium,      ....       297 

Ruthenium. — Oxides  of  ruthenium.     Ruthenic  acid,      .  .  ,      298 

Iridium. — Extraction  from  the  native  osmiridium  alloy,  .  .       299 

Tabular  view  of  the  analysis  of  platinum  ores.     Summary  of  the 

group  of  platinoid  metals,  ......       300 

Davyum,    .........       301 

Gold. — Washing  for  gold  dust.    Smelting  of  auriferous  ores ;  with  lead  ; 
with  pyrites.    Amalgamation  of  gold  ores.    Standard  gold.     Testing 
and  assaying  gold,       .......       302 

Physical  properties  of  gold.     Gold  leaf.     Ruby  gold.    Manufacture  of 

gold  thread.     GUding,         ......       303 

Oxides  and  chlorides  of  gold.    Fulminating  gold.    Sel  cCor.     Purple  of 

Cassius,        ........       304 

Chemical  principles  op  the  manufacture  op  glass. — Window  glass. 
Plate  glass.      Crown  and  Flint   Glass.     Production  of  coloured 
glasses,  ........       305 

Chemistry  op  the  manufacture  of  pottery  and  porcelain. — Sevres 
porcelain.    English   porcelain.    Stoneware.    Earthenware.    Bricks. 
Dinas  firebricks.     Blue  bricks,  .....       306 

Chemistry  op  building  materials. — Varieties  of   building  stones. 
Freestone.   Portland  and  Bath  stones.    Magnesian  limestones.    Test 
of  resistance  of  building  stones  to   frost.      Mortar.      Hydraulic 
cements.     Concrete,  .......      307 

h 


XVlll  CONTENTS. 

Paraci'aph 

Gunpowder.^— ^t7re  or  saltpetre.    Grough  nitre.    Conversion  of  sodium 
nitrate    into    potassium    nitrate.    Artificial    production    of   nitre 
in  the  nitre  heaps.     Saltpetre-refining.      Properties  of  saltpetre. 
Relation  to  combustible  bodies.     Charcoal  for  gunpowder.    Composi- 
tion of  charcoal  prepared  at  diflferent  temperatures.     Sulphur  for 
gunpowder.     Tests  of  its  purity.     Functions  of  sulphur  in  gun- 
powder.     Manufacture  of  gunpowder.     Incorporation.     Pressing. 
Granulating  or  coming.     Glazing,     .....       308 

Properties    of  gunpowder. — Eft'ects    of   air,    water,    and    heat    upon 

powder,        ........       309 

Products  of  explosion  of  gunpoivder.-^Difierence  in  results  obtained  by 

different  experimenters.     Most  recent  experiments,  .  .       310 

Calculation  of  the  force  of  fired  gunpowder. — Gas  furnished  by  calcula- 
tion from  a  given  quantity  of  powder.    Temperature  of  the  gas  at 
instant  of  explosion.     Specific  heats  of  the  products  of  explosion. 
Expansion  of  the  gas  by  heat.     Mechanical  equivalent  of  gun- 
powder.   Effect  of  size  of  grain  on  the  firing  of  powder.    Blasting- 
powder,        .  .  .  .  .  .  .  .311 

Effect  of  variations  cf  atmospheric  pressure  on  the  combustion  of  gun- 
powder. — Manufacture  of  gunpowder  in  the  laboratory,  .  .  312 
Chemistry  of  fuel. — Calorific  value  of  fuel  calculated.  Theoretical 
and  actual  calorific  values.  Difference  between  calorific  value  and 
calorific  intensity.  Calculation  of  the  calorific  intensity  of  carbon 
burning  in  oxygen  and  in  air.  Calculation  of  the  calorific  intensity 
of  hydrogen  burning  in  air.  Calculation  of  the  calorific  intensity 
of  fuel  containing  carbc^n,  hydrogen,  and  oxygen.  Theoretical  and 
actual  calorific  intensities.  Waste  of  heat  in  furnaces.  Economy 
of  heat  in  Siemens'  regenerative  furnace.  Table  of  composition, 
calorific  values,  and  intensities  of  ordinary  fuels,      .            .  .       313 


ORGANIC  CHEMISTRY. 

Introductory.     Classification  of  organic  compounds,        .  .  .       314 

Cyanogen  and  its  compounds. — History  of  cyanogen,  .  .  .       315 

Yellow  prussiate  of  potash  or  potassium  ferrocyanide.      Prussian 

blue.      Hydroferrocyanic  acid.      Hydrocyanic  or  prussic  acid. 

Mercuric  cyanide.     Formylamine.     Carbodiamine,  .  .       316 

Preparation  and  properties  of   cyanogen.     Potassium  cyanide  and 

cyanate.     Cyamelide.     Cyanic  acid.     Potassium  sulpho-cyanide. 

Hydrosulphocyanic  acid.    Liebig's  test  for  prussic  acid.  Chrysean. 

Cyanogen  iodide,    .  .  .  .  .  .  .317 

Red  prussiate  of  potash  or  potassium  ferricyanide.     TurnbuU's  blue. 

Ferricyanogen  and  other  compound  cyanogen  radicals,     .  .       318 

Chlorides  of  cyanogen.  Cyanuric  acid.  Cyanide  of  phosphorus,  .  319 
Nitroprussides.  Hadow's  and  Stadeler's  investigation  of  their  consti- 
tution. Economical  preparation  of  sodium  nitroprusside,  .  320 
Tlie  fulminates. — Preparation  of  fulminate  of  mercury.    Its  properties. 

Percussion  cap  composition.     Fulminate  of  silver.     Experiments 

with  the  fulminates.     Chemical  constitution  of  the  fulminates. 

Fulminurates  or  isocyanurates,       .  .  .  .  .321 


CONTENTS.  xiX 

Paragraph 

Prodttcts  of  the  destructive  distillation  of  coal.    Manufacture 

of  coal  gas.     Composition  of  coal-tar,  ....       322 

Coal-naphtlia.     Separation  of  its  constituents  by  fractional  distilla- 
tion, ........      323 

Benzene.     Benzene  chloride.     Trichlorhydrine  ofphenose.     Phenose,       324 
AnilLne.     Its  preparation  from  nitrobenzene.     Production  of  colouring 

matters  from  aniline,  ......       325 

Coal-tar  dyes. — Mauve  or  aniline-purple.     Mauveine.      Magenta  or 

aniline-red.     Rosaniline  and  its  salts.     Leucaniline.     Chrysani- 

line  or  aniline-yellow.     Triphenylic  rosaniline  or  aniline-blue. 

Ethyliodate  of  tri-ethyl-rosaniline.     Hydrocyan-rosaniline,  .       326 

Chemical  constitution  of  aniline.     Formation  from  phenic  acid  and 

ammonia.     Picoline.     Quinoline.     Diazobenzene,         .  .327 

Benzene  series  of  homologous  hydrocarbons.     Their  relation  to  the 
aromatic  acids.     Homologous  nitro-compounds  and  bases  de- 
rived from  them,  ......       328 

Carbolic  acid.     Preparation  from  the  dead-oil  of  coal-tar.     Examina- 
tion of  commercial  carbolic  acid.     Tribromophenole,     .  .       329 
Carbazotic   or   picric   acid.     Chloropicrine.     The    phenyle   series. 

Kresylic  acid,       .......       330 

Naphthalene.      Magdala  red.     Substitution  products  from  naph- 
thalene.     Phthalic  acid.       Connexion   of  naphthalene  with 
the  phenyle  series.     Authracena     Phenanthrene.     Chrysene. 
Pyrene,   .  .     •       .  .  .  .  .  .331 

Products  of  thf  destructive  distillation  of  wood. — Proximate 
constituents  of  wood.     Cellulose.     Vasculose.     Lignine.     Composi- 
tion  of  different  woods.     Products  of  the  action  of  heat  upon 
wood,  ........       332 

Wood-naphtha    or    methylic    alcohol.     Purification.     Methyle-com- 
pounds.    Oil  of  winter-green.    Metamerism  illustrated  by  methyle 
formiate  and  acetic  acid,     ......       333 

Paraffine.     Extraction  from  wood-tar.     Parafl^eoil.     Eupittonie  acid. 
Stockholm  tar.   Petroleum.   Rangoon  tar.   Bitumen  or  asphaltum. 
Ozokerite.     Vaseline,  ......       334 

Oil  of  turpentine  and  substances  allied  to  it. — Colophony.     Isomeric 

modifications  of  turpentine.     Artificial  camphor,  .  .  .       335 

The  turpentine  series  of  hydrocarbons.     Essential  oils,         .  .       336 

Camphors.     Common  camphor.     Borneo  camphor,  .  .  .       337 

Balsams.     Balsam  of  Peru.     Storax.     Styrole  and  metastyrole,        .       338 
Resins.     Copal.     Lac.     Amber.     Varnishes.     Benzoin.     Benzoic 

acid,         .  .  .  .  .  .  .  .339 

Oil  of  bitter  almonds  and  its  derivatives — Benzoyle  series. — 
FoiTuation  of  bitter  almond  oil.     Amygdaline.     Emulsine.     Ben- 
zoine.     Benzoyle.     Benzoic  anhydride,  ....       340 

Oil    of    Cinnamon. — Cinnamic     acid.     Cinnamyle.      Cummin     oil. 

Cuminic  acid,  .......       341 

Saligjne  and  its  derivatives — Glucosides. — Saligenine  ;  its  chlori- 
nated derivatives.  Salicylic  acid.  Monobasic  diatomic  acids.  Oil 
of  spiraea.     Benzoyle-salicyle.     Coniferine.     Vanilline,        .  .       342 

Populine  or  benzoyle  salicine.     Phloridzine.     Quercitrine.     Esculine. 

Paviine.     Saponine.     Picrotoxine,  ....       343 


3CX  CONTENTS. 

Paragraph 

Essential  oils  containing  sulphur — Allyle  series. — Formation  of 
essence  of  mustard.    Myronic  acid.    Allyle  iodide.    Artificial  forma- 
tion of  essences  of  mustard  and  garlic.     Allylic  alcohol.     Allylene,      344 
Gum-resins,  Caoutchouc. — Vulcanised  caoutchouc.     Gutta  percha,        .       345 
Gums. — Arabine.     Mucic  acid.     Gum  tragacanth,        .  .  .      346 

Starch. — Manufacture  of  starch.     Composition  of  the  potato  ;  of  wheat ; 

of  rice.    Properties  of  starch.     Sago.     Tapioca,        .  .  .       347 

Conversion  of  starch  into  dextrine  and  grape-sugar,     .  .  .      348 

Germination  of  seeds. — Malting. — Action  of  diastase  on  starch.     Com- 
position of  malted  and  unmalted  barley,  and  of  malt-dust,  .       349 
Brewing. — Composition  of  the  hop.     Nature  of  yeast.     Alcoholic  fer- 
mentation.    Composition  of  beer.    Viscous  fermentation,  .      350 
Acetification — Manufacture  of  Vinegar.     The  quick  vinegar  proces-s,   .       351 
Bread. — Composition  of  gluten.     Process  of  bread-making.     Aerated 

bread.     Leaven.     New  and  stale  bread,         ....      352 

The  Sugars. — Production  of  sugar  from  cotton,  paper,  and  other  varieties 
of  cellulose.     Action  of  sulphuric  acid  on  cellulose.     Vegetable 
parchment.     Hydro-cellulose  ;  cause  of  dry  rot.     Sugar  of  fruits  or 
fructose.     Conversion  of  cane-sugar  into  fructose,     .  .  .      353 

Extraction  of  cane-sugar. — Vacuum  pans.     Su^ar-refining,        .  .       354 

Beetroot  sugar.   Maple  sugar.  Sugar-candy.  Barley-sugar.  Caramel,      355 
Chemical  properties  of  the  sugars.     Compounds  of  sugar  with  bases. 
Action  of  solutions  of  the  sugars  upon  polarised  light.     Ethyle- 
glucose,    ........       356 

Mannite.     Glycyrrhizine,       ......      357 

Gun-cotton  and  substances  allied  to  it. — Pyroxyline.    Preparation 

of  gun-cotton  in  the  laboratory,  .....       358 

Manufacture  of  gun-cotton. — Abel's  process,       ....       359 

Chemical  composition  of  gun-cotton.  Trinitro-cellulose  or  cellulo- 

trinitrine.     Eeconversion  of  gun-cotton  into  ordinary  cotton,   .       360 
Products  of  the  explosion  of  gun-cotton.    Explosion  of  loose  and  con- 
fined gun-cotton.    Karolyi's  experiments.    Effects  of  gun-cotton 
and  gunpowder  compared,  .  .  .  .  .361 

Properties  of  gun-cotton  compared  with  those  of  gunpowder,  .      362 

Behaviour  of  gun-cotton  with  solvents,  ....       363 

Collodion- cotton.     Action  of  weak  nitro-sulphuric  mixtures  upon 
cotton.     Preparation  of  soluble  cotton  for  collodion.     Process 
for  making  balloons  of  collodion.     Artificial  ivory,       .  .      364 

Xyloidine.     Nitromanuite,     ......       365 

Wine  and  Spirits. — Preparation  and  composition  of  wines.    Proportion 

of  alcohol  in  wines,     .......       366 

Distilled  spirits.    Brandy,  whisky,  gin,  &c.     Potato-spirit,     .  .      367 

The  Alcohols  and  their  derivatives. — General  formula  of  alcohols 
of  the  vinic  class.  Table  of  the  vinic  or  ethylic  class  of  alcohols, 
with  their  sources,  common  names,  and  formulae.  Gradation  in  pro- 
perties of  the  homologous  alcohols.  Table  of  their  boiling-points 
and  vapour  densities.  Chemical  definition  of  an  alcohol.  General  ^ 
formulae  for  the  derivation  of  an  aldehyde,  an  acid,  and  an  ether 
from  an  alcohol.  Table  of  the  acetic  series  of  acids  with  their  sources 
and  formulfe.  General  description  of  the  acetic  series.  The  olefines 
or  olefiant  gas  series  of  hydi'ocarbons,  ....      368 


CONTENTS. 


XXI 


Paragraph 
Alcohol  as  the  type  of  its  class.     Preparation  of  absolute  alcohol,        .      369 
Ether.    Continuous  etherifying  process.     Preparation  of  ethylic  iodide,      370 
The  alcohol-radicals. — Isolation  of  ethyle.     General  formula  of  alcohol- 
radicals.     Duplex  constitution  of  the  alcohol-radicals.     Hydrides 
of  alcohol-radicals  or  marsh  gas  hydrocarbons,      .  .  .371 

Compound  ethers. — Oxalic    ether.      Oxalovinic  acid.      Acetic   ether. 
Nitrous   ether.     Nitric   ether.     Hydroxylamine   prepared    from 
nitric    ether.      Perchloric    ether.      Boracic    and    silicic    ether. 
Carbonic    ether.      Formation  of    ethyle    orthocarbonate    from 
chloropicrine.     Phosphovinic  acid.     True  sulphuric  ether.     Oil 
of  wine,        ........       372 

Sulphovinic  or  sulphethylic  acid.     Its  preparation,  ,  .      373 

Viuic  acids  not  formed  by  monobasic  acids,  ....       374 

TJieory  of  etherification. — Formation  of  double  ethers,    .  .  .       375 

Water-type  view  of  alcohols  and  ethers.     Potassium  and  sodium 

alcohols.     Aluminium  alcohols.     Thallium  alcohol,      .  .       376 

Sulphuretted  derivatives  of  the  alcohols.     Mercaptan,  .  .       377 

Hydrocyanic  ether,  ......       378 

Kakodyle-series — Organo-metallic  bodies. — Alcarsin.    Chloride  of 

kakodyle.     Kakodylic  acid.     Cyanide  of  kakodyle,  .  .       379 

Preparation  and  properties  of  zinc-ethyle.    Zinc-methyle.    Zinc-amyle. 
Potassium-ethyle.      Sodium- ethyle.     Arsenio-dimethyle  or  kako- 
dyle.    Arsenio-diethyle  or  ethyle-kakodyle,  .  .  .       380 
Arsenio-trimethyle.   Arsenio-triethyle.  Stibethyle.  Mercuric  methide. 
Aluminium  ethide.      Triborethyle.      Boric  methide.     Silicium- 
ethyle,,         ........       381 

Table  of  the  compounds  of  alcohol-radicals  with  inorganic  elements  ; 
with  their  formulae  and  inorganic  types.     Constitution  of  the 
organo-metallic  radicals,     ......       382 

Organic  alkaloids — Ammonias. — Table  of  the  alkaloids,  with  their 

sources  and  formulae.    Theories  of  the  constitution  of  the  alkaloids,       383 
Ethylated  ammonias  and   their  derivatives. — Ethylamine.     Diethyla- 
mine.     Triethylamine.     Hydrate  of  tetrethylium.     Complex  am- 
monias.    Diphenylamine.     Alkali  green,  .  .  .       384 
Investigation  of  the  constitution  of  the  alkaloids.     Monamines,    .  .       385 
Poly-ammonias ;  their  constitution,       .....       386 

Diamines.     Ethylene-diamine.     Aromatic  diamines.     Paxaniline,   .       387 
Triamines.     Carbotriamine.     Synthesis   of  guanidine.   Melaniline. 

Aniline  colours  probably  triamines,        ....       388 

Tetramines.     Tetrammonium-bases,  .....       389 

Ammonia-bases  formed  in    putrefaction   and   destructive  distilla- 
tion.    Trimethylamine  ;  its  useful  applications,  .  .       390 
Ammonias  and  ammonium  bases  containing  phosfplwrus,  arsenic,  and 

antimony.     Triethyl-phosphine,     .  .  .       '      .  .391 

Platammonium-compou7ids,         ......       392 

Amides.     Oxamide.     Oxamic  acid,  .....       393 

Nitriles.     Imides,  .......       394 

Constitution  of  the  amides.     Benzamide.     Salicylamide,      .  .       395 

Metal-amides. — Tripotassamide.     Zinc-amide.     Zinc-acetimide,  .       396 

Derivatives  of  the  alcohols. — Chloroform.     Chloral,  .  .       397 

Perfume-etliers. — Pine-apple  and  pear  essences.     Apple-oil,       .  .       398 


XXll  CONTENTS. 

Paragraph 
Aldehydes. — Preparation  and  properties  of  vinic  aldehyde,     Aldol. 
Constitution  and  synthesis  of  the  aldehydes.     Oil  of  rue.    Action 
of  aldehydes  on  the  ammonia-bases,  ....       399 

Acetones  or  ketones. — Synthesis  of  acetic  acetone.     Methyle-valeryle 

acetone.     Metacetone,         ......       400 

The  essential  oils  regarded  as  aldehydes,       ....       401 

Polyatomic  alcohols.     Glycol. — Preparation  and  properties  of  glycol. 
Glycolic  acid  ;  its  relations  to  oxalic  acid.     Lactic  series  of  acids. 
Conversion  of  the  oxalic  into  the  lactic  series.     Synthesis  of  leucic 
acid.    Conversion  of  a  diatomic  into  a  monatomic  alcohol.    Water- 
type  view  of  polyatomic  alcohols,  .....       402 

Acetic  acid — The  fatty  acid  series. — Acetates.    Acetone.    Chlora- 

cetic  acids.     Synthesis  of  acetic  acid,  ....       403 

Anhydrides  of  organic  acids. — Acetic  anhydride.     Duplex  constitution 
of  the  anhydrides.     Peroxides  of  organic  radicals.    Acetic  and 
benzoic  peroxides.     Ethyle  peroxide,  ....       404 

Formic  acid.     Synthesis  of  formic  acid.     Furfurole.     Butyric  acid. 

Synthetical  formation  of  acids  of  the  acetic  series.     Ethacetic, 

dimethacetic,  or  butyric  acid.     Diethacetic  acid.    Ethylated 

and  methylated  acetones.     Valerianic  acid,        .  .  .       405 

Separation  of  volatile  acids  by  the  method  of  partial  saturation,     .      406 

Soap. — Composition  of  the  neutral  fats.     Stearine,  oleine,  palmitine. 

Action  of  alkalies  upon  them.     Preparation  of  the  fatty  acids,     .      407 
Candles. — Decomposition  of  fats  by  sulphuric  acid.     Saponification  by 

superheated  steam,  ......       408 

Synthesis  of  natural  fats. — Glycerides.     Boro-glyceride,  .  .       409 

Properties  of  glycerine.     Acroleine.     The  acrylic  series  of  acids. 

The  allyle  series.     Glycerine  formed  from  propane,      .  .       410 

Eelatiou  between  glycerine    and    mannite.      Mannite-glycerides. 

Stearic  glucose.     Gluco-tartaric  acid,      .  .  .  .411 

Nitroglycerine. — Its  preparation  and  properties.     Dynamite,  .  .      412 

Oils  and  Fats. — Palmitine.    Oleine.    Margarine.    Oleic  acid.    Sebacic 
acid.     Dibasic  fatty  acid  series.     Linseed  oil.     Drying  oils.     Castor 
oiL     Butter.     Spermaceti.     Wax.     Table  of  the  neutral  fats  and 
fatty  acids,  with  their  formulae,  sources,  and  fusing-points,  .  .413 

Vegetable  acids. — Oxalic  acid.     Its  manufacture  from  sawdust.    Con- 
stitution of  the  oxalates,         .  .  .  .  .  .414 

Tartaric  acid.    Preparation  from  cream  of  tartar.    Tartar-emetic.    Con- 
version of  tartaric  into  succinic  and  malic  acids,    .  .  ,415 
Racemic  acid.      Hemihedrism  of  the  tartrates.      Dextrotartaric  and 

Isevotartaric  acids.     Analysis  and  synthesis  of  racemic  acid,        .       416 
Citric  acid.    Preparation  from  lemon-juice.    Conversion  of  citric  acid 

into  acetic  and  butyric  acids,  .  .  .  .  .417 

Malic  acid.    Extraction  from  rhubarb  and  from  mountain  ash  berries. 

Sorbic  and  parasorbic  acids.    Asparagine,  .  .  .      418 

Tannic  acid.     Preparation  of  ink.    Tanning  of  hides.    Morocco.    Kid. 

Wash-leather.     Buckskin,  .  ,  .  .  .419 

Gallic  acid.    Its  formation  from  tannic  acid.    Pyrogallol,     Analysis 

of  air  by  potash  and  pyrogallol.     Phloroglucol,      .  .  .       420 

Vegetable  alkaloids. — Extraction  of  the  alkaloids  from  opium.    Mor- 
phine, codeine,  narcotine.     Meconic  acid,      .  .  .  .      '!21 


CONTENTS.  xxiii 

Poragiaph 

Extraction  of  quinine  from  Peruvian  bark.    Quinoidine.    Quinic  acid, 

Quinone  and  hydroquinone,  .  .  .  .  .       422 

Theine  or  caffeine.     Composition  of  coffee  and  tea.     Coflfee-roasting. 
Caffeol.    Extraction  of  caffeine  from  them.    Theobromine.    Cocoa 
and  chocolate.     Methyle-theobromine  or  caffeine,  .  .  .       423 

Strychnine.     Extraction   from  nwx  vomica.     Brucine.     Detection  of 

small  quantities,  of  strychnine.     Curarine,  .  .  .       424 

Nicotine.     Extraction  from  tobacco.     Composition  of  tobacco.     Pre- 
paration of  snuff,     .......       425 

Vegetable  colouring  matters. — Chlorophyll.  Phylloxanthina  Phyl- 

locyanine.     Colouring  matters  of  flowers.     Cyanine.     Saffron.     Saf- 

flower ;  carthaniine.  Annatto ;  bixine.   Weld ;  luteoline.    Dye-woods. 

Madder.     Rubian.     Alizarine.     Artificial  alizarine.     Turmeric,      .       436 

Colouring    Tnatters  prepared  from   lichens. — Litmus,   archil,   cudbear. 

Orcine.     Orceine.     Azolitmine.     Erythrite,  .  .  .427 

Indigo. — Preparation  of  indigo  blue.     Indican.     White  or  reduced 

indigo.     Dyeing  with  indigo.     Artificial  indigo,    .  .  .       428 

Animal  colouring  matters. — Lac.     Carmine,       ....       429 

Dyeing  and  calico-printing. — Use  of  mordants.     Dyeing  red,  blue, 

yellow,  brown,  black,  ......       430 

Printing  in  patterns.     Resists  and  discharges,  .  .  .431 

Animal  chemistry. — Special  difficulties  attending  its  study.     Chemistry 
of  milk — Cream.     Preparation   of   butter.     Coagulation  of    milk. 
Preparation  of  lactic  acid.      Conversion  of  lactic  into  propionic 
acid.     Preparation  of  cheese.     Caseine.    Legumine.    Sugar  of  milk. 
Composition   of   milk  from    different  animals.      Adulteration   of 
milk,  .  .  ,  ,  .  ,  ,  .  ,432 

Chemistry    of   blood. — Composition    of   blood    globules.       Nucleine. 
Colouring  matter  of  blood.     Composition   of  liquor  sanguinis. 
Albumen.     Fibrine.     Proteine.     Eggs,      ....       433 

Composition  of  flesh. — Kreatine.     Inosite  or  sugar  of  flesh.     Liebig's 

extract.     Cooking  of  meat.     Myosine,        ....       434 

Gelatine.     Chondrine.    Manufacture  of  glue.     Composition  of  wool 

and  silk,  ........       435 

Chemistry  of  urine. — Urea.     Artificial  formation  of  urea.     Cyanamide,       436 
Constitution  of  urea.     Ethyl-urea.     Ureides,  .  .  .       437 

Uric  acid.     Alloxan.     Alloxantine.     Murexide,        .  .  .       438 

Hippuric  acid  ;  its  relation  to  benzoic  acid.     Glycocoll.     Average 

composition  of  human  urine,       .....       439 

Chemistry  of  vegetation.— Components  of  the  food  of  plants  ;  their 
sources.     Process  of  formation  of  a  fertile  soil  from  a  barren  rock. 
Action  of  manures.     Fallowing.     Rotation   of  crops.     Growth   of 
plants  from  seeds.     Ripening  of  fruits.     Pectose.     Pectine.     Pectic 
and  pectosic  acids.     Restoration  of  the  elements  of  plants  to  the  air. 
Preservation  of  wood  from  decay,     ■ .  .  .  .  .       440 

Nutrition  of  animals. — Chemistry  of  digestion.     Pepsine.     Composi- 
tion of  bile.     Taurine.     Cholesterine.     Chemistry  of  the  circula- 
tion.    Composition  of  food,    .  .  .  .  .  .441 

Changes  in  the  animal  body  after  death. — Restoration  of  its  ele- 
ments to  the  earth  and  air.     Nature  of  putrefaction.     Ptomaines,  .       442 


XXIV 


ATOMIC  WEIGHTS. 


ATOMIC   WEIGHTS.* 


Aluminium, 

Al'" 

27t 

Mercury, 

Hg' 

or  Hg" 

200 

Antimony, 

.      Sb' 

'  or  Sb^ 

120+ 

Molybdenum, 

Mo" 

96 

Arsenic, 

.      As" 

'  or  As' 

75 

Nickel, 

Ni" 

or  Ni'" 

59 

Barium, 

. 

Ba" 

137 

Niobium,     . 

. 

Nb' 

94 

Bismuth, 

.      Bi" 

'  or  Bi' 

210 

Nitrogen,     . 

N'" 

or  Hi" 

14 

Boron, 

B"' 

10-9 

Osmium, 

. 

Os" 

199 

Bromine, 

. 

Br' 

80 

Oxygen, 

. 

0" 

16 

Cadmium, 

. 

Cd" 

112-3 

Palladium,  . 

Pd" 

or  Pd' 

106-5 

Caesium, 

. 

Cs' 

133 

Phosphorus, 

P'" 

orP' 

31 

Calcium, 

Ca" 

40 

Platinum,     . 

Pt" 

or  Pt" 

197-1 

Carbon, 

. 

C" 

12 

Potassium,  . 

. 

K' 

39-1 

Cerium, 

. 

Ce" 

141-6 

Ehodium,     . 

. 

Ro'" 

104-3 

Chlorine, 

cr 

35-5 

Rubidium,  . 

, 

Rb' 

85-3 

Chromium, 

.       Cr'" 

or  Cr'' 

52-5 

Ruthenium, 

. 

Ru" 

104-2 

Cobalt, 

.      Co" 

or  Co"' 

59 

Selenium,     . 

. 

Se" 

79-5 

Copper, 

.       Cu' 

or  Cu" 

63-5 

Silicon, 

. 

Si" 

28 

Didymium, 

. 

Di" 

146 

Silver, 

. 

Ag' 

108 

Erbium, 

. 

E" 

112-6 

Sodium, 

Na' 

23 

Fluorine, 

. 

F' 

19 

Strontium,  . 

Sr" 

87-5 

Gallium, 

Ga'" 

69-9 

Sulphur, 

. 

S" 

32 

Glucinum, 

G" 

9-2 

Tantalum,    . 

. 

Ta' 

182 

Gold, 

Au'" 

196-6 

Tellurium,    . 

. 

Te" 

129 

Hydrogen, 

H' 

1 

Thallium,     . 

, 

Tl' 

204 

Indium, 

In'" 

113-4 

Thorinum,    . 

Th" 

231-5 

Iodine, 

. 

I' 

127 

Tin,     . 

Sn" 

or  Sn" 

118 

Iridium, 

Ir" 

197-1 

Titanium,     . 

, 

Ti" 

50 

Iron,    . 

Fe" 

orFe'" 

56 

Tungsten,    . 

W" 

184 

Lanthanium, 

. 

La" 

139 

Uranium,     . 

U" 

or  U'" 

120 

Lead,  . 

Pb" 

207 

Vanadium,  . 

V" 

or  V 

51-3 

Lithium, 

. 

L' 

7 

Yttrium, 

. 

Y" 

61-7 

Magnesium, 

Mg" 

24-3 

Zinc,  . 

. 

Zn" 

65 

Manganese, . 

Mn"  or  Mn'' 

55 

Zirconium,  . 

Zr" 

895 

*  The  accent  or  index  affixed  to  each  symbol  expresses  the  number  of  atoms  of  hydrogen 
for  which  the  atomic  weight  of  the  element  is  usually  exchangeable  in  chemical  combina- 
tions.    (See  page  247). 

t  Corrected  by  Mallet ;  fonnerly  27-5. 

X  Corrected  by  Cooke ;  formerly  122. 


INTRODUCTION. 


1.  Chemistry  investigates  and  compares  the  properties  of  all  the  various 
kinds  of  matter,  and  endeavours  to  account  for  the  difference  in  these 
properties.  In  order  to  do  this  it  seeks  to  comprehend  the  relations 
between  the  ultimate  particles  or  atoms  of  matter  which  are  incapable  of 
further  subdivision. 

Matter,  in  a  chemical  sense,  is  anything  which  possesses  weight 

The  finest  state  of  division  of  matter  with  which  we  are  acquainted  is 
that  of  gas,  the  particles  of  which  are  so  minute  as  to  be  invisible,  so  that 
on  looking  at  a  glass  vessel  filled  with  air  or  any  other  colourless  gas,  it 
is  impossible  to  say  whether  it  contains  any  matter  or  is  perfectly  empty, 
that  is,  a  vacuum.  The  doubt  may  be  resolved  by  heating  the  vessel, 
which  would  have  no  effect  upon  a  vacuum,  but  would  cause  the  gas  to 
expand  and  to  exert  a  greater  pressure  than  befora  This  expansion  of 
the  gas  proves  that  it  consists  of  a  number  of  particles  w^hich  separate 
to  a  greater  distance  from  each  other  when  they  are  heated.  These 
particles  are  called  molecules.* 

Molecules  {First  definition) ;  the  smallest  physical  particles  of 
matter. 

{Second  definition) ;  those  particles  of  matter  which  may  be  removed 
to  a  greater  distance  from  each  other  by  the  action  of  heat,  without 
changing  the  identity  of  the  matter. 

If  a  definite  volume  of  gas  be  measured  at  the  temperature  of  melting 
ice  (0°  C),  and  be  then  heated  to  a  temperature  of  273°  C.  and  again 
measured,  it  is  found  to  occupy  twice  as  much  space  as  before,  showing 
that  its  molecules  have  been  removed  to  twice  the  original  distance  from 
each  other. 

This  happens  in  the  case  of  every  gas,  so  long  as  its  identity  remains 
unchanged.  Since  this  similarity  in  expansion  by  rise  of  temperature 
is  observed  for  all  temperatures,  it  is  inferred  that  equal  volumes  of  all 
gases  at  the  same  temperature  contain  the  same  number  of  molecides. 
This  is  commonly  referred  to  as  the  Law  of  Avogadro. 

In  the  study  of  physical  changes,  a  molecule^  being  the  smallest 
physical  particle  of  matter,  may  be  taken  as  occupying  unit  of  volume,  but 
this  would  not  be  convenient  in  chemistry,  as  will  appear  from  the  follow- 
ing considerations. 

If  a  definite  volume  of  hydrogen  gas  measured  at  0°  C.  be  raised 
to  a  higher  temperature,  its  increased  volume  can  always  be  calculated 
by  adding  to  the  volume  at  0°  as  many  times  or^^cl^  of  that  volume  as 

*  Diminutive,  from  moles,  a  mass. 


*Z  INTRODUCTION. 

there  are  degrees  above  0°,  since  it  suffers  a  regular  expansion  of  ^^^rd  of  its 
bulk  at  0°  for  each  rise  of  1°  in  temperature. 

But  if  a  definite  volume  of  steam  be  raised  to  a  very  high  temperature, 
its  volume  is  found  to  become  half  as  large  again  as  that  of  the  hydrogen 
at  the  same  temperature.  For  the  steam  has  undergone  a  change  in 
identity,  having  suffered  a  chemical  decomposition  into  hydrogen  and 
oxygen,  and  the  volume  of  the  hydrogen  is  twice  that  of  the  oxygen. 

Hence,  if  one  volume  of  steam  be  raised  to  a  very  high  temperature, 
it  becomes  one  volume  of  hydrogen  and  half  a  volume  of  oxygen. 

If  a  molecule  be  taken  as  one  volume,  it  would  appear  that  one 
molecule  of  steam  is  decomposed  into  one  molecule  of  hydrogen  and  half 
a  molecule  of  oxygen. 

It  appears  then  that  when  the  identity  of  a  gas  is  changed  some  of 
its  molecules  are  halved ;  these  half  molecules  are  called  atoms.  There 
is  no  indication  of  the  possibility  of  any  further  division. 

Atom  (First  definition)  ;  the  smallest  imaginable  particle  of  matter. 

It  is  evidently  convenient  to  adopt  this  as  the  chemical  unit  of  matter, 
since  it  is  not  susceptible  of  any  further  change. 

{Second  definition  of  an  atom) ;  that  quantity  of  matter,  in  the  state  of 
gas,  which  occupies  one  volume. 

Since  the  half  molecules  are  called  atoms^  we  can  give  a  third  definition 
of  a  molecule  as  that  quantity  of  matter  in  the  state  of  gas  which 
occupies  two  volumes. 

The  action  of  a  very  high  temperature  upon  steam,  therefore,  is  to 
resolve  or  decompose  two  volumes  or  one  molecule  of  steam  into  two 
volumes  or  atoms  of  hydrogen  and  one  volume  or  atom  of  oxygen. 

But  the  hydrogen  and  oxygen  are  in  the  condition  of  atoms  only  at 
the  moment  of  separation  from  each  other;  if  they  are  subsequently 
examined,  they  present  the  ordinary  physical  properties  of  gases,  show- 
ing that  they  are  composed  of  molecules.  Hence  atoms  have  no 
permanent  existence  in  a  separate  state,  but  are  always  united  to  form 
molecules.  Indeed,  since  a  molecule  is  the  physical  unit  of  matter,  a 
half  molecule  would  be  a  physical  impossibility  ;  an  atom,  therefore,  is  a 
metaphysical  conception. 

{Fourth  definition  of  a  molecule) ;  the  smallest  quantity  of  matter  which 
is  capable  of  a  separate  existence. 

{Third  definition  of  an  atom);  the  smallest  quantity  of  matter  which  is 
capable  of  existing  in  a  molecule. 

It  is  customary  to  select  hydrogen  as  the  standard  chemical  unit  with 
which  all  atoms  and  molecules  are  compared.  This  selection  is  justified 
by  the  consideration  that  hydrogen  is  the  lightest  substance  known,  so 
that  a  very  small  weight  of  hydrogen  admits  of  very  accurate  measure- 
ment, and  the  weights  of  the  molecules  of  all  other  bodies  are  multiples 
of  that  of  hydrogeo. 

The  unit  of  weight  now  very  generally  adopted  by  scientific  chemists  is 
one  gramme  of  hydrogen,  which  measures  11  "19  litres  at  0°  C  and  76 
mm.  Bar. 

Hence,  the  unit  of  volume  is  11 '19  litres.  Since  the  weight  of  an 
atom  represents  the  weight  of  one  volume  of  a  gas  (by  the  second 
definition  of  an  atom),  it  is  evident  that  the  relative  weights  of  the  atoms 
of  different  gases  may  be  found  by  comparing  the  weights  of  equal 
volumes;  e.g., 


INTRODUCTION. 


11-19  litres  of 
Hydrogen,  weigh  1  grm. 
Oxygen,         „     16     „ 
Nitrogen,       „     14     ., 
Chlorine,       ,,    35  "5  „ 


Atomic  weight. 

1 

16 

14 

35-5 


The  relative  weights  of  the  molecules  are  obtained  in  a  similar  way, 
hut  they  are  referred  to  2  as  representing  the  standard  molecular  weight 
of  hydrogen  (by  the  third  definition  of  molecule) ;  e.g., 


11-19  X 

2  litres,  of 

Molecular  weight 

Hydrogen, 

weigh  2  grms,                        2 

Oxygen, 

„    32     , 

32 

Water-vapour 

„    18     , 

18 

Nitrogen, 

„    28     , 

28 

Ammonia, 

„    17    , 

17 

Chlorine, 

„    71     , 

71 

Hydrochloric 

acid,  ,,    36-5  , 

36-5 

Definition  of  atomic  weight. — The  number  of  grammes  of  a  simple  or" 
elementary  substance  which  occupy  11 '19  litres  in  the  state  of  gas  at 
0°  C.  and  760  mm.  Bar. 

Definition  of  molecular  weight.-^The  number  of  grammes  of  any 
substance  which  occupy  22*38  litres  in  the  state  of  gas  at  0°  C.  and  760 
mm.  Bar. 

Those  molecules  which  are  composed  of  atoms  of  the  same  kind  are 
termed  Elements;  those  which  contain  atoms  of  different  kinds  are 
Compounds.  The  greater  number  of  the  64  elements  at  present  known  to 
exist  have  not  yet  been  measured  in  the  state  of  gas,  so  that  their  relative 
atomic  weights  have  not  been  determined  in  the  manner  stated  above. 

But  in  such  cases,  some  compound  which  contains  the  element  may  be 
obtained  in  the  form  of  gas,  and  from  this  the  relative  atomic  weight 
may  be  found. 

Second  definition  of  atornic  iveight. — The  smallest  weight  of  an 
element  which  can  be  found  in  two  volumes  (22-38  litres)  of  any  of  its 
gaseous  compounds. 

Thus  carbon  has  never  been  measured  in  the  state  of  vapour,  but  its 
atomic  weight  is  inferred  to  be  12  times  that  of  hydrogen,  because  no 
less  than  12  grammes  of  carbon  are  contained  in  22-38  litres  of  any  of  the 
numerous  gases  formed  by  the  combination  of  carbon  with  other  elements. 

In  the  rare  cases  in  which  no  gaseous  compound  of  the  element  is 
known,  the  atomic  weight  is  inferred  on  the  grounds  of  chemical 
analogy,  or  it  is  ascertained  from  the  specific  heat  of  the  element. 

2.  The  elements  known  at  present  are  64  in  number,  and  are  divided 
into  metallic  and  non-metallic  elements. 

The  Non-Metallic  Elements  are  (15). 


Oxygen. 

Sulphur. 

Fluorine. 

Hydrogen. 

Selenium. 

Chlorine. 

Nitrogen. 

Tellurium. 

Bromine. 

Carbon. 

Phosphorus. 

Iodine. 

Boron. 

Arsenic* 

Silicon. 

*  In  many  English  chemical  works  arsenic  is  classed  among  the  metals,    which  it 
resembles  in  some  of  its  properties. 


INTRODUCTION. 


The  Metals  are  (49). 


Ciesiura. 

Rubidium. 

Potassium. 

Sodium. 

Lithium. 

Barium. 

Strontium. 

Calcium. 

Magnesium. 

Aluminium. 

Gallium. 

Glucinum. 

Zirconium. 

Thorinum. 

Yttrium. 

Erbium. 

Cerium. 

Lanthanum. 

Didyminm. 

Niobium. 

Zinc. 

Nickel. 

Cobalt. 

Iron. 

Manganese. 

Chromium. 

Cadmium. 

Uranium. 

Indium. 

Copper. 
Bismuth. 
Lead. 
Thallium. 

Tin. 

Titanium. 

Tantalum. 

Molybdenum. 

Tungsten. 

Vanadium. 

Antimony. 

Mercury. 

Silver. 

Gold. 

Platinum. 

Palladium. 

Rhodium. 

Ruthenium. 

Osmium, 

Iridium. 

The  strict  definition  of  a  metal  will  be  given  hereafter. 

Many  of  these  elements  are  so  rarely  met  with,  that  they  have  not 
received  any  useful  application,  and  are  interesting  only  to  the 
professional  chemist.  This  is  the  case  with  selenium*  and  tellurium, 
among  the  non-metallic  elements,  and  with  a  large  number  of  the  metals. 

The  following  list  includes  those  elements  with  which  it  is  important 
that  the  general  student  should  beconie  familiar,  together  with  the  symbolic 
letters  by  which  it  is  customary  to  represent  them,  for  the  sake  of 
brevity,  in  chemical  writings  : — 


Non-Metallic  Elements  of  practical  importance  (13). 


Oxygen, 

0 

Sulphur,          S 

Fluorine,         F 

Hydrogen, 

Nitrogen, 

Carbon, 

H 

N 
C 

Phosphorus,     P 
Arsenic,           As 

Chlorine,          CI 
Bromine,         Br 
Iodine,             I 

Boron, 

B 

Silicon, 

Si 

Metallic  Elements  of  practical  impa 

rtance  (26). 

Potassium, 

K    {Kalium) 

Cadmiun 

1,        Cd 

Sodium, 

Na  {Natrium) 

Uranium 

u 

Barium, 

Ba 

Copper, 

Cu  (Cuprum) 

Strontium, 

Sr 

Bismuth, 

Bi 

Calcium, 

Ca 

Lead, 

Pb  (Plumbum) 

Magnesium, 

Mg 

Tin, 

Sn  [Stannum) 

Aluminium, 

Al 

Titanium 

Ti 

Zinc 

Zn 

Tungsten 

,         W  ( Wol/ramium) 

Nickel, 

Ni 

Antimon 

y,       Sb  (Stibium) 

Cobalt, 

Co 

Mercury, 

Hg  (Hydrargyrum) 

Iron, 

Fe  {Ferrum) 

Silver, 

Ag  (Argentum) 

Manganese, 

Mn 

Gold, 

Au  (Aurum) 

Chromium, 

Cr 

Platinum 

Pt 

Although  the  39  elements  here  enumerated  are  of  practical  importance, 
man}'  of  them  derive  their  importance  solely,  from  their  having  met  with 


*  Tlie  remarkable  electrical  relations  of  selenium  have  led  to  some  recent  useful  applica- 
tions. 


INTRODUCTIOK 


useful  applications  in  tlie  arts.  The  number  of  elements  known  to  play 
an  important  part  in  the  chemical  changes  concerned  in  the  maintenance  of 
animal  and  vegetable  life  is  very  limited. 


Elements  concerned  in  the  Chemical  Changes  taking  place  in  Life. 


Non 

-Metallic. 

Metallic. 

Oxygen 

Sulphur. 

Potassium.                Aluminium. 

Hydrogen. 

Sodium. 

Nitrogen. 

Phosphorus. 

Iron. 

Carbon. 

Calcium.                   Manganese. 

Chlorine. 

Magnesium. 

Silicon. 

Iodine. 

These  elements*  will,  of  course,  possess  the  greatest  importance  for 
those  who  study  Chemistry  as  a  branch  of  general  education,  since  a 
knowledge  of  their  properties  is  essential  for  the  explanation  of  the 
simplest  chemical  changes  which  are  daily  witnessed. 

The  student  who  takes  an  interest  in  the  useful  arts  will  also  acquaint  - 
himself  with  the  remainder  of  the  39  elements  of  practical  importance, 
whilst  the  mineralogist  and  professional  chemist  must  extend  his  studies 
to  every  known  element 

By  far  the  greater  proportion  of  the  various  materials  supplied  to  us  by 
animals  and  vegetables  consists  of  the  four  elements — oxygen,  hydrogen, 
nitrogen,  and  carbon ;  and  if  we  add  to  these  the  two  most  abundant 
elements  in  the  mineral  world,  silicon  and  aluminium,  we  have  the  six 
elements  composing  the  bulk  of  all  matter. 

The  symbols  of  the  chemical  elements  represent  their  atomic  weights, 
thus  H  represents  one  part  by  weight  of  hydrogen,  0  represents  16  parts 
by  weight  of  oxygen,  and  C  represents  12  parts  by  weight  of  carbon. 
Each  symbol  therefore  represents  one  volume  of  the  element  in  the 
gaseous  state. 

The  molecules  (or  two  gaseous  volumes)  are  represented,  as  a  rule,  by 
writing  the  figure  2  below  and  to  the  right  of  the  symbol,  thus  Hj 
represents  a  molecule  or  two  parts  by  weight,  or  two  volumes,  of 
hydrogen;  63  =  a  molecule  or  32  parts  by  weight,  or  two  volumes,  of 
oxygen. 

The  mere  contact  or  mixture  of  substances  is  expressed  by  the  sign 
+  ;  thus  H,  +  CI2  would  imply  that  a  molecule  of  hydrogen  had  been 
brought  into  contact  with  a  molecule  of  chlorine. 

Chemical  Attraction  is  the  force  which  holds  the  atoms  of  a 
molecule  together.  Chemical  Combination  is  the  exchange  of  atoms  in 
one  molecule  for  those  in  another,  by  which  some  new  kind  of  matter 
is  produced.  For  example,  chemical  combination  takes  place  between 
hydrogen  and  chlorine,  to  form  hydrochloric  acid,  the  change  being 
represented  by  the  chemical  equation  H,  +  Cl2  =  2HCl,  which  implies 
that  the  molecules  of  hydrogen  and  chlorine  exchange  atoms. 

It  will  be  seen  from  the  statements  made  above,  that  this  equation  also 
implies  that  2  parts  by  weight  of  hydrogen  and  35-5  x  2  parts  by  weight 
of  chlorine,  yield  36*5  x  2  parts  by  weight  of  hydrochloric  acid. 

The  equation  also  informs  us  that    2  volumes  of   hydrogen  and   2 


6  INTRODUCTION. 

volumes  of  chlorine  would  combine  to  form  4  volumes  of  hydrochloric 
acid. 

It  must  be  remembered  that  a  chemical  equation  is  only  a  short  mode 
of  expressing  the  result  of  an  experiment,  and  cannot  be  used  like  a 
mathematical  equation,  to  effect  the  solution  of  a  problem. 

A  chemical  equation  may  be  written  to  express  what  is  likely  to  result 
from  the  action  of  different  molecules  upon  each  other,  but  it  has  no  value 
until  verified  by  experiment 

Chemical  Decomposition  is  the  separation  of  the  atoms  composing  a 
molecule,  which  must  precede  the  formation  of  a  new  molecule.  Thus, 
the  decomposition  of  steam  by  a  very  high  temperature  is  expressed  by 
the  equation  2H2O  =  2H2  +  Og,  which  conveys  the  information  that  two 
molecules  or  4  volumes,  or  36  parts  by  weight  of  steam,  have  suffered 
chemical  decomposition,  and  have  formed  two  molecules  or  4  volumes  or 
4  parts  by  weight  of  hydrogen,  and  one  molecule  or  2  volumes,  or  32  parts 
by  weight  of  oxygen. 

3.  Compound  substances  are  commonly  classified  by  the  chemist  into 
Organic  and  Inorganic  compounds ;  and  although  it  is  impossible  strictly 
to  define  the  limits  of  each  class,  the  division  is  a  convenient  one  for  the 
purposes  of  study. 

Organic  substances  may  be  defined  as  those  for  which  we  are  indebted 
to  the  operation  of  animal  or  vegetable  life,  such  as  starch,  sugar,  &(;. 

Inorganic  substances  are  obtained  from  the  mineral  world  without  the 
intervention  of  life ;  as  common  salt,  alum,  &c. 

Organic  substances  always  contain  carbon,  generally  also  hydrogen 
and  oxygen,  and  very  frequently  nitrogen. 


INOEGANIC    CHEMISTRY. 


CHEMISTKY  OF  THE  NON-METALLIC  ELEMENTS 
AND  THEIR  COMPOUNDS. 


THE    ELEMENTS    OF    WATER 

4.  A  century  has  not  yet  elapsed  since  water  ceased  to  be  regarded  as 
an  elementary  form  of  matter.  It  was  first  resolved  into  its  constituent 
elements,  hydrogen  and  oxygen,  by  subjecting  it  to  the  influence  of  the 
voltaic  current,  which  decomposes  or  analyses  the  water  by  overcoming 
the  chemical  attraction  by  which  its  elements  are  held  together. 

An  arrangement  for  this  purpose  is  represented  in  fig.  1. 


Fis.  1. 


-Electrolysis  of  water. 


The  glass  vessel  A  contains  water,  to  which  a  little  sulphuric  acid  has  been  added  to 
increase  its  power  of  conducting  electricity,  for  pure  water  conducts  so  imperfectly  that 
it  is  decomposed  with  great  ditticulty.  B  and  C  are  platinum  jtlates  bent  into  a  cylin- 
drical form,  and  attached  to  the  stout  platinum  wires,  which  are  passed  through  corks  in 
the  lateral  necks  of  the  vessel  A,  and  are  connected  by  binding  screws  with  the  copper 
wires  D  and  E,  which  proceed  from  the  galvanic  battery  G.  H  and  0  are  glass  cylin- 
ders with  brass  caps  and  stop-cocks,  and  are  enlarged  into  a  bell-shape  at  their  lower 
ends  for  the  collection  of  a  considerable  volume  of  gas.  These  cylinders  are  filled 
with  the  acidulated  water,  by  sucking  out  the  air  through  the  opened  stop-cocks  ;  on 
closing  these,  the  pressure  of  the  air  will,  of  course,  sustain  the  column  of  water  in 


8 


ELECTROLYSIS  OF  WATER. 


the  cylinders.  G  is  a  Grove's  battety,  consisting  of  five  cells  or  earthenware  vessels 
(A,  fig.  2)  filled  with  diluted  .sulphuric  acid  (one  measure  of  oil  of  vitriol  to  four  of 
water).  In  each  of  these  cells  is  placed  a  bent  plate  of  zinc  (B),  which  has  been 
aiiuilgamatcd  or  rubbed  with  mercury  (aud  diluted  sulphuric  acid)  to  protect  it  from 
corrosion  by  the  acid  when  the  battery  is  not  in  use.      Within  the  curved  portion  of 


Fig.  3. 

When  the  connexion  is  established  by  means  of  the  wires  D  and  E  with  the 
composing  cell"  (A),   the 


Fig.  2. 
this  plate  rests  a  small  flat  vessel  of  unglazcd  earthenware  (C),  filled  with  strong 
nitric  acid,  in  which  is  immersed  a  sheet  of  platinum  foil  (D).     The  platinum  (D)  of 

each  cell  is  in  contact,  at  its  upper  edge, 
with  the  zinc  (B)  in  the  adjoining  cell  (fig. 
3),  so  that  at  one  end  (P,  fig.  1)  of  the 
battery  there  is  a  free  platinum  plate,  and  at 
the  other  (Z)  a  free  zinc  plate.  These  plates 
are  connected  with  the  wires  D  and  E  by 
means  of  the  copper  jilates  L  and  K,  attached 
to  the  ends  of  the  wooden  trough  in  which 
the  cells  are  arranged.  The  wire  D  (fig.  1), 
which  is  connected  with  the  last  zinc  plate 
of  the  battery,  is  often  called  the  "  nega- 
tive pole  ; "  whilst  E,  in  connection  with  the 
last  platinum  plate,  is  called  the  ^^  positive 
pole." 

~       "  ~ de- 

vanic  current  "  is  commonly  said  to  pass  along  the 
wire  E  to  the  platinum  plate  C,  through  the 
acidulated  water  in  the  decomposing  cell,  to  the 
platinum  plate  B,  aud  thence  along  the  wire  D 
back  to  the  battery. 

A  very  elegant  apparatus  (fig.  4)  has  been 
devised  by  Di*.  Hofmann  for  exhibiting  the  de- 
composition of  water  by  the  galvanic  current. 
The  water  displaced  by  the  gases  accumulating 
in  the  tubes  h,  o,  collects  in  the  bulb  b  upon  the 
longer  branch,  and  exerts  the  pressure  necessarj' 
to  force  the  gases  out  when  the  stop-cocks  are 
opened.  The  stop-cocks  being  made  of  glass,  are 
not  corroded  by  the  acid. 

5.  During  this  "  passage  of  the  current " 
(which  is  only  a  figurative  mode  of  express- 
ing the  transfer  of  the  electric  influence), 
the  water  intervening  between  the  plates  B 
and  C  is  decomposed,  its  hydrogen  being 
attracted  to  the  plate  B  (negative  pole), 
and  the  oxygen  to  the  plate  C  (positive 
pole)^  The  gases  can  be  seen  adhering  in 
minute  bubbles  to  the  surface  of  each  plate, 
and  as  they  increase  in  size  they  detach 
themselves,  rising  through  the  acidulated 
"water  in  the  tubes  H  and  0,  in  which  the 
Fig.  4.— Electrolysis  of  water.        two  gases  are  collected. 

Since  no  transmission  of  gas  is  observed  between  the  two  plates,  it  is 


ELlSCTEOLYSIS  OF  WATER. 


evident  that  the  H  and  0  separated  at  any  given  moment  from  each  plate 
do  not  result  from  the  decomposition  of  one  particle  of  water,  but  from 
tvfo  particles,  as  represented  in  fig.  5,  where  A  represents  the  particles  of 
crater  lying  between  the  plates  P  and  Z  before  the  "current"  is  passed, 
and  B  the  state  of  the  particles  when  the  current  has  been  established. 
P  is  (the  positive  pole)  in  connexion  with  the  last  platinum  plate  of  the 
battery,  and  Z  is  (the  negative  pole)  in  connexion  with  the  last  zinc 
plate. 


ooooooooo 


HHMHHHHHH 


OOOOOOOO 


HHHHMHHH 


+  -J-  +  1-  +  -I-  +  + 

Fig.  5. 
The  signs  +  and  -  made  use  of  in  B  refer  to  a  common  mode  of  account- 
ing for  the  decomposition  of  water  by  the  battery,  on  the  supposition  that 
the  oxygen  is  in  a  negatively  electric  condition,  and  therefore  attracted  by 
the  positive  pole  P ;  whilst  the  hydrogen  is  in  a  positively  electric  condi- 
tion, and  is  attracted  by  the  negative  pole  Z. 

The  decomposition  of  compounds  by  galvanic  electricity  is  termed  elei'- 
trolyds*  When  a  compound  of  a  mefcil  with  a  non-inetal  is  decomposed 
in  this  manner,  the  metal  is  usually  attracted  to  the  (negative)  pole  in 
connexion  with  the  zinc  plate  of  the  battery,  whilst  the  non-metal  is 
attracted  to  the  (positive)  pole  connected  with  the  platinum  plate  of  the 
battery. 

Hence  the  metals  are  frequently  spoken  of  as  electro-positive  elements, 
and  the  non-metals  as  electro-negative. 

6.  If  the  passage  of  the  "  current  "  be  interrupted  when  the  tube  H  has 
become  full  of  gas,  the  tube  0  will  be  only  half  full,  since  water  contains 
hydrogen  and  oxygen  in  the  proportion  of  two  volumes  of  hydrogen  to  one 
volume  of  oxygen.  When  the  \\dder  portions  of  the  tubes  (fig.  1)  are 
also  filled,  the  two  gases  may  be  distinguished  by  opening  the  stop-cocks 
in  succession,  and  presenting  a  burning  match.  The  hydrogen  will  be 
known  by  its  kindling  with  a  slight  detonation,  and  burning  with  a  very 
pale  flame  at  the  jet ;  whilst  the  oxygen  will  very  much  increase  the 
brilliancy  of  the  burning  match,  and  if  a  spark  left  at  the  extremity  of  the 
match  be  presented  to  the  oxygen,  the  spark  will  be  kindled  into  a  flame. 

Another  method  of  effecting  the  decomposition  of  water  by  electricity 
consists  in  passing  a  succession  of  electric  sparks  through  steam.  It  is 
probable  that  in  this  case  the  decomposition  is  produced  rather  by  the 
intense  heat  of  the  spark  than  by  its  electric  influence. 

Por  this  purpose,  however,  the  galvanic  battery  does  not  suffice,  since 
no  spark  can  be  passed  through  any  appreciable  interval  between  the  wires 
of  the  battery, — a  fact  which  electricians  refer  to  in  the  statement  that 
although  the  quantity  of  electricity  developed  by  the  galvanic  battery  is 
large,  its  tension  is  loo  low  to  allow  it  to  discharge  itself  in  sparks  like 
the  electricity  from  the  machine  or  from  the  induction-coil,  which  pos- 
sesses a  very  high  tension,  though  its  quantity  is  small. 

7.  The   most   convenient   instrument   for   producing  a  succession  of 

*  "RXeKTpov  (amber — root  of  electricity  ;  Xi/w,  to  loosen. 


10 


DECOMPOSITION  OF  STEAM. 


electric  sparks  is  the  induction-coil,  by  the  aid  of  which  the  electric  in- 
fluence of  even  a  weak  galvanic  battery  may  be  so  accumulated  as  to 
become  capable  of  discharging  itself  in  sparks,  such  as  are  obtained  from 
the  electrical  machine. 

Fig.  6  represents  the  arrangement  for  exhibiting  the  decomposition  of  steam  by 
the  electric  spark. 

A  is  a  half-pint  flask  furnished  with  a  cork  in  which  three  holes  are  bored  :  in  one 
of  these  is  inserted  the  bent  glass  tube  B,  which  dips  beneath  the  surface  of  the  water 
in  the  trough  C. 


Fig.  6. — Decomposition  of  steam  by  electric  sparks. 

D  and  E  are  glass  tubes,  in  each  of  which  a  platinum  wire  has  been  sealed  so  as 
to  project  about  an  inch  at  both  ends  of  the  tube.  These  tubes  are  thrust  through 
the  holes  in  the  cork,  and  the  wires  projecting  inside  the  flask  are  made  to  approach 
to  within  about  xVth  of  an  inch,  so  that  the  spark  may  easily  pass  between  them. 

The  flask  is  somewhat  more  than  half  filled  with  water,  the  cork  inserted,  and  the 
tube  B  allowed  to  dip  beneath  the  water  in  the  trough,  the  wires  in  D  and  E  being 
connected  with  the  thin  copper  wires  passing  from  the  induction  coil  F,  which  is 
connected  by  stout  copper  wires  with  the  small  battery  G. 

The  water  in  the  flask  is  boiled  for  about  fifteen  minutes,  until  all  the  air  con- 
t  lined  in  the  flask  has  been  displaced  by  steam.  When  this  is  the  case,  it  will  be 
found  that  if  a  glass  test-tube  (H)  filled  with  water  be  inverted*  over  the  orifice  of 
the  tube  B,  the  bubbles  of  steam  will  entirely  condense,  with  the  usual  sharp  rattling 
.sound,  and  only  insignificant  bubbles  of  air  will  rise  to  the  top  of  the  test-tube.  If 
now,  whilst  the  boiling  is  still  continued,  the  handle  of  the  coil  (F)  be  turned  .<» 
iis  to  cause  a  succession  of  sparks  to  pass  through  the  steam  in  the  flask,  large 
bubbles  of  incondensable  gas  will  accumulate  in  the  tube  H.  This  gas  consists  of 
the  hydrogen  and  oxygen  gases  in  a  mixed  state,  having  been  released  from  their 
combined  condition  in  water  by  the  action  of  the  electric  sparks.  The  gas  may  be 
tested  by  closing  the  mouth  of  the  tube  H  with  the  thumb,  raising  it  to  an  upright 
position,  and  applying  a  lighted  match,  when  a  sharp  detonation  will  indicate  the 
recombination  of  the  gases,  t 

It  has  long  been  known  that  a  very  intense  heat  is  capable  of  decomposing  water. 
The  temperature  required  for  the  purpose  is  below  the  melting  point  of  platinum,  as 
may  be  shown  by  the  apparatus  represented  in  fig.  7. 

A  platinum  tube  {t)  is  heated  by  the  burner  h,  the  construction  of  which  is  shown 
at  the  bottom  of  the  cut.  It  consists  of  a  wide  brass  tube,  from  which  the  coal-gas 
issues  through  two  rows  of  holes,  between  which  oxygen  is  suj)plied  through  the  holes 
in  the  narrow  tube,  brazed  into  a  longitudinal  slit  between  the  two  rows  of  holes  in 
the  gas  tube.  The  oxygen  is  supplied  from  a  gas  bag  or  gas-holder,  with  which  the 
pipe  (o)  is  connected. 

The  flask  (/)  containing  boiling  water  is  furnished  with  a  perforated  cork,  carrying 
a  brass  tube  {a),  which  slips  into  one  end  of  the  platinum  tube,  into  the  other  end  of 

*  The  end  of  the  tube  B  should  be  bent  upwards  and  thrust  into  a  perforated  cork  with 
notches  cut  down  the  sides.  By  slipping  this  cork  into  the  neck  of  the  test-tube,  the  latter 
will  be  held  firmly. 

t  With  a  powerful  coil,  a  cubic  inch  of  explosive  gas  may  be  collected  in  about  fifteen 
minutes. 


ACTION  OF  METALS  ON  WATER.  11 

which  another  brass  tube  (c)  is  slipped  ;  this  is  prolonged  by  a  glass  tube  attached  by 
iudia-nibber,  so  as  to  deliver  the  gas  under  a  small  jar  standing  upon  a  bee-hive  shelf 
in  a  trough. 

The  platinum  tube  is  not  heated  until  the  whole  apparatus  is  full  of  steam,  and  no 


Fig.  7. — Decomposition  of  steam  by  heat, 

more  bubbles  of  air  are  seen  to  rise  through  the  water  in  the  trough  ;  the  gas  burner 
is  then  lighted,  and  the  oxygen  turned  on  until  the  platinum  tube  is  heated  to  a  very 
bright  red  heat ;  bubbles  of  the  mixture  of  hydrogen  and  oxygen  resulting  from  the 
decomposition  of  the  water  may  then  be  collected  in  the  small  jar,  and  afterwards 
exploded  by  applying  a  flame. 

8.  In  the  preceding  experiments,  the  force  of  chemical  attraction  hold- 
ing the  particles  of  oxygen  and  hydrogen  together  in  the  form  of  water, 
has  been  overcome  by  the  physical  forces  of  heat  and  electricity.  But 
water  may  be  more  easily  decomposed  by  acting  upon  it  with  some 
element  which  has  sufficient  chemical  energy  to  enable  it  to  displace 
the  hydrogen. 

Xo  non-metallic  element  is  capable  of  effecting  this  at  the  ordinary 
temperature. 

Among  the  practically  important  metals,  there  are  five  which  have  so 
powerful  an  attraction  for  oxygen  that  it  is  necessary  to  preserve  them  in 
bottles  filled  with  some  liquid  free  from  that  element,  such  as  petroleum 
(composed  of  carbon  and  hydrogen),  to  prevent  them  from  combining 
with  the  oxygen  of  the  atmosphere.  These  metals  are  capable  of  decom- 
posing water  with  great  facility. 

Metals  wJi  ich  decompose  icafer  at  the  ordinary/  temperature. — Potassium, 
Sodium,  Barium,  Strontiimi,  Calcium. 

9.  "WTien  a  piece  of  potassium  is  thrown  upon  water,  it  takes  fire  and  bums 
with  a  fine  violet  flame,  floating  about  as  a  melted  globule  upon  the  surface 
of  the  water,  and  producing  in  the  act  of  combination  enough  heat  to 
kindle  the  hydrogen  as  it  escapes.  The  violet  colour  of  the  flame  is  due 
to  the  presence  of  a  little  potassium  in  the  form  of  vapour.  The  same 
results  ensue  if  the  potassium  be  placed  on  ice.  The  water  in  which  the 
potassium  has  been  dissolved  will  be  found  soapy  to  the  touch  and  taste^ 
and  will  have  a  remarkable  action  upon  certain  colouring  matters.  Paper 
coloured  with  the  yellow  dye  turmeric  becomes  brown  when  dipped  in  it, 
and  paper  coloured  with  red  litmus  {archil)  becomes  blue.  Substances 
possessing  these  properties  have  been  known  from  a  very  remote  period 


12  ALKALIES  AND  ACIDS. 

as  all-aUne  substances,  apparently  because  they  were  first  observed  by  the 
alchemists  in  the  ashes  of  plants  called  Icali. 

The  alkalies  are  amongst  the  most  useful  of  chemical  agents. 

Definition  of  an  alkali. — A  compound  substance,  very  soluble  in  water, 
turning  litmus  blue  and  turmeric  brown. 

These  alkaline  properties  are  directly  opposed  to  the  characters  of  sour 
or  acid*  substances^  such  as  vinegar  or  vitriol,  which  change  the  blue 
litmus  to  red. 

When  an  acid  liquid  such  as  vinegar  (acetic  acid)  or  vitriol  (sulphuric 
acid)  is  added  to  an  alkaline  liquid,  the  characteristic  properties  of  the 
latter  are  destroyed,  the  alkali  being  neAitralised. 

An  acid  substance  may  be  known  by  its  property  of  neutralising  an 
alkali  (either  entirely  or  partly). 

The  minute  investigation  into  the  action  of  potassium  upon  the  water 
would  require  considerable  manipulative  skill  It  would  be  necessary  to 
weigh  accurately  the  potassium  employed,  to  evaporate  the  resulting 
solution  in  a  silver  basin  (most  other  materials  being  corroded  by  the 
alkali),  and  after  all  the  water  had  been  expelled  by  heat,  to  ascertain  the 
composition  of  the  residue  by  a  chemical  analysis. 

It  would  be  found  to  contain  by  weight,  1  part  of  hydrogen,  16  parts 
of  oxygen,  and  39*1  parts  of  potassium. 

Since  Avatcr  contains  2  parts  by  weight  of  hydrogen,  combined  with 
16  parts  of  oxygen,  it  is  evident  that  the  product  of  the  action  of  potas- 
sium on  water  is  formed  by  the  substitution  of  39*1  parts  of  potassium 
for  1  part  of  hydrogen. 

It  is  found  that  whenever  potassium  takes  the  place  of  hydrogen  in  a 
compound,  39  "l  parts  of  the  former  are  exchanged  for  one  of  the  latter,  and 
this  is  generally  expressed  by  stating  that  39"1  is  the  chemical  equivalent 
of  potassium. 

The  chemical  equivalent  of  a  metal  expresses  the  weight  which  is 
required  to  be  substituted  for  one  part  by  weight  of  hydrogen  in  its 
compounds. 

The  action  of  potassium  upon  water  is  an  example  of  the  production  of 
Compounds  by  substitution  of  one  element  for  another,  a  mode  of  forma- 
tion which  is  far  more  common  than  the  production  of  compounds  by 
direct  combination  of  their  elements. 

If  the  symbol  K  be  taken  to  represent  39 '1  parts  by  weight  of  potas- 
sium, its  action  upon  water  would  be  represented  by  the  chemical  equation 

H2O   +   K   =   KOH    +    H. 

Water.  Caustic  potash.t 

But  since  the  atoms  cannot  exist,  except  in  combination  as  molecules, 
it  would  be  strictly  correct  to  write  the  equation  thus  : 

2H2O   -H   K2   =    2K0H   +   Ho. 

Since  the  molecular  equation  can  always  be  obtained  by  doubling  the 
atomic  equation,  the  latter  will  be  most  commonly  given  in  this  work, 
as  involving  fewer  numbers. 

*  From  cLKv,  a  point,  referring  to  the  pungency  or  sharpness  of  the  acid  taste. 

i  Caustic,  from  Kaiw,  to  bum,  in  allusion  to  its  corrosive  properties  ;  and  potash,  from 
its  having  been  originally  prepared  from  the  washings  of  wood  ashes  boiled  down  in  iron 
pots  and  decomposed  by  lime. 


ACTION  OF  METALS  ON  WATER. 


13 


Sodium  has  a  less  powerful  attraction  for  oxygen  than  potassium,  and 
does  not  usually  take  fire  when  thrown  into  cold  water,  although  it  is  at 
once  fused  by  the  heat  evolved.  By  holding  a  lighted  match  over  the 
globule  as  it  swims  upon  the  water,  the  hydrogen  may  be  kindled,  when 
its  flame  is  bright  yellow,  from 
the  presence  of  the  sodium.  The 
solution  will  be  found  strongly 
alkaline  from  the  soda  produced. 
By  placing  the  sodium  on  a  piece 
of  blotting  paper  laid  on  the  water, 
it  may  be  made  to  ignite  the 
hydrogen  spontaneously,  because 
the  paper  keeps  it  stationary,  and 
prevents  it  from  being  so  rapidly 
cooled  by  the  water.  Several  cubic 
inches  of  hydrogen  may  easily  be 
collected  by  placing  a  piece  of 
sodium  as  large  as  a  pea  in  a  small 


Fig.  8. 


wire-gauze  box  (A,  fig.  8),  and  holding  it  under  an  inverted  cylinder  (B) 
filled  with  water  and  standing  on  a  bee-hive  ehelf. 

The  product  of  the  action  of  sodium  upon  water  contains  1  part  by 
weight  of  hydrogen,  16  of  oxygen,  and  23  of  sodium,  so  that  the  23  parts 
of  sodium  have  been  exchanged  for,  or  been  found  chemically  equivalent 
to,  1  part  of  hydrogen. 

Taking  the  symbol  Xa  to  present  23  parts  by  weight  of  sodium,  its 
action  would  be  expressed  thus — 

H^O    +   Na   =   NaOH   +   H, 

Caustic  soda. 

Barium,  strontium,  and  calcium  decompose  water  less  rapidly  than 
potassium  and  sodium. 

The  tendency  of  heat  to  separate  the  elements  of  water  being  known, 
it  might  be  expected  that  metals  which  refuse  to  decompose  water  at  the 
ordinary  temperature,  would  be  induced  to  do  so  if  the  temperature  were 
raised,  and  accordingly  magnesium  and  manganese,  which  are  without 
action  upon  cold  Avater,  decompose  it  at  the  boiling  point,  disengaging 
hydrogen,  and  producing  magnesia  (MgO,  a  feebly  alkaline  earth),  and 
oxide  of  manganese  (MnO). 

But  the  greater  number  of  the  common  metals  must  be  raised  to  a  much 
higher  temperature  than  this  in  order  to  enable  them  to  decompose  water. 
The  following  metals  will  abstract  the  oxygen  from  water  at  high  tem- 
peratures, those  at  the  commencement  of  the  list  requiring  to  be  heated 
to  redness  (about  lUOO''  F.),  and  the  temperature  required  progressively 
increasing  until  it  attains  whiteness  for  those  at  the  end  of  the  list. 

Metals  which  decompose  water  at  a  temperature  above  a  red  heat. — 
Zinc,  Iron,  Chromium,  Cobalt,  Nickel,  Tin,  Antimony,  Aluminium,  Lead, 
Bismuth,  Copper. 

The  noble  metals,  as  they  are  called,  which  exhibit  no  tendency  to 
oxidise  in  air,  are  incapable  of  removing  the  oxygen  from  water,  even  at 
high  temperatures. 

Metals  which  are  incapable  of  decomposing  water. — Mercury,  Silver, 
Gold,  Platinum. 


14 


PREPARATION  OF  HYDR0G1<:N. 


Metals  decompose  water  more  readily  when  they  are  placed  in  a  state  of  electrical 
polarisation  by  contact  with  other  metals  more  electro-negative  than  themselves. 
Thus  zinc,  in  contact  with  precipitated  copper,  will  decompose  water  at  the  ordinary 
temperature,  hydrogen  being  evolved,  and  zinc  hydrate  separated  in  white  ilakes. 

HYDROGEK 

10,  Preparation  of  hydrogen. — The  simplest  process,  chemically  speak- 
ing, for  preparing  hydrogen  in  quantity,  consists  in  passing  steam  over 
red-hot  iron.     An  iron  tube  (A,  fig.  9)  is  filled  with  iron  nails  and  fixed 


Fig.  9.  — Preparation  of  hydrogen  from  steam. 


across  a  furnace  (B),  in  which  it  is  heated  to  redness  by  a  charcoal  fire. 
A  current  of  steam  is  then  passed  through  it  by  boiling  the  water  in  the 
flask  (C),  which  is  connected  with  the  iron  tube  by  a  glass  tube  (D)  and 
perforated  corks.  The  hydrogen  is  collected  from  the  glass  tube  (G)  in 
cylinders  (E)  filled  with  water,  and  inverted  in  the  trough  (F)  upon  the 
bee-hive  shelf  (H),  the  first  portions  being  allowed  to  escape,  as  containing 
the  air  in  the  apparatus.  The  iron  combines  with  the  oxgyen  of  the 
water  to  form  the  black  oxide  of  iron  (FcgO^)  which  will  be  found  in  a 
,  crystalline  state  upon  the  surface  of  the  metal.  The  decomposition  is 
represented  by  the  equation 

4H,0   -h   Fcg   =   FegO^   +   Hg. 

Water.  Black  oxide  of  iron. 

The  weight  of  an  atom  of  iron  is  56  times  that  of  an  atom  of  hydrogen; 
hence  the  Fcg  in  the  above  equation  represent  66  x  3,  or  168  parts  by 
Aveight  of  iron. 

The  process  by  which  hydrogen  is  most  commonly  prepared  consists  in 
dissolving  iron  or  zinc  in  a  mixture  of  sulphuric  acid  and  water. 

Zinc  is  the  most  convenient  metal  to  employ  for  the  preparation  of 
hydrogen  in  this  way.  It  is  used  either  in  small  fragments  or  cuttings, 
or  as  granulated  zinc,  prepared  by  melting  it  in  a  ladle  and  pouring  it 
from  a  height  of  three  or  four  feet  into  a  pailful  of  water.  The  zinc 
is  placed  in  the  bottle  (A,  fig.  10),  covered  with  water  to  the  depth  of 


MOXATOMIC  AND  DIATOMIC  ELEMENTS. 


15 


two  or  three  inches,  and  diluted  sulphuric  acid  slowly  poured  in  through 
the  funnel  tube  (B)  until  a  pretty  brisk  effervescence  is  observed.  The 
hydrogen  is  unable  to  essape 
through  the  funnel  tube, 
since  the  end  of  it  is  beneath 
the  surface  of  the  water,  but 
it  passes  off  through  the  bent 
tube  (C),  and  is  collected 
over  water  as  usual,  the  first 
portion  being  rejected  as  con- 
taining air. 

By  allowing  the  solution 
left  in  the  bottle  to  cool, 
crystals  of  zinc  sulphate 
{white  vitriol)  may  be  ob- 
tained. 

It  will  be  noticed  that 
the  liquid  becomes  very  hot 
during  the  action  of  the  acid  upon  the  zinc,  the  heat  being  produced  by 
the  combination  which  is  taking  place.  The  black  flakes  which  separate 
during  the  solution  of  the  zinc  consist  of  metallic  lead,  which  is  always 
present  in  the  zinc  of  commerce,  and  much  accelerates  the  evolution 
of  hydrogen  by  causing  galvanic  action.  Pure  zinc  placed  in  coijtact 
with  diluted  sulphuric  acid  evolves  hydrogen  very  slowly. 

The  preparation  of  hydrogen  by  dissolving  zinc  in  diluted  sulphuric 
acid  may  be  represented  by  the  equation  * 


Fig.  10. — Preparation  of  hydrogen. 


2^JW4   +   Zn   =   ZnSO^   +   ^^g- 


H2SO 

Sulphuric  acid. 


Ho 


Zinc  sulpliate. 


The  symbol  Zn  here  represents  1  atom  of  zinc,  which  is  65  times  as 
heavy  as  the  atom  of  hydrogen.  An  atom  of  zinc  has  here  displaced  2 
atoms  of  hydrogen,  whereas  it  was  found  that  an  atom  of  potassium  dis- 
placed only  1  atom  of  hydrogen,  which  is  often  expressed  by  saying  that 
potassium  is  a  monatoniic  element,  i.e.,  is  exchangeable  for  1  atom  of 
hydrogen. 

But  since  Q5  parts  of  zinc  displace  2  parts  of  hydrogen,  zinc  is  a  diatomic 
element,  i.e.,  is  exchangeable  for  2  atoms  of  hydrogen.  This  is  commonly 
expressed  by  writing  the  symbol  of  zinc  thus — Zn". 

It  may  be  supposed  that  the  atom  of  a  monatomic  element,  such  as  hydrogen  or 
potassium,  exerts  its  chemical  attraction  in  one  direction  only,  as  represented,  by  a 
single  line  or  bond  attached  to  the  symbol,  thus  H  -  ,K  -  ;  whilst  a  diatomic  element, 
such  as  zinc,  exerts  chemical  attraction  in  two  directions,  represented  by  attaching 
two  lines  to  the  symbol,  thus— Zn-,  or  Zn  =  .  Since  an  atom  of  oxygen  combines 
with  two  atoms  of  hydrogen,  it  must  also  exert  chemical  attraction  in  two  directions, 

so  that  a  molecule  of  water  may  be  represented  as  H 0 H.     The  displacement 

of  half  the  hydrogen  by  potassium  (p.  12)  then  produces  K  —  0  —  H,  caustiQ 
potash,  and  the  displacement  of  both  atoms  of  hydrogen  by  zinc  produces  Zn  =  =  0, 
or  zinc  and  oxygen  united  by  both  their  bonds  of  chemical  attraction,  forming  zinc 
oxide. 


*  In  this  equation  the  excess  of  water  which  must  be  added  to  dissolve  the  zhic  sulphate 
is  not  set  down.  Hydrogen  could  not  be  prepared  according  to  the  equation  as  it  stands, 
because  the  zinc  sulphate  would  collect  round  the  metal  and  prevent  further  action. 


16  PROPERTIES  OF  HYDROGEX. 

Iron  might  be  used  instead  of  zinc,  and  the  solution,  when  evaporated, 
would  then  deposit  crystals  of  green  vitriol  or  copperas  (sulphate  of  iron, 
or  ferrous  sulphate,  FeSO^),  the  action  of  iron  upon  the  sulphuric  acid 
being  represented  by  the  equation 

H2SO4   +   Fe   =   FeSO^   +   H2. 

Salpbnric  acid.  Ferrons  sulphate. 

which  shows  that  1  atom  (56)  of  iron  has  taken  the  place  of  2  atoms  of 
hydrogen,  and  that  the  iron  is  diatomic,  like  zinc. 

Hydrogen  has  been  prepared  cheaply  in  large  quantity  by  heating  a  mixture  of 
slaked  lime  with  anthracite  coal  in  an  iron  retort ;  C  +  CaO  +  2H2O  =  CaCOj  +  H4. 
On  passing  steam  over  the  residue  ;  CaCOg  =  CaO  +  CO,  :  hence,  if  enough  carbon  be 
employed  in  the  beginning,  large  quantities  of  hydrogen  may  be  obtained  by  steaming 
ami  heating  alternately. 

11.  Physical  properties  of  hydrogen. — This  gas  is  invisible,  and  in- 
odorous when  pure.  The  hydrogen  obtained  by  the  ordinary  methods  has 
a  very  disagreeable  smell,  caused  by  the  presence  of  minute  quantiti&s  of 
compounds  of  hydrogen  with  sulphur,  arsenic,  and  carbon ;  but  the  gas 
prepared  with  pure  zinc  and  sulphuric  acid  is  quite  free  from  smeU.  It 
is  liquefied  with  extreme  difficulty,  requiring  a  pressure  of  650  atmo- 
spheres at  —  220°  F.  ( -  140°  C).  Tlie  most  remarkable  physical  property 
of  hydrogen  is  its  lightness.  It  is  the  lightest  of  all  kinds  of  matter, 
being  about  —  as  heavy  as  air,  and  ryx^nr  ^^  heavy  as  water. 

The  lightness  of  hydrogen  may  be  demonstrated  by  many  interesting  experiments. 
Soap  bubbles  or  small  balloons  (of  collodion,  for  example, )  will  ascend  very  rapidly  if 
inflated  with  hydrogen.  A  light  beaker  glass  may  be  accurately  weighed  in  a  pair 
of  scales  ;  it  may  then  be  held  with  its  mouth  downwards,  and  the  hydrogen  poured 
up  into  it  from  another  vessel.  It  it  be  then  replaced  upon  the  scale-pan  with  its 
mouth  downwards,  it  will  be  found  very  much  lighter  than  before.  Another  form 
of  the  experiment  is  represented  in  fig,  11,  where  a  light  glass  shade  has  been  sus- 
pended from  the  balance  and  counterpoised,  the  equilibrium  being,  of  course,  at  once 
disturbed  when  hydrogen  is  poured  up  into  the  shade.  If  a  stoppered  gas  jar  full 
of  hydrogen  be  held  with  its  mouth  downwards,  and  a  piece  of  smouldering  brown 
paper  held  under  it,  the  smoke,  which  would  rise  freely  in  the  air,  is  quite  unable 
to  rise  through  the  hydrogen,  and  remains  at  the  mouth  of  the  jar  uutU  the  stopper 
is  removed,  when  the  hydrogen  quickly  rises  and  the  smoke  follows  it. 

12.  The  employment  of  hydrogen  for  filling  balloons  renders  a  know- 
ledge of  the  relation  between  the  weights  of  equal  volumes  of  hydrogen 
and  atmospheric  air  of  great  importance.  The  number  expressing  this 
relation  is  termed  the  Specific  Grairity  of  hydrogen. 

(Definition, — The  specific  gravity  of  a  gas  or  vapour  is  its  weight  as 
compared  with  that  of  an  equal  volume  of  some  other  gas,  selected  as  a 
standard,  at  the  same  temperature  and  pressure.) 

If  the  weight  of  a  giveil  volume  of  purified  and  dried  air  be  repre- 
sented as  unity,  an  equal  volume  of  hydrogen,  at  the  same  temperature 
and  pressure,  would  weigh  0*0692,  which  is  expressed  by  saying  tliat  the 
specific  gravity  of  hydrogen  (air=  1)  is  0'0692, 

In  ascertaining  the  weights  of  definite  volumes  of  gases,  it  is  of  the 
crreatest  importance  that  they  should  have  some  definite  temperature  and 
jiressure,  since  the  volume  of  a^yen  weight  of  gas  is  augmented  by  the 
increase  of  temperature  and  by  decrease  in  pressure.     In  England  it  is 


UNITS  OF  GASEOUS  VOLUME. 


17 


usual  to  state  the  weights  of  gases  at  the  temperature  of  60°  on  tlie 
Fahrenheit  thermometer,  and  under  a  pressure  of  30  inches  of  mercury  in 
the  barometer,  these  being  regarded  as  the  average  conditions  of  the 
climate. 


Fig.  n. 

On  the  Continent  the  standard  pressure  is  very  nearly  the  same,  being 
760  millimetres  of  the  barometric  column,  or  29 '922  inches;  but  the 
standard  temperature  is  that  of  melting  ice^  or  0°  on  the  centigrade  scale, 
corresponding  to  32°  F.,  a  temperature  to  which  gases  may  be  reduced  at 
will,  by  surrounding  with  melting  ice  the  vessels  in  which  they  are 
collected  for  the  purpose  of  being  weighed. 

One  grain  of  hydrogen,  at  60°  F.  and  30  inches  Bar.,  measures  46-73 
cubic  inches. 

Expressed  on  the  Continental  system,  one  gramme  (15-43  grains)  of 
hydrogen,  at  0°  C.  and  760  mm.  Bar.,  measures  11  •19  litres  (one  litre  = 
61-024  cubic  inches  =  1*76  pints). 

It  is  now  easy  to  calculate  how  much  zinc  it  would  be  necessary  to  dissolve  in 
sulphuric  acid  in  order  to  obtain  any  desired  volume,  say  100  cubic  feet  (172,800 
cubic  inches)  of  hydrogen.  Referring  to  the  equation  for  the  preparation  of  hydro- 
gen, Zn  +  H2S04  =  H2  +  2nS04,  and  remembering  that  Zn  represents  65  parts  by 
weight  of  zinc,  and  H^j  represent  2  parts  by  weight  of  hydrogen— 


2  grs.  H 
93-46  cub.  in. 


grs.  Zn 
65 


Cub.  in. 
172800 


a;  (  =  12018  grs.  zinc) 


13.  It  will  be  observed,  in  the  experiment  with  the  balance  (fig.  11), 
that  the  gas  gradually /a//,",- out  of  the  jar,  notwithstanding  its  lightness, 
and  is  replaced  by  air ;  so  that,  after  a  time,  the  equilibrium  is  restored, 
proving  that  the  molecules  of  hydrogen  possess  motion  which  is  independent 
of  gravitation.  This  is  evident  also  from  another  consideration.  The 
total  weight  of  the  molecules  of  hydrogen  in  one  cubic  centimetre  of 
the  gas  at  0°  C.  and  760  mm.  Bar.  is  only  -0000896  gramme,  and  yet  its 

B 


18  DIFFUSION  OF  GASES. 

pressure  upon  the  sides  of  the  vessel  containing  it  amounts  to  1033  grammes 
per  square  centimetre. 

The  weight  of  a  single  molecule  of  hydrogen  has  heen  calculated  to  be 
not  greater  than  one  ten- thousand-millionth  of  a  gramme,  and  21  trillions 
of  them  are  calculated  to  be  contained  in  one  cubic  centimetre.  This 
enormous  number  of  molecules,  moving  with  great  velocity  and  delivering 
successive  blows  on  the  sides  of  the  vessel,  give  rise  to  the  pressure  of 
the  gas. 

Hence  the  pressure  of  a  gas  will  vary  with  the  weight  of  its  mole- 
cules, and  with  their  velocity.  If  in  be  taken  to  represent  the  weight 
of  a  molecule,  and  v  its  velocity,  mv  will  express  the  momentum  of  each 
molecule ;  but  the  pressure  depends  not  only  on  the  momentum  of  each 
molecule,  but  on  the  number  of  blows  delivered  by  each  molecule  in  equal 
times,  which  will  increase  with  the  velocity  of  the  molecule.  Hence 
mv  X  V  or  mv^  will  represent  the  pressure  of  the  gas.  Suppose  this  pressure 
to  be  some  constant  unit  of  pressure,  represented  by  1,  then  m«2  =  1,  and 

,     1  1 

V^  =  —  .     ox  V=   —f—  , 

m  sIm 

showing  that  the  velocities  of  the  molecules  of  gases  vary  inversely  as  the 
square  roots  of  their  molecular  weights.  But  the  molecvdar  weights  of 
the  gases  represent  the  weights  of  equal  volumes  (see  p.  3),  or  the 
specitic  gravities  of  the  gases,  so  that  the  velocities  of  the  molecules  of 
gases  vary  inversely  as  the  square  roots  of  their  specific  gravities. 

The  absolute  velocity  of  the  molecules  of  a  gas  may  be  calculated  when 
the  pressure,  the  temperature,  and  the  weight  of  a  given  volume  of  the 
gas  are  known.  It  has  thus  been  determined  that  the  absolute  velocity  of 
a  molecule  of  hydrogen  at  0°  C.  and  760  mm.  Bar.  is  6050  feet  per  second. 
Oxygen  is  16  times  as  heavy  as  hydrogen,  hence  the  velocity  of  the  oxygen 

molecule,  for  the  same  temperature  and  pressure,  would  be  -j^^  =  ^  th 

that  of  the  hydrogen  molecule,  or  1512  feet  per  second. 

This  view  of  the  constitution  of  gases  (known  as  the  kinetic  theory, 
from  Kivqa-fs,  motion)  explains  their  remarkable  physical  properties. 
If  a  vessel  of  hydrogen  at  760  mm.  pressure  were  opened  into  a  vacuum, 
the  molecules  of  hydrogen  would  escape  into  the  vacuum  with  a  velocity 
of  6050  feet  per  second.  If  the  vessel  be  opened  in  air,  the  velocity  of 
the  hydrogen  molecules  will  be  retarded  by  collision  with  the  air-molecules, 
but  the  gas  still  escapes  very  rapidly. 

The  nitrogen  and  oxygen  gases,  which  are  mixed  together  in  air^  being 
respectively  14  and  16  times  as  heavy  as  hydrogen,  their  molecules  have 
a  lower  velocity,  and  are  not  carried  into  the  vessel  so  rapidly  as  the 
hydrogen  passes  out.  In  order  to  render  this  evident,  the  opening 
of  the  vessel  should  be  closed  by  some  material  having  very  minute 
pores,  so  as  to  retard  the  exchange  of  the  gases,  and  to  measure  the  relative 
velocities  of  their  molecules,  or  the  rates  of  diffusion  of  the  gases. 

The  difftision  tube  (fig.  12)  employed  for  this  purpose  is  a  elass  tube  (A)  closed 
at  one  euii  by  a  plate  of  plaster  of  Paris  (B).     If  this  tube  be  filled  with  hydrogen,  *  and 

*  Tills  tube  must  be  filled  by  displacement  (see  fig.  18),  in  order  not  to  wet  the  plaster. 
A  piece  of  sheet  caoutchouc  may  be  tied  over  the  plaster  of  Paris,  so  that  diffusion  may 
not  commence  until  it  is  removed. 


DIFFUSION  OF  GASES. 


19 


Fig.  12. 


its  open  end  immersed  in  coloured  water,  the  water  will  be  observed  to  rise  rapidly 

in  the  tube,  on  account  of  the  rapid  escape  of  the  hydrogen  through  the  pores  of  the 

plaster.     Tlie  external  air,  of  course,  passes  into  the  tube  through  the  pores  at  the 

same  time,  but  much  leas  rapidly  than  the  hydrogen  passes  out,  so  that  the  ascent  of 

the  column  of  water  (C)  marks  the  difference  between 

the  volume  of  hydrogen  which  passes  out,  and  that  of 

air  which  passes  into  the  tube  in  a  given  time,   and 

allows  a  measurement  to  be  made  of  the  rate  of  diffusion; 

that  is,  of  the  velocity  with  which  the  gas  issues  as 

compared  with  the  velocity  with  which  the  air  enters, 

this  velocity  being  always  taken  as  unity.*     To  deter- 
mine the  rate  of  diffusion,  it  is  of  course  necessary  to 

maintain  the  water  at  the  same  level  within  and  without 

the  diffusion  tube,   so  as  to  exclude  the  influence  of 

pressure. 
To  prove  that  the  ascent  of  the  hydrogen  due  to  its 

lightness  is  not  instrumental  in  drawing  up  the  water 

in  the  diffusion  tube,  the  experiment  may  be  made  as 

in   fig.    13,    where  the  plate   of  plaster   (o)   is   turned 

downwards,  so  that  the  diffusion  is  made  to  take  place 

in  opposition  to  the  action   of  gravity.     This  tube  is 

filled  by  passing  hydrogen  in  through  the  tube  (s),  and 

allowing  the  air  to  escape  through  (<),  wliich  is  afterwards 

closed  by  a  cork.     The  plaster  of  Paris  (o)  is  tied  over  with  caoutchouc  whilst  the 

tube  is  filled. 

Since  the  relation  between  the  weights  of  equal  volumes  of  hydrogen  and  air  is 

that  of  0  '069  :  1 ,  the  rates  of  diffusion  will  be  as 

1  :  V0'069 — that  is,  hydrogen  will  diffuse  about 

3  "8  times  as  rapidly  as   atmospheric  air,   or   3  "8 

measures  of  hydrogen  %\ill  pass  out  of  the  diffusion 
tube  whilst  one  measure  of  air  is  passing  in  through 
the  plaster.  In  a  similar  manner  hydrogen  would 
escape  through  minute  openings  with  four  times 
the  velocity  of  oxygen  ;  and  laboratory  experience 
shows  that  a  cracked  jar,  or  a  bottle  with  a  badly 
fitting  stopper,  may  often  be  used  to  retain  oxygen, 
but  not  hydrogen. 

A  very  striking  illustration  of  the  high  rate  of 
diffusion  of  hydrogen  is  arranged  as  represented  in 
fig.  14.  A  is  a  cylinder  of  porous  earthenware 
(such  as  are  employed  in  galv^anic  batteries)  closed 
at  one  end,  and  furnished  at  the  other  with  a 
perforated  caoutchouc  stopper  or  a  cork  bung, 
through  which  passes  a  glass  tube  B,  about  six 

feet  long,  and  half  an  inch  in  diameter.  The  bung  is  made  air-tight  by  coating  it 
with  sealing  wax  dissolved  in  spirit  of  wine.  This  tube  being  supported  so  that  its 
lower  end  dips  about  an  inch  below  the  surface  of  water,  a  jar  of  coal-gas  is  held  over 
the  porous  cylinder,  when  the  velocity  of  the  particles  of  the  gas  is  manifested  by 
their  being  forced  (not  only  out  of  the  mouth  of  the  jar  0,  which  is  open  at  the 
bottom,  but  also)  through  the  pores  of  the  earthenware  jar,  the  air  from  which  is 
violently  driven  out,  as  if  by  blowing,  through  the  tube,  and  is  seen  bubbling  u)> 
rapidly  through  the  water.  When  the  air  has  ceased  to  bubble  out,  and  a  large 
volume  of  gas  has  entered  the  porous  jar,  the  bell-jar  C  is  removed,  when  the  gas 
escapes  so  rapidly  through  the  pores,  that  a  column  of  tw'enty  to  thirty  inches 
of  water  is  drawn  rapidly  up  the  tube  B.  If  the  greatest  height  to  which  the  water 
ascends  be  marked,  and  when  it  has  returned  to  its  former  level,  a  jar  of  hydrogen 
be  held  over  the  porous  cylinder,  it  will  be  found  that  the  above  phenomena  are 
manifested  in  a  much  higher  degi'ee,  showing  that  coal-gas,  being  heavier  than 
hydrogen,  does  not  pass  nearly  so  rapidly  through  the  pores  of  the  eai-thenware  as 
hydrogen  does. 


Fi<:.  13. — Diffusion  tube. 


*  Air  being  a  mixture  of  nitrogen  and  oxygen,  its  rate  of  diffusion  is  intermediate 
between  the  rates  of  those  gases  ;  however,  since  the  proportions  of  the  gases  are  very 
nearly  constant,  no  error  of  any  magnitude  arises. 


20 


PROPERTIES  OF  HYDROGEN. 


By  connecting  the  porous  cylinder  A,  by  means  of  a  short  piece  of  tube,  ^vith  a  two- 
necked  bottle,  like  that  represented  in  fig.  10,  and  passing  through  a  cork  in  the 
other  neck,  a  piece  of  tube  reaching  to  the  bottom  of  the  bottle  and  drawn  out  to  an 

open  point  at  its  upper  extremity  (fig.  19),  water 
may  be  forced  out  in  a  stream  of  two  or  three 
feet  in  height  by  holding  the  jar  of  hydrogen  over 
the  porous  cylinder. 

The  great  difference  in  the  rates  of  diffusion  of 
hydrogen  and  oxygen  may  be  easily  shown  by  the 
arrangement  represented  in  fig.  15.  A  is  a  jar 
filled  with  a  mixture  of  two  volumes  of  oxygen 
with  one  volume  of  hydrogen,  communicating 
through  the  stop-cock  and  flexible  tube  with  the 
glass  tube  B,  which  is  fitted  tlirough  a  perforated 
cork  in  the  bowl  of  the  common  tobacco-pipe  C, 
the  sealing-waxed  end  of  which  dips  under  water 
in  the  trough  D.  By  opening  the  stop-cock  and 
pressing  the  jar  down  in  the  water,  the  mixed 
gases  may  be  forced  rapidly  through  the  pipe, 
and  if  a  small  cylinder  (E)  be  filled  with  them, 
the  mixture  will  be  found  to  detonate  violently 
on  the  approach  of  a  flame.  But  if  the  gas  be 
made  to  pass  very  slowly  through  the  pipe  (at  the 
rate  of  about  a  cubic  inch  per  minute),  the 
hydrogen  will  diff"use  through  the  pores  of  the 
pipe  so  much  faster  than  the  oxygen,  that  the  gas 
collected  in  the  cylinder  will  contain  so  little 
hydrogen  as  to  be  no  longer  explosive,  and  to 
exhibit  the  property  of  oxygen  to  rekindle  a  partly 
extinguished  match. 

If  two  jars  of  the  same  size,  one  made  of  glass 
and  the  other  of  porous  earthenware,  be  filled  with 
the  explosive  mixture  by  holding  them  over  the 
stop-cock  of  the  jar  A,  and  be  then  closed  with 
glass  plates  and  set  aside  for  a  few  seconds,  it  will 
be  found  that  the  gas  in  the  earthen  jar  will 
rekindle  a  spark  on  a  match,  whilst  that  in  the 
glass  jar  will  explode. 

The  rapid  diff"usion  of  hydrogen  through  paper 
may  be  shown  by  laying  a  flat  piece  of  filter-paper 
upon  the  mouth  of  a  cylinder  of  hydrogen,  when 
the  gas  may  be  kindled  on  the  upper  surface.  On 
repeating  the  experiment  with  a  cylinder  of  coal- 
gas,  only  the  pale  flame  of  the  hydrogen  will 
appear  above  the  paper.  If  a  mixture  of  hydrogen 
and  oxygen  be  employed,  the  hydrogen  will  be 
seen  burning  before  the  explosion  takes  place. 
A  cylinder  containing  2  vols.  H  and  1  vol.  of  0,  if  covered  with  filter-paper,  will  be 
found  to  contain  little  else  but  oxygen  after  a  minute  or  two. 


Fig.  14. 


14.  Chemical  p^'operties  of  hydrogen. — The  most  conspicuous  chemical 
property  of  hydrogen  is  its  disposition  to  burn  in  air  when  raised  to  a 
moderately  high  temperature,  entering  into  combination  with  the  oxygen 
of  the  air  to  form  water.  The  formation  of  water  during  the  combustion 
of  hydrogen  gave  rise  to  its  name  (uSw/),  water). 

Since  an  atom  of  oxygen  combines  with  two  atmns  of  hydrogen  to  form  water,  the 
gases  will  not  combine  unless  under  the  influence  of  some  force,  such  as  heat  or  elec- 
tricity, to  assist  in  resolving  their  molecules  into  the  constituent  atoms. 

On  introducing  a  taper  into  an  inverted  jar  of  hydrogen  (fig.  16),  the  flame  of  the 
taper  will  be  extinguished,  but  the  hydrogen  will  burn  with  a  pale  flame  at  the 
mouth  of  the  jar,  and  the  taper  may  be  rekindled  at  its  flame  by  slowly  withdraw- 
ing it. 


PROPERTIES  OF  HYDROGEN. 


21 


The  lightness  and  combustibility  of  hydrogen  may  be  illustrated  simultaneously 
by  some  interesting  experiments.  If  two  equal  gas  cylinders  be  filled  with  hydrogen, 
and  held  \yith  their  mouths  respectively  upwards  and  .downwards,  it  will  be  found 
on  testing  each  with  a  taper  after  the  same  interval,  that  the  hydrogen  has  entirely 
escaped  from  the  cylinder  held  with  its  mouth  upwards,  whilst  the  other  still  remains 
nearly  filled  with  gas. 

The  hydrogen  may  be  scooped  out  of  the  jar  A  (fig.  17)  with  the  small  cylinder  B 
attached  to  a  handle.  On  removing  B,  and  applying  a  taper  to  it,  the  gas  will  take 
tire. 


Fig.  15. — Separation  of  hydrogen  and  oxygen  by  atmolysis.* 

A  cylinder  may  be  filled  with  hydrogen  by  displacement  of  air  (fig.  18),  if  the  tube 
from  the  hydrogen  bottle  be  passed  up  into  it. 


Fig.  16. 


Fig.  17. 


Fig.  18. 


If  such  a  dry  cylinder  of  hydrogen  be  kindled  whilst  held  with  its  mouth  down- 
wards, the  formation  of  water  during  the  combustion  of  the  hydrogen  will  be  indi- 
cated by  the  deposition  of  dew  upon  the  sides  of  the  cylinder. 

*  This  term  has  been  applied  to  the  separation  of  gases  by  diflusion  ;  a-r/xos,  vapour; 
X'lio,  to  loosen. 


22 


EXPLOSION  OF  HYDROCEN  AND  AIR. 


By  softening  a  piece  of  glass  tube  in  the  flame  of  a  spirit-lamp,  drawing  it  out  and 

tiling  it  across  in  the  narrowest  part  (fig.   19),  a  jet  can  be  made  from  which  the 

hydrogen  may  be  burnt.     This  jet  may  be  fitted  by  a  perforated  cork  to  any  common 

^^  bottle  for  containing  the  zinc 

y  "^^  I  ■  "'  '^^  C        and  sulphuric  acid  (fig.  20). 

The  hydrogen  must  be  allowed 
to  escape  for  some  minutes  before 
applying  a  light,  because  it  forms 
an  explosive  mixture  with  the 
*'8'  •^^"  air  contained  in  the  bottle.     This 

may  be  proved,  without  risk,  by  placing  a  little  granulated  zinc  in  a  soda-water 
bottle,  pouring  upon  it  some  diluted  sulphuric  acid,  and  quickly  inserting  a  perforated 
cork,  carrying  a  piece  of  glass  tube  about  three  inches  long,  and  one-eighth  of  an  inch 
wide.  If  this  tube  be  immediately  applied  to  a  flame,  the  mixture  of  air  and  hydro- 
gen will  explode,  and  the  cork  and  tube  will  be  projected  to  a  considerable  distance. 

By  inverting  a  small  test-tube  over  the  jet  in  fig.  20,  a  specimen  of  the  hydrogen 
may  be  collected,  and  may  be  kindled,  to  see  if  it  burns  quietly,  before  lighting 
the  jet. 

A  dry  glass,  held  over  the  flame,  will  collect  a  considerable  quantity  of  water, 
formed  by  the  combustion  of  the  hydrogen. 

The  combustion  of  hydrogen  produces  a  greater  heating  effect  than  that 
of  an  equal  weight  of  any  other  combustible  body.  It  has  been  deter- 
mined that  1  gr,  of  hydrogen,  in  the  act  of  combining  with  8  grs..of 
oxygen,  produces  enough  heat  to  raise  62,031  grs.  of  water  from  32°  F. 
to  33°  F.  (or  34,462  grs.  from  0°  C.  to  1°  C.)  The  temperature  of  the 
hydrogen  flame  is  probably  about  1830°  C.  Notwithstanding  its  high 
temperature,  the  flame  of  hydrogen  is  almost  devoid  of  illuminating 
power,  on  account  of  the  absence  of  solid  particles. 

15.  If  a  taper  be  held  several  inches  above  a  cylinder  of  hydrogen, 
standing  with  its  mouth  upwards,  the  gas  will  be  kindled  with  a  loud 


Fiff.  20. 


Fig.  21. 


explosion,  because  an  explosive  mixture  of  hydrogen  and  air  is  formed  in 
and  around  the  mouth  of  the  cylinder. 

If  a  stoppered  glass  jar  (fig.  21)  be  filled  with  hydrogen,  and  supiwrted  upon  three 
blocks,  it  will  be  found,  if  the  hydrogen  be  kindled  at  the  neck  of  the  jar,  that  it  will 
Inirn  quietly  until  air  has  entered  from  below  in  sufficient  proportion  to  form  an 
explosive  mixture,  which  will  then  explode  with  a  loud  report. 

The  same  experiment  may  be  tried  on  a  smaller  scale,  with  the  two-necked  copper 
Vessel  (fig.  22),  the  lower  aperture  being  opened  some  few  seconds  after  the  hydrogen 
has  been  kindled  at  the  upper  one. 


PROPEETIES  OF  OXYGEN.  23 

The  explosion  of  the  mixture  of  hydrc.gen  and  air  is  due  to  the  sudden 
expansion  caused  by  the  heat  generated  in  the  combination  of  the  hydrogen 
with  the  oxygen  throughout  the  mixture.  After 
the  explosion  of  the  mixture  of  hydrogen  and  air 
(oxygen  and  nitrogen),  the  substances  present  are 
steam  (resulting  from  the  combination  of  the 
hydrogen  and  oxygen)  and  nitrogen,  which  are 
expanded  by  the  heat  developed  in  the  combination, 
to  a  volume  far  greater  than  the  vessel  can  contain, 
so  that  a  portion  of  the  gas  and  vapour  issues  very 
suddenly  into  the  air  around,  the  collision  with 
which  produces  the  report. 

If  pure  oxygen  be  substituted  for  air,  the  ex-  „. 

plosion  will  be  more  violent,  because  the  mixture  ®" 

is  not  diluted  with  the  inactive  nitrogen.     The  further  study  of  this 
subject  must  be  preceded  by  that  of  oxygen. 

OXYGEN^. 

0  =  16  parts  by  weight  =  1  vol.  16  grains  =  46  7  cub.  in.  at  60°  F.  and  30"  Bar. 
16  grammes  =  ll'2  litres  at  0°  C.  and  760  mm.  Bar. 

16.  Oxygen  is  the  most  abundant  of  the  elementary  substances.  It  con- 
stitutes about  one-fifth  (by  volume)  of  atmospheric  air,  where  it  is  merely 
mixed,  not  combined,  with  the  nitrogen,  which  composes  the  bulk  of  the 
remainder.  Water  contains  eight-ninths  (by  weight)  of  oxygen;  whilst 
silica  and  alumina,  which  compose  the  greater  part  of  the  solid  earth  (as 
far  as  we  know  it),  contain  about  half  their  weight  of  oxygen. 

Before  inquiring  which  of  these  sources  will  most  conveniently  furnish 
pure  oxygen,  it  will  be  desirable  for  the  student  to  acquire  some  know- 
ledge of  the  properties  of  this  element,  and  of  the  chemical  relations 
which  it  bears  to  other  elementary  bodies,  for  without  such  knowledge  it 
will  be  found  very  difficult  to  understand  the  processes  by  which  oxygen 
is  procured. 

17.  Physical  properties  of  oxygen. — From  the  fact  of  its  occurring  in  an 
uncombined  state  in  the  atmosphere,  it  will  be  inferred  that  oxygen  is 
perfectly  invisible,  and  without  odour.  It  is  liquefied  with  difficulty, 
requiring  a  pressure  of  320  atmospheres  at  -  220°  F.  (  -  140°  C.)  Oxygen 
gas  is  a  little  more  than  one-tenth  heavier  than  air,  which  is  expressed  in 
the  statement  that  its  specific  gravity  is  1*1 057. 

In  the  study  of  theoretical  chemistry,  it  is  expedient  to  select  hydro- 
gen instead  of  air  as  the  standard  with  which  the  specific  gravities  of 
gases  are  compared;  for,  since  the  atomic  weights  are  also  referred  to 
hydrogen  as  the  unit,  and  the  atomic  weights  represent  the  weights  of 
equal  volumes,  the  numbers  expressing  the  atomic  weights  of  the  ele- 
mentary gases  are  identical  with  their  specific  gravities  (H  =  l).  Thus 
the  specific  gravity  of  oxygen  (H  =  l)  is  16.  It  will  be  found  con- 
venient to  remember  that  the  specific  gravity  of  a  gas  or  vapour  is  the 
iceight  of  one  volume. 

18.  Chemical  properties  of  oxygen. — This  element  is  remarkable  for  the 
wide  range  of  its  chemical  attraction  for  other  elementary  bodies,  with  all 
of  whichj  except  one,  it  is  capable  of  entering  into  combination.  Fluonne 
ii  the  only  element  which  is  not  known  to  unite  with  oxygen. 


24 


COMBUSTIOX. 


With  nearly  all  the  elements  oxygen  combines  in  a  direct  manner; 
that  is  without  the  intervention  of  any  third  substance. 

There  are  oidy  seven  elements  (among  those  of  practical  importance) 
which  do  not  U7iite  in  a  direct  manner  with  oxygen,  viz.,  chlorine,  bromine, 
iodine,  fluorine,  gold,  silver,  platinum. 

(Definition. — The  compounds  of  oxygen  with  other  elements  are 
called  Oxides.) 

The  act  of  combination  with  oxygen,  or  oxidation,  like  all  other  acts  of 
chemical  combination,  is  attended  with  the  development  of  heat*  When 
the  heat  thus  produced  is  sufficient  to  render  the  particles  of  matter 
luminous,  the  act  of  combination  is  styled  combustion. 

(Definition. — Comhustion  is  chemical  combination  attended  with  heat 
and  light.) 

19.  Phosphorus,  the  only  non-metal  which  combines  with  oxygen  at  the 
ordinary  temperature,  affords  a  good  illustration  of  these  propositions. 
This  element,  a  solid  at  the  ordinary  temperature,  is  preserved  in  bottles 
filled  with  water,  on  account  of  the  readiness  with  which  the  oxygen  of 
the  air  combines  with  it  If  a  small  piece  of  phosphorus  be  dried  by 
gentle  pressure  between  blotting  paper,  and  exposed  to  the  air,,  its  par- 
ticles begin  to  combine  at  once  with  oxygen,  and  the  heat  thus  developed 
slightly  raises  the  temperature  of  the  mass. 

^ow,  heat  generally  encourages  chemical  union,  so  that  the  effect  of 
this  rise  of  temperature  is  to  induce  a  more  extensive  combination  of  the 
phosphorus  with  the  oxygen,  causing  a  greater  development  of  heat  in  a 
given  time,  until  the  temperature  is  sufficient  to  render  the  particles 
brilliantly  luminous,  and  a  true  case  of  combustion  results — the  combina- 
tion of  the  phosphorus  with  oxygen,  attended  with  production  of  heat 
and  light. 
(Definition. — Combustion  in  air  is  the  chemical  combination  of  the 

elements  of  the  combustible  with  the 
oxygen  of  the  air,  attended  with  de- 
velopment of  heat  and  light.) 

If  a  dry  glass  (fig.  23)  be  placed  over 
the  burning  phosphorus,  the  thick 
white  smoke  which  proceeds  from  it 
may  be  collected  in  the  form  of  snowy 
flakes.  These  flakes  are  commonly 
termed  phosphoric  anhydride,^  and 
are  composed  of  80  parts  by  weight 
of  oxygen,  and  62  parts  of  phos- 
phorus (P2O5). 


Fig.  23. 


If  the  white  flakes  are  exposed  to  the  air  for  a  short  time,  they  attract 
moisture  and  become  little  drops,  which  have  a  very  sour  or  acid  taste. 
It  was  mentioned  at  page  12  that  all  substances  which  have  such  a  taste 


•  Though  this  heat  is  not  always  perceptible  by  the  thermometer  or  by  the  senses. 
Thus,  when  chalk  is  dissolved  in  an  acid,  no  heat  is  perceived,  because  all  the  heat  attend- 
ing the  union  of  the  lime  with  the  acid  is  consumed  in  converting  the  carlionic  acid  from 
the  solid  chalk  into  a  gas.  To  explain  the  manifestation  of  heat  in  the  act  of  chemi- 
cal combination  falls  within  the  province  of  the  physicist  rather  than  of  the  chemist. 
Modern  writers  attribute  it  to  the  motion  of  the  molecules  which  compose  the  combining 
masses. 

+  A  nkydride,  ot  without  water,  from  av,  negative,  and  vcutp,  water. 


OXYGEN. 


25 


have  been  found  also  to  be  capable  of  changing  the  blue  colour  of  litmus  * 
to  red,  whence  the  chemist  is  in  the  habit  of  employing  paper  dyed  with 
blue  litmus  for  the  recognition  of  an  acid. 

(Definition. — Anhydride,  a  compound  which  produces  an  acid  when 
brought  into  contact  with  water.) 

For  the  exact  definition  of  an  acid  see  page  27. 

During  the  slow  combination  of  phosphorus  with  the  oxygen  of  the  air, 
before  actual  combustion  commences,  only  48  parts  of  oxygen  unite  with 
G2  parts  of  phosphorus,  forming  the  subs  Dance  called  plwsphorous 
anhydride  (P^CJg). 

(Definition. — The  endings  -ous  and  -ic  distinguish  between  two  com- 
pounds formed  by  oxygen  with  the  same  element ;  -ous  implying  the 
smaller  proportion  of  oxygen.) 

Unless  the  temperature  of  the  air  be  rather  high,  the  fragment  of  phos- 
phorus will  not  take  tire  spontaneously,  but  its  combustion  may  always 
be  ensured  by  exposing  a  larger  surface  to  the  action  of  the  air.  As  a 
general  rule,  a  fine  state  of  division  favours  chemical  combination,  because 
the  attractive  force  inducing  combination  operates  only  between  sub- 
stances in  actual  contact ;  and  the  smaller  the  size  of  the  particles,  the 
more  completely  will  this  condition  be  fulfilled. 

Thus  if  a  small  fragment  of  dry  phosphorus  be  placed  in  a  test-tube,  and  dissolved 
in  a  little  bisulphide  of  carbon,  the  solution  when  poured  upon  blotting  paper  (fig. 
24),  will  part  with  the  solvent  by  evapor- 
ation, leaving  the  phosphorus  in  a  very  Kl 
finely  divided  state  upon  the  surface  of 
the  paper,  where  it  is  so  rapidly  acted 
on  by  the  oxygen  of  the  air  that  it  bursts 
spontaneously  into  a  blaze. 

Though  the  light  emitted  by 
phosphorus  burning  in  air  is  very 
brilliant  it  is  greatly  increased  when  ^^' 

pure  oxygen  is  employed ;  for  since  the  nitrogen  with  which  the  oxygen 
in  air  is  mixed  takes  no  part  in  the  act  of  combustion,  it  impedes  and 
moderates  the  action  of  the  oxygen.  Each  volume  of  the  latter  gas  is 
mixed,  in  air,  with  four  volumes  of  nitrogen,  so  that  we  may  suppose 
five  times  as  many  particles  of  oxygen  to 
come  into  contact,  in  a  given  time,  with 
the  particles  of  the  phosphorus  immersed 
in  the  pure  gas,  which  will  account  for 
the  great  augmentation  of  the  tempera- 
ture and  light  of  the  burning  mass. 


To  demonstrate  the  brilliant  combustion  of 
phosphorus  in  oxygen,  a  piece  not  larger  than 
a  good-sized  pea  is  placed  in  a  little  copper  or 
iron  cup  upon  an  iron  stand  (fig.  25),  and  Fig.  25. 
kindled  by  being  touched  with  a  hot  wire  (for 
even  in  pure  oxygen  spontaneous  combustion 

cannot  be  ensured).     The  globe,  having  been  previously  filled  with  oxygen,  and  kept 
in  a  plate  containing  a  little  water,  is  placed  over  the  burning  phosphorus.  + 


-Phosphorus  burning  in 
oxygen. 


*  A  colouring  matter  prepared  from  a  lichen,  Roccdla  tinctoria ;  the  cause  of  the 
change  of  colour  will  be  more  easily  understood  hereafter. 

t  This  globe  should  be  of  thin,  well-annealed  glass,  and  is  sure  to  be  broken  if  too 
large  a  piecs  of  phosphorus  be  employed. 


26 


OXYGEN  WITH  NON-METALS. 


It  will  be  observed  that  the  same  white  clouds  of  phosphoric  anhydride 
are  formed,  whether  phosphorus  is  burnt  in  oxygen  or  in  air,  exemplify- 
ing the  fact  that  a  stchstance  willcomhine  with  the  same  proportion  of  oxygen 
whether  its  combicstion  be  effected  in  ^^wre  oxygen  or  in  atmospheric  air. 
The  apparent  increase  of  heat  is  due  to  the  combustion  of  a  greater  weight 
of  phosphorus  in  a  given  time  and  space.  The  total  heating  effect  pro- 
duced by  the  combustion  of  a  given  weight  of  phosphorus  is  the  same 
whether  air  or  pure  oxygen  be  employed. 

20.  Sulphur  (brimstone)  affords  an  example  of  a  non-metallic  element 
which  will  not  enter  into  combination  with  oxygen  until  its  temperature 
has  been  raised  very  considerably.  When  sulphur  is  heated  in  air,  it 
soon  melts ;  and  as  soon  as  its  temperature  reaches  500°  F.  it  takes  hre, 
burning  with  a  pale  blue  flame.  If  the  burning  sulphur  be  plunged  into 
a  jar  of  oxygen,  the  blue  light  will  become  very  brilliant,  but  the  same 
act  of  combination  takes  place — 32  parts  by  weight  of  oxygen  uniting  with 
32  parts  of  sulphur  to  form  sulphurous  acid  gas  (SOg),  which  may  be  recog- 
nised in  the  jar  by  the  well-known  suffocating  smell  of  brimstone  matches. 

The  experiment  is  most  conveniently  performed  by  heating  the  sulphur 
in  a  deflagrating  spoon  (A,  fig.  26),  which  is  then  plunged  into  the  jar  of 

oxygen,  its  collar  (B)  resting  upon  the 
neck  of  the  jar,  which  stands  in  a  plate 
containing  a  little  water.  The  water  ab- 
sorbs a  part  of  the  sulphurous  acid  gas, 
and  will  be  found  capable  of  strongly  red- 
dening litmus  paper.  It  is  possible  to 
produce,  though  not  by  simple  combus- 
tion, a  compound  of  sulphur  with  half 
as  much  more  oxygen  (SOg  sulphuric 
anhydride),  showing  that  a  substance  does 
%  not  always  take  up  itsfidl  share  of  oxygen 
ichen  burnt. 

The  luminosity  of  the  flame  of  sulphur 

Fig.  26.  —Sulphur  burning  in         is  far  inferior  to  that  of  phosphorus,  be- 

oxygen.  cause,  in  the  former  case,  there  are  no 

extremely  dense  particles  in  the  flame  corresponding  to  those  of  the 

phosphoric  oxide  produced  in  the  combustion  of  phosphorus. 

21.  Carbon,  also  a  non-metallic  element,  requires  the  application  of  a 
higher  temperature  than  sulphur  to  induce  it  to  enter  into  direct  union 
with  oxygen ;  indeed,  perfectly  pure  carbon  appears  to  require  a  heat 
approaching  whiteness  to  produce  this  effect.  But  charcoal  (the  carbon  in 
which  is  associated  with  not  inconsiderable  proportions  of  hydrogen 
and  oxygen)  begins  to  burn  in  air  at  a  much  lower  temperature ;  and  if  a 
piece  of  wood  charcoal,  with  a  single  spot  heated  to  redness,  be  lowered 
into  a  jar  of  oxygen,  the  adjacent  particles  will  soon  be  raised  to  the 
(jonibining  temperature,  and  the  whole  mass  will  glow  intensely,  32  parts 
by  weight  of  oxygen  uniting  with  12  parts  of  carbon  to  form  carbonic 
acid  gas  (COg),  which  will  redden  a  piece  of  moistened  blue  litmus  paper 
suspended  in  the  jar,  though  much  more  feebly  than  either  sulphurous  or 
phosphoric  acid.  It  should  be  remembered  that  carbon  is  an  essential 
cnnstituent  of  all  ordinary  fuel,  and  carbonic  acid  gas  is  always  produced 
by  its  combustion. 


OXYGEN  WITH  METALS. 


27 


It  will  be  noticed  that  the  combustion  of  the  charcoal  is  scarcely 
attended  with  Hame ;  and  when  pure  carbon  (diamond,  for  example) 
is  employed,  no  flame  whatever  is  produced  in  its  combustion,  because 
carbon  is  not  convertible  into  vapour,  and  all  flame  is  vopour  or  rjas  in  the 
act  of  combustion  ;  hence,  only  those  substances  burn  vnth  flame  which  are 
capable  of  yielding  combiistible  gases  or  vapours. 

22.  The  three  examples  of  sulphur,  phosphorus,  and  carbon  suffi- 
ciently illustrate  the  tendency  of  non-metals  to  form  acids  by  union  with 
oxygen  and  water,  which  originally  led  to  the  adoption  of  its  name,  derived 
from  o^us,  acid,  and  yewao),  I  produce.  All  the  non-metallic  elements, 
except  hydrogen  and  fluorine,  are  capable  of  forming  anhydrides  by  their 
union  idth  oxygen. 

Definition  of  an  acid. — A  compound  containing  hydrogen,  which,  when 
in  contact  with  an  alkali  (p.  12)  exchanges  its  hydrogen,  or  a  portion  of 
it,  for  the  alkali-metal. 

For  example — 


HCl         + 

'drochloric  add. 

XaOH 

Soda. 

=      NaCl               + 
Sodium  chloride. 

H,0 

Water. 

Sulphuric  acid. 

2K0H 

Potash. 

=       K2SO4              + 
Potassium  sulphate. 

2H2O 
Water. 

H3PO,       + 

Phosphoric  acid. 

2XaOH 

Soda. 

=     Na.,HP04     + 

Sodium  phosphate. 

2H.,0 

Water. 

23.  The  metals,  as  a  class,  exhibit  a  greater  disposition  to  unite  directly 
with  oxygen,  though  few  of  them  will  do  so  in  their  ordinary  condition, 
and  at  the  ordinary  temperature.  Several  metals,  such  as  iron  and  lead, 
are  superficially  oxidised  when  exposed  to  air  under  ordinary  conditions, 
but  this  would  not  be  the  case  unless  the  air  contained  water  and  car- 
bonic acid  gas,  which  favour  the  oxidation  in  a  very  decided  manner. 
Among  the  metals  which  are  of  importance  in  practice,  five  only  are 
oxidised  by  exposure  to  dry  air  at  the  ordinary  temperature,  viz., potassium, 
sodium,  barium,  strontium^  and  calcium,  the  attraction  of  these  metals  for 
oxygen  being  so  powerful  that  they  must  be  kept  under  petroleum,  or  some 
similar  liquid  free  from  oxygen.  On  the  other  hand,  three  of  the  com- 
mon metals,  silver,  gold,  and  platinum,  have  so  little  attraction  for 
oxygen  that  they  cannot  be  induced  to  unite  with  it  directly,  even  at 
high  temperatures. 

If  a  lump  of  sodium  be  cut  across  wdth  a  knife,  the  fresh  surfaces  will 
exhibit  a  splendid  lustre,  but  will  very  speedily  tarnish  by  combining 
with  oxygen  from  the  air,  which  gives  rise  to  a  coating  of  sodium  oxide, 
and  this  to  some  extent  protects  the  metal  beneath  from  oxidation.  The 
freshly  cut  sodium  shines  in  the  dark  like  phosphorus.  Even  when  the 
attraction  of  the  sodium  for  oxygen  is  increased  by  the  application  of 
heat,  it  is  long  before  the  mass  of  sodium  is  oxidised  throughout,  unless 
the  temperature  be  sufficiently  high  to  convert  a  portion  of  the  sodium 
into  vapour,  which  bursts  through  the  crust  of  oxide,  and  burns  with  a 
yellow  flame.  If  the  spoon  containing  the  sodium  (see  fig.  26)  be  now 
plunged  into  a  jar  of  oxygen,  the  yellow  flame  ^dll  be  far  more  brilliant. 

Sixteen  parts  by  weight  of  oxygen  here  combine  with  46  parts  of 
sodium  to  form  disodium  oxide  (Na^O),  which  remains  in  the  spoon  in  a 


28  OXYGEN  WITH  METALS. 

fused  state.  When  the  spoon  is  cool,  it  may  be  placed  in  water,  which 
will  dissolve  the  oxide,  converting  it  into  the  alkali  soda, 

NagO   +   HgO   =   2NaH0 

Water.  Soda. 

24.  Zinc  will  serve  as  an  example  of  a  metal  which  has  no  disposition 
to  enter  into  combination  with  oxygen  at  the  ordinary  temperature,*  but 
which  is  induced  to  unite  with  it  by  a  very  moderate  heat.  If  a  little 
zinc  {spelter)  be  melted  in  a  ladle  or  crucible,  and  stirred  about  with  an 
iron  rod,  it  burns  with  a  beautiful  greenish  Hame,  produced  by  the  union 

of  the  vapour  of  zinc  ^?ith  the  oxygen  of 
the  air.  But  the  combustion  is  i'ar  more 
brilliant  if  a  piece  of  zinc-foil  be  made 
into  a  tassel  (fig.  27),  gently  warmed  at 
the  end,  dipped  into  a  little  flowers  of 
sulphur,  kindled,  and  let  down  into  a  jar 
of  oxygen,  when  the  flame  of  the  burning 
sulphur  will  ignite  the  zinc,  which  burns 
with  great  brilliancy.  On  withdrawing 
what  remains  of  the  tassel  after  the  com- 
bustion is  over,  it  will  be  found  to  con- 
Fig.  27. -Zinc  burning  in  oxygen,      g-^^  ^j  ^  friablef  mass,  which  has  a  fine 

yellow  colour  while  hot,  and  becomes  white  as  it  cools.  This  is  the  zinc 
oxide  (ZnO),  formed  by  the  union  of  16  parts  by  weight  of  oxygen  with 
65  parts  of  zinc.       , 

The  zinc  oxide  does  not  possess  the  properties  of  an  acid  or  an  alkali, 
and  belongs  to  another  class  of  compounds  termed  hoses,  which  are  not 
soluble  in  water  as  the  alkalies  are,  but,  like  them,  are  capable  of  neutral- 
ising, either  partly  or  entirely,  the  acids.  Thus,  if  the  zinc  oxide  were 
added  to  diluted  sulphuric  acid  as  long  as  the  acid  would  dissolve  it,  the 
well-known  corrosive  properties  of  the  acid  would  be  destroyed,  although  it 
would  still  retain  the  power  of  reddening  blue  litmus,  and  the  solution  would 
now  contain  a  new  substance,  or  salt,  called  zinc  sulphate  (ZnSO^). 

(Definition. — A  base  is  a  compound  body  which  is  capable  of  neutral- 
ising an  acid,  either  partly  or  entirely.) 

It  will  be  observed  that  an  alkali  is  only  a  particular  species  of  base, 
and  might  be  defined  as  a  base  which  is  very  soluble  in  water. 

(Definition. — A.  salt  is  a  compound  formed  when  the  hydrogen  in  an 
acid  is  replaced,  either  entirely  or  partly,  by  a  metal ;  thus,  sodium 
chloride,  NaCl,  is  formed  by  the  replacement  of  the  Hin  HCl,  hydrochloric 
acid,  by  sodium  ;  sodium  phosphate,  Na^HPO^,  is  formed  from  phosphoric 
acid,  H3PO4,  by  the  replacement  of  two-thirds  of  the  hydrogen  by  sodium.) 

25.  Iron,  in  its  ordinary  form,  like  zinc,  is  not  oxidised  by  dry  air  or 
oxygen  at  the  ordinary  temperature ;  but  if  it  be  heated  even  to  only 
500°  F.  a  film  of  oxide  of  iron  forms  upon  its  surface,  and  as  the  heat  is 
increased  the  thickness  of  thfe  film  increases,  until  eventually  it  becomes  so 
thick  that  it  can  be  detached  by  hammering  the  surface,  as  may  be  seen 
in  a  smith's  forge.  If  an  iron  rod  as  thick  as  the  little  finger  be  heated 
to  whiteness  at  the  extremity,  and  held  before  the  nozzle  of  a  powerful 

*  Unless  water  and  carbonic  acid  gas  be  present,  as  in  common  air. 
+  Fi-iable,  easily  crumbled  or  disintegrated. 


OXIDES. 


29 


Fig.  28. 


these 


Watch-spring  burning 
in  oxygen. 

cases  is  really  a  com- 


bellows,  it  will  burn  brilliantly,  throwing  off  sparks  and  dropping  melted 
oxide  of  iron.  If  a  stream  of  oxygen  be  substituted  for  air,  the  combus- 
tion is  of  the  most  brilliant  description,  A  watch-spring  (iron  combined 
with  about  1  per  cent,  of  carbon)  may  be 
easily  made  to  burn  in  oxygen  by  heating 
it  in  a  flame  till  its  elasticity  is  destroyed, 
and  coiling  it  into  a  spiral  (A,  fig.  28),  one 
end  of  which  is  fixed,  by  means  of  a  cork, 
in  the  deflagrating  collar  B ;  if  the  other 
end  be  filed  thin  and  clean,  dipped  into  a 
little  sulphur,  kindled  and  immersed  in  a 
jar  of  oxygen  (C)  standing  in  a  plate  of 
water,  the  burning  sulphur  will  raise  the 
iron  to  the  point  of  combustion,  and  the 
spring  will  be  converted  into  molten  drops 
of  oxide. 

The  black  oxide  of  iron  formed  in  all 
bination  of  two  distinct  oxides  of  iron,  one  of  which  contains  16  parts  by 
weight  of  oxygen  and  56  parts  of  iron,  and  would  be  written  FeO,  whilst 
the  other  contains  48  parts  of  oxygen  and  112  parts  of  iron,  expressed  by 
the  formula  Fe203.  To  distinguish  them,  the  former  is  usually  called 
protoxide  of  iron  (TrpcoTos,  first)  or  fem'ous  oxide,  and  the  latter  sesquioxide 
(in  allusion  to  the  ratio  of  one  and  a  half  to  one  between  the  oxygen  and 
the  metal)  or  ferric  oxide.  The  sesquioxide  of  iron  combined  with  water 
constitutes  ordinary  rust. 

The  black  oxide  usually  contains  one  combining  weight  of  each  oxide, 
so  that  it  would  be  written  FeO.FegOg,  or  FegO^.  It  is  powerfully 
attracted  by  the  magnet,  and  is  often  called  magnetic  oxide  of  iron.  The 
abundant  magnetic  ore  of  iron,  of  which  the  loadstone  is  a  variety,  has  a 
similar  composition. 

Iron  in  a  very  fine  state  of  division  will  take  fire  spontaneously  in  air 
as  certainly  as  phosphorus.  PyrophoHc  iron  can  be  obtained  (by  a  process 
to  be  described  hereafter)  as  a  black  powder,  which  must  be  preserved  in 
.sealed  tubes.  "When  the  tube  is  opened,  and  its  contents  thrown  into  the 
air,  oxidation  takes  place,  and  is  attended  with  a  vivid  glow.  In  this 
case  the  red  sesquioxide  of  iron  is  produced  instead  of  the  black  oxide. 

Both  these  oxides  of  iron  are  capable  of  neutralising,  or  partly  neu- 
tralising, acids,  and  are,  therefore,  basic  oxides  or  bases,  like  the  oxides  of 
zinc  and  sodium  obtained  in  previous  experiments.  So  general  is  the 
disposition  of  metals  to  form  oxides  of  this  class,  that  it  may  be  regarded 
as  one  of  the  distinguishing  features  of  a  metal,  for  no  non-metal  ever 
forms  a  base  with  oxygen. 

(Definition. — A  metal  is  an  element  capable  of  forming  a  base*  bj 
combining  with  oxygen.) 

Many  metals  are  capable  also  of  forming  anhydrides  with  oxygen ; 
thus,  tin  forms  stannic  anhydride  (SnO.,),  antimony  forms  antimonic  anhy- 
dride (Sb.^Oj),  and  it  is  always  found  that  the  anhydride  of  a  metal  con- 
tains a  larger  proportion  of  oxygen  than  any  of  the  other  oxides  which 
the  metal  may  happen  to  form. 

26.  There  is  a  third  class  of  oxides,  termed  the  indifferent  oxides,  be- 

*  The  metal  tungsten  appears  at  present  to  be  an  exception  to  this  rule,  no  well-defined 
basic  oxide  of  this  metal  being  known. 


30 


PREPARATION  OF  OXYGEN. 


cause  they  are  neither  anhydrides  nor  bases  ;  such  oxides  may  be  formed 
either  by  non-metals  or  metals  ;  thus  water  (HjO),  the  oxide  of  hydrogen, 
is  an  indifferent  oxide,  and  the  black  oxide  or  binoxide  of  manganese 
(MnOg)  is  an  example  of  an  indifferent  metallic  oxide. 

27.  Preparation  of  Oxygen. — For  almost  all  the  useful  arts  in  which 
uncombined  oxygen  is  required,  the  diluted  gas  contained  in  atmospheric 
air  is  sufficient,  since  the  nitrogen  mixed  with  it  does  not  interfere  with 
its  action. 

From  atmospheric  air  pure  oxygen' was  first  obtained  by  Lavoisier  towards 
the  end  of  the  last  century.  His  process  is  far  too  tedious  to  be  employed 
as  a  general  method  of  preparing  oxygen,  but  it  affords  a  very  good  example 
of  the  relation  of  heat  to  chemical  attraction.  Some  mercury  was  poured 
into  a  glass  flask  with  a  long  narrow  neck,  •which  was  placed  on  a 
furnace,  so  that  its  temperature  might  be  constantly  maintained  at  about 
660°  F.  for  twelve  days.  The  mercury  boiled,  and  a  portion  of  it  was 
converted  into  vapour,  which  condensed  in  the  neck  of  the  flask  and  ran 
back  again.  Eventually  part  of  the  mercury  was  converted  into  a  red 
powder,  having  combined  with  the  oxygen  of  the  air  (or  undergone  oxida- 
tion) to  form  the  red  oxide  of  mercury.  The  nitrogen  of  the  air  does  not 
enter  into  combination  with  the  mercury. 

By  heating  this  oxide  of  mercury  to  a  temperature  approaching  a  red 
heat  (about  1000°  F.)  it  is  decomposed  into  mercury  and  oxygen  gas 
(HgO  =  Hg  +  0). 

It  is  very  generally  found,  as  in  this  instance,  that  heat  of  moderate 
intensity,  will  favour  the  operation  of  chemical  attraction,  whilst  a  more 
intense  heat  will  annul  it. 


Fig.  29.  — Preparation  of  oxygen  from  oxide  of  mercury. 

For  the  purpose  of  experimental  demonstration,  the  decomposition  of  the  oxide  of 
mercury  may  be  conveniently  effected  in  the  apparatus  represented  by  fig.  29,  where 
the  oxide  is  placed  in  the  German  glass  tube  A,  and  heated  by  the  bunsen's  gas- 
burner  B,  the  metallic  mercury  being  condensed  in  the  bend  C,  and  the  oxygen  gas 
collected  in  the  gas  cylinder  D,  filled  with  water,  and  standing  upon  the  bee-hive 
shelf  of  the  pneumatic  trough  E.  It  may  be  identified  by  its  property  of  kindling  into 
fiame  the  spark  left  at  the  end  of  a  wooden  match.  If  the  heat  be  continued  for  a 
suthcient  length  of  time,  the  whole  of  the  oxide  of  mercury  will  disappear,  being 
resolved  into  its  elements.     In  technical  language,  the  mercury  is  said  to  be  redtuxd. 

Upon  the  first  application  of  heat  the  red  oxide  suffers  a  physical  change,  in 
consequence  of  which  it  becomes  black ;  but  its  red  colour  returns  again  if  it  be 
allowed  to  cool. 

A  much  cheaper  process  for  obtaining  unmixed  oxygen  from  the  air  is 
now  employed  upon  the  large  scale.  It  depends  upon  the  principle  that 
the  oxides  of  manganese,  when  heated  in  contact  witli  alkalies  and  air. 


EXTIIACTION  OF  OXYGEN  FROM  AIR. 


31 


are  capable  of  absorbing  the  oxygen  from  the  air,  and  of  subsequently 
giving  it  up  again  if  heated  in  a  current  of  steam. 

To  illustrate  this  process,  about  four  ounces  of  dry  sodium  manganate  (which  maj^ 
be  purchased  cheaply  in  a  crude  state)  are  introduced  into  a  porcelain  tube*  {t,  iig.  30) 
fixed  in  a  furnace.  One  end  of  the  tube  is  connected  with  a  two-branched  glass  tube, 
so  that  either  a  current  of  air  may  be  passed  through  it  by  the  tube  a,  or  a  cuiTent  of 
steam  from  the  flask  iv.  On  heating  the  manganate  in  the  tube  to  dull  redness,  and 
passing  the  steam  over  it,  oxygen  is  evolved,  and  may  be  collected  in  the  jar  o. 

2Na.,Mn04     +     2H2O     =     4NaH0     +     Mn^Os     +     O3 

Sodium  ^        .  Sesquioxide  of 

manganate.  v^^^ci,  ^  o^-u-.         manganese. 

If  the  current  of  steam  be  discontinued  and  the  air  be  slowly  passed  through  the 
tube  a,  the  oxygen  of  the  air  will  be  absorbed,  and  its  nitrogen  may  be  collected  in 
the  Jar  n. 

4NaH0   +   Mn^jOa   +   3(0   +   N4)  =   •2Na2Mn04   +   211  fi  +   Nj^ . 
Air. 

If  the  proper  temperature  be  employed,  the  stream  of  gas  issuing  from  the  tube 
may  be  constantly  kept  up,  and  may  be  made  to  consist  of  oxygen  or  nitrogen 
accordingly  as  steam  or  air  is  passed  through  the  tube.  The  current  of  air  is  regu- 
lated by  the  nipper-tab  c. 

The  gas-furnace  represented  in  fig.  30  consists  of  a  row  of  twelve  Bunsen  burners, 


Fig.  30.  — Extraction  of  oxygen  from  air. 

each  having  a  stop-cock  by  which  the  flame  is  regulated.  The  horizontal  pipe  b, 
from  which  they  spring,  is  capable  of  being  raised  or  lowered  at  pleasure.  The 
porcelain  tube  t  is  laid  in  a  semi-cylindrical  trough  made  of  stout  iron  rods,  and 
filled  with  pieces  of  pumice-stone  or  fire-brick.  Above  this  is  placed  a  corresponding 
trough,  so  that  the  tube  is  entirely  surrounded  by  glowing  material.t  The  heat 
must  be  applied  gradually  to  avoid  splitting  the  tube. 

28.  The  only  other  natural  source  from  which  it  has  been  found  con- 
venient to  prepare  pure  oxygen,  is  a  black  mineral  composed  of  manganese 
and  oxygen.  It  is  found  in  some  parts  of  England,  but  much  more 
abundantly  in  Germany  and  Spain,  whence  it  is  imported  for  the  use  of 

*  A  copper  tube  with  screw-caps,  into  which  narrow  brass  or  copper  tubes  are  brazed, 
may  be  advantageously  substituted  tor  the  porcelain  tube.  The  process  is  much  facilitated 
by  mixing  the  manganate  of  soda  with  an  equal  weight  of  oxide  of  copper. 

+  This  burner,  as  well  as  the  burner  described  at  page  10,  was  constructed'for  me  by  Mr. 
Rowley,  formerly  of  the  Royal  Military  Academy,  Woolwich,  whose  readiness  in  perceiving 
the  intention  of  an  apparatus,  and  in  improving  upon  the  original  idea  as  the  work  pro- 
ceeded, rendered  his  co-operation  in  arranging  experimental  illustrations  of  the  gi'eatest 
service  to  me 


32  PREPARATION  OF  OXYGEN. 

the  bleacher  and  glass-maker.  Its  commercial  name  is  manganese,  but  it 
is  known  to  chemists  as  hinoxide  of  manganese  or  manganese  dioxide 
(MnOg),  and  to  mineralogists  by  several  names  designating  different 
varieties.  The  most  significant  of  these  names  is  pyrolusite,  referring  to 
the  facility  with  which  it  may  be  decomposed  by  heat  {irvp,  fire,  and 
Xvw,  to  loosen). 

One  of  the  cheapest  methods  of  preparing  oxygen  consists  in  heating 
small  fragments  of  this  black  oxide  of  manganese  in  an  iron  retort,  placed 
in  a  good  fire,  the  gas  being  collected  in  jars  filled  with  water,  and  stand- 
ing upon  the  shelf  of  the  pneumatic  trough,  or  in  a  gas-holder  or  gas-bag, 
if  large  quantities  are  required. 

The  attraction  existing  between  manganese  and  oxygen  is  too  powerful 
to  allow  the  metal  to  part  with  the  whole  of  its  oxygen  when  heated,  so 
that  only  one-third  of  the  oxygen  is  given  off  in  the  form  of  gas,  a  brown 
oxide  of  manganese  being  left  in  the  retort.* 

29.  By  far  the  most  convenient  source  of  oxygen,  for  general  use  in  the 
laboratory,  is  the  artificial  salt  called  chlorate  of  potash,  or  potassium 

chlorate,  which  is  largely  manufactured 
for  fireworks,  percussion-cap  composi- 
tion, &c.  If  a  few  crystals  of  this 
salt  be  heated  in  a  test-tube  over  a 
spirit-lamp  (fig.  31),  it  soon  melts  to  a 
clear  liquid,  which  presently  begins  to 
boil  from  the  disengagement  of  bubbles 
of  oxygen,  easily  recognised  by  intro- 
ducing a  match  with  a  spark  at  the  end 
into  the  upper  part  of  the  tube.  If 
the  action  of  heat  be  continued  until  no 
more  oxygen  is  given  off,  the  residue 
Yia.  31.  ill  tli6  tube  will  be  the  salt  termed 

potassium  chloride, 

KCIO3       =       KCl      +     O3. 

Potassium  chlorate.      Potassium  chloride. 

To  ascertain  what  quantity  of  oxygen  would  be  furnished  by  a  given  weight  of 
the  chlorate,  the  combining  weights  must  be  brought  into  use.  Referring  to  the 
table  of  atomic  weights,  it  is  found  that  K  =  39,  0  =  16,  and  CI  =  35  "5 ;  hence  the 
molecular  weight  of  chlorate  of  potash  is  easily  calculated. 

One  atomic  weight  of  potassiuum,  .  .  39 

,,  ,,  chlorine,  .  .  35 '5 

Three  atomic  weights  of  oxygen,  .  .  48 

KC103  =  122-5 
So  that  122*5  grains  of  chlorate  would  yield  48  grains  of  oxygen. 

Since  16  grains  of  oxygen  measure  46*7  cubic  inches  (p.  23)  the*48  grs.  will  measure 
140  cubic  inches. 

Hence  it  is  found  that  122 '5  grains  of  potassium  chlorate  would  give  140  cubic 
inches  of  oxygen  measured  at  60°  F.  and  30  in.  Bar. 

If  one  gallon  (277 '276  cubic  inches)  of  oxygen  be  required,  212-6  grains  of  chlorate 
must  be  used,  or  rather  more  than  half  an  ounce. 

*  Expressed  in  the  form  of  an  equation  :  SMnOg      =      Mn304    -f     O2 . 

Black  oxide  of     Bi-own  oxiile  of 
manganese.  manganese. 


WATER, 


33 


Since  tlie  complete  decomposition  of  the  potassium  chlorate  alone  re- 
quires a  more  intense  heat  than  a  glass  vessel  will  usually  endure,  it  is 
customary  in  preparing  oxygen  for  chemical  purposes  to  facilitate  the 
decomposition  of  the  chlorate  by  mixing  it  with  about  one-fifth  of  its 
weight  of  powdered  black  oxide  of  manganese,  when  the  whole  of  the 
oxygen  is  given  off  at  a  comparatively  low  temperature,  though  the  oxide 
of  manganese  itself  suffers  no  change,  and  its  action  has  not  yet  received 
any  explanation  which  is  quite  satisfactory. 

Fig.  32  shows  a  very  convenient  arrangement  for  preparing  and  collecting  oxygen 
for  the  purpose  of  demonstrating  its  relations  to  combustion.     A  is  a  Florence  flask, 


Fig.  32. — Preparation  of  oxygen. 

in  which  the  glass  tube  B  is  fixed  by  a  perforated  cork.  C  is  a  tube  of  vulcanised 
india-rubber.  The  gas-jar  is  filled  with  water,  and  supported  upon  a  bee-hive  shelf 
made  of  earthenware.  If  pint  gas-jars  be  employed,  300  grains  of  the  chlorate  of 
potash,  mixed  with  60  grains  of  binoxide  of  manganese,  will  furnish  a  sufficient 
supply  of  gas  for  the  ordinary  experiments.  The  binoxide  of  manganese  should  be 
thoroughly  dried  by  moderately  heating  it  in  a  crucible  before  being  mixed  with  the 
chlorate  of  potash.  It  is  also  advisable  to  test  it  by  heating  a  little  of  it  with  the 
chlorate,  since  charcoal  and  sulphuret  of  antimony,  which  form  very  explosive  mix- 
tures with  chlorate  of  potash,  have  sometimes  been  sold  by  mistake  for  binoxide  of 
manganese.  The  heat  must  be  moderated  according  to  the  rate  at  which  the  gas  is 
evolved,  and  the  tube  C  must  be  taken  out  of  the  water  before  the  lamp  is  removed, 
or  the  contraction  of  the  gas  in  cooling  will  suck  the  water  back  into  the  flask.  The 
first  jar  of  gas  will  contain  the  air  with  which  the  flask  was  filled  at  the  commence- 
ment of  the  experiment.     The  oxygen  obtained  will  have  a  slight  smell  of  chlorine . 

WATER 

30.  Synthesis  of  Water  from  its  elements. — It  has  been  seen  already 
(p.  22)  that  the  combination  of  hydrogen  with  oxygen  to  form  water  is 
attended  with  great  evolution  of  heat  and  consequent  expansion,  and 
hence  the  mixture  of  these  gases  is  found  to  explode  violently  on  contact 
with  flame. 

The  experiment  may  be  made  safely  in  a  soda-water  bottle.  The  bottle  is  filled 
with  water,  and  inverted  with  its  mouth  beneath  the  surface  of  the  water  ;  enough 
oxygen  is  then  passed  up  into  it  to  fill  one-third  of  its  volume  ;  if  the  remainder  of 
the  water  be  then  displaced  by  hydrogen,  and  the  mouth  of  the  bottle  be  presented 
to  the  flame  of  a  spirit-lamp,  a  very  violent  explosion  will  result,  attended  with  a 
vivid  blue  flash  in  the  bottle.  If  the  mouth  of  the  bottle  be  presented  towards  a 
screen  of  paper,  at  a  distance  of  20  or  30  inches,  the  paper  will  be  violently  torn  to 
pieces,  bearing  witness  to  the  concussion  between  the  expanded  steam  issuing  from 
the  bottle  and  the  external  air. 

C 


34 


SYNTHESIS  OF  WATEE. 


If  some  of  the  mixture  of  oxygen  with  twice  its  volume  of  hydrogen  be  introduced 
into  a  capped  jar  (fig.  33),  provided  with  a  piece  of  caoutchouc  tubing  and  a  small 
glass  tube,  and  pressed  down  in  a  trough  of  water,  soap-bubbles  may  be  inflated  with 
it,  which  will  ascend  rapidly  in  the  air,  and  explode  violently  when  touched  with  a 
flame,  which  must  not,  of  course,  be  applied  to  the  bubble  until  it  is  at  some  distance 
awaj'  from  the  tube,  for  fear  of  exploding  the  mixture  in  the  jar. 


Fig.  33. 

31.  In  order  to  demonstrate  the  production  of  water  in  the  explosion,  the  Caven- 
dish etidiometer  *  (fig.  34)  is  employed.  This  is  a  strong  glass  vessel,  with  a  stopper 
firmly  secured  by  a  clamp  (A),  and  provided  with  two  platinum  wires  (P),  which  pass 
through  the  stopper,  and  approach  very  near  to  each  other  within  the  eudiometer,  so 


Fig.  34.  Fig.  35. 

that  the  electric  spark  may  easily  be  passed  between  them.  By  screwing  the  stop- 
cock B  into  the  plate  of  an  air-pump,  the  eudiometer  may  be  exhausted.  It  is  then 
screwed  on  to  the  jar  represented  in  fig.  35,  which  contains  a  mixture  of  two  measures 
of  hydrogen  with  one  measure  of  oxygen,  standing  over  water.  On  opening  the  stop- 
cocks between  the  two  vessels,  the  eudiometer  becomes  filled  with  the  mixture,  and 
the  quantity  which  has  entered  is  indicated  by  the  rise  of  the  water  in  the  jar.  The 
glass  stop-cock  C  having  been  closed  to  prevent  the  brass  cap  from  being  forced  ott' 
by  the  explosion,  the  eudiometer  is  again  screwed  on  to  its  foot,  and  an  electric  spark 
passed  between  the  platinum  wires,  either  from  a  Leyden  jar  or  an  induction  coil, 
when  the  two  gases  will  combine  with  a  vivid  flash  of  light,  f  attended  with  a  very 

*  So  named  from  evSios,  fine  or  clear,  and  fie-rpov,  a  measure,  because  an  instrument 
upon  the  same  principle  has  been  used  to  determine  the  degree  of  purity  of  the  atmosphere. 
The  eudiometer  was  emyloyed  by  Cavendish  about  the  year  1770,  for  the  synthesis  of  water. 

■t*  bince  the  steam  produced  at  the  moment  of  combination  is  here  prevented  from  expand- 
ing, the  heat  which  would  have  expanded  it  is  saved,  so  that  the  temperature  is  higher 
and  the  flash  of  light  brighter  than  when  the  combination  is  effected  in  an  open  vessel 


SYNTHESIS  QP  WATEE. 


35 


slight  concussion,  since  there  is  no  collision  with  the  external  air.  For  an  instant 
a  mist  is  perceived  within  the  eudiometer,  which  condenses  into  fine  drops  of  dew, 
consisting  of  the  water  formed  by  the  combination  of  the  gases,  which  was  here 
induced  by  the  high  temperature  of  the  electric  spark,  as  it  was  in  the  former  experi- 
ment by  the  high  temperature  of  the  flame.  If  the  gases  have  been  mixed  in  the 
exact  proportion  of  two  measures  of  hydrogen  to  one  measure  of  oxygen,  the  eudio- 
meter will  now  be  again  vacuous,  and  if  it  be  screwed  on  to  the  capped  jar,  may  be 
filled  a  second  time  with  the  mixture,  which  may  be  exploded  in  the  same  manner. 

The  entire  disappearance  of  the  gases  may  be  rendered  obvious  to  the  eye  by 
exploding  the  mixture  over  mercury.  For  this  purpose  the  mixed  gases  should  be 
collected  from  water  itself,  which  is  strongly  acidified  with  sulphuric  acid,  and 
decomposed  in  the  voltameter  (A,  fig.  36)  by  the  aid  of  five  or  six  cells  of  Grove's 
battery.  The  voltameter  contains  two  platinum  plates  (B),  attached  to  the  platinum 
wires  C  and  D,  which  are  connected  with  the  opposite  poles  of  the  battery.  The 
first  few  bubbles  of  the  mixture  of  hydrogen  and  oxj'gen  evolved  having  been  allowed 
to  escape,  in  order  to  displace  the  air,  the  gas  may  be  collected  in  the  small  eudio- 
meter (E),  %vhich  has  been  previously  filled  with  water.     This  eudiometer  is  a  cylinder 


Fig.  36. — Detonating  gas  collected  from  voltameter. 

of  very  thick  glass,*  closed  at  one  end,  and  having  two  stout  platinum  wires  cemented 
into  holes  drilled  near  the  closed  end,  the  wires  approaching  sufficiently  near  to  each 
other  to  allow  the  passage  of  the  electric  spark.  Having  been  filled  with  the  mixture 
of  hydrogen  and  oxygen  from  the  voltameter,  the  eudiometer  is  closed  with  the  finger, 
and  transferred  to  a  basin  containing  mercury,  where  it  is  pressed  firmly  down  upon 
a  stout  cushion  of  india-rubber,  and  the  spark  passed  through  the  mixed  gases, 
either  from  the  coil  or  the  Leyden  jar.  The  combustion  takes  place  with  violent 
concussion,  but  without  noise ;  and  since  the  eudiometer  is  vacuous  after  the  gases 
have  combined,  the  cushion  will  be  found  to  be  very  firmly  pressed  against  its  open 
end.  On  loosening  the  cushion,  the  mercury  will  be  violently  forced  up  into  the 
eudiometer,  which  will  be  completely  filled  with  it,  proving  that  when  an  electric 
spark  is  passed  through  the  mixture  of  2  volumes  of  hydrogen  and  1  volume  of 
oxygen,  no  residue  of  gas  remaias.t 

32.  The  knowledge  of  the  volumes  in  which  hydrogen  and  oxygen 
combine,  is  turned  to  account  in  the  analysis  of  gases,  to  ascertain  the 
proportion  of  hydrogen  or  oxygen  contained  in  them.  Suppose,  for 
example,  it  he  required  to  determine  the  amount  of  oxygen  in  a  sample 
of  atmospheric  air ;  the  latter  is  mixed  with  hydrogen,  in  more  than  suffi- 
cient quantity  to  combine  with  the  largest  proportion  of  oxygen  which 

*  The  bore  of  the  eudiometer  should  be  about  half  an  inch  in  diameter,  and  the  thick-' 
ness  of  its  sides  about  ftbs  of  an  inch  ;  its  length  is  7  inches. 

f  This  fact  may  also  be  demonstrated  with  the  siphon  eudiometer,  showm  in  fig.  37,  by 
confining  about  a  cubic  inch  of  the  explosive  mixture  in  the  closed  limb,  over  water,  and 
stopping  the  open  limb  securely  with  a  cork,  so  as  to  leave  a  space  filled  with  air  between 
the  cork  and  the  water.  The  eudiometer  must  be  very  firmly  fixed  on  a  stand,  or  it  will 
be  broken  by  the  concussion.  After  it  has  been  proved,  it  may  be  held  in  the  hand,  as 
in  the  figure.  By  firing  mixtures  of  hydrogen  and  oxygen,  in  difi'erent  proportions,  in  the 
same  manner,  it  may  be  shown  that  any  excess  of  either  gas  above  the  ratio  of  2H  :  0  will 
remain  uncombined  after  the  explosion.  Care  is  required  in  these  experiments,  since 
eudiometers  are  often  burst  by  the  explosion  of  the  mixture  of  2  volumes  of  hydrogen  \vith 
1  volume  of  oxygen. 


36 


EUDIOMETRIC  ANALYSIS  OF  AIR. 


% 


could  be  present,  and  when  the  combination  has  been  induced  by  the 
electric  spark,  the  volume  of  gas  which  has  disappeared  (2  volumes  H  +  1 
volume  0)  has  only  to  be  divided  by  three  to  give  the  volume  of  the 
oxygen. 

A  bent  eudiometer  (fig.  37)  is  generally  employed  for  this  pui-pose.  Having  been 
completely  filled  with  water,  it  is  inverted  in  the  trough,  and  the  specimen  of  air  is 
introduced  (say  0'5  cubic  inch).  The  open  limb  is  then  closed  by  the  thnmb,  and 
the  eudiometer  turned  so  as  to  transfer  the  air  to  the  closed 
limb.  A  stout  glass  rod  is  thrust  down  the  open  limb,  so 
as  to  displace  enough  water  to  equalise  the  level  in  both 
limbs,  in  order  that  the  volume  of  the  air  may  not  be 
diminished  by  the  pressure  of  a  higher  column  of  water  in 
the  open  limb.  The  volume  of  the  mcluded  air  having  been 
accurately  noted,  the  open  limb  of  the  tube  is  again  filled 
up  with  water,  inverted  in  the  trough,  and  a  quantity  of 
hydrogen  introduced,  equal  to  about  half  the  volume  of  the 
air.  This  having  been  transferred,  as  before,  to  the  closed 
limb,  the  columns  of  water  are  again  equalised,  and  the 
volume  of  the  mixture  of  air  and  hydrogen  ascertained. 
The  open  limb  is  now  firmly  closed  with  the  thumb  and 
the  electric  spark  passed  through  the  mixture,  either  from 
the  Leyden  jar  or  the  induction-coil.  On  removing  the 
thumb,  after  the  explosion,  the  volume  of  gas  in  the  closed  limb  will  be  found  to  have 
diminished  very  considerably.  Enough  water  is  poured  into  the  open  limb  to 
equalise  the  level,  and  the  volume  of  gas  is  observed.  If  this  volume  be  subtracted 
from  the  volume  before  explosion,  the  volume  of  gas  which  has  disappeared  will  be 
ascertained,  and  one-third  of  this  will  represent  the  oxygen,  which  has  condensed 
with  twice  its  volume  of  hydrogen  into  the  form  of  water.  Thus  the  numbers 
recorded  will  be — 


^^ 


Fig.  37. 
Siphon  eudiometer. 


Volume  of  air  analysed. 

Volume  of  air  mixed  with  hydrogen, 
After  explosion, 

Difference 
(|H  and  JO)      , 

•30,  divided  by  three  =  10  cub.  in.  of  oxygen. 


0*50  cub.  in. 

0-75      „ 
0-45      ,, 

•30      „ 


In  exact  experiments,  a  correction  would  be  required  for  any  variation  of 
the  temperature  or  barometric  pressure  during  the  progress  of  the  analysis. 

33.  It  will  have  been  observed,  in  the  experiment  upon  the  synthesis 
of  water  in  the  Cavendish  eudiometer,  that  the  volume  of  water  obtained 
is  very  small  in  comparison  with  that  of  the  gases  before  combination, 
nearly  2600  volumes  of  the  mixed  gases  being  required  to  form  1  volume 
of  the  liquid.  But  it  is  evident  that  no  comparison  can,  with  propriety, 
be  made  between  the  volume  of  a  compound,  in  the  liquid  or  solid  state, 
and  that  of  its  components  in  the  gaseous  state,  since  the  particles  of 
the  former  are  under  the  influence  of  the  cohesive  force  from  which  those 
of  the  latter  are  free.  For  the  purposes  of  such  a  comparison  the  volume 
of  the  compound  body  must  be  taken  under  precisely  the  same  physical 
conditions  as  the  volume  of  its  components. 

If  the  mixture  of  hydrogen  and  oxygen  be  measured  and  exploded  at 
or  above  the  boiling-point  of  water,  it  is  found  that  the  steam  produced 
occupies  two-thirds  of  the  volume  of  the  mixed  gases^  measured  at  the 
same  temperature  and  atmospheric  pressura  Hence,  two  volumes  of 
hydrogen  combine  vrith  one  volume  of  oxygen  to  form  two  volume  of 
aqueous  vapour,  at  the  same  temjyerature  arid  pressure. 


SYNTHESIS  OF  WATEE. 


37 


Tlie  combination  of  hydrogen  and  oxygen  in  a  vessel  heated  above 
the  boiling-point  of  water  is  effected  in  the  apparatus  contrived  by  Dr. 
Hofmann,  and  represented  in  fig.  38,  where  the  closed  limb  of  the  eudio- 
meter is  surrounded  by  a  tube  through  which  the  vapour  of  boiling 
fousel  oil,  having  a  temperature  of  270°  F.,  is  passed  from  a  flask  con- 
nected with  the  wide  tube  by  a  cork  and  a  short  wide  piece  of  bent  glass 
tubing,  jacketed  with  caoutchouc 
to  prevent  loss  of  heat.  The 
vapour  of  fousel  oil  passes  out 
of  the  wide  tube,  through  the 
tube  t  which  enters  the  cork  at 
the  bottom,  and  conducts  the 
vapour  into  a  glass  worm  (w)  im- 
mersed in  a  jar  through  which 
cold  water  is  allowed  to  flow,  as 
shown  by  the  arrows.  The  closed 
limb  of  the  eudiometer  having 
been  filled  with  mercury,  a  small 
quantity  of  the  mixture  of  hydro- 
gen and  oxygen  obtained  from 
the  voltameter  (fig.  36)  is  intro- 
duced into  it  through  a  tube 
passed  down  the  open  limb,  the 
displaced  mercury  being  run  out 
through  the  tube  c,  which  is 
closed  by  a  nipper-tap.  The 
closed  limb  is  then  heated  by  the 
vapour,  and  the  mercury  in  the 
two  limbs  levelled  from  time  to 
time  by  running  a  little  out 
through  c,  until  the  gas  in  the  closed  limb  no  longer  expands.  Its  volume 
is  then  observed,  an  inch  more  mercury  poured  into  the  open  limb,  which 
is  then  tightly  closed  by  a  cork,  and  the  spark  from  the  induction-coil 
(fig.  6)  is  passed  by  the  wires  -  and  +.  After  the  explosion  the  cork 
is  removed,  and  the  mercury  levelled  in  the  two  limbs,  when  the  volume 
of  the  steam  will  be  found  to  be  just  two-thirds  of  the  volume  of  the  gas 
before  the  explosion.  On  cooling  down,  the  steam  condenses,  and  the 
mercury  entirely  fills  the  closed  limb  of  the  eudiometer. 

The  experiment  may  be  made  at  the  boiling-point  of  water,  by  intro- 
ducing water  instead  of  fousel  oil  into  the  flask.  The  condensing 
apparatus  may  then  be  dispensed  with,  and  the  tube  t  left  open  to  the  air. 

That  2  volumes  of  steam  should  contain  2  volumes  of  hydrogen  and 
1  volume  of  oxygen  would  appear,  on  physical  grounds,  impossible,  since 
two  bodies  cannot  occupy  the  same  space  at  the  same  time ;  but  it  must 
be  remembered  that  the  two  bodies  in  question  have  lost  their  indi- 
viduality in  consequence  of  their  chemical  combination,  by  which  they 
have  become  one  body — water. 

34.  The  synthesis  of  water  by  weight  cannot  be  effected  with  accuracy 
by  weighing  the  gases  themselves,  on  account  of  their  large  volume.  It  is 
therefore  accomplished  by  passing  an  indefinite  quantity  of  hydrogen  over 
a  known  weight  of  pure  hot  oxide  of  copper,  when  the  hydrogen  combines 


Fig.  38. — Synthesis  of  water  above  212° 


38 


RECIPROCAL  COMBUSTION. 


with  the  oxygen  of  the  oxide  to  form  water.  The  loss  of  weight  suffered 
by  the  oxide  of  copper  gives  the  amount  of  oxygen ;  and  if  this  be  deducted 
from  the  weight  of  the  water,  that  of  the  hydrogen  will  be  ascertained. 

The  apparatus  employed  for  this  purpose  is  represented  in  fig.  39.  h  is  the  bottle 
in  which  hydrogen  is  generated  from  diluted  sulphuric  acid  and  zinc  ;  the  gas  passes 
in  2^  through  solution  of  potash,  which  absorbs  any  sulphuretted  hydrogen ;  then 
through  s,  containing  pumice-stone  (used  on  account  of  its  porous  character),  saturated 
with  a  strong  solution  of  nitrate  of  silver,  which  removes  arsenic  and  antimony  from 
the  hydrogen  ;  the  gas  then  passes  through  w,  contaioing  pumice  saturated  with  oil 


Fig.  39. — Synthesis  of  water  by  weight. 

of  vitriol  to  absorb  moisture.  The  bulb  c,  with  the  oxide  of  copper,  is  weighed  before 
and  after  the  experiment,  as  are  the  globe  g,  for  condensing  the  water,  and  the  tube 
t,  containing  pumice  and  oil  of  vitriol,  to  absorb  the  aqueous  vapour.  Of  course,  the 
bulb  c  must  not  be  heated  until  the  hydrogen  has  displaced  all  the  air  from  the 
,  apparatus. 

35.  It  is  evident  that,  although  hydrogen  is  generally  designated  the 
combustible  gas,  and  oxygen  the  supporter  of  combustion,  the  application  of 
these  terms  depends  entirely  upon  circumstances,  since  the  phenomenon 
of  combustion  is  a  repicrocal  operation  in  which  both  elements  have  an 
equal  share. 

This  may  be  illustrated  by  a  simple  experiment.  The  hydrogen  and  oxygen  reser- 
voirs, *  H  and  0,  fig.  40,  are  connected  with  two  bent  glass  tubes  passing  through  a 

cork  into  an  ordinaiy  lamp  glass  e, 
upon  the  upper  opening  of  which  a 
piece  of  tin-plate  is  laid.  In  order  to 
prevent  the  ends  of  the  glass  tubes  from 
being  fused  by  the  burning  gases,  little 
platinum  tubes,  made  by  rolling  up 
pieces  of  platinum  foil,  are  placed  in 
the  orifices,  and  the  glass  is  melted 
round  them  by  the  blowpipe  flame. 
The  hydrogen  being  lighted,  and  the 
oxygen  turned  on  to  about  the  same 
extent,  the  lamp-glass  is  placed  over 
the  cork,  when  the  hydrogen  burns 
steadily.  If  the  oxygen  be  slowly 
turned  off,  the  flame  will  gradually 
leave  the  hydrogen  tube  and  come  over 
to  the  oxygen,  which  will  continue 
burning  in  the  atmosphere  of  hydrogen. 
By  again  turning  on  the  oxygen,  the 
_,.,„„.  ,         ,       .  flame  may  be  sent  over  to  the  hvdrogen 

Fig.  40. -Reciprocal  combustion.  ^ube.     With  a  little  care  the  flame 

may  be  made  to  occupy  an  intermediate  position  between  the  two  burners,  and  to 
leap  from  one  to  the  other  at  pleasure. 

*  These  are  the  wrought-iron  vessels  in  which  hydrogen  and  oxygen  are  condensed  under 
the  pressure  of  a  few  atmospheres  by  Mr.  Orchard  of  Kensington.  They  are  far  more  con- 
veuieut  than  gas-bags  or  gas-holders. 


OXYHYDROGEN  BLOWPIPE. 


39 


Fig.  41. — Oxybydrogen  blowpipe. 


36.  The  great  energy  with  which  hydrogen  combines  with  oxygen  is 
turned  to  account  for  the  purpose  of  producing  the  highest  temperature 
which  can  be  obtained  by  any  chemical  process. 

The  oxyhydrogen  blowpipe  (fig.  41)  is  an  apparatus  for  burning  a  jet  of  hydrogen 
mixed  with  half  its  volume  of  oxygen.  The  gases  are  supplied  from  separate  gas- 
holders (or  bags  with  pressure-boards  and  weights) 
through  the  tubes  H  and  0,  which  conduct  them 
into  tlie  brass  sphere  B.  Each  of  these  tubes  is 
provided  with  a  valve  of  oiled  silk  opening  out- 
wards, so  as  to  prevent  the  passage  of  either  gas 
into  the  receptacle  containing  the  other.  The  tube 
A  is  stuffed  with  thin  copper  wires,  which  would 
rapidly  conduct  away  the  heat  and  extinguish 
the  flame  of  the  mixed  gases  burning  at  the  jet, 
should  it  tend  to  pass  back  and  ignite  the  mixture 
in  B.  The  stop-cocks  D  and  E  allow  the  flow  of 
the  gases  to  be  regulated  so  that  they  may  mix  in 
the  right  proportions.  If  the  hydrogen  be  kindled 
first,  it  will  be  found  that  as  soon  as  the  oxygen 
is  turned  on,  the  flame  is  reduced  to  a  very  much 
smaller  volume,  because  the  undiluted  oxygen 
required  to  maintain  it  occupies  only  one-fifth  of  the  volume  of  the  atmospheric  air, 
from  which  the  hydrogen  was  at  first  supplied  with  oxygen.  The  heat  developed  by 
the  combustion  being  therefore  distributed  over  a  much  smaller  area,  the  temperature 
at  any  given  point  of  the  flame  must  be  much  higher,  and  very  few  substances  are 
capable  of  enduring  it  without  fusion.*  Lime  is  one  of  these;  and  if  a  cylinder  of 
lime  be  supported,  as  at  L  (fig.  41),  in  the  focus  of  the  flame,  its  particles  become 
heated  to  incandescence,  and  a  light  is  obtained  which  is  visible  at  night  from  very 
great  distances,  so  as  to  be  well  adapted  for  signalling  and  light-houses.  For  such 
purposes  coal-gas  is  often  used  instead  of  hydrogen  {oxycalcium  light). 

If  a  shallow  cavity  be  scooped  in  a  lump  of 
quicklime,  a  few  scraps  of  platinum  placed  in  it, 
and  exposed  to  the  oxyhydrogen  flame  (fig.  42),  a 
fused  globule  of  platinum  of  very  considerable  size 
may  be  obtained  in  a  few  seconds.  By  employing 
a  little  furnace  made  of  lime,  Deville  has  succeeded 
in  fusing  platinum  in  quantities  sufficient  to  cast 
large  ingots,  a  result  unattainable  by  any  other 
furnace.  Pipeclay,  which  resists  the  action  of  all 
ordinary  furnace-heats,  may  be  fused  into  a  glass  in  this  flame,  whilst  gold  and  silver 
are  instantaneously  melted,  and  vaporised  into  a  dense  smoke. 

37.  In  its  chemical  relations  to  other  elements,  hydrogen  is  diametri- 
cally opposed  to  oxygeiL  Whereas  the  latter  combines  directly  with  the 
greater  number  of  the  elements,  hydrogen  will  enter  into  direct  combina- 
tion with  very  few  ;  oxygen,  clilorine,  bromine,  iodme,  carbon,  and  sulphur 
(the  three  last  with  difficulty)  are  the  only  elements  which  unite  in  a 
direct  manner  with  hydrogen,  and  of  these  only  chlorine  and  bromine 
combine  with  hydrogen  at  the  ordinary  temperature,  though  not  without 
exposure  to  light.  Again,  whilst  fluorine  is  not  known  to  form  any  com- 
pound with  oxygen,  its  combination  with  hydrogen  (hydrofluoric  acid)  is 
one  of  the  most  stable  compounds  known,  and  it  may  be  safely  asserted 
that  fluorine  in  the  free  state  would  combine  with  hydrogen  even  more 
readily  than  chlorine  does.  AU  the  metals  form  compounds  with  oxygen, 
but  very  few  combinations  of  metals  with  hydrogen  have  been  obtamed. 
Indeed,  in  its  relations  to  other  elements,  hydrogen  closely  resembles  the 
metals,  though  it  does  not  fall  within  the  definition  of  a  metal  given 


The  temperature  of  this  flame  has  been  estimated  at  about  3000°  C 


40  SOLUTION  AND  CRYSTALLISATION. 

above,  since  it  does  not  form  a  base  with  oxygen,  and  its  combinations 
with  the  salt-radicals  (chlorine,  &c.)  are  acids,  and  not  salts,  as  is  the  case 
■with  metals. 

In  the  course  of  some  experiments  upon  the  power  possessed  by  metals 
of  absorbing  (or  occluding)  gases  at  high  temperatures,  and  retaining  them 
after  cooling,  Graham  found  that  the  metal  palladium  could  be  made  to 
absorb  nearly  one  thousand  times  its  volume  of  hydrogen  at  the  tempera- 
ture of  boiling  water.  Finding  that  the  metallic  characters  of  the  palla- 
dium were  not  destroyed,  as  would  be  the  case  if  it  had  combined  with  a 
non-metallic  substance,  Graham  was  inclined  to  believe  in  the  metallic 
character  of  hydrogen,  or  hydrogenium,  as  he  termed  it.  But  since  the 
hydrogen  is  very  easily  recovered  by  moderately  heating  the  palladium, 
and  the  absorption  of  large  volumes  of  gases  by  solid  bodies,  without 
alteration  in  the  properties  of  the  latter,  is  not  at  all  uncommon,  the  con- 
clusion is  scarcely  justified.*  The  hydrogen  associated  with  palladium, 
however,  has  far  more  active  properties  than  ordinary  hydrogen,  for  it 
often  combines  spontaneously  with  the  oxygen  of  the  air,  and  will  unite 
with  chlorine  and  iodine  even  in  the  dark. 

38.  Chemical  Relations  of  Water  to  otJier  Snhstances. — In  its 
chemical  relations  water  presents  this  very  remarkable  feature,  that 
although  it  is  an  indifferent  oxide,  its  combining  tendencies  extend  over 
a  wider  range  than  those  of  any  other  compound.  Its  combinations  with 
other  substances  are  generally  called  hydrates.  Water  combines  with 
two  of  the  elementary  substances,  viz.,  chlorine  and  bromine,  forming  an 
exception  to  the  general  rule,  that  combination  does  not  take  place  between 
elementary  and  compound  bodies.  No  other  element  is  even  dissolved  by 
water  in  any  considerable  quantity.  One  part  of  iodine  is  dissolved  by 
500  parts  of  cold  water,  but  no  chemical  combination  appears  to  take 
place.  Oxygen,  hydrogen,  and  nitrogen  are  dissolved  by  water  in  very 
small  quantity,  but  become  only  mechanically  diffused  through  it,  and 
do  not  enter  into  chemical  combination. 

When  water  acts  upon  a  compound  body,  it  may  either  effect  a  simple 
solution,  or  may  enter  into  chemical  combination  with  it. 

Simple  solution  appears  to  be  a  purely  physical  phenomenon  not 
accompanied,  of  necessity,  by  any  chemical  action.  The  dissolved  sub- 
stance, in  such  cases,  is  otherwise  unchanged  in  properties,  and  there  is 
no  manifestation  of  heat,  as  in  cases  of  chemical  combination.  On  the 
contrary,  there  is  a  reduction  of  temperature,  such  as  is  always  noticed  in 
the  merely  physical  change  from  the  solid  to  the  liquid  form.  For 
example,  common  saltpetre  (nitre  or  nitrate  of  potash),  when  shaken  with 
water,  is  rapidly  dissolved,  the  water  becoming  sensibly  colder.  If  fresh 
portions  of  saltpetre  be  added  till  the  water  is  unable  to  dissolve  any 
more,  it  will  be  found  that  1000  grs.  of  water  (at  60°  F.)  have  dissolved 
about  300  grs.  of  saltpetre.  Such  a  solution  would  be  called  a  cold  satiir 
rated  solution  of  saltpetre.  If  the  solution  be  set  aside  in  an  open  vessel, 
the  water  will  slowly  pass  off  in  vapour,  and  the  saltpetre  will  be  gradually 
deposited,  its  particles  arranging  themselves  in  the  regular  geometrical 
shape  of  the  six-sided  prism,  which  is  its  common  crystalline  foi-m.  The 
crystals  of  saltpetre  do  not  contain  any  water  :  they  are  anhydrous. 

*  On  the  other  hand,  recent  experiments  have  indicated  the  formation  of  a  compound  of 
1  atom  of  hydrogen  with  2  atoms  of  palladium.  The  compounds  K2H  and  NaaH  have 
also  been  examined;  the  density  of  the  H  in  all  three  compounds  is  found  to  be  0"62. 


SUPERSATUEATED  SOLUTIONS. 


41 


Fig.  43. 


If  saltpetre  be  added  to  boiling  water  (in  a  porcelain  evaporating  dish, 
fig.  43),  and  stirred  (with  a  glass  rod)  until  the  water  refuses  to  dissolve 
any  more,  1000  grs.  of  water  -will  be  found  to  have  dissolved  about  2000 
grs.;  this  would  be  called  a  hot  saturated  solution. 

As  a  general  rule,  solids  are  dissolved  more 
quickly  and  in  larger  quantity  by  hot  water 
than  by  cold. 

One  of  the  commonest  methods  of  crystal- 
lising a  solid  substance,  consists  in  dissolving 
it  in  hot  water,  and  allowing  the  solution  to 
cool  slowly.  The  more  slowly  it  cools,  the 
larger  and  more  symmetrical  are  the  crystals. 

A  hot  saturated  solution  is  not  generally  the 
best  for  crystallising,  because  it  deposits  the 
dissolved  body  too  rapidly.  Thus  the  hot 
solution  of  saltpetre  prepared  as  above  would 
solidify  to  a  mass  of  minute  crystals  on  cooling ; 
but  if  1000  grs.  of  saltpetre  be  dissolved  in  4 
measured  ounces  of  boiling  water,  it  will  form  crystals  of  2  or  3  inches 
long  when  slowly  cooled  (in  a  covered  vessel).  If  the  solution  be  stirred 
while  cooling,  the  crystals  will  be  very  minute,  having  the  appearance  of 
a  white  powder. 

Some  soHds,  however,  refuse  to  crystallise^  even  from  a  hot  saturated 
solution,  if  it  be  kept  absolutely  undisturbed. 

Sulphate  of  soda  affords  a  good  example  of  this.  If  the  crystallised  sulphate  be 
added  to  boiling  water  in  a  flask,  as  long  as  it  is  dissolved,  the  water  will  take  into 
solution  more  than  twice  its  weight  of  the  salt,  yielding  a  solution  which  boils  at 
220°  F.  If  this  solution  be  allowed  to  cool  in  the  open  flask,  an  abundant  crystallisa- 
tion will  take  place,  for  cold  water  will  dissolve  only  about  one- third  of  its  weight  of 
crystallised  sulphate.  But  if  the  flask  (which  should  be  globular)  be  tightly  corked 
whilst  the  solution  is  boiling,  it  may  be  kept  for  several  days  without  crystallising, 
although  moved  about  from  one  place  to  another.  In  this  condition  the  solution^is 
said  to  be  super-saturated.  On  withdramng  the  cork,  the  air  entering  the  partly 
vacuous  space  above  the  liquid  will  be  seen  to  disturb  the  surface  slightly,  and  from 
that  point  beautiful  prismatic  crystals  will  shoot  through  the  liquid  until  the  whole 
has  become  a  nearly  solid  mass.  A  considerable  elevation  of  temperature  is  observed, 
ttonsequent  upon  the  passage  from  the  liquid  to  the  solid  form.  If  the  solution  of 
sulphate  of  soda  be  somewhat  weaker,  containing  exactly  two-thirds  of  its  weight  of 
the  crystals,  it  may  be  cooled  without  crystallising,  even  in  vessels  covered  with 
glass  plates,  but  a  touch  with  a  glass  rod  will  start  the  crystallisation  immediately.* 

A  super-saturated  solution  may  always  be  made  to  crystallise  by  dropping  in  a 
minute  crystal  of  the  salt  present  in  the  liquid. 

Minute  solid  particles  {nuclei)  derived  from  the  air  appear  to  be  instrumental  in 
causing  the  crystallisation  of  super-saturated  solutions.  If  the  solution  of  sulphate 
of  soda  containing  two-thirds  of  its  weight  of  the  crystallised  salt  be  allowed  to  cool 
in  a  flask  closed  by  a  cork  furnished  witli  two  tubes  closed  with  plugs  of  cotton  wool, 
it  will  be  found  that  on  withdrawing  the  plugs  and  blowing  air  through  one  of  the 
tubes  dipjjing  into  the  solution,  crystallisation  does  not  take  place,  apparently  be- 
cause the  air  has  been  deprived  of  the  particles  capable  of  causing  it ;  for  if  air 
be  blown  through  the  same  solution  with  the  bellows,  it  solidifies  almost  instan- 
taneously. 

A  most  beautiful  illustration  of  the  power  of  unfiltered  air  to  start  crystallisation 
is  afi"orded  by  a  solution  of  alum  which  has  been  saturated  at  194°  F.t  and  allowed  to 

*  It  is  very  remarkable  that,  if  the  glass  rod  has  been  recently  heated,  it  mil  not  cause 
the  crystallisation  even  after  it  has  been  cool  for  some  time. 

t  J.  M.  Thomson  recommends  a  solution  of  alum  in  half  its  weight  of  water  for  this 
experiment. 


42  WATER  OF  CRYSTALLISATION. 

cool  in  a  flask,  the  mouth  of  which  is  closed  by  a  plug  of  cotton  wool.  In  this  state 
it  may  be  kept  for  weeks  without  crystallising,  but  on  withdrawing  the  plug,  crystal- 
lisation will  be  seen  to  commence  at  a  few  points  on  the  surface  immediately  under 
the  opening  of  the  neck,  and  will  spread  slowly  from  these,  octahedral  crystals  of 
alum  of  half  an  inch  or  more  in  diameter  being  built  up  in  a  few  seconds,  the  tempera- 
ture, at  the  same  time,  I'ising  very  considerably. 

In  the  laboratory,  stirring  is  always  resorted  to  in  order  to  induce  crystallisation, 
if  it  does  not  take  place  spontaneously.  Thus  it  is  usual  to  test  for  potash  in  a 
solution  by  adding  tartaric  acid,  which  should  cause  the  formation  of  minute  crystals 
of  bitartrate  of  potash  {cream  of  tartar),  but  the  test  seldom  succeeds  unless  the  solu- 
tions are  briskly  stirred  together  with  a  glass  rod.  An  amusing  illustration  of  this 
is  afforded  by  pouring  a  solution  of  tartaric  acid  into  a  solution  of  saltpetre,  and 
allowing  the  clear  mixture  to  run  over  a  large  plate  of  glass.  Letters  traced  on  the 
glass  with  the  finger  will  now  be  rendered  visible  by  the  deposition  of  the  crystals  of 
bitartrate  of  potash  upon  the  glass. 

39.  The  crystals  of  sodium  sulphate  produced  in  the  above  experiments 
contain,  in  a  state  of  combination  with  the  salt,  more  than  half  their 
weight  of  water.     Their  composition  is — 

Anhydrous  sodium  sulphate  (Na2S04)  142  parts,  or  one  molecule, 
Water 180     ,,      or  ten  molecules, 

as  expressed  by  the  formula  !Na2SO4.10H2O.  If  some  of  the  crystals 
be  pressed  between  blotting-paper  to  remove  adhering  w^ater,  and  left 
exposed  to  the  air,  they  will  gradually  effloresce,  or  become  covered  with  a 
white  opaque  powder.  This  powder  is  the  anhydrous  sodium  sulphate 
into  which  the  entire  crystals  would  ultimately  become  converted  by 
exposure  to  air.  Since  most  crystals  containing  water  have  their  crystalline 
form  destroyed  or  modified  by  the  loss  of  the  water,  it  is  commonly 
spoken  of  as  water  of  crystallisation. 

Coloured  salts,  containing  water  of  crystallisation,  generally  change 
colour  when  the  water  is  removed.  The  sulphate  of  copper  (blue  stone) 
affords  an  excellent  example  of  th^s.  The  beautiful  blue  prismatic  crystals 
of  this  salt  contain — 

Anhydrous  sulphate  of  copper  (CUSO4)  159 '5  parts,  or  one  molecule, 
Water    .         .  .         .         .        90*0      „      or  five  molecules, 

as  expressed  by  the  formula  CuSO^.SHgO. 

When  these  are  exposed  to  the  air  at  the  ordinary  temperature  they 
remain  unchanged ;  but  if  heated  to  the  boiling-point  of  water  they 
become  opaque,  and  may  be  easily  crumbled  down  to  a  white  powder. 
This  powder  contains — 

Anhydrous  sulphate  of  copper  (CUSO4)  159  '5  parts,  or  one  molecule. 
Water 18         ,,       or  one  molecule, 

and  would  therefore  be  represented  by  CuSO^.HgO.  The  four  molecules 
of  water,  which  have  been  expelled,  constituted  the  water  of  crystallisation, 
upon  which  the  form  and  colour  of  the  sulphate  of  copper  depend.  If 
the  white  powder  be  moistened  with  water,  combination  takes  place,  with 
great  evolution  of  heat,  and  the  blue  colour  is  reproduced.  The  one 
molecule  of  water  which  still  remains  is  not  expelled  until  the  salt  is 
heated  to  390°  F.  (199°  C),  proving  that  it  is  held  to  the  sulphate  of 
copper  by  a  more  powerful  chemical  attraction.  On  this  account  it  is 
spoken  of  as  toater  of  constitution,  and  in  order  that  the  formula  of  the 
salt  may  exhibit  the  difference  between  the  water  of  constitution  and  of 
crystallisation,  it  is  usually  written  CuSO^.HgO.^Aq.* 

*  Aqua,  water. 


HYDRATES — NATURAL  WATERS.  43 

(Definition. — Watei'  of  crystallisation  of  salts  is  that  which  is  gene- 
rally expelled  at  212°  F.  (100°  C),  and  is  connected  with  the  form  and 
colour  of  the  crystals.  Water  of  constitution  is  not  generally  expelled  at 
212°  F.,  and  is  in  more  intimate  connexion  with,  the  chemical  properties  of 
the  salt.) 

Several  of  the  so-caUed  sympathetic  inks  employed  for  writings  which 
are  invisible  until  heated,  depend  upon  the  change  of  colour  which  results 
from,  the  loss  of  water  of  crystallisation.  Characters  written  with  a  weak 
solution  of  chloride  of  cobalt  and  allowed  to  dry,  are  very  nearly  in- 
visible, since  the  pink  colour  of  so  small  a  quantity  of  the  salt  is  scarcely 
noticed ;  but  on  warming  the  paper,  the  pink  hydrated  chloride  of  cobalt 
(CoCl2.6Aq.)  loses  water  of  crystallisation,  and  the  blue  chloride  with  1 
Aq.  is  produced.  On  exposure  to  air  this  again  absorbs  water,  and  the 
writing  fades  away. 

Some  salts  have  so  great  a  tendency  to  combine  with  water  that  they 
become  moist  or  deliquesce  when  exposed  to  air.  This  deliquescence  is 
exhibited  in  a  marked  degree  by  chloride  of  calcium,  and  its  great  attrac- 
tion for  water  is  turned  to  advantage  in  drying  air  and  other  gases  by 
passing  them  through  tubes  filled  with  the  salt. 

Nearly  all  salts  appear  to  combine  with  water  at  very  low  temperatures  ; 
such  compounds,  which  are  decomposed  at  temperatures  above  0°  C,  have 
been  termed  cryo-hydrates  (Kpvos,  frost). 

40.  Most  bases  are  capable  of  combining  with  water  to  form  hydrates, 
as  exemplified  in  the  slaking  of  Hme.  Anhydrous  lime  or  quick-hme 
(CaO),  when  wetted  with  water,  combines  with  it,  evolving  much  heat, 
and  crumbling  to  a  loose  bulky  powder,  which  is  hydrate  of  lime  or  slaked 
lime  (CaO.HgO).  At  a  red  heat  the  water  is  expelled,  and  anhydrous 
hme  remains. 

41.  According  to  modern  views,  based  upon  the  fact  that  several 
hydrates  do  not  yield  water  when  heated,  the  hydrate  of  a  metal  is  defined 
as  a  compound  formed  by  the  replacement  of  a  part  of  the  hydrogen  in 
water  by  a  metal ;  thus  potassium  hydrate  KHO  is  formed  from  water 
HgO  by  the  replacement  of  H  by  K ;  calcium  hydrate  Ca(H0)2  is  formed 
from  two  molecules  of  water  (H20)2  by  the  replacement  of  Hg  by 
(diatomic)  calcium.  The  imaginary  group  HO,  hydroxyle,  would  then  be 
the  radical  of  the  hydrates,  which  are  often  termed  hydroxides. 

42.  Water  from  Natural  Sources. — Pure  water  is  not  found  in 
natura  Eain  is  the  purest  form  of  natural  water,  but  contains  certain 
gases  which  it  collects  from  the  atmosphere  during  its  fall.  As  soon  as 
it  reaches  the  earth  it  begins  to  dissolve  small  portions  of  the  various 
solid  materials  with  which  it  comes  in  contact,  and  thus  becomes  charged 
with  salts  and  other  substances  to  an  extent  varying,  of  course,  with  the 
nature  of  the  soQs  and  rocks  which  it  has  touched,  and  attaining  its 
highest  point  in  sea  water,  which  contains  a  larger  proportion  of  saline 
matters  than  water  from  any  other  natural  source. 

If  a  quantity  of  rain,  spring,  river,  or  sea  water  be  boiled  in  a  flask 
furnished  with  a  tube  also  filled  with  the  water,  and  passing  under  a  gas 
cylinder  standing  in  a  trough  of  the  same  water  (fig.  44),  it  will  be  found 
to  give  off  a  quantity  of  gas  which  was  previously  held  in  solution  by 
the  water,  and  is  now  set  free  because  gases  are  less  soluble  in  hot  than  in 


44 


WATER  OF  WELLS,  SPRINGS,  AND  RIVERS. 


Fig.  44. 


cold  water.  The  quantity  of  this  gas  will  vary  according  to  the  source  of 
the  water,  but  it  will  always  be  found  to  contain  the  gases  existing  in 
atmospheric  air,  viz.,  nitrogen,  oxygen,  and  carbonic  acid  gas.     One  gallon 

of  rain  water  will  generally 
furnish  about  4  cubic  inches 
of  nitrogen,  2  cubic  inches  of 
oxygen,  and  1  cubic  inch 
of  carbonic  acid  gas.  .It  is 
worthy  of  remark,  that  the 
nitrogen  and  oxygen  have 
been  dissolved  by  the  water, 
not  in  the  proportions  in 
which  they  exist  in  the 
atmosphere  (4N  :  10),  but  in 
the  proportions  in  which  they 
ought  to  be  dissolved,  if  it  be 
true  that  they  exist  in  the  air 
in  the  condition  of  mere 
mechanical  admixture.  The 
oxygen  thus  carried  down 
from  the  air  by  rain  appears  to  be  serviceable  in  maintaining  the  respiration 
of  aquatic  animals,  and  in  conferring  upon  river  waters  a  self-purifying 
power,  by  acting  upon  certain  organic  matters  which  would  probably 
prove  hurtful  to  animals,  and  converting  them  into  harmless  products  of 
oxidation.  In  the  cases  of  rivers  contaminated  with  the  sewage  of  towns, 
this  action  of  the  dissolved  oxygen  is  probably  of  great  importance.  The 
carbonic  acid  dissolved  in  rain  water  also  probably  serves  some  useful 
purposes  in  the  chemical  economy  of  nature.     (See  Carhom'c  Acid.) 

The  co-efficient  of  solubility  of  a  gas  expresses  the  volume  of  gas  absorbed  by  one 
volume  of  water.  The  numbers  '02989  and  •01478  respectively  represent  the  volumes 
of  oxygen  and  nitrogen  absorbed  by  one  volume  of  water,  when  exposed  to  the  action 
of  either  gas,  in  a  pure  state,  at  59°  F.  (15°  C. ).  When  a  mixture  of  gases  is  brought 
into  contact  with  water,  the  proportions  in  which  the  gases  are  absorbed  can  be  ascer- 
tained by  multiplying  the  co-efficient  of  solubility  of  each  gas  into  its  proportion  by 
volume  in  the  mixture.  Thus,  when  water  is  exposed  to  air,  containing  i  volume  of 
oxygen  and*  volume  of  nitrogen,  the  quantities  dissolved  by  1  volume  oT  water  are, — 

Oxygen i         x  -02989     -     '00597 

Nitrogen,  .         .         .         ,         ^         x  '01478     =      '01182 

or  almost  exactly  2  volumes  of  N  to  1  volume  of  0. 

43.  The  waters  of  wells,  springs,  and  rivers,  and  especially  those  of 
the  two  first-named  sources,  differ  very  much  from  each  other,  according 
to  the  nature  of  the  layers  of  rock  or  earth  over  or  through  which  they 
have  passed,  and  from  which  they  dissolve  a  great  variety  of  substances, 
some  of  which  are  familiar  to  us  in  daily  life,  while  others  are  only  met 
with  in  chemical  collections.  Under  the  former  head  may  be  enumerated 
Glauber's  salt  (sodium  sulphate),  common  salt  (sodium  chloride),  Epsom 
salt  (magnesium  sulphate),  gypsum  (calcium  sulphate),  chalk  (calcium 
carbonate),  common  magnesia  (magnesium  carbonate),  carbonic  acid,  and 
silica. 

Among  the  substances  known  only  to  the  chemist  may  be  mentioned 
sulphuretted  hydrogen,  potassium  sulphate,  potassium  chloride,  calcium 
chloride,  magnesium  chloride,  phosphates,  bromides  and  iodides  of  calcium 


HARD  WATERS.  45 

and  magnesium  (rarely),  aluminium  sulphate,  carbonate  of  iron  (ferrous 
carbonate),  and  certain  vegetable  substances.* 

The  well  waters  of  certain  localities  (as,  for  example,  those  of  large  towns) 
also  frequently  contain  salts  of  nitric  and  nitrous  acids,  and  of  ammonia. 

The  waters  of  springs  and  rivers  do  not  differ  very  materially  from 
well  waters  as  to  the  nature  of  the  substances  which  they  contain,  though, 
in  the  case  of  river  waters  more  particularly,  the  quantity  of  these  sub- 
stances is  materially  influenced  by  the  conditions  of  rapid  motion  and 
exposure  to  air  under  which  such  waters  are  placed. 

Household  experience  has  established  a  classification  of  the  waters 
from  natural  sources  into  soft  and  hard  waters — a  division  which  depends 
chiefly  upon  the  manner  in  which  they  act  upon  soap.  If  a  piece  of 
soap  be  gently  rubbed  in  soft  water  (rain  water,  for  example)  it  speedily 
furnishes  a  froth  or  lather,  and  its  cleansing  powers  can  be  readily 
brought  into  action  ;  but  if  a  hard  water  (spring  water)  be  substituted  for 
rain  water,  the  soap  must  be  rubbed  for  a  much  longer  time  before  a 
lather  can  be  produced,  or  its  effect  in  cleansing  rendered  evident;  a 
number  of  white  curdy  flakes  also  make  their  appearance  in  the  hard 
water,  which  were  not  seen  when  soft  water  was  used.  The  explanation 
of  this  difference  is  a  purely  chemical  one. 

Soap  is  formed  by  the  combination  of  a  fatty  acid  with  an  alkali ;  it  is 
manufactured  by  boUing  oil  or  fat  with  potash  or  soda,  the  former  for 
soft,  the  latter  for  hard  soaps.  In  the  preparation  of  ordinary  hard  soap, 
the  soda  takes  from  the  oil  or  fat  two  acids, — stearic  and  oleic  acid, — 
which  exist  in  abundance  in  most  varieties  of  fat,  and  unites  with  them 
to  form  soap,  which  in  chemical  language  would  be  spoken  of  as  a  mix- 
ture of  stearate  and  oleate  of  sodium,. 

If  soap  be  rubbed  in  soft  water  until  a  little  of  it  has  dissolved,  and 
some  Epsom  salts  (magnesium  sulphate)  be  dissolved  in  water,  and 
poured  into  the  soap  water,  curdy  flakes  will  be  produced,  as  when  soap 
is  rubbed  in  hard  water,  and  the  soap  water  will  lose  its  property  of  froth- 
ing when  stirred;  the  magnesium  sulphate  has  decomposed  the  soap,  form- 
ing sodium  sulphate,  which  remains  dissolved  in  the  water,  and  insoluble 
curdy  flakes,  which  consist  of  stearate  and  oleate  of  magnesium. 

Similar  to  the  effect  of  the  magnesium  sulphate  is  that  of  hard  waters  ; 
their  hardness  is  attributable  to  the  presence  of  the  different  salts  of 
calcium  and  magnesium,  all  of  which  decompose  the  soap  in  the  manner 
exemplified  above  ;  the  peculiar  properties  of  the  soap  in  forming  a  lather 
and  dissolving  grease  can  therefore  be  manifested  only  when  a  sufiicient 
quantity  has  been  employed  to  decompose  the  whole  of  the  salts  of  calcium 
and  magnesium  contained  in  the  quantity  of  water  operated  on,  and  thus  a 
considerable  amount  of  soap  must  be  rendered  useless  when  hard  water  is 
employed. 

On  examining  the  interior  of  a  kettle  in  Avhich  spring,  well,  or  river 
water  has  been  boiled,  it  will  be  found  to  be  coated  more  or  less  thickly 
with  a  fur  or  incrustation,  generally  of  a  brown  colour,  and  the  harder 
the  water  the  more  speedily  will  this  incrustation  be  deposited.  A 
chemical  examination  shows  this  deposit  to  consist  chiefly  of  calcium 
carbonate  in  the  form  of  minute  crystals,  which  may  be  discovered  by  the 

*  Although  it  is  certainly  known  that  the  acids  and  bases  capable  of  forming  the  salts 
here  enumerated  may  be  detected  in  spring  and  river  waters,  their  exjict  distribution 
amongst  each  other  is  still  a  matter  of  uncertainty. 


46  INCRUSTATIONS  IN  BOILERS. 

microscope ;  it  usually  contains,  in  addition,  some  magnesium  carbonate, 
calcium  sulphate,  and  small  quantities  of  sesquioxide  of  iron  (rust),  and 
vegetable  matter,  the  last  two  substances  imparting  its  brown  colour.  In 
order  to  explain  the  formation  of  this  deposit,  it  is  necessary  to  become 
acquainted  with  the  particular  condition  in  which  the  calcium  carbonate 
exist  in  natural  waters ;  it  is  hardly  dissolved  to  any  perceptible  extent 
by  pure  water,  though  it  may  be  dissolved  in  considerable  quantity  by 
carbonic  acid.  This  statement,  which  is  of  great  importance  in  connexion 
with  natural  waters,  may  be  verified  in  the  following  manner  : — A  little 
slaked  lime  is  well  shaken  up  in  a  bottle  of  distilled  or  rain  water,  which 
is  afterwards  set  aside  for  an  hour  or  two ;  as  soon  as  that  portion  of  the 
lime  which  has  not  been  dissolved  has  subsided,  the  clear  portion  is  care- 
fully poured  into  a  glass,  and  a  little  soda  water  or  solution  of  carbonic 
acid  in  water  is  added  to  it ;  the  first  addition  of  the  carbonic  acid  to  the 
lime  water  causes  a  milkiness,  due  to  the  formation  of  minute  particles 
of  calcium  carbonate ;  this  being  insoluble  in  the  water,  separates  from 
it,  or  precipitates,  and  impairs  the  transparency  of  the  liquid ;  a  further 
addition  of  carbonic  acid  water  renders  the  liquid  again  transparent,  for 
the  carbonic  acid  dissolves  the  calcium  carbonate  which  has  separated. 

If  this  clear  solution  be  introduced  into  a  flask,  and  boiled  over  the 
spirit-lamp  or  gas-flame,  it  will  again  become  turbid,  for  the  free  carbonic 
acid  will  be  expelled  by  the  heat,  and  the  calcium  carbonate  will  be 
deposited,  not  now,  however,  in  so  fine  a  powder  as  before,  but  in  small, 
hard  grains,  which  have  a  tendency  to  fix  themselves  firmly  upon  the 
sides  of  the  flask,  and,  when  examined  by  the  miscroscope,  are  seen  to 
consist  of  small  crystals. 

In  a  similar  manner,  when  natural  waters  are  boiled,  the  carbonic 
acid  gas  which  they  contain  is  expelled,  and  the  carbonates  of  calcium 
magnesium  and  iron  are  precipitated,  since  they  are  insoluble  in  water 
which  does  not  contain  carbonic  acid.  But,  by  the  ebullition  of  the  water, 
a  portion  of  it  has  been  dissipated  in  vapour,  and  if  there  be  much  calcium 
sulphate  present,  the  quantity  of  water  left  may  not  be  sufiicient  to  retain 
the  whole  of  the  salt  in  solution ;  and  this  is  the  more  likely  to  happen, 
because  calcium  sulphate  requires  about  500  parts  of  water  to  dissolve  it  ;* 
a  quantity  of  calcium  sulphate,  then,  is  liable  to  be  deposited  together  with 
the  carbonates,  and,  should  the  water  contain  much  vegetable  matter,  this  is 
often  deposited  in  an  insoluble  condition,  the  whole  eventually  forming 
together  a  hard  compact  mass,  composed  of  successive  thin  layers,  on  the 
bottom  aud  sides  of  the  vessel  in  which  the  water  has  been  boiled.  The 
"  furring "  of  a  kettle  is  objectionable,  chiefly  in  consequence  of  its 
retarding  the  ebullition  of  the  water,  since  the  deposit  is  a  very  bad  con- 
ductor of  heat,  and  therefore  impedes  the  transmission  of  heat  from  the 
fire  to  the  water ;  hence  the  common  practice  of  introducing  a  rouud  stone 
or  marble  into  the  kettle,  in  order,  by  its  perpetual  rolling,  to  prevent  the 
jjarticles  of  calcium  carbonate  from  forming  a  compact  layer.  In  steam 
boilers,  however,  even  more  serious  inconvenience  than  loss  of  time  some- 
times arises  if  this  deposit  be  allowed  to  accumulate,  and  to  form  a  thick 
layer  of  badly  conducting  material  on  the  bottom  of  the  boiler,  since  the 

*  Calcium  sulphate  has  been  found  nearly  insoluble  in  water  having  a  higher  tempera- 
ture thau  212°  F.,  as  would  be  the  case  in  boilers  worked  under  pressure,  so  that  it  would 
readily  be  deposited.  It  is  said  that  waters  containing  little  or  no  calcium  sulphate  yield 
a  loose  and*  friable  deposit. 


CALCAREOUS  WATEKS.  ,  '      47 

latter  is  then  liable  to  liecome  red  hot,  and  should  the  incrustation  happen 
to  crack,  and  allow  the  water  to  reach  the  red  hot  metal,  so  violent  a  dis- 
engagement of  steam  follows,  that  boilers  have  been  known  to  burst  under 
the  sudden  pressure.  But  even  though  this  calamity  be  escaped,  the 
wear  and  tear  of  the  boiler  is  very  much  increased  in  consequence  of  the 
formation  of  this  deposit,  since  its  hardness  often  renders  it  nec;essary  to 
detach  it  with  the  hammer,  much  to  the  injury  of  the  iron  boiler-plates, 
which  are  also  subject  to  increased  oxidation  and  corrosion  in  consequence 
of  the  high  temperature  which  the  incrustation  permits  them  to  attain 
by  preventing  their  contact  with  the  water.  Many  propositions  have 
been  brought  forward  for  the  prevention  of  these  incrustations  ;  some  sub- 
stances have  been  used,  of  which  the  action  appears  to  be  purely  mechani- 
cal, in  preventing  the  aggregation  of  the  deposited  particles.  Clay,  saw- 
dust, and  other  matters  have  been  employed  with  this  view;  but  the 
action  of  sal  ammoniac,  which  has  also  been  found  efficacious,  must  be 
explained  upon  purely  chemical  principles.  When  this  salt  is  boiled  with 
calcium  carbonate,  mutual  decomposition  ensues,  resulting  in  the  production 
of  calcium  chloride  and  ammonium  carbonate,  of  which  salts  the  former 
is  very  soluble  in  water,  while  the  latter  passes  off  in  vapour  with  the 
steam.* 

The  deposit  formed  in  boUers  fed  with  sea  water  consists  chiefly  of 
calcium  sulphate  and  magnesium  hydrate,  the  latter  resulting  from  the 
decomposition  of  the  magnesium  chloride  present  in  sea  water. 

The  incrustations  formed  in  cisterns  and  pipes  by  hard  water  are  also 
produced  by  the  carbonates  of  calciaim  and  magnesium  deposited  in  conse- 
quence of  the  escape  of  the  free  carbonic  acid  which  held  them  in  solution. 
Many  interesting  natural  phenomena  may  be  explained  upon  the  same 
principle.  The  so-called  petrifying  springs,  in  many  cases,  owe  their  re- 
markable properties  to  the  considerable  quantity  of  calcium  carbonate  dis- 
solved in  carbonic  acid  which  they  contain ;  when  any  object,  a  basket,  for 
example,  is  repeatedly  exposed  to  the  action  of  these  waters,  it  becomes 
coated  with  a  compact  layer  of  the  carbonate,  and  thus  appears  to 
have  suffered  conversion  into  limestone.  The  celebrated  waters  of  the 
Sprudel  at  Carlsbad,  of  San-Filippo  in  Tuscany,  and  of  Saint  Allyre 
in  Auvergne.  are  the  best  instances  of  this  kind. 

The  stalactites  and  stalagmites,^  which  are  formed  in  many  caverns 
or  natural  grottoes  (fig.  45),  afford  beautiful  examples  of  the  gradual 
separation  of  calcium  carbonate  from  water  charged  with  carbonic  acid. 
Each  drop  of  water,  as  it  trickles  through  the  roof  of  the  cavern,  becomes 
surrounded  with  a  shell  of  calcium  carbonate,  the  length  of  which  is  pro- 
longed by  each  drop  as  it  falls,  till  a  stalactite  is  formed,  varying  in  colour 
according  to  the  nature  of  the  substances  which  are  separated  from  the 
water  together  with  the  carbonate  (such  as  the  oxides  of  iron  and  vege- 
table matter);  and  as  each  drop  falls  from  the  point  of  the  stalactite  upon 
the  floor  of  the  cavern,  it  deposits  there  another  shell,  which  grows,  like 
the  upper  one,  but  in  the  opposite  direction,  and  forms  a  stalagmite,  thus 
adorning  the  grotto  with  conical  pillars  of  calcium  carbonate,  sometimes, 
as  in  the  case  of  the  oriental  alabaster,  variegated  with  red  and  yellow, 
and  applicable  to  ornamental  purposes. 

*  Solutions  of  the  caustic  alkalies,  of  alkaline  carbonates,  and  arsenites,  are  also  occa- 
sionally employed  to  prevent  the  formation  of  incrustations  in  boilers, 
f  From  aToXaXfio,  to  drop ;  (rraXayfJia,  a  drop. 


48 


SOFTENING  WATERS. 


Fig.  45. — Stalactite  cavern. 


When  water  which  has  been  boiled  for  some  time  is  compared  with 
unboiled  water  from  the  same  source,  it  will  be  found  to  have  become 

much  softer,  and  this  can 
now  be  easily  explained, 
for,  a  considerable  portion 
of  the  salts  of  calcium  and 
magnesium  having  separ- 
ated from  the  water,  the 
latter  is  not  capable  of 
decomposing  so  large  a 
quantity  of  soap.  The 
amount  of  hardness  which 
is  thus  destroyed  by  boil- 
ing is  generally  spoken  of 
as  temporary  hardness,  to 
distinguish  it  from  the 
permanent  hardness  due  to 
the  soluble  salts  of  calcium 
and  magnesium  which  still 
remain  in  the  boiled  water. 
It  is  customary  with  analy- 
tical chemists,  in  reporting 
upon  the  quality  of  natural  waters,  to  express  the  hardness  by  a  certain 
number  of  degrees  which  indicate  the  number  of  grains  of  chalk  or  car- 
bonate of  calcium  which  would  be  dissolved  in  a  gallon  of  water  containing 
carbonic  acid,  in  order  to  render  its  hardness  equal  to  that  of  the  water 
examined,  that  is,  to  render  it  capable  of  decomposing  an  equal  quantity  of 
soap.  Thus,  when  a  water  is  spoken  of  as  having  16  degrees  of  hardness, 
it  is  implied  that  16  grs.  of  calcium  carbonate  dissolved  in  a  gallon  of 
water  containing  carbonic  acid,  would  render  that  gallon  of  water  capable  of 
decomposing  as  much  soap  as  a  gallon  of  the  water  under  consideration. 

The  utility  of  a  water  for  household  purposes  must  be  estimated,  there- 
fore, not  merely  according  to  the  total  number  of  degrees  of  hardness 
which  it  exhibits,  but  also  by  the  proportion  of  that  hardness  which  may 
be  regarded  as  temporary,  that  is,  which  disappears  when  the  water  is 
boiled.  Thus,  the  total  hardness  of  the  New  Eiver  water  amounts  to 
nearly  15  degrees,  that  of  the  Grand  Junction  Company  to  14  degrees,  and 
yet  these  waters  are  quite  applicable  to  household  uses,  since  their  hard- 
ness is  reduced  by  boiling  to  about  5  degrees.  It  has  been  ascertained 
that  every  degree  of  hardness  in  water  gives  rise  to  a  waste  of  about  10  grs. 
of  soap  for  every  gallon  of  water  employed,  and  hence  the  use  of  100 
gallons  of  Thames  or  I^ew  River  water  in  washing  will  be  attended  with 
the  loss  of  about  2  lbs.  of  soap ;  this  loss  is  reduced,  however,  to  about 
one-third  when  the  temporary  hardness  has  been  destroyed  by  boiling. 
The  addition  of  washing  soda  (sodium  carbonate)  removes  not  only  the 
teraporary,  but  also  the  permanent  hardness  due  to  the  presence  of  the 
sulphates  of  calcium  and  magnesium  in  the  water,  for  both  these  salts  are 
decomposed  by  the  sodium  carbonate  which  separates  the  calcium  and 
magnesium  as  insoluble  carbonates,  while  sodium  sulphate  remains  dis- 
solved in  the  water.*     The  household  practice  of  boiling  the  water,  and 

*CaS04       +       NajCOj        =        NaaSOi       +       CaCOs 
Calcium  sulphate.    Sodium  carbonate.    Sodium  sulpliate.    Calcium  carbonate. 


ORGANIC  MATTER  IN  WATER.  49 

adding  a  little  washing  soda,  is  therefore  very  efficacious  in  removing 
the  hardness.  Clark's  ].)rocess  for  softening  waters  depends  upon  the 
neutralisation  of  the  free  carbonic  acid  contained  in  the  water  by  the 
addition  of  a  certain  quantity  of  lime ;  the  calcium  carbonate  so  produced 
separates  together  with  the  carbonates  of  calcium  and  magnesium,  which 
were  previously  retained  in  solution  by  the  free  carbonic  acid  ;  this 
process,  therefore,  affects  chiefly  the  temporary  hardness ;  moreover,  the 
earthy  carbonates  which  are  separated  appear  to  remove  from  the  water 
a  portion  of  the  organic  matter  which  it  contains,  and  thus  effect  a  very 
important  purification.  The  water  under  treatment  is  mixed, in  large  tanks, 
with  a  due  proportion  of  lime  previously  diffused  through  water  (the 
quantity  necessary  having  been  determined  by  preliminary  experiment), 
and  the  mixture  allowed  to  settle  until  perfectly  clear,  when  it  is  drawn 
off  into  reservoirs.* 

Waters  which  are  turbid  from  the  presence  of  clay  in  a  state  of  sus- 
pension, are  sometimes  purified  by  the  addition  of  a  small  quantity  of 
alum  or  sulphate  of  alumina,  when  the  alumina  is  precipitated  by  the 
calcium  carbonate,  and  carries  down  with  it  mechanically  the  suspended 
clay,  leaving  the  water  clear. 

The  organic  matter  contained  in  waters  may  be  vegetable  matter  dis- 
solved from  the  earth  with  which  it  has  come  in  contact,  or  resulting 
from  the  decomposition  of  plants,  or  it  may  be  animal  matter  derived 
either  from  the  animalcules  and  fish  naturally  existing  in  it,  or  from  the 
sewage  of  towns,  and,  in  the  case  of  well  waters,  from  surface  drainage. 
It  is  a  pretty  generally  received  opinion  that  such  of  these  organic  matters 
as  are  very  susceptible  of  chemical  change  have  an  injurious  effect  upon 
the  system  of  persons  drinking  the  water,  and  it  is  now  usual,  in  examin- 
ing Avater  as  to  its  fitness  for  consumption,  to  ascertain  how  much  of  the 
organic  matter  is  in  a  changeable  condition,  by  determining  with  the  aid 
of  a  solution  of  potassium  permanganate  the  amount  of  oxygen  necessary 
to  effect  its  conversion  into  more  stable  forms. 

It  is  believed  upon  good  medical  authority,  that  cholera,  diarrhoea,  and 
typhoid  fever  are  propagated  by  certain  spores  or  germs,  which  are  present 
in  the  evacuations  of  persons  suffering  from  those  maladies,  and  are 
conveyed  into  water  which  is  allowed  to  become  contaminated  by 
sewage. 

On  this  account,  much  attention  is  paid,  in  the  analysis  of  water 
intended  for  drinking,  to  the  detection  of  organic  matters  containing 
nitrogen  (so-called  allmminoid  matters)  which  would  be  conveyed  into  the 
water  in  such  evacuations.  The  analytical  operations  required  for  this 
purpose  require  great  care  and  skill,  and  the  conclusions  to  be  drawn  from 
their  results  are  by  no  means  finally  agreed  upon  among  scientific 
chemists. 

There  are,  however,  certain  simple  tests,  which  may  often  determine  whether  it  is 
worth  while  to  undertake  a  more  elaborate  examination  of  the  water. 

1.  Pour  half  a  pint  of  the  water  into  a  wide-mouthed  bottle  or  decanter,  close  it 
with  the  stopper  or  with  the  palm  of  the  hand,  and  shake  it  violently  up  and  down. 
If  an  offensive  odour  is  then  perceived,  the  water  is  probably  contaminated  by 
sewage-gas,  and  possibly  with  other  constituents  from  the  same  source. 

2.  Add  to  a  little  of  the  water  a  drop  or  two  of  dilute  sulphuric  acid,  and  enough 
■potassium  permanganate  {Condy's  red  fluid  or  ozonised  water)  to  tinge  it  of  a  faint 

*  Thames  and  New  River  water  are  softened,  in  this  way,  to  3'5,  or  to  a  lower  point  than 
by  an  hour's  boiling. 

D 


50  MINERAL  WATEKS. 

rose  colour  ;  cover  the  vessel  with  a  glass  plate  or  a  saucer.  If  the  ]>ink  tinge  be 
still  visible  after  the  lapse  of  a  t^uarter  of  an  hour,  the  water  is  probably  whole- 
some. 

3.  Pour  a  little  solution  of  silver  nitrate  {lunar  caustic)  into  a  carefully  cleaned 
glass,  and  see  that  it  remains  transparent  ;  then  pour  in  some  of  the  water  ;  should 
a  strong  milkiness  appear,  which  is  not  cleared  up  on  adding  a  little  diluted  nitric 
acid,  the  water  probably  contains  much  sodium  chloride,  which  is  always  found  in 
sewage-water,  but  seldom  in  wholesome  waters  in  any  large  quantity,  unless  near  the 
sea-coast. 

To  render  an  impure  water  fit  to  drink,  a  chemist  would  naturally  recommend 
distillation,  but  in  many  cases  this  is  impracticable,  and  the  consumer  may  protect 
himself  to  a  great  extent  bj'  boiling  the  water,  or  by  filtering  it  through  char- 
coal or  spongy  iron,  or  by  applying  Clark's  process  (p.  49),  or  treating  it  with  alum 
(p.  49). 

44.  One  of  the  most  important  points  to  be  taken  into  account  in 
estimating  the  qualities  of  a  water  is  its  action  upon  lead,  since  this  metal 
is  unfortunately  so  generally  employed  for  the  storage  and  transmission  of 
water,  and  cases  frequently  occur  in  which  the  health  has  been  seriously 
injured  by  repeated  small  doses  of  compounds  of  lead  taken  in  water 
which  has  been  kept  in  a  leaden  cistern.  If  a  piece  of  bright  freshly 
scraped  lead  be  exposed  to  the  air,  it  speedily  becomes  tarnished  from  the 
formation  of  a  thin  film  of  the  oxide  of  lead,  produced  by  the  action  of 
the  atmospheric  oxygen ;  this  oxide  of  lead  is  soluble  in  water  to  some 
extent,  and  hence,  when  lead  is  kept  in  contact  with  water,  the  oxygen 
which  is  dissolved  in  it  acts  upon  the  metal,  and  the  oxide  so  produced 
is  dissolved  by  the  water ;  but  fortunately,  different  waters  act  with  very 
difi'erent  degi-ees  of  rapidity  upon  the  metal,  according  to  the  nature  of 
the  substances  which  tliey  contain. 

The  film  of  oxide  which  forms  upon  the  surface  of  the  lead  is  insoluble, 
or  nearly  so,  in  water  containing  much  sulphate  or  carbonate  of  calcium,  .so 
that  hard  waters  may  generally  be  kept  without  danger  in  leaden  cisterns, 
but  soft  waters,  and  those  which  contain  nitrites  or  nitrates,  should  not 
be  drunk  after  contact  with  lead.  Nearly  all  waters  which  have  baen 
stored  in  leaden  cisterns  contain  a  trace  of  the  metal,  and  since  the 
action  of  this  poison,  in  minute '  doses,  upon  the  system  is  so  gradual 
that  the  mischief  is  often  referred  to  other  causes^  it  is  much  to  be 
desired  that  lead  should  be  discarded  altogether  for  the  construction  of 
cisterns. 

To  detect  lead  in  a  water,  fill  a  glass  tumbler  with  it,  place  this  on  white  paper, 
add  a  drop  or  two  of  diluted  nitric  acid,  and  some  hydrosulphuric  acid,  a  dark 
brown  tinge  will  be  seen  on  looking  through  it  from  above. 

Mineral  waters,  as  they  are  popularly  called,  are  simply  spring  waters 
containing  so  large  a  quantity  of  some  ingredient  as  to  have  a  decided 
medicinal  action.  They  are  differently  named  according  to  the  nature  of 
their  predominating  constituent.  Thus,  a  chalybeate  water  contains  a 
considerable  quantity  of  a  salt  of  iron  (usually  ferrous  carbonate  dissolved 
by  free  carbonic  acid) ;  an  acidulous  water  is  distinguished  by  a  large  pro- 
portion of  carbonic  acid,  and  is  well  exemplified  in  the  celebrated  Seltzer 
water ;  a  sulphureous  or  hepatic  water  has  the  nauseous  odour  due  to  the 
presence  of  sulphuretted  hydrogen.  The  Harrogate  water  is  eminently 
sulphureous.  Saline  waters  are  such  as  contain  a  large  quantity  of  some 
salt ;  thus  the  saline  springs  of  Cheltenham  are  rich  in  common  salt  and 
sodium  sulphate. 

The  chalybeate  waters,  which   are  by  no  means  uncommon,  become 


DISTILLATION. 


51 


brown  when  exposed  to  the  air,  and  deposit  a  msty  sediment  which  con- 
sists of  the  ferric  hydrate,  formed  by  the  action  of  the  oxygen  of  the 
air  on  the  carbonate."* 

45.  Sea  water  contains  the  same  salts  as  are  found  in  waters  from  other 
natural  sources,  but  is  distinguished  by  the  very  large  proportion  of 
sodium  chloride  (common  salt).  A  gallon  of  sea  water  contains  usually 
about  2500  grains  of  saline  matter,  of  which  1890  grains  consist  of 
common  salt.  The  circumstance  that  clothes  wetted  with  sea  water  never 
become  perfectly  dry  is  to  be  ascribed  chiefly  to  the  magnesium  chloride 
present  in  the  water,  which  is  'distinguished  by  its  tendency  to  deliquesce 
or  become  damp  in  moist  air.  There  are  two  elements,  bromine  and 
iodine,  which  are  found  combined  with  metals  in  appreciable  quantity 
in  sea  water,  though  they  are  of  somewhat  rare  occurrence  in  other  waters 
derived  from  natural  sources. 

46.  By  distillation  pure  water  may  be  obtained  from  most  spring  and 
river  waters. 

(Definition. — Distillation  is  the  conversion  of  a  liquid  into  a  vapour, 
and  its  recondensation  into  the  liquid  form  in  another  vessel. ) 

Fig.  46  represents  the  ordinary  form  of  still  in  common  use,  in  which  A  is  a  copper 
boiler  containing  the  water  to  be  distilled  ;  B  the  head  of  the  still,  which  lifts  out  at 
b,  and  is  connected 
by  the  neck  C  with 
the  worm  D,  a  tin 
j)ipe  coiled  round  in 
the  tub  E,  and  issu- 
ing at  F.  The  steam 
from  the  boiler,  pass- 
ing into  the  worm, 
is  condensed  to  the 
liquid  state,  being 
cooled  by  the  water 
in  contact  with  the 
worm  ;  this  water, 
becoming  heated, 
passes  off  tbrougli 
the  pipe  G,  being 
replaced  by  cold 
water,  which  is 
allowed  to  enter 
through  H.t 

Another  form  of 
apparatus  for  dis- 
tillation of  water 
and  other  liquids  is 

shown  in  fig.  47.  A  is  a  stoppered  retort,  the  neck  of  which  fits  into  the  tube  of  a 
Liebig's  condenser  (B),  which  consists  of  a  glass  tube  (C)  fitted  by  means  of  corks 
into  a  glass,  copper,  or  tinned  iron  tube  D,  into  which  a  stream  of  cold  water  is 
passed  by  the  funnel  E,  the  heated  water  running  out  through  the  upper  tube  F. 
The  water  furnished  by  the  condensation  of  the  steam  passes  through  the  quilled 
receiver  G,  into  the  flask  H.  Heat  is  gradually  applied  to  the  retort  by  a  ring  gas- 
burner. 

Many  special  precautions  are  requisite  in  order  to  obtain  absolutely 

*  2FeC03  -f   0  -1-  3H.p  =  FeaCOH)^ 

Ferrous  WatPr  Vemc 

arbonate.  waiBi.  hydrate. 

+  A  rosette  gas-burner  (K)  on  Biiiissn's  principle  is  very  convenient  for  a  small  still  of 
this  description. 


Fig.  46. 


+  2C0., 
Carbon 
dioxide. 


52 


PHYSICAL  PROPERTIES  OF  WATER. 


pure  distilled  water  for  refined  experiments,  but  for  ordinary  purposes  the 
common  methods  of  distillation  yield  it  in  a  sufficiently  pure  condition. 


47.  — Distillation — Liebis's  condenser. 


The  saline  matters  present  in  the  water  are  of  course  left  behind  in  the 
still  or  retort.  Sea  water  is  now  frequently  distilled  on  board  ship  when 
fresh  water  is  scarce.  The  vapid  and  disagreeable  taste  of  distilled  water, 
which  is  due  to  its  having  been  deprived  of  the  dissolved  air  during  the 
distillation,  is  remedied  by  the  use  of  Normandy's  apparatus,  which  pro- 
vides for  the  restoration  of  the  expelled  air. 

47.  The  physical  properties  of  water  are  too  well  known  to  require 
any  detailed  description.  Its  specific  gravity  in  the  liquid  state  is  =  1, 
being  taken  as  the  standard  to  which  the  specific  gravities  of  liquid  and 
solid  bodies  are  referred. 

(Definition. — The  specific  gravity  of  a  liquid  or  solid  body  is  its 
weight  as  compared  with  that  of  an  equal  volume  of  pure  water  at  60°  F., 
15°-5C.) 

Water  assumes  the  solid  form,  under  ordinary  circumstances,  at  32°  F. 
(0°  C),  and  may  be  obtained  in  six-sided  prismatic  crystals.  Snow  con- 
sists of  beautiful  stellate  groupings  of  these  crystals.  Ice  has  the  specific 
gravity  0'9184.  In  the  act  of  freezing,  water  expands  very  considerably, 
so  that  174  volumes  of  water  at  60°  F.  become  184  volumes  of  ice.  The 
breakage  of  vessels,  splitting  of  rocks,  &c.,  by  the  congelation  of  water, 
are  due  to  this  expansion.  Water  passes  off  in  vapour  at  all  temperatures, 
the  amount  of  vapour  evolved  in  a  given  time  of  course  increasing  with 
the  temperature.     The  boiling-point  of  water  is  212°  F.  (100°  C.) 

(Definition. — The  boiling-point  of  a  liquid  is  the  constant  temperature 
indicated  by  a  thermometer,  immersed  in  the  vapour  of  the  boiling  liquid, 
in  the  presence  of  a  coil  of  platinum  wire,  to  faciltate  disengagement  of 
vapour,  and  at  a  pressure  of  30  in.,  762  mm.  Bar.) 

At  and  above  212°  F.  at  the  ordinary  atmospheric  pressure  (30  in.  Bar.), 
water  is  an  invisible  vapour  of  specific  gravity  0*622  (air  =  1).  One 
cubic  inch  of  water  at  60°  F.  becomes  1696  cubic  inches  of  vapour  at 
212°  F. 

Since  the  specific  gravity  of  a  gas  or  vapour  is  the  weight  of  one 


PEROXIDE  OF  HYDROGEN.  53 

volume  (p.  16),  and  the  molecule  of  a  compound  gas  occupies  two 
volumes,  the  spenfic  gravity  of  a  comjjound  gas  or  vapmir,  re/erred  to 
hydrogen  as  the  standard,  is  the  half  of  its  molecular  weight. 

Thus  the  molecular  weight  of  steam  being  18,  its  specific  gravity 
(H  =  l)  wouldbe9. 

If  the  specific  gravity  in  relation  to  air  be  required,  it  may  be  obtained 
by  multiplying  half  the  molecular  weight  by  0*0692,  which  represents 
the  specific  gravity  of  hydrogen  referred  to  air  as  the  unit.  Thus  the 
specific  gravity  of  steam  (air  =1)  is  9xO"0692  =  "6228. 

48.  Pcroodde  of  hydrogen  or  hydric  peroxide,  H^Og.  This  compound  is  seldom  met 
with  iu  nature,  and  has  no  very  important  useful  application  in  the  arts,  but  it 
possesses  very  great  interest  for  the  student  of  chemical  philosophy,  because  it  helps 
to  throw  some  light  upon  the  molecular  constitution  of  the  elements. 

To  prepare  the  peroxide  of  hydrogen,  some  baryta  (BaO)  is  heated  in  a  current  of 
oxj'^gen,  when  it  becomes  converted  into  the  barium  dioxide  (BaOg).  If  this  be 
powdered,  suspended  in  water,  and  acted  upon  by  a  stream  of  carbonic  acid  gas,  the 
water  becomes  charged  with  the  hydric  peroxide  ;  Ba02+H20  +  C0.2  =  BaC03+H202. 
The  barium  carbonate  is  allowed  to  subside,  and  the  clear  solution  of  hydric  peroxide 
poured  off. 

To  prepare  pure  hydric  peroxide,  some  barium  dioxide  (BaOj)  is  heated  to  the 
temperature  at  which  it  begins  to  evolve  oxygen,  and  dissolved  in  as  little  diluted 
nitric  acid  as  possible.  To  this  solution  one  of  barium  hydrate  (baryta  water)  is 
added;  the  precipitate,  BaOj.SHgO  is  washed  by  decantation,  and  decomposed  by 
diluted  sulphuric  acid,  care  being  taken  not  to  render  the  liquid  acid,  BaOg  +  H2SO4 

=  H,02  +  BaS04- 

The  precipitate  is  allowed  to  subside,  and  the  clear  liquid  evaporated  in  the  ex- 
hausted receiver  of  the  air-pump  over  a  dish  of  oil  of  vitriol  to  absoi'b  the  water,  which 
evaporates  much  more  rapidly  than  the  peroxide.  The  pure  hydric  ])eroxide  is  a 
syrupy  liquid  of  sp.  gr.  1  453,  with  a  very  slight  chlorous  odour.  Its  most  remark- 
able feature  is  the  facility  with  which  it  is  decomposed  into  water  and  oxygen.* 
Even  at  70°  F.  it  begins  to  evolve  bubbles  of  oxygen.  At  212°  it  decomposes  with 
violence.  The  mere  contact  with  certain  metals,  such  as  gold,  platinum,  and  silver, 
which  have  no  direct  attraction  for  oxygen,  will  cause  the  decomposition  of  the 
peroxide  without  any  chemical  alteration  of  the  metal  itself,  t  Manganese  dioxide 
decomposes  it  without  undergoing  any  apparent  change.  The  most  surprising  effect 
is  that  which  takes  place  with  silver  oxide.  If  a  drop  of  hj'dric  peroxide  be  allowed 
to  fall  upon  silver  oxide,  which  is  a  brown  powder,  decomposition  takes  place  with 
explosive  violence  and  gi'eat  evolution  of  heat,  the  silver  oxide  losing  its  oxygen,  and 
becoming  grey  metallic  silver.  J  The  oxides  of  gold  and  platinum  are  acted  upon  iu 
a  similar  manner. 

These  very  extraordinary  changes,  which  were  fonnerly  described  as  catalytic  actions, 
are  now  generally  accounted  for  by  the  hypothesis  that  the  oxygen  in  the  oxide  of 
silver,  &c.,  exists  in  a  condition  different  from  that  of  the  second  atom  of  oxygen  in 
the  hydric  peroxide,  and  that  these  two  conditions  of  oxygen  have  a  chemical  attrac- 
tion for  each  other,  similar  to  that  which  exists  between  different  elements.  If  the 
oxygen  in  the  silver  oxide  be  represented  as  electro-negative  oxygen  (see  5),  as  its 
relation  to  the  metal  would  lead  us  to  expect,  and  the  second  atom  of  oxygen  in  the 
hydric  peroxide  be  represented  as  electro -positive  oxygen,  the  mutual  decomposition 
of  the  two  compounds  might  be  represented  by  the  equation, 

-  4-  -  -f 

Ag-^O  +  HjOO  =  Ags  -f  HgO  -f-  0  0. 

The  elementary  substances,  with  few  exceptions,  have  molecules  composed  of  two 
atoms,  which  may  be  due  to  the  circumstance  that  each  atom  is  associated  with  an 

*  The  presence  of  a  little  free  acid  renders  it  rather  more  stable,  whilst  free  alkali  has 
the  opposite  effect.  A  solution  of  hydric  peroxide,  containing  a  little  hydrochloric  acid,  is 
now  sold  for  medicinal  and  photographic  uses. 

+  Such  inexplicable  changes  as  this  are  sometimes  included  under  the  general  denomina- 
tion of  catalysis,  or  decomposition  by  contact. 

*  If  ammonia  be  very  carefully  added  to  silver  nitrate  until  the  precipitate  formed  at 
first  is  only  just  re-dissolved,  the  solution  will  give  a  lustrous  deposit  of  metallic  silver  on 
addition  of  a  little  hydric  peroxide,  and  gently  heating. 


64  OZONE. 

equal   amount  of  opposite  electricity,    and  is  therefore  the  complement  of  the 
other. 

If  hydric  peroxide,  even  in  diluted  solution,  be  added  to  potassium  perman- 
ganate acidified  with  sulphuric  acid,  the  red  colour  is  entirely  destroyed,  and  bubbles 
of  oxj'gen  are  evolved,  causing  effervescence;  Kj[Mn208  +  3H2S04  +  5H5jOj  =  KjS04 
+  2MnS04  +  8H20  +  50j,.  Here  Og  from  the  hydric  peroxide  have  united  with  0, 
from  the  permanganate. 

These  experiments  support  the  conclusion  arrived  at  by  the  reasoning  at  page  2,  that 
the  molecule  or  ultimate  physical  particle  of  oxygen  is  really  composed  of  2  atoms. 

A  very  striking  reaction  of  hydric  peroxide  is  that  with  chromic  acid.  If  a  solution 
of  H.2O2  be  added  to  a  weak  solution  of  potassium  bichromate  acidified  with  sul- 
phuric acid,  the  beautiful  blue  colour  of  perchromic  acid  appears  :  KgCrgOy  +  H0SO4  + 
2H202  =  K.2S04  +  3H20  +  H2Cr208.  After  a  few  minutes,  the  blue  colour  cnanges 
to  a  very  pale  green,  the  perchromic  acid  being  decomposed  by  the  sulpliuric  acid, 
yielding  the  green  chromium  sulphate,  and  free  oxygen  which  adheres  in  bubbles  to 
the  side  of  the  vessel,  HgCr^Og  +  3H2SO4  =  Cr2(S()4)3  +  4H2O  +  O4.  If  the  blue  solution 
be  shaken  with  a  little  ether  which  dissolves  the  perchromic  acid  and  rises  with  it 
to  the  surface  where  it  forms  a  blue  layer,  the  colour  is  much  more  lasting,  and  very 
minute  quantities  of  hydric  peroxide  may  thus  be  detected. 

49.  Ozone. — This  is  the  name  given  to  a  modified  form  of  oxygen,  of  the  true 
nature  of  which  there  is  still  some  doubt,  as  it  has  never  been  obtained  unmixed  with 
ordinary  oxygen,  but  it  appears  to  be  formed  by  the  union  of  3  atoms  of  oxygen 
(occupying  3  volumes),  to  produce  a  molecule  of  ozone  (occupying  2  volumes). 
Just  as  hydric  peroxide  (HgOg),  may  be  regarded  as  formed  by  the  combination  of 
a  molecule  of  water  (HgO)  with  an  atom  of  oxygen,  so  ozone  may  be  viewed  as  a 
combination  of  a  molecule  of  oxygen  (Og)  with  an  atom  of  oxygen.  It  woukl  then  be 
half  as  heavy  again  as  ordinary  oxygen,  and  experiment  has  shown  that  its  rate  of 
diffusion  is  in  accordance  with  this  view. 

It  derives  its  name  from  its  peculiar  odour  {oCeiv,  to  smell),  which  is  often  perceived 
in  the  air  of  the  sea  or  of  the  open  country,  and  in  linen  which  has  been  dried  in 
country  air.  According  to  Hartley,  1  volume  of  ozone  in  2^  million  vols,  of  air 
may  be  perceived  by  the  smell.  Oxygen  appears  to  be  capable  of  assuming  this 
ozonised  condition  under  various  circumstances,  the  principal  of  which  are,  the 
passage  of  silent  electric  discharges,*  and  the  contact  with  substances  (such  as 
phosphorus)  undergoing  slow  oxidation  in  the  presence  of  water.  A  minute 
proportion  of  the  oxygen  obtained  in  the  decomposition  of  water  by  the  galvanic 
current  also  exists  in  the  ozonised  condition,  as  may  be  perceived  by  its  odour. 

The  use  of  Siemens'  induction  tube  (fig.  48)  affords  the  readiest  method  of  demon- 
strating the  characteristic 
properties  of  ozone.  This 
apparatus  consists  of  a 
tube  (A)  coated  internally 
with  tin-foil  (or  silvered 
on  the  inside),  and  sur- 
rounded with  another  tube 
(B),  which  is  coated  with 
tin -foil  on  the  outside. 
AVhen  the  inner  and  outer 
coatings  are  placed  in  con- 
nexion with  the  wires  of 
an  induction  coil  by  means 
Fig.  48.— Tube  for  ozonising  air  by  induction.  of  the  screws  (CD),  and  a 

stream  of  air  or  oxygen 
(dried  by  passing  through  oil  of  vitriol)  is  passed  through  (E)  between  the  two  tubes, 
a  strong  odour  is  perceived  at  the  orifice  (F). 

Several  forms  of,  apparatus  upon  this  principle  have  been  constnicted  for  obtaining 
large  volumes  of  ozonised  air.  Plates  of  glass  coated  with  tin-foil  will  ozonise  the  air 
between  them  when  the- coatings  are  connected  with  opposite  poles  of  the  induction- 
coil.  A  wide  glass  tube  or  cylinder  with  a  platinum  wire,  or  a  piece  of  platiiium-foil 
inside,  connected  with  one  pole  of  the  coil,  and  a  platinum  wire  wound  round  it 
externally,  connected  with  the  other  pole  of  the  coil,  will  ozonise  the  air  passed 
through  it.     When  large  quantities  of  ozone  are  required,  it  is  found  expedient  to 

*  It  is  the  odour  of  ozone  which  is  perceived  in  working  an  ordinary  electrical 
machine. 


PROPERTIES  OF  OZONE.  55 

employ  concentric  cylinders  filled  with  water,  which  serves  to  keep  down  the  tempera- 
ture, and  may  be  employed,  instead  of  a  metallic  coating,  to  receive  the  charge  of 
electricity. 

The  ordinary  chemical  test  for  ozone  is  a  damp  mixture  of  starch  vdth.  potassium 
iodide.  100  grains  of  starch  are  well  mixed  in  a  mortar  with  a  measured  ounce  of 
cold  water,  and  the  mixture  is  slowly  poured  into  5  ounces  of  boiling  water  in  a 
porcelain  dish,  with  occasional  stirring.  The  thin  starch-paste  thus  obtained  is 
allowed  to  cool,  and  a  few  drops  of  solution  of  pure  potassium  iodide  are  added,  the 
mixture  being  well  stirred  with  a  glass  rod.  If  this  mixture  be  brushed  over  strips 
of  white  cartridge  paper,  these  will  remain  unchanged  in  ordinaiy  air ;  but  when  they 
are  exposed  to  ozonised  air  (such  as  that  which  has  passed  through  the  induction 
tube),  they  will  immediately  assume  a  blue  colour.  The  ozonised  oxygen  being  more 
active,  or  endowed  with  more  powerful  chemical  attraction  than  ordinary  oxygen, 
abstracts  the  potassium  from  the  potassium  iodide  (KI),  and  sets  free  the  iodine,  which 
has  the  specific  property  of  imparting  a  blue  colour  to  starch.  The  intensity  of  the 
blue  tint  is  proportionate  to  the  quantity  of  iodine  liberated,  and  therefore  to  that 
of  tlie  ozonised  oxygen  present,  and  hence,  by  reference  to  a  standard  scale  of  colours 
previously  agreed  upon,  the  ozone  may  be  expressed  in  degrees.  The  result,  however, 
is  affected  by  so  many  trifling  circumstances,  that  it  is  doubtful  whether  such  deter- 
minations of  the  quantity  of  ozone  are  to  be  considered  trustworthy.  More  satis- 
factory tests  are  afforded  by  papers  imjiregnated  with  manganese  sulphate  or  lead 
acetate,  which  become  brown  from  the  formation  of  the  binoxides  of  those  metals 
under  the  influence  of  ozone. 

If  the  ozonised  air  issuing  from  F  be  passed  into  a  solution  of  indigo  {sulphindigotic 
add  largely  diluted)  ths  blue  colour  will  soon  disappear,  since  tlie  ozone  oxidises  the 
indigo,  and  gives  rise  to  products  which,  in  a  diluted  state,  are  nearly  colourless. 
Ordinary  oxygen  is  incapable  of  bleaching  indigo  in  this  manner.  If  the  ozone  is 
passed  through  a  tube  of  vulcanised  caoutchouc,  this  will  soon  be  perforated  by  the 
corrosive  eH"ect  of  the  ozone,  whilst  ordinary  oxygen  would  be  without  effect  upon  it. 
If  ozonised  air  be  passed  into  a  flask  with  a  little  mercury  at  the  bottom,  the  surface 
of  the  mercury  will  soon  become  tarnished  by  the  formation  of  oxide,  and  when  the 
mercury  is  shaken  round  the  flask  it  will  adhere  to  the  sides,  which  is  not  the  case 
with  pure  mercury. 

If  the  ozone  from  F  be  made  to  pass  slowly  through  a  glass  tube  heated  in  the 
centre  by  a  spirit-lamp,  it  will  be  found  to  lose  its  power  of  afl'ecting  the  iodised 
starch-paper,  the  ozone  having  been  reconverted  into  ordinary  oxygen  under  the  influ- 
ence of  heat;  2(00.^)  =  3(03).  A  temperature  of  300°  F.  is  sufficient  to  effect  this  change. 
It  has  been  observed  that  a  given  volume  of  oxygen  diminishes  when  a  portion  of  it 
is  converted  into  ozone  by  the  silent  electric  discharge,  and  that  it  regains  its  original 
volume  when  the  ozone  is  reconverted  by  heat,  proving  that  the  ozonised  form  of 
oxygen  is  denser,  or  occupies  less  space  than  the  ordinary  form. 

When  a  given  quantity  of  oxygen  is  electrised,  or  subjected  to  the  action  of  surfaces 
charged  with  opposite  electricities,  only  one-fifth,  at  mo.st,  is  converted  into  ozone  ; 
but  if  the  ozone  be  now  removed  by  some  substance  which  absorbs  it,  a  fresh  quantity 
of  the  oxygen  may  be  ozonised. 

The  researches  of  Brodie  have  shown  that  either  one,  two,  or  three  atoms  of  oxygen  in 
ozone  may  be  absorbed,  according  to  the  nature  of  the  oxidisable  substance  employed. 
Thus,  where  a  neutral  solution  of  potassium  iodide  is  acted  on  by  ozone, 

OO2  (2  volumes)   -f   2KI   -f-   HgO  =  2KH0   +   \^  +  0^  (2  volumes), 

the  atom  of  oxygen  being  removed  without  diminution  in  the  volume  of  the  gas.  But 
if  the  solution  of  potassium  iodide  be  acidified  (and  thus  converted,  virtually,  into  a 
solution  of  hydriodic  acid), 

OO2  (2  volumes)   +   4HI   =  2H2O   -f   I4  +   0  (1  volume), 
the  volume  being  here  reduced  by  one-half.     "When  chloride  of  tin  (stannous  chloride) 
mixed  with  hydrochloric  acid  is  brought  in  contact  with  ozone,  the  latter  is  entirely 
absorbed,  converting  the  stannous  chloride  into  stannic  chloride, 

OO4  +   SSnClj  +   6HC1  =   SSnCl^  +   SHaO. 
Oil  of  turpentine  and  some  other  substances  also  absorb  the  ozone  entirely. 

By  placing  a  freshly-scraped  stick  of  phosphorus  (scraped  under  water  to  avoid 
inflammation)  at  the  bottom  of  a  quart  bottle,  with  enough  water  to  cover  half  of  it, 
and  loosely  covering  the  bottle  with  a  glass  plate,  enough  ozone  may  be  accumulated 
in  a  few  minutes  to  be  readily  recognised  by  the  odour  and  the  iodised  starch. 


56 


OZONE. 


Fig.  49. 


The  water  at  the  bottom  of  the  bottle  is  found  to  contain,  besides  the  phosphorons 
and  phosphoric  acids,  formed  by  the  slow  oxidation  of  the  phosphorus,  some  hydrii; 

Seroxide,  whence  it  has  been  sujtposed  that  the  formation   of  ozone  is  due  to  the 
ecomposition  of  a  molecule  of  oxygen  into  electro-negative  oxygen,  which  combines 
with  another  molecule  of  oxygen  to  form  ozone,  and  electro- positive  oxygen  which 
combines  with  a  molecule  of  water  to  form  hydric  peroxide.     Thus, 
-+  '         +  - 

Oj  -f  00  -I-  HjjO  =  HgOO  +   OgO. 

This  view  is  supported  by  the  circumstance,  that  hydric  peroxide  appears  to  be 
produced  in  every  case  where  ozone  is  formed  in  the  presence  of  water. 

When  ozonised  oxygen  is  shaken  with  hydric  peroxide,  the  above  equation  is 
reversed,  water  and  ordinary  oxygen  resulting. 

If  a  few  drops  of  ether  be  poured  into  a  quart  beaker  (fig.  49),  taking  care  to  avoid 
the  vicinity  of  a  flame,  and  pieces  of  iodised  starch-paper  and  blue  litmus  paper  be 

suspended  upon  a  glass  rod  laid  across  the  mouth 
of  the  beaker,  they  will  be  found  unaffected  by  the 
mixture  of  ether  vapour  and  air  ;  but  if  a  hot  gla.ss 
rod  be  plunged  into  the  beaker,  the  heated  ether 
vapour  will  undergo  oxidation,  producing  pungent 
acid  vapours,  which  redden  the  blue  litmus,  whilst 
the  formation  of  ozone  will  be  indicated  by  the 
blue  iodised  starch.* 

Ether  and  essential  oils,  such  as  turpentine, 
slowly  absorb  oxygen  from  the  air,  thus  acquiring 
the'property  of  bleaching  indigo  and  of  blueing  tlie 
mixture  of  potassium  iodide  and  starch  ;  hence 
they  were  formerly  believed  to  contain  ozone,  but 
they  do  not  answer  to  all  the  tests  for  that  sub- 
stance. Thus,  ozone  imparts  a  blue  colour  to  the 
resin  of  guaiacum,  but  the  old  turpentine  or 
ether  will  not  do  so.t  If  a  little  hydric  peroxide 
be  dissolved  in  ether,  it  exhibits  the  same  property 
as  the  ether  which  has  absorbed  oxygen  from  the  air,  and  it  is,  therefore,  sometimes 
called  "  ozonic  ether."  The  solution  of  hydric  peroxide  in  ether  (obtained  by  shaking 
the  aqueous  solution  of  the  peroxide  with  ether)  is  employed  by  Dr.  Day  for  the 
recognition  of  blood  stains.  Contact  with  blood  decomposes  hydric  peroxide,  and  the 
oxygen  which  is  liberated  is  capable  of  blueing  guaiacum  resin.  Accordingly,  if  a 
blood-stain  be  moistened  with  tincture  of  guaiacum  (a  solution  of  the  resin  in  spirit 
of  wine),  and  afterwards  with  the  ethereal  solution  of  hydric  peroxide  (ozonic  ether), 
it  acquires  an  intense  blue  colour,  which  may  be  detected,  even  on  a  coloured  fabric, 
by  pressing  a  piece  of  white  blotting-paper  upon  it. 

Ozone  has  attracted  much  notice,  because  a  minute  proportion  of  the  oxygen  in  the 
atmosphere  appears  sometimes  to  be  present  in  this  form,  and  its  active  properties 
have  naturally  led  to  the  belief  that  it  must  exercise  some  influence  upon  the  sanitary 
condition  of  the  air.  This  idea  is  encouraged  by  the  circumstance  that  no  indications 
of  ozone  can  be  perceived  in  crowded  cities,  where  there  are  so  many  oxidisable 
substances  to  consume  the  active  oxygen,  whilst  the  air  in  the  open  country  and  at 
the  sea-side  does  give  evidence  of  its  presence.  Some  chemists  assert  that  their 
experiments  have  demonstrated  the  very  important  fact  that  a  portion  of  the  oxygen 
developed  by  growing  plants  is  in  the  ozonised  form,  but  the  evidence  on  the 
subject  is  conflicting.  Houzeau  fixes  the  maximum  proportion  of  ozone  at  Turnnnrth 
of  the  volume  of  air.  The  proportion  is  highest  in  May  and  June,  lowest  in 
December  and  January. 

Ozonised  oxygen  exhibits  a  sky-blue  colour  when  viewed  along  a  column  of  one 
metre  in  length.  The  blue  colour  becomes  very  deep  under  a  pressure  of  several 
atmospheres,  and  indications  of  the  liquefaction  of  the  ozone  are  observed  at -^3°  C. 
It  has  been  suggested  that  the  blue  colour  of  the  sky  is  due  to  our  regarding  it  through 
the  ozonised  atmosphere.+ 

*  The  oxygen  obtained  by  the  action  of  warm  sulphuric  acid  on  barium  dioxide  or  on 
crystallised  potassium  pennangnate,  resembles  ozone  in  its  odour  and  action  on  the  iodised 
starch  paper. 

f  Kingzett  has  shown  that  the  action  of  air  on  oil  of  turpentine  produces  an  organic 
substance  which  yields  hydric  peroxide  when  acted  on  by  water.     (See  Turpentine.) 

t  "On  the  Absorption  of  Solar  Rays  by  Atmospheric  Ozone,"  Hartley,  Journ.  Chem.  Soc., 
March  1881. 


ATMOSPHERIC  AIR. 


57 


In  want  of  stability,  ozone  resembles  hydric  peroxide  ;  contact  with  manganese 
dioxide  converts  it  into  ordinary  oxj'gen.  Even  shaking  with  powdered  glass  will 
de-ozonise  the  ozonised  oxvgen. 


ATMOSPHERIC  AIR 

50.  Atraosplieric  air  consists  chiefly  of  a  mixture  of  nitrogen  with  one- 
fifth  of  its  volume  of  oxygen,  and  very  small  proportions  of  carbonic 
acid  gas  and  ammonia.  Vapour  of  water  is  of  course  always  present  in  the 
atmosphere  in  varying  proportions.  Since  the  atmosphere  is  the  recep- 
tacle for  all  gaseous  emanations,  other  substances  may  be  discovered  in 
it  by  very  minute  analysis,  but  in  proportions  too  small  to  have  any  per- 
ceptible influence  upon  its  properties.  Thus  marsh-gas  or  light  carburetted 
hydrogen,  sulphuretted  hydrogen,  and  sulphurous  acid  gas,  can  often  be 
traced  in  it,  the  two  last  especially  in  or  near  towns. 

Although  the  proportion  of  oxygen  in  the  air  at  a  given  spot  may  be 
much  diminished,  and  that  of  carbonic  acid  gas  increased,  by  processes  of 
oxidation  (such  as  respiration  and  combustion)  taking  place  there,  the 
operation  of  wind  and  of  diffusion  so  rapidly  mixes  the  altered  air  with 
the  immensely  greater  general  mass  of  the  atmosphere^  that  the  variations 
in  the  composition  of  air  in  different  places  are  very  slight.  Thus  it  has 
been  found  that  the  proportion  of  oxygen  in  the  air  in  the  centre  of 
Manchester  was,  at  most,  only  0*2  per  cent.  beloAv  the  average. 

The  proportions  in  which  the  oxygen  and  nitrogen  are  generally  pre- 
sent in  atmospheric  air,  freed  from  water  and  carbonic  acid  gas,  are — 
nitrogen,  79  "19  per  cent,  by  volume,  or  76*  99  per  cent,  by  weight ;  oxygen, 
20 '81  per  cent,  by  volume,  23 'Ol  per  cent,  by  weight. 

The  proportion  of  aqueous  vapour  may  be  stated,  on  the  average,  as  1  '4 
per  cent,  by  volume,  orO'87  per  cent,  by  weight  of  the  air.  The  carbonic 
acid  gas  may  be  generally  estimated  at  0*04  per  cent,  by  volume,  or  0*06 
per  cent,  by  weight  of  the  air.*  The  total  weight  of  atmospheric  air 
surrounding  the  globe  exceeds  300,000  million  tons. 

The  relative  proportions  of  oxygen  and  nitrogen  in  air  may  be  exhibited  by  sus- 
pending a  stick  of  phosphorus  upon  a  wire  stand  (A,  fig.  50)  in  a  measured  volume  of 
air  confined  over  water.  The  cylinder  (B)  should 
have  been  previously  divided  into  five  equal  spaces 
by  measuring  water  into  it,  and  marking  each  space 
by  a  thin  line  of  Brunswick  black.  After  a  few 
hours,  the  phosphorus  will  have  combined  with  the 
whole  of  the  oxygen  to  form  phosphorous  and  phos- 
phoric acids,  which  are  absorbed  by  the  water, 
leaving  four  of  the  spaces  occupied  by  nitrogen. 

The  same  result  may  be  arrived  at  in  a  much 
shorter  time  by  burning  the  phosphorus  in  the  con- 
fined portion  of  air. 

A  fiagment  of  phosphorus,  dried  by  careful  pres- 
sure between  blotting-paper,  is  placed  upon  a  con-  ^ 
venient  stand  (A,  fig.  51)  and  covered  with  a  tall  % 
jar,  having  an  opening  at  the  top  for  the  insertion 
of  a  well-fitting  stopper  (which  should  be  greased 
with  a  little  lard),  and  divided  into  seven  parts  of 
equal  cajiacity.  The  jar  should  be  placed  over  the  stand  in  such  a  manner  that  the 
water  may  occupy  the  two  lowest  spaces  into  which  the  jar  is  divided.  The  stopper 
of  the  jar  is  furnished  with  a  hook,  to  which  a  piece  of  biass  chain  (B)  is  attached, 
long  enough  to  touch  the  phosphorus  when  the  stopper  is  inserted.     The  end  of  this 


Fig.  50. 


Reiset  finds  somewhat  less  than  "03  per  cent,  by  volume. 


5B 


ANALYSIS  OF  AIR. 


chain  is  heated  in  the  flame  of  a  lamp,  and  the  stopper  tightly  fixed  in  its  place.  On 
allowing  the  hot  chain  to  touch  tlie  phosphorus,  it  bursts  into  vivid  combustion, 
tilling  the  jar  with  thick  white  fumes,  and  covering  its  sides,  for  a  few  moments, 

with  white  flakes  of  phosphoric  anhydride. 
At  the  commencement  of  the  experiment,  the 
water  in  the  jar  will  be  depressed,  in  conse- 
quence of  the  expansion  of  the  air,  due  to  the 
heat  produced  in  the  burning  of  the  phos- 
phorus, but  presently,  when  the  combustion 
begins  to  decline,  the  water  again  rises,  and 
continues  to  do  so  until  it  has  ascended  to  the 
line  (C),  so  as  to  occupy  the  place  of  one-fifth 
of  tlie  air  employed  in  the  experiment.  The 
l>hosphorus  will  then  have  ceased  to  burn,  the 
white  flakes  upon  the  sides  of  the  jar  will  liave 
acquired  the  appearance  of  drops  of  moisture, 
and  the  fumes  will  have  gradually  disappeared, 
until,  in  the  course  of  half-an-hour,  the  air 
remaining  in  the  jar  will  be  as  clear  and  trans- 
parent as  before,  the  whole  of  the  phosphoric 
anhydride  having  been  absorbetl  by  the  water. 
The  jar  should  now  be  sunk  in  water,  so  that  the  latter  may  attain  to  the  same  level 
without  as  within  the  jar.  On  removing  the  stopper,  it  will  be  found  that  the 
nitrogen  in  the  jar  will  no  longer  support  the  combustion  of  a  taper. 

In  the  rigidly  accurate  determination  of  the  relative  proportions  of  oxygen  and 
nitrogen  in  the  air,  it  is  of  course  necessary  to  guard  against  any  error  arising  from 
the  presence  of  the  water,    carbonic  acid  gas,    and  ammonia.     With  this  view, 


Fig.  51. 


Fig.  52. — Exact  analysis  of  air. 

Dumas  and  Boussingault,  to  whom  we  are  chiefly  indebted  for  our  exact  knowledge  of 
the  composition  of  the  air,  caused  it  to  pass  through  a  series  of  tubes  (A,  fig.  62)  con- 
taining potash,  in  order  to  remove  the  carbonic  acid 
gas,  then  through  a  second  series  (B)  containing  sul- 
phuric acid,  to  absorb  the  ammonia  and  water;  the 
purified  air  then  passed  through  a  glass  tube  (C)  tilled 
with  bright  copper  heated  to  redness  in  a  charcoal 
furnace,  which  removed  the  whole  of  the  oxj'gen,  and 
the  nitrogen  passed  into  the  large  globe  (N). 

Both  the  tube  (containing  the  copper)  and  the  globe 
were  carefully  exhausted  of  air  and  accurately  weighed 
before  the  experiment ;  on  connecting  the  globe  and 
the  tube  with  the  purifying  apparatus,  and  slowly 
opening  the  stop-cocks,  the  pressure  of  the  external  air 
caused  it  to  flow  through  the  series  of  tubes  into  the 
globe  destined  to  receive  the  nitrogen.  When  a  con- 
siderable quantity  of  air  had  passed  in,  the  stop-cocks 
were  again  closed,  and  after  cooling,  the  weight  of  the 
globe  was  acccurately  determined.  The  diflerence 
between  this  weight  and  that  of  the  empty  globe,  before 
the  experiment,  gave  the  weight  of  the  nitrogen  which 
had  entered  the  globe  ;  but  this  did  not  represent  the 
whole  of  the  nitrogen  contained  in  the  analysed  air,  for 
the  tube  containing  the  copper  had,  of  course,  remained 
full  of  nitrogen  at  the  close  of  the  exjieriment.  This 
tube,  having  been  weighed,  was  attached  to  the  air- 
pump,  the  nitrogen  exhausted  from  it,  and  the  tube  again  weighed ;  the  (iifference 
between  the  two  weighings  furnished  the  weight  of  the  nitrogen  remaining  in  the 


Fig.  53. 


ANALYSIS  OF  AfR.  59 

tube,  and  was  added  to  the  weight  of  that  received  in  the  globe.     The  oxygen  was 
represented  by  the  increase  of  the  weisrht  of  the  exhausted  tube  containing  the  copper, 
which  was  partially  converted  into  oxide  of  copper,  by  combining  with  the  oxygen  of 
the  air  passed  through  it. 
The  calculation  of  the  result  of  the  analysis  is  here  exemplified  : — 

■Weight  of  Grains. 

Globe  (N)  with  nitrogen  (at  the  conclusion),       .  .  .     3076 

Exhausted  globe  (at  the  commencement), 


Nitrogen  received  into  the  globe, 

Tube  (C)  with  residual  nitrogen  (at  the  conclusion), 
Exhausted  tube  (at  the  conclusion), 

Nitrogen  remaining  in  the  tube, 
Add  nitrogen  received  into  the  globe, 


3000 
76 


2574 
2573 


1 
76 


Total  nitrogen  in  the  air  analysed,  .  .         77 

Exhausted  tube  (C)  with  oxidised  copper  (at  the  conclusion),  .     2573 

,,  ,,         metallic  copper  (at  tlft  commencement),  2560 

Oxygen  in  the  air  analsyed,  .  .  .  .        .         23 

The  ratio  of  the  nitrogen  to  the  oxygen,  therefore,  is  that  of  23  0 :  77  N,  or 
1  0  :  3  "347  N.  100  parts  by  weight  of  the  air  purified  from  water,  carbonic  acid  gas, 
and  ammonia,  contain  77  parts  of  nitrogen  and  23  parts  of  oxygen. 

51.  The  nitrogen  remaining  after  the  removal  of  the  oxygen  from  air  in 
the  above  experiments  was  so  called  on  account  of  its  jiresence  in  nitre 
(saltpetre  KNOg).  In  physical  properties  it  resembles  oxygen,  but  is 
somewhat  lighter  than  that  gas,  its  specific  gravity  being  0*9713. 

This  difference  in  the  specific  gravities  of  the  two  gases  is  well  exhibited  by 
the  arrangement  shown  in  fig.  53.  A  jar  of  oxygen  (0)  is  closed  with  a  glass 
plate,  and  placed  upon  the  table.  A  jar  of  nitrogen  (N),  also  closed  with  a  glass 
plate,  is  placed  over  it,  so  that  the  two  gases  may  come  in  contact  when  the  glass 
plates  are  removed.  The  nitrogen  will  float  for  some  seconds  above  the  oxygen,  and 
if  a  lighted  taper  be  quickly  introduced  through  the  neck  of  the  upper  jar,  it  will  be 
extinguished  in  passing  through  the  nitrogen,  and  will  be  rekindled  brilliantly  when 
it  reaches  the  oxygen  in  the  lower  jar. 

It  might  at  first  sight  appear  surprising  that  oxygen  and  nitrogen, 
though  of  diff'erent  specific  gravities,  should  exist  in  uniform  proportions 
in  all  parts  of  the  atmosphere,  unless  in  a  state  of  chemical  combination ; 
but  an  acquaintance  with  the  property  of  diffusion  (see  13)  possessed  by 
gases,  teaches  us  that  gases  loill  mix  tcith  each  other  in  opposition  to 
gravitation,  and  when  mixed  mill  alicays  remain,  so. 

It  was  shown  by  Graham  that  a  partial  separation  of  the  nitrogen  and  oxygen  in  air 
may  be  effected,  on  the  same  principle  as  that  of  hydrogen  and  oxygen  at  page  20, 
by  taking  advantage  of  the  difference  in  their  rates  of  diffusion.  He  devised, 
however,  a  more  convenient  process,  founded  upon  the  dialytic  passage  of  the  gases 
through  caoutchouc,  which  he  ascribed  to  the  absorption  of  the  gas  by  the  solid 
material  upon  one  side,  and  its  escape  on  the  other. 

A  bag  (ffi,  fig.  54)  is  made  of  a  fabric  composed  of  a  layer  of  caoutchouc  between  two 
layers  of  silk,  such  as  that  employed  for  waterproof  garments ;  a  piece  of  carpet 
is  placed  inside  the  bag  to  keep  the  sides  apart/,  and  the  edges  of  the  bag  are  made 
perfectly  air-tight  with  solution  of  caoutchouc.  To  maintain  a  vacuum  within  the  bag, 
it  is  supported  by  a  rod  v,  and  attached  to  Sprengel's  air-jnimp,  in  which  a  stream  of 
mercury,  allowed  to  flow  from  a  funnel  {f)  down  a  tube  (c)  six  feet  long,  draws  the  air 
out  of  the  bag,  through  a  lateral  tube  (A),  until  all  the  air  is  exhausted,  which  is 


60 


DIALYSIS  OF  AIR. 


indicated  by  the  barometer  tube  h,  the  lower  end  of  which  dips  into  a  cistern  of  mer- 
cury.    When  the  mercury  in  this  tube  stands  at  almost  exactly  the  same  height  as 

the  standard  barometer,  the  exhaustion  is 
complete.  If  a  test-tube  (d)  filled  with  mer- 
cury be  now  inverted  over  the  end  of  the  long 
tube  c,  which  is  bent  upwards  for  that  i)urpo.«e, 
the  bubbles  of  air  which  are  drawn  through 
the  sides  of  the  vacuous  bag,  and  carried  down 
the  long  tube  by  the  little  pistons  of  liquid 
mercury  as  they  fall,  will  pass  up  into  the 
test-tube  ;  when  the  latter  is  filled  with  the 
gas,  its  mouth  is  closed  with  the  thumb, 
withdrawn  from  the  mercury,  and  a  match 
\vith  a  spark  at  the  end  inserted,  when  the 
spark  will  burst  out  into  flame,  showing  that 
the  specimen  of  air  collected  is  much  richer 
in  oxygen  than  ordinary  atmospheric  air. 
The  overflow  tube  g  delivers  the  mercury 
which  is  to  be  returned  to  the  funnel/. 

The  dialytic  passage  of  oxj'gen  through 
caoutchouc  into  a  vacuum  is  twice  as  rajnd  as 
that  of  nitrogen,  so  that  the  air  collected  in 
the  tube  contains  twice  as  much  oxygen  as  the 
external  air. 

This  dialytic  passage  of  gases  through  solids 
is  quite  unconnected  with  the  diffusibility  of 
the  gases,  and  appears  to  depend  rather  upon 
the  chemical  nature  of  the  gas  and  of  the 
solid.  It  is  thus  connected  with  the  occlusion 
of  gases  by  solids,  exemplified  in  the  case  of 
palladium  and  hydrogen  at  page  40.  It  is  in 
consequence  of  this  dialytic  passage  that  tubes 
of  iron  or  platinum,  which  are  quite  imper- 
meable by  hydrogen  at  the  ordinary  temper- 
ature, will  allow  it  to  pass  rapidly  through 
their  walls  at  high  tempemtures. 

That  air  is  simply  a  mechanical  mixture  of  its  component  gases  is  amply 
proved  by  the  circumstance  that  it  possesses  all  the  properties  which 
would  be  predicted  for  a  mixture  of  these  gases  in  such  proportions  ; 
whilst  the  essential  feature  of  a  chemical  compound  is,  that  its  properties 
cannot  be  foreseen  from  those  of  its  constituents. 

The  absence  of  active  chemical  properties  is  a  very  striking  feature  of 
nitrogen,  and  admirably  adapts  it  for  its  function  of  diluting  the  oxygen 
in  the  atmosphere. 

The  chemical  relations  of  air  to  animals  and  plants  will  be  more  appro- 
priately discussed  hereafter.     (See  Carbonic  Acid,  Anwionia.) 

In  considering  the  composition  of  air,  much  attention  has  been  directed 
of  late  years  to  the  dust  or  minute  particles  of  solid  matter  which, 
although  much  heavier  than  air,  are  suspended  in  it  by  the  action  of 
currents,  and  may  always  be  detected  by  a  beam  from  the  sun  or  the 
electric  lamp  or  the  lime-light,  which  would  be  invisible  along  its  track 
through  optically  pure  air. 

The  fine  particles  of  mineral  substances  present  in  the  dust  are  the 
probable  cause  of  the  crystallisation  of  super-saturated  solutions  of  salts 
(p.  41)  when  exposed  to  air.  The  vegetable  particles  appear  to  contain 
minute  seeds  which  germinate  when  deposited  in  certain  liquid  or  moist 
solid  substances,  and  give  rise  to  mould,  mildeio,  and  fermentation.  The 
animal  particles  are  believed  to  contain  the  germs  by  the  agency  of  which 
certain  forms  of  disease  are  spread. 


Fig.  54. — Sprebgel's  pump. 
Dialysis  of  air. 


CAEBON".  61 

CARBOK 

C  =  12  parts  by  weight.* 

52.  This  eleraent  is  especially  remarkable  for  its  uniform  presence  in 
organic  substances.  The  ordinary  laboratory  test  by  which  the  chemist 
decides  whether  a  substance  under  examination  is  of  organic  origin,  con- 
sists in  heating  it  with  limited  access  of  air,  and  observing  whether  any 
blackening  from  separation  of  carbon  {carbonisation)  ensues. 

Few  elements  are  capable  of  assuming  so  many  different  aspects  as 
carbon.  It  is  met  with  transparent  and  colourless  in  the  diamond,  opaque, 
black,  and  quasi-metallic  in  graphite  or  black  lead,  dull  and  porous  in 
wood  charcoal,  and  under  new  conditions  in  anthracite,  coke,  and  gas- 
carbon. 

In  nature,  free  carbon  may  be  said  to  occur  in  the  forms  of  diamond, 
graphite,  and  anthracite  (the  other  varieties  of  coal  containing  considerable 
proportions  of  other  elements). 

Apart  from  its  great  beauty  and  rarity,  the  diamond  possesses  a  special 
interest  in  chemical  eyes,  from  its  having  perplexed  philosophers  up  to 
the  middle  of  the  last  century,  notwithstanding  the  simplicity  of  the  ex- 
periments required  to  demonstrate  its  true  nature.  The  first  idea  of  it 
appears  to  have  been  obtained  by  ^N'ewton,  when  he  perceived  its  great 
power  of  refracting  light,  and  thence  inferred  that,  like  other  bodies 
possessing  that  property  in  a  high  degree,  it  would  prove  to  be  com- 
bustible {"  an  unctuous  substance  coagulated  ").  When  the  prediction 
was  verified,  the  burning  of  diamonds  was  exhibited  as  a  marvellous 
experiment,  but  no  accurate  observations  appear  to  have  been  made  till 
1772,  when  Lavoisier  ascertained,  by  burning  diamonds  suspended  in  the 
focus  of  a  burning  glass  in  a  confined  portion  of  oxygen,  that  they  were 
entirely  converted  into  carbonic  acid  gas.  In  more  recent  times  this 
experiment  has  been  repeated  with  the  utmost  precaution,  and  the 
diamond  has  been  clearly  demonstrated  to  consist  of  carbon  in  a  crystal- 
lised state. 

A  still  more  important  result  of  this  experiment  was  the  exact  determination  of 
the  composition  of  carbon  dioxide,  without  which  it  would  not  be  possible  to  ascertain 
exactly  the  proportion  of  carbon  in  any  of  its  numerous  compounds,  since  it  is  always 
weighed  in  that  form.  / 

The  most  accurate  experiments  upon  the  synthesis  of  carbon  dioxide  have  been 
conducted  with  the  arrangement  represented  in  fig  55. 

Within  the  porcelain  tube  A,  which  is  heated  to  redness  in  a  charcoal  fire,  was 
placed  a  little  platinum  tray,  accurately  weighed,  and  containing  a  weighed  quantity 
of  fragments  of  diamond.  One  end  of  the  tube  was  connected  with  a  gas-holder  B, 
containing  oxygen,  which  was  thoroughly  purified  by  passing  through  the  tube  (J, 
containing  potash  (to  absorb  any  carbonic  acid  gas  and  chlorine  which  it  might 
contain),  and  dried  by  passing  over  pumice  soaked  with  concentrated  sulphuric  acid 
in  D  and  E.  To  the  other  end  of  the  porcelain  tube  A,  there  was  attached  a  glass 
tube  F,  also  heated  in  a  furnace,  and  containing  oxide  of  copper  to  convert  into 
carbonic  acid  gas  any  carbonic  oxide  which  might  have  been  formed  in  the  combus- 
tion of  the  diamond.  The  carbonic  acid  gas  was  then  passed  over  pumice  soaked 
with  sulphuric  acid  in  G,  to  remove  any  traces  of  moisture,  and  afterwards  into  a 
weighed  bulb-apparatus  H,  containing  solution  of  potash,  and  two  weighed  tubes 
I,  K,  containing,  respectively,  solid  potash  and  sulphuric  acid  on  pumice,  to  guard 
against  the  escape  of  aqueous  vapour  taken  up  by  the  excess  of  oxygen  in  its  passage 
through  the  bulbs  H.     The  increase  of  weight  in  H,  I,  K,  represented  the  carbonic 

*  The  volume  occupied  by  carbon  iu  the  form  of  vapour  is  not  known,  its  vapour  never 
having  been  obtained  in  a  measurable  form. 


62 


SYNTHESIS  OF  CARBON  DIOXIDE. 


acid  gas  formed  in  the  combustion  of  an  amount  of  diamond  indicated  by  the  loss  of 
weight  suffered  by  the  platinum  tray,  and  the  difference  between  the  diamond  con- 
sumed and  the  carbonic  acid  gas  formed  would  express  the  amount  of  oxygen  which 


Fig.  56. 


Fig.  55. — Exact  synthesis  of  carbonic  acid  gas. 

had  combined  with  the  carbon.  A  large  number  of  experiments  conducted  in  this 
manner,  both  with  diamond  and  graphite,  showed  that  12  parts  of  carbon  furnished 
44  parts  of  carbonic  acid  gas,  and  consumed,  therefore,  32  parts  of  oxygen. 

A  convenient  arrangement  for  burning  a  diamond  in  oxygen 
is  shown  in  fig.  56.  The  diamond  is  supported  in  a  short  helix 
of  platinum  wire  A,  which  is  attached  to  the  copper  wires  B  B, 
passing  through  the  cork  C,  and  connected  with  the  terminal 
wires  of  a  Grove's  battery  of  five  or  six  cells.  The  globe  having 
been  filled  with  oxygen  by  passing  the  gas  down  into  it  till  a 
match  indicates  that  the  excess  of  oxygen  is  streaming  out  of 
the  globe,  the  cork  is  inserted,  and  the  wires  connected  with 
the  battery.  When  the  heat  developed  in  the  platinum  coil,  by 
the  passage  of  the  current,  has  raised  the  diamond  to  a  full  red 
heat,  the  connexion  with  the  batterj-  may  be  interrupted,  and  the  diamond  will 
continue  to  burn  with  steady  and  intense  brilliancy. 

To  an  observer  unacquainted  with  the  satisfactory  nature  of  this  de- 
monstration, it  would  appear  incredible  that  the  transparent  diamond,  so 
resplendent  as  to  have  been  reputed  to  emit  light,  should  be  identical  in 
its  chemical  composition  with  graphite  {plumbago  or  black  lead)  from 
which,  in  external  appearance,  it  differs  so  widely.  Eor  this  difference  is 
not  confined  to  their  colour ;  in  crystalline  form  they  are  not  in  the  least 
alike,  the  diamond  occurring  generally  in  octahedral  crystals,  while  gra- 
phite is  found  either  in  ammyhous  masses  (that  is,  having  no  definite 
crystalline  form),  or  in  six-sided  plates  which  are  not  geometrically  allied 
with  the  form  assumed  by  the  diamond.  Carbon,  therefore,  is  dimorphous, 
or  occurs  in  two  distinct  crystalline  forms.  Even  in  weight,  diamond  and 
grajiliite  are  very  dissimilar,  the  former  having  an  average  specific  gravity 
of  3  5  and  the  latter  of  2  "3.     Again,  a  crystal  of  diamond  is  the  hardest 


COMBUSTION  OF  DIAMOND.  63 

of  all  substances,  whence  it  is  used  for  cutting  and  for  writing  upon  glass, 
but  a  mass  of  graphite  is  soft  and  easily  cut  with  a  knife.  The  diamond 
is  a  non-conductor  of  electricity,  but  the  conducting  power  of  graphite 
renders  it  useful  in  the  electrotype  process. 

Diamonds  are  chiefly  obtained  from  Golconda,  Borneo,  and  the  Brazils. 
They  usually  occur  in  sandstone  rock  or  in  mica  slate.  The  hardness  of 
the  diamond  renders  it  necessary  to  employ  diamond-dust  for  the  purpose 
of  cutting  and  polishing  it,  which  is  eflected  with  the  aid  of  a  revolving 
disk  of  steel,  to  the  surface  of  which  the  diamond-dust  is  applied  in  the 
form  of  a  paste  made  with  oil.  The  crystal  in  its  natural  state  is  best 
fitted  for  the  purpose  of  the  glazier,  for  its  edges  are  usually  somewhat 
curved,  and  the  angle  formed  by  these  cuts  the  glass  deeply,  while  the 
augle  formed  by  straight  edges,  like  those  of  an  ordinary  jeweller's  dia- 
mond, is  only  adapted  for  scratching  or  writing  upon  glass.  Drills  with 
diamond  points  have  been  employed  in  tunnelling  through  hard  rocks. 
The  diamond-dust  used  for  polishing,  &c.,  is  obtained  from  a  dark  amor- 
phous diamond  found  at  Bahia  in  the  Brazils ;  1 000  ounces  annually  are 
said  to  have  been  occasionally  obtained  from  this  source.  When  burnt, 
the  diamond  always  leaves  a  minute  proportion  of  ash  of  a  yellowish 
colour  in  which  silica  and  oxide  of  iron  have  been  detected.  A  genuine 
diamond  may  be  known  by  its  combining  the  three  qualities  of  extreme 
hardness,  enabling  it  to  scratch  hardened  steel,  high  specific  gravity 
(3*52),  and  insolubility  in  hydrofluoric  acid.  Sapphire  (Al^Og)  is  nearly 
as  hard  as  diamond,  but  its  specific  gravity  is  about  4. 

Although  the  diamond,  when  preserved  from  contact  with  the  air,  may 
be  heated  very  strongly  in  a  furnace,  without  suffering  any  change,  it  is 
not  proof  against  the  intense  heat  of  the  discharge  taking  place  between 
two  carbon  points  attached  to  the  terminal  wires  of  a  powerful  galvanic 
battery.  If  the  experiment  be  performed  in  a  vessel  exhausted  of  air,  the 
diamond  becomes  converted  into  a  black  coke-like  mass  which  closely 
resembles  graphite  in  its  properties. 

Graphite  always  leaves  more  ash  than  the  diamond,  consisting  chiefly 
of  the  oxides  of  iron  and  manganese,  with  particles  of  quartz,  and  some- 
times titanic  dioxide.  The  purest  specimens  are  those  of  compact  amor- 
phous graphite  from  Borrowdale  in  Cumberland  ;  an  inferior  variety, 
imported  from  Ceylon,  is  crystalline,  being  composed  of  hexagonal  plates. 
Graphite  is  obtained  artificially  in  the  manufacture  of  cast  iron  :  in  some 
cases,  a  portion  of  the  carbon  of  the  cast  iron  separates  in  cooling,  in  the 
form  of  crystalline  scales  of  graphite,  technically  called  kish.  In  the 
grey  variety  of  cast  iron  these  scales  of  graphite  are  diffused  through  the 
mass  of  the  metal,  and  are  left  undissolved  when  the  iron  is  dissolved  by 
an  acid. 

Graphite  is  far  more  useful  than  the  diamond,  for,  in  addition  to  its 
application  in  black-lead  pencils,  and  for  covering  the  surface  of  iron  iu 
order  to  protect  it  from  rust,  it  is  largely  employed  in  admixture  with 
clay,  for  the  fabrication  of  the  black-lead  crucibles  or  bhte  pots,  as  they 
are  commonly  called,  which  are  so  valuable  to  the  metallurgist  for  their 
power  of  resisting  high  temperatures  and  sudden  change  of  temperature. 
Graphite  is  also  sometimes  employed  for  lubricating,  to  diminish  friction 
in  machinery,  and  for  facing  or  imparting  a  glazed  surface  to  gunpowder. 

(Anthracite  and  the  other  varieties  of  coal  will  be  described  in  a 
separate  section.) 


64  PREPARATION  OF  CHARCOAL. 

53.  Several  varieties  of  carbon,  obtained  by  artificial  processes,  are 
employed  in  the  arts.  The  most  important  of  these  are  lamp  black,  wood 
charcoal,  and  animal  charcoal.* 

Lamp  black  approaches  more  nearly  in  composition  to  pure  carbon  than 
either  of  the  others,  and  is  the  soot  obtained  from  the  imperfect  combus- 
tion of  resinous  and  tarry  matters  (or  of  highly  bituminous  coal),  from 
which  source  it  derives  the  small  quantities  of  resin,  of  nitrogen,  and  sul- 
phur which  it  contains.  The  uses  of  this  substance,  as  an  ingredient  of 
pigments,  of  printing-ink,  and  of  blacking,  depend  evidently  more  upon 
its  black  colour  than  upon  its  chemical  properties. 

Diamond  black  is  a  very  pure  variety  of  lamp  black  obtained  by  the 
imperfect  combustion  of  the  natural  hydrocarbon  gas  of  the  Ohio  petro- 
leum region. 

Spanish  black  is  charcoal  made  from  waste  cork. 

Wood  charcoal  presents  more  features  which  arrest  the  attention  of  the 
chemist,  as  well  on  account  of  its  specific  properties,  as  of  the  influence 
exercised  by  the  method  adopted  for  obtaining  it,  upon  its  fitness  for 
the  particular  purpose  which  it  may  be  destined  to  serve. 

If  a  piece  of  wood  be  heated  in  an  ordinary  fire,  it  is  speedily  con- 
sumed, with  the  exception  of  a  grey  ash  consisting  of  the  incombustible 
mineral  substances  which  it  contained  ;  if  the  experiment  were  performed 
in  such  a  manner  that  the  products  of  combustion  of  the  wood  could  be 
collected,  these  would  be  found  to  consist  of  carbonic  acid  gas 
and  water;  woody  fibre  is  composed  of  carbon,  hj'drogen,  and  oxygen 
(CgHj^Og),  and  when  it  is  burnt,  the  oxygen,  in  conjunction  with  more 
oxygen  derived  from  the  air,  converts  the  carbon  and  hydrogen  into  carbon 
dioxide  and  water.  But  if  the  wood  be  heated  in  a  glass  tube,  closed  at 
one  end,  it  will  be  found  impossible  to  reduce  it,  as  before,  to  an  ash,  for 
a  mass  of  charcoal  will  remain,  having  the  same  form  as  that  of  the  piece 
of  wood ;  in  this  case,  the  oxygen  of  the  air  not  having  been  allowed  free 
access  to  the  wood,  no  true  combustion  has  taken  place,  but  the  wood  has 
undergone  destructive  distillation,  that  is,  its  elements  have  arranged  them- 
selves, under  the  influence  of  the  high  temperature,  into  different  forms  of 
.combination,  for  the  most  part  simpler  in  their  chemical  composition  than 
the  wood  itself,  and  capable,  unlike  the  wood,  of  enduring  that  temperature 
without  decomposition ;  thus,  it  is  merely  an  exchange  of  an  unstable 
for  a  stable  equilibrium  of  the  particles  of  matter  composing  the  wood. 

(Definition. — Destriictive  distillation  is  the  resolution  of  a  complex 
substance  into  simpler  forms  under  the  influence  of  heat,  out  of  contact 
with  air.) 

The  vapours  issuing  from  the  mouth  of  the  tube  wiU  be  found  acid  to 
blue  litmus  paper ;  they  have  a  peculiar  odour,  and  readily  take  fire  on 
contact  with  flame.  These  wUl  be  more  particularly  noticed  hereafter, 
as  they  contain  some  very  useful  substances.  The  charcoal  which  is  left 
is  not  pure  carbon,  but  contains  considerable  quantities  of  oxygen 
and  hydrogen  with  a  little  nitrogen,  and  the  mineral  matter  or  ash  of 
the  wood. 

When  the  charcoal  is  to  be  used  for  fuel,  it  is  generally  prepared  by 
a  process  in  which  the  heat  developed  by  the  combustion  of  a  portion 

*  The  tenn  pseudo-carbons  has  heen  proposed  for  bodies  of  this  description  characterised 
by  a  high  percentage  of  carbon,  and,  in  many  respects,  simulating  the  element  itself  (Cross 
and  Be  van,  PhiL  Mag.,  May  1882). 


PREPARATION  OF  CHARCOAL. 


65 


Fig.  57.  — Charcoal  heap. 


of  the  wood  is  made  to  eifect  the  charring  of  the  rest.     With  this  view 

the  billets  of  wood  are  built  up  into  a  heap  (fig.  57)  around  stakes  driven 

into  the   ground,  a   passage 

being  left  so  that  the  heap 

may  be  kindled  in  the  centre. 

This  mound  of  wood,  which 

is  generally  from  30  to  50  feet 

in  diameter,  is  closely  covered 

with  turf  and  sand,  except  for 

a  few  inches  around  the  base, 

where  it  is  left  uncovered  to 

give  vent  to  the  vapour  of 

water  expelled  from  the  wood 

in  the  first  stage  of  the  process.     When  the  heap  has  been  kindled  in  the 

centre,  the  passage  left  for  this  purpose  is  carefully  closed  up.     After  the 

combustion  has  proceeded  for  some  time,  and  it  is  judged  that  the  wood  is 

perfectly  dried,  the  open  space  at  the  base  is  also  closed,  and  the  heap  left 

to  smoulder  for  three  or  four  weeks,  when  the  m  ood  is  perfectly  carbonised. 

Upon  an  average,  22  parts  of 
charcoal  are  obtained  by  this 
process  from  100  of  wood. 

A  far  more  economical  process 
for  preparing  charcoal  from  wood 
consists  in  heating  it  in  a  per- 
forated iron  case  or  slip  (F,  fig. 
58)  placed  in  an  iron  retort 
A,  from  which  the  gases  and 
vapours  are  conducted  by  the 
pipe  L  into  the  furnace  B,  where 
they  are  consumed. 

On  the  small  scale,  the  opera- 
tion may  be  conducted  in  a  glass 
retort,  as  shown  in  fig.  59,  where 
the  water,  tar,  and  naphtha  are 


Fig.  58. — Charcoal  retort. 


deposited  in  the  globular  receiver,  and  the  inflammable  gases  are  collected 
over  water. 

The  infusibility  of  the  charcoal  left  by  wood  accounts  for  its  very 
great  porosity,  upon  which 
some  of  its  most  remarkable 
and  useful  properties  de- 
pend. The  application  of 
charcoal  for  the  purpose  of 
"  sweetening"  fish  and  other 
food  in  a  state  of  incipient 
putrefaction  has  long  been 
practised,  and  more  recently 
charcoal  has  been  employed 
for  deodorising  all  kinds 
of  putrefying  and  ofi'eusive 
animal  or  vegetable  matter.  This  property  of  charcoal  depends  upon  its 
j)ower  of  absorbing  into  its  pores  very  considerable  quantities  of  the  gases, 
especially  of  those  which  are  easily  absorbed  by  water.     Thus,  1  cubic 


Fig.  59.  — Distillation  of  wood. 


66 


ABSORPTION  OF  GASES  BY  CHARCOAL. 


inch  of  charcoal  is  capable  of  absorbing  about  100  cubic  inches  of  ammonia 
gas  and  50  cubic  inches  of  sulphuretted  hydrogen,  both  which  are  con- 
spicuous among  the  offensive  results  of  putrefaction.  This  condensation  of 
gases  by  charcoal  is  a  mechanical  effect,  and  does  not  involve  a  chemical 
combination  of  the  charcoal  with  the  gas ;  it  is  exhibited  most  powerfully 
by  charcoal  which  has  been  recently  heated  to  redness  in  a  closed  vessel, 
and  cooled  out  of  contact  with  air  by  plunging  it  under  mercury.  Eventu- 
ally the  offensive  gases  absorbed  by  the  charcoal 'are  chemically  acted  on 
by  the  oxygen  of  the  air  in  its  pores.  A  cubic  inch  of  wood  charcoal  absorbs 
nearly  10  cubic  inches  of  oxygen,  and  when  the  charcoal  containing  the 
gas  thus  condensed  is  presented  to  another  gas  which  is  capable  of  under- 
going oxidation,  this  latter  gas  is  oxidised  and  converted  into  inodorous 
products.  Thus,  if  charcoal  be  exposed  to  the  action  of  air  containing 
sulphuretted  hydrogen  gas  (HgS),  it  condenses  within  its  pores  both  this 
gas  and  the  atmospheric  oxygen,  which  slowly  converts  it  into  sulphuric 
acid  (HgSOJ. 

The  great  porosity  of  wood  charcoal  is  strikinglj'  exhibited  by  attaching  a  piece  of 
lead  to  a  stick  of  charcoal  (fig.  60),  so  as  to  sink  it  in  a  cylinder  of  water,  which  is 
then  placed  under  the  receiver  of  the  air-pump.  On  exhausting  the  air,  innumerable 
bubbles  will  start  from  the  pores  of  the  charcoal,  causing  brisk  effervescence.  If  a 
glass  tube  16  or  18  inches  long  be  thoroughly  filled  with  ammonia  gas  (fig.  61),  sup- 
ported in  a  trough  containing  mercury,  and  a  small  stick  of  recently  calcined  char- 
coal introduced  through  the  mercury  into  the  tube,  the  charcoal  will  absorb  the 
ammonia  so  rapidly  that  the  mercury  will  soon  be  forced  up  and  fill  the  tube, 
carrying  the  charcoal  up  with  it.  On  removing  the  charcoal,  and  placing  it  upon 
the  hand,  a  sensation  of  cold  will  be  perceived  from  the  rapid  escape  of  ammonia, 
perceptible  by  its  odour. 


Fig.  60. 


Fig.  61. 

By  exposing  a  fragment  of  recently  calcined  wood-charcoal  under  a  jar  filled  with 
hydrosulphuric  acid  gas  for  a  few  minutes,  so  that  it  may  become  saturated  with 
the  gas,  and  then  covering  it  with  a  jar  of  oxygen,  the  latter  gas  will  act  upon 
the  former  with  such  energy  that  the  charcoal  will  burst  into  vivid  combustion. 
Tlie  jar  must  not  be  closed  air-tight  at  the  bottom,  or  the  sudden  expansion  may 
burst  it.  Charcoal  in  powder  exposed  in  a  porcelain  crucible  may  also  be  employed 
ill  the  same  way.  It  should  be  pretty  strongly  heated  in  the  covered  crucible,  and 
allowed  to  become  neaisly  cool  before  being  exposed  to  the  hydrosulphuric  acid. 

Charcoal  prepared  from  hard  woods  absorbs  the  largest  volume  of  gas.  Thus  log- 
wood charcoal  has  been  found  to  absorb  111  times  its  volume  of  the  ammoniacal  gas. 
Charcoal  made  from  the  shell  of  the  cocoa-nut  is  even  more  absorbent,  although 
its  pores  are  quite  invisible,  and  its  fracture  exhibits  a  semi-metallic  lustre. 

As  the  gases  which  are  evolved  in  putrefaction  are  of  a  poisonous  char- 
acter, the  power  of  wood  charcoal  to  remove  them  acquires  great  practical 


DEODOKISIXG  AND  DECOLORISING  BY  CHARCOAL. 


67 


importance,  and  i-s  applied  in  very  many  cases ;  the  charcoal  in  coarse 
powder  is  thickly  strewn  over  matters  from  which  the  effluvium  proceeds, 
or  is  exposed  in  shallow  trays  to  the  air  to  be  sweetened,  as  in  the  wards 
of  hospitals,  &c.  It  has  even  been  placed  in  a  ilat  box  of  wire  gauze  to 
be  fixed  as  a  ventilator  before  a  window  through  which  the  contaminated 
air  might  have  access,  and  respirators  constructed  on  the  same  principle 
have  been  found  to  afford  protection  against  poisonous  gases  and  vapours. 
The  ventilating  openings  of  sewers  in  the  streets  are  also  fitted  with 
cases  containing  charcoal  for  the  same  purpose.  Water  is  often  filtered 
through  charcoal  in  order  to  free  it  from  the  noxious  and  putrescent 
organic  matters  which  it  sometimes  contains.  For  all  such  uses  the  char- 
coal should  have  been  recently  heated  to  redness  in  a  covered  vessel,  in 
order  to  expel  the  moisture  which  it  at- 
tracts when  exposed  to  the  air ;  and  the 
charcoal  which  has  lost  its  power  of 
absorption  Avill  be  found  to  regain  it  in 
great  measure  when  heated  to  redness. 

This  power  of  absorption  which  char- 
coal possesses  is  not  confined  to  gases, 
for  many  liquid  and  solid  substances 
are  capable  of  being  removed  by  that 
agent  from  their  solution  in  water.  This 
is  most  readily  traced  in  the  case  of 
substances  which  impart  a  colour  to  the 
solution,  such  colour  being  often  removed 
by  the  charcoal ;  if  port  wine  or  infusion 
of  logwood  be  shaken  with  powdered 
charcoal  (especially  if  the  latter  has  been 
recently  heated  to  redness  in  a  closed 
crucible),  the  Kquid,when  filtered  through 

blotting-paper  (fig.  62),  will  be  found  to  have  lost  its  colour  •  the  colouring 
matter,  however,  seems  merely  to  have  adhered  to  the  charcoal,  for  it  may 
be  extracted  from  the  latter  by  treatment  with  a  weak  alkaline  liquid. 

The  decolorising  power  of  wood  charcoal  is  very  feeble  in  comparison 
with  that  possessed  by  hone-hlach  or  animal  charcoal,  which  is  ob- 
tained by  heating  bones  in  vessels  from  which  the  air  is  excluded. 
Bones  are  composed  of  about  one-third  of  animal  and  two-thirds  of 
mineral  substances,  the  latter  including  calcium  phosphate,  which 
amounts  to  more  than  half  the  weight  of  the  bone,  and  a  little  calcium 
carbonate.  "When  bone  is  heated,  as  in  a  retort,  so  that  air  is  not 
allowed  to  have  free  access  to  it,  the  animal  matter  undergoes  destructive 
distillation,  its  elements — carbon,  hydrogen,  nitrogen,  and  oxygen — 
assuming  other  forms,  the  greater  part  of  the  three  last  elements,  together 
with  a  portion  of  the  carbon,  escaping  in  different  gaseous  and  vaporous 
products,  while  a  considerable  proportion  of  the  carbon  remains  behind, 
intimately  mixed  with  the  earthy  ingredients  of  the  bone,  and  con- 
stituting the  substance  known  as  animal  charcoal.  The  great  differ- 
ence between  the  products  of  the  destructive  distillation  of  bone  and  of 
wood  deserves  a  passing  notice.  If  a  fragment  of  bone  oe  a  shaving  of 
horn  be  heated  in  a  glass  tube  closed  at  one  end,  the  vapours  which  are 
evolved  will  be  found  strongly  alkaline  to  test-papers,  while  those  fur- 
nished by  the  wood  were  acid ;  this  difference  is  to  be  ascribed  mainly 


Fig.  62.— Filtration. 


68  CARBON. 

to  the  presence  of  nitrogen  in  the  bone,  wood  being  nearly  free  from 
that  element ;  it  will  be  found  to  hold  good,  as  a  general  rule,  that  the 
results  of  the  destructive  distillation  of  animal  and  vegetable  matters 
containing  much  nitrogen  are  alkaline,  from  the  presence  of  ammonia 
(NHg)  and  similar  compounds,  while  those  furnished  by  non-nitro- 
genised  substances  possess  acid  characters :  the  peculiar  odour  which  is 
emitted  by  the  heated  bone  is  characteristic,  and  affords  us  a  test  by 
which  to  distinguish  roughly  between  nitrogenised  and  non-nitrogenised 
bodies. 

An  examination  of  the  charred  mass  remaining  as  the  ultimate  result 
of  the  action  of  heat  upon  bone,  shows  it  to  contain  much  less  carbon 
than  that  furnished  by  wood,  for  the  bone-charcoal  contains  nearly  nine- 
tenths  of  its  weight  of  phosphate  (with  a  little  carbonate)  of  calcium ;  the 
consequence  of  the  presence  of  so  large  an  amount  of  earthy  matter  must 
be  to  extend  the  particles  of  carbon  over  a  larger  space,  and  thus  to 
expose  a  greater  surface  for  the  adhesion  of  colouring  matters,  &c.  This 
may  partly  help  to  explain  the  very  great  superiority  of  bone-black  to 
wood  charcoal  as  a  decolorising  agent,  and  the  explanation  derives  support 
from  the  circumstance,  that  when  animal  charcoal  is  deprived  of  its  earthy 
matter,  for  chemical  uses,  by  washing  with  hydrochloric  acid,  its  decolor- 
ising power  is  very  considerably  reduced.  The  application  of  this  variety 
of  charcoal  is  not  confined  to  the  chemical  laboratory,  but  extends  to 
manufacturing  processes.  The  sugar  refiner  decolorises  his  syrup  by  filter- 
ing it  through  a  layer  of  animal  charcoal,  and  the  distiller  employs  char- 
coal to  remove  the  fousel  oil  with  which  distilled  spirits  are  frequently 
contaminated. 

Carbon  is  remarkable,  among  elementary  bodies,  for  its  indisposition  to 
enter  directly  into  combination  with  the  other  elements,  whence  it  follows 
that  most  of  the  compounds  of  carbon  have  to  be  obtained  by  indirect 
processes.  This  element  appears,  indeed,  to  be  incapable  of  uniting  with 
any  other  at  the  ordinary  temperature,  and  this  circumstance  is  occasion- 
ally turned  to  useful  account,  as  when  the  ends  of  wooden  stakes  are 
charred  before  being  plunged  into  the  earth,  when  the  action  of  the 
atmospheric  oxygen,  which,  in  the  presence  of  moisture,  would  be  very 
active  in  effecting  the  decay  of  the  wood,  is  resisted  by  the  charcoal  into 
which  the  external  layer  has  been  converted.  The  employment  of  black- 
load  to  protect  metallic  surfaces  from  rust  is  another  application  of 
the  same  principle.  At  a  high  temperature,  however,  carbon  combines 
readily  with  oxygen,  sulphur,  and  with  some  of  the  metals,  and,  at  a 
very  high  temperature,  even  with  hydrogen.  The  tendency  of  carbon  to 
combine  with  oxygen  under  the  influence  of  heat,  is  shown  when  a  piece 
of  charcoal  is  strongly  heated  at  one  point,  when  the  carbon  at  this  point 
at  once  combines  with  the  oxygen  of  the  surrounding  air  (forming  car- 
bonic acid  gas),  and  the  heat  developed  by  this  combustion  raises  the  neigh- 
bouring particles  of  carbon  to  the  temperature  at  which  the  element  unites 
with  oxygen,  and  thus  the  combustion  is  gradually  propagated  throughout 
tlie  mass,  which  is  ultimately  converted  entirely  into  carbonic  acid  gas, 
nothing  remaining  but  the  white  ash,  composed  of  the  mineral  substances 
derived  from  the  wood  employed  for  preparing  the  charcoal.  It  is  worthy 
of  remark,  that  if  charcoal  had  been  a  better  conductor  of  heat,  it  would 
not  have  been  so  easily  kindled,  since  the  heat  applied  to  any  point  of 
the  mass  would  have  been  rapidly  diffused  over  its  whole  bulk,  and  this 


FOKMATION  OF  COAL.  69 

point  could  not  have  attained  the  high  temperature  requisite  for  its 
ignition,  until  the  whole  mass  had  been  heated  nearly  to  the  same  degree ; 
this  is  actually  found  to  be  the  case  in  charcoal  which  has  been  very 
strongly  heated  (out  of  contact  with  air),  when  its  conducting  power  is 
greatly  improved,  and  it  kindles  with  very  great  difficulty.  The  calorific 
value  of  carbon  is  represented  by  the  number  8080,  that  is,  1  gr.  of 
carbon,  when  burnt  so  as  to  form  carbonic  acid  gas,  is  capable  of  raising 
8080  grs.  of  water  from  O''  C.  to  1°  C. 

A  given  weight  of  charcoal  will  produce  twice  as  much  available  heat 
as  an  equal  weight  of  wood,  since  the  former  contains  more  actual  fuel 
and  less  oxygen,  and  much  of  the  heat  evolved  by  the  wood  is  absorbed 
or  rendered  latent  in  the  steam  and  other  vapours  which  are  produced  by 
the  action  of  heat  upon  it.  The  attraction  possessed  by  carbon  for  oxygen 
at  a  high  temperature  is  turned  to  account  in  metallurgic  operations,  when 
coal  and  charcoal  are  employed  for  extracting  the  metals  from  their  com- 
pounds with  oxygen.* 

The  unchangeable  solidity  of  carbon  is  another  remarkable  feature.  It 
is  stated  that  some  approach  has  been  made,  at  extremely  high  tempera- 
tures, to  the  fusion  and  vaporisation  of  carbon,  but  it  cannot  be  said  to 
have  been  fairly  established  that  this  element  is  able  to  exist  in  any  other 
than  the  solid  form.  Nor  can  any  substance  be  found  by  the  aid  of 
which  carbon  may  be  brought  into  the  liquid  form  by  the  process  of 
solution  ;  for  although  charcoal  gradually  disappears  when  boiled  with 
sulphuric  and  nitric  acids,  it  does  not  undergo  a  simple  solution,  but  is 
converted,  as  will  be  seen  hereafter,  into  carbon  dioxide. 

The  very  striking  diflPerence  in  properties  exhibited  by  diamond,  graphite, 
and  charcoal,  lead  to  the  belief  that  they  consist  of  dissimilar  carbon 
molecules.  The  investigation  of  the  specific  heats  of  these  three  varieties 
affords  some  grounds  for  the  belief  that  the  diamond  molecule  consists 
of  four  atoms,  the  graphite  molecule  of  three  atoms,  and  the  charcoal 
molecule  of  two  atoms  of  carbon. 

54.  Coal. — The  various  substances  which  are  classed  together  under 
the  name  of  coal  are  characterised  by  the  presence  of  carbon  as  a  largely 
predominant  constituent,  associated  with  smaller  quantities  of  hydrogen, 
oxygen,  nitrogen,  sulphur,  and  certain  mineral  matters  which  compose  the 
ash.  Coal  appears  to  have  been  formed  by  a  peculiar  decomposition  or 
fermentation  of  buried  vegetable  matter,  resulting  in  the  separation  of  a 
large  proportion  of  its  hydrogen  in  the  form  of  marsh-gas  (CH^),  and 
similar  compounds,  and  of  its  oxygen  in  the  form  of  carbonic  acid  gas 
(CO.,),  the  carbon  accumulating  in  the  residue.  Thus,  cellulose  (CgH^gOj), 
which  constitutes  the  bulk  of  woody  fibre,  might  be  imagined  to  decom- 
pose according  to  the  equation  2CqH^q05  =  SCH^-h  SCOg  +  Cg,  and  the 
occurrence  of  marsh-gas,  and  of  the  paraffin  hydrocarbons  of  similar 
composition,  as  well  as  of  carbonic  acid  gas,  in  connexion  with  deposits 
of  coal,  supports  this  account  of  its  formation.  Marsh-gas  and  carbonic 
acid  gas  are  the  ordinary  products  of  the  fermentation  of  vegetable  matter, 
and  a  spontaneous  carbonisation  is  often  witnessed  in  the  "heating"  of 
damp  hay.     But  just  as  the  action  of  heat  upon  wood  produces  a  charcoal 

*  Easily  reducible  oxides,  such  as  oxide  of  lead,  give  carbon  dioxide  when  heated  with 
charcoal;  2PbO-t-C=Pb.2  +  C0.2,  but  oxides  which  are  not  easily  reducible,  such  as  oxide 
of  zinc,  give  carbonic  oxide  ;  ZnO  +  C^CO-i-Zu, 


70  VARIETIES  OF  COAL. 

containing  small  quantities  of  the  other  organic  elements,  so  the  carbon* 
ising  process  by  which  the  plants  have  been  transformed  into  coal  has 
left  behind  some  of  the  hydrogen,  oxygen,  and  nitrogen ;  the  last,  as  well 
probably  as  a  little  of  the  sulphur,  having  been  derived  from  the  vegetable 
albumen  and  similar  substances  which  are  always  present  in  plants.  The 
chief  part  of  the  sulphur  is  generally  present  in  the  form  of  iron  pyrites, 
derived  from  some  extraneous  source.  The  examination  of  a  peat-bog  is 
very  instructive  with  reference  to  the  formation  of  coal,  as  affording  ex- 
amples of  vegetable  matter  in  every  stage  of  decomposition,  from  that  in 
which  the  organised  structure  is  still  clearly  visible,  to  the  black  carbon* 
aceous  mass  which  only  requires  consolidation  by  pressure  in  order  to 
resemble  a  true  coal. 

In  some  cases  an  important  part  in  the  formation  of  coal  may  have 
been  played  by  slow  oxidation  or  decay  of  the  vegetable  matter  at  the 
expense  of  atmospheric  oxygen  held  in  solution  by  water ;  since  the 
hydrogen  of  the  compound  would  be  removed  by  oxidation  taking  place 
at  a  low  temperature,  giving  rise  to  a  gradual  increase  in  the  percentage 
of  carbon. 

The  three  principal  varieties  of  coal — lignite,  bituminous  coal,  and 
anthracite — present  us  with  the  material  in  different  stages  of  carbonisa- 
tion ;  the  lignite,  or  brown  coal,  presenting  indications  of  organised  struc- 
ture, and  containing  considerable  proportions  of  hydrogen  and  oxygen, 
while  anthracite  often  contains  little  else  than  carbon  and  the  mineral 
matter  or  ash.  The  following  table  shows  the  progressive  diminution  in 
the  proportions  of  hydrogen  and  oxygen  in  the  passage  from  wood  to 
anthracite  : — 


Carbon. 

Hydrogen. 

Oxygen 

100 

12-18 

83-07 

100 

9-85 

55-67 

100 

8-37 

42-42 

100 

6-12 

21-23 

100 

2-84 

1-74 

Wood,  .... 
Peat,  .... 
Lignite, 

Bituminous  coal,   . 
Anthracite,    . 

The  relative  number  of  atoms  of  C,  H,  and  0  contained  in  the  above 
may  be  compared  in  the  following  formulae,  which  must  not,  however, 
be  taken  as  representing  separate  chemical  compounds  of  a  definite 
character  : — 

Oak,  .         .     CiyH.2^0ii    I     Cannel,        .         .     C^^B-^^O.^ 

Peat,  .         .     CgoHgaOg  Caking  coal,  .     C45H34O2 

Lignite,      .         .     CgvHggOy      |     Anthracite,.         .     C^oHjgO 

The  combustion  of  coal  is  a  somewhat  complex  process,  in  consequence 
of  the  re-arrangement  which  its  elements  undergo  when  the  coal  is  sub- 
jected to  the  action  of  heat. 

As  soon  as  a  flame  is  applied  to  kindle  the  coal,  the  heated  portion 
undergoes  destructive  distillation,  evolving  various  combustible  gases  and 
vapours,  which  take  fire  and  convey  the  heat  to  remoter  portions  of  the 
coal.  Whilst  the  elements  of  the  exterior  portion  of  coal  are  undergoing 
combustion,  the  heat  thus  evolved  is  submitting  the  interior  of  the  mass 
to  destructive  distillation,  resulting  in  the  production  of  various  com- 
pounds of  carbon  and  hydrogen.  Some  of  these  products,  such  as  marsh- 
gas  (CH^)  and  olefiant  gas  (C2H4),  burn  without  smoke,  while  others, 
like  benzene  (CgHg)  and  naphthalene  (Ci^Hg),  which  contain  a  very  large 
proportion  of  carbon,  undergo  partial   combustion,  and  a  considerable 


VAKIETIES  OF  COAL.  71 

quantity  of  carbon,  not  meeting  with  enough  heated  oxygen  in  the  vicinity 
to  burn  it  entirely,  escapes  in  a  very  finely  divided  state  as  smoke  or 
soot,  which  is  deposited  in  the  chimney,  mixed  with  a  little  carbonate  of 
ammonia  and  small  quantities  of  other  products  of  the  distillation  of 
coal.  When  the  gas  has  been  expelled  from  the  coal,  there  remains  a 
mass  of  coke  or  cinder,  which  burns  with  a  steady  glow  until  the  whole 
of  its  carbon  is  consumed,  and  leaves  an  ash,  consisting  of  the  mineral 
substances  present  in  the  coal.  The  final  results  of  the  perfect  combus- 
tion of  coal  would  be  carbonic  acid  gas  (CO2),  water  (HgO),  nitrogen,  a  little 
sulphurous  acid  gas  (SOg),  and  ash.  The  production  of  smoke  in  a  fur- 
nace supplied  with  coal  may  be  prevented  by  charging  the  coal  in  small 
quantities  at  a  time  in  front  of  the  fire,  so  that  the  highly  carbonaceous 
vapours  must  come  in  contact  with  a  large  volume  of  heated  air  before 
reaching  the  chimney.  In  arrangements  for  consuming  the  smoke,  hot 
air  is  judiciously  admitted  at  the  back  of  the  fire,  in  order  to  meet  and 
consume  the  heated  carbonaceous  particles  before  they  pass  into  the 
chimney. 

The  difference  in  the  composition  of  the  several  varieties  'of  coal  gives 
rise  to  a  great  difference  in  their  mode  of  burning. 

The  following  table  exhibits  the  composition  of  representative  speci- 
mens of  the  four  principal  varieties  : — 

Composition  of  Coal. 

Bituminous 

Coal. 
78-57 

5-29 

1-84 
12-88 

0-39 

1-03 


Lignite 

Carbon, 

66-32 

Hydrogen, 
Nitrogen, 

5-63 
0-56 

Oxygen, 
Sulphur. 
Ash,*     '.       . 

22-86 
2-36 
2-27 

Wigan  Cannel. 

Antliracite. 

80-06 

90-39 

5-53 

3-28 

2-12 

0-83 

8-09 

2-98 

1-50 

0-91 

2-70 

1-61 

100-00  100-00  100-00  100-00 

The  lignites  furnish  a  much  larger  quantity  of  gas  under  the  action  of 
heat,  and  therefore  burn  with  more  flame  than  the  other  varieties, 
leaving  a  coke  which  retains  the  form  of  the  original  coal;  while  bitumi- 
nous coal  softens  and  cakes  together, — a  useful  property,  since  it  allows 
even  the  dust  of  such  coal  to  be  burnt,  if  the  fire  be  judiciously  managed. 
Anthracite  {stone  coal  or  Welsh  coal)  is  much  less  easily  combustible 
than  either  of  the  others,  and,  since  it  yields  but  little  gas  when  heated, 
it  usually  burns  with  little  flame  or  smoke.  This  variety  of  coal  is  so 
compact  that  it  will  not  usually  burn  in  ordinary  grates,  but  is  much 
employed  for  furnaces.     (See  Chemistnj  of  Fuel.) 

Jet  resembles  cannel  coal  in  composition. 

Accidents  occasionally  arise  from  the  spontaneous  combustion  of  coal, 
especially  when  shipped  in  a  damp  state.  This  appears  to  be  due,  in 
some  cases,  to  the  development  of  heat  by  the  action  of  atmospheric 
oxygen  on  the  iron-pyrites  or  coal-hrasses  contained  in  the  coaL  Some- 
times the  coal  itself  may  be  capable  of  slow  combination  with  oxygen, 
and  unless  due  provision  be  made  for  the  escape  of  the  heat,  its  accumula- 
tion may  raise  the  temperature  to  a  dangerous  degree. 

*  The  ash  of  coal  consists  chiefly  of  silica,  alumina,  and  peroxide  of  iron. 


72  NATURAL  SOURCES  OF  CARBONIC  ACID  GAS. 

55.  Carbon  is  capable  of  combining  with  oxygen  in  two  proportions, 
forming  the  compounds  known  as  carbonic  oxide  (CO)  and  carbon  dioxide 
(CO,). 

Carbon  Dioxide  or  Carbonic  Acid  Gas. 
COj-44  j)arts  by  weight  =  2  vols.  44  grammes  =  22 -38  litres. 

56.  It  has  been  already  mentioned  that  carbonic  acid  gas  is  a  com- 
ponent of  the  atmosphere,  which  usually  contains  about  4  volumes  of 
carbonic  acid  gas  in  10,000  volumes  of  air.  This  gas  is  chiefly  formed  by 
the  operation  of  the  atmospheric  oxygen  in  supporting  combustion  and 
respiration. 

All  substances  used  as  fuel  contain  a  large  proportion  of  carbon,  which, 
in  the  act  of  combustion,  combines  with  the  oxygen,  and  escapes  into  the 
atmosphere  in  the  form  of  carbonic  acid  gas. 

In  the  process  of  respiration,  the  carbonic  acid  gas  is  formed  from  the 
carbon  contained  in  the  different  portions  of  the  animal  frame  to  which 
oxygen  is  conveyed  by  the  blood;  the  latter,  in  passing  through  the 
lungs,  gives  out,  in  exchange  for  the  oxygen,  a  quantity  of  carbonic  acid 
gas  produced  by  the  union  of  a  former  supply  of  oxygen  with  the  carbon 
of  the  diflFerent  organs  to  which  the  blood  is  supplied,  which,  as  they  are 
constantly  corroded  and  destroyed  by  this  oxidising  action  of  the  blood,  are 
repaired  by  the  supply  of  food  taken  into  the  body.  This  conversion  of 
carbon  of  the  organs  into  carbonic  acid  gas  will  be  again  referred  to  ;  it 
will  be  at  once  evident  that  it  must  be  concerned  in  the  maintenance  of 
the  animal  heat. 

The  leaves  of  plants,  under  the  influence  of  light,  have  the  power  of 
decomposing  the  carbonic  acid  gas  of  the  atmosphere,  the  carbon  of  which 
is  applied  to  the  production  of  vegetable  compounds  forming  portions  of 
the  organism  of  the  plant,  and  when  this  dies,  the  carbon  is  restored,  after 
a  lapse  of  time  more  or  less  considerable,  to  the  atmosphere,  in  the  same 
form,  namely,  that  of  carbonic  acid  gas,  in  which  it  originally  existed 
there.  If  a  plant  should  have  been  consumed  as  food  by  animals,  its 
carbon  will  have  been  eventually  converted  into  carbonic  acid  gas  by 
respiration;  the  use  of  the  plant  as  fuel,  either  soon  after  its  death  (wood), 
or  after  the  lapse  of  time  has  converted  it  into  coal,  will  also  consign  its 
carbon  to  the  air  in  the  form  of  carbonic  acid  gas.  Even  if  the  plant  be 
left  to  decay,  this  process  involves  a  slow  conversion  of  its  carbon  into 
carbonic  acid  gas  by  the  oxygen  of  the  air.* 

Putrefaction  and  fermentation  are  also  very  important  processes  con- 
cerned in  restoring  to  the  air,  in  the  form  of  carbonic  acid  gas,  the  carbon 
contained  in  dead  vegetable  and  animal  matter.  Although,  in  a  popular 
sense,  these  two  processes  are  distinct,  yet  their  chemical  operation  is  of 
the  same  kind,  consisting  in  the  resolution  of  a  complex  substance  into 
simpler  forms,  produced  by  contact  with  some  minute  living  plant  or 
animal.  The  discussion  of  the  true  nature  of  the  process  (which  is  even 
now  somewhat  obscure)  would  be  prematui-e  at  this  stage,  and  it  will 

*  In  the  dark,  according  to  Boussingault,  plants  evolve  carbonic  acid  gas.  He  found  that 
a  sfjuare  metre  (39 '37  inches  square)  of  oleander  leaves  decomposed,  in  sunlight,  on  an 
average,  1  '108  litre  (67  "6  cubic  inches)  of  carbonic  acid  gas  every  hour ;  whilst  the  same  extent 
of  le^f,  in  the  dark,  emitted  0*07  litre  (4-27  cubic  inches)  of  carbonic  acid  gas  in  the  hour. 
Even  under  the  influence  of  light,  flowers  have  been  found  to  absorb  oxygen  and  evolve 
carbonic  acid  gas. 


SOURCES  0^  CARBONIC  ACID  GAS. 


73 


suffice  for  the  present  to  state  that  carbonic  acid  gas  is  one  of  the  simpler 
forms  into  which  the  carbon  is  converted  by  the  metamorphosis  which 
ensues  so  quickly  upon  the  death  of  animals  and  vegetables. 

The  production  of  carbonic  acid  gas  in  combustion, 
respiration,  and  fermentation,  may  be  very  easily  proved  by 
expei'iment.  If  a  dry  bottle  be  placed  over  a  burning  wax 
taper  standing  on  the  table,  the  sides  of  the  bottle  will  be 
covered  with  dew  from  the  combustion  of  the  hydrogen  in 
the  wax  ;  and  if  a  little  clear  lime-water  be  shaken  in  the 
bottle,  the  milky  deposit  of  calcium  carbonate  will  indi- 
cate the  formation  of  the  carbonic  acid  gas. 

By  arranging  two  bottles,  as  represented  in  fig.  63,  and 
inspiring  through  the  tube  A,  air  will  bubble  through  the 
lime-water  in  B,  before  entering  the  lungs,  and  will  then 
be  found  to  contain  too  little  carbonic  acid  gas  to  produce 
a  milkiness,  but  on  expiring  the  air,  it  will  bubble  through 
C,  and  will  render  the  lime-water  in  this  bottle  very  dis- 
tinctly turbid. 

If  a  little  sugar  be  dissolved  in  eight  or  ten  times  its 
weight  of  warm  (not  hot)  water,  in  the  flask  A  (fig.  64), 
and  a  little  dried  yeast,  pi'eviously  rubbed  down  with  water, 
added,  fermentation  will  commence  in  the  course  of  an 
hour  or  less,  and  carbonic  acid  gas  may  be  collected  in  the 
jar  B. 


Fio:.  63. 


57.  In  the  mineral  kingdom,  carbon  dioxide  is  pretty  abundant.  The 
gas  issues  from  the  earth  in  some  places  in  considerable  quantity,  as 
at  ^N^auheim,  where  there 
is  said  to  be  a  spring  ex- 
haling about  1,000,000  lbs. 
of  the  gas  annually.  Many 
spring  waters,  those  of 
Seltzer  and  Pyrmont,  for 
example,  are  very  highly 
charged  with  the  gas. 

But  it  occurs  in  far  larger 
quantity  in  the  immense 
deposits  of  limestone,  mar- 
ble, and  chalk,  which  com- 
pose so  large  a  portion  of 
the  crust  of  the  globe. 
Calcium  carbonate  is  also 
met  with  in  the  animal 
kingdom.       Oyster  -  shells  Fig-  64. 

contain  98  per  cent,  and  egg-shells  97  per  cent,  of  it,  and  pearls  contain 
about  two-thu'ds  of  their  weight. 

The  expulsion  of  the  carbonic  acid  gas  from  limestone  (CaCOg)  forms 
the  object  of  the  process  of  li7ne  burning,  by  which  the  large  supply  of  lime 
(CaO)  is  obtained  for  building  and  other  purposes.  But  if  it  be  required 
to  obtain  the  carbonic  acid  gas  without  regard  to  the  lime,  it  is  better  to 
decompose  the  carbonate  with  an  acid. 

Preparation  of  carbonic  acid  gas. — The  form  of  the  calcium  carbonate, 
and  the  nature  of  the  acid  employed,  are  by  no  means  matters  of  indifference. 
If  dilute  sulphuric  acid  be  poured  upon  fragments  of  marble,  the  effer- 
vescence which  occurs  at  first  soon  ceases,  for  the  surface  of  the  marble 


74 


PROPERTIES  OF  CARBONIC  ACID  GAS. 


becomes  coated  with  the  nearly  insoluble  calcium  sulphate,  by  which  it  is 
protected  from  the  further  action  of  the  acid — 


CaC03   +   H2SO4   =   CaSO^   +   Bf>   + 

Mai'ble.         Sulphuric  acid.     Sulpiiate  of 
lime. 


CO. 


if  the  marble  be  finely  powdered,  or  if  powdered  chalk  be  employed,  each 
particle  of  the  carbonate  will  be  acted  upon.  When  lumps  of  calcium 
carbonate  are  acted  upon  by  hydrochloric  acid,  there  is  no  danger  that  any 
will  escape  the  action  of  the  acid,  for  the  calcium  chloride  produced  is 
one  of  the  most  soluble  salts — 


CaCOg 

+    2HC1   = 

CaClg   +    HgO    +    COg. 

Marble. 

Hydrochloric 
acid. 

Calcium 
chloride. 

For  the  ordinary  purposes  of  experiment,  carbonic  acid  gas  is  most 
easily  obtained  by  the  action  of  dilated  hydrochloric  acid  upon  small 

fragments  of  marble  (fig.  65),  the  latter 
being  covered  with  water,  and  hydro- 
chloric acid  poured  in  through  the  funnel- 
tube.  The  gas  may  be  collected  by  down- 
ward displacement. 

58.  Properties  of  carbon  dioxide. — Car- 
bonic acid  gas  is  invisible,  like  the  gases 
already  examined,  but  is  distinguished  by 
a  peculiar  pungent  odour,  as  is  perceived 
in  soda-water.  It  is  more  than  half  as 
heavy  again  as  atmospheric  air,  its  specific 


Fig.  65. 


-Preparation  of  carbonic 
acid  gas. 

gravity  being  1*529,  which  causes  its  accumulation  near  the  floor  of  such 
confined  spaces  as  the  Grotto  del  Cane,  where  it  issues  from  fissures  in 
the  rock. 


Fig.  66. 

The  higli  specific  gravity  of  carbonic  acid  gas  may  be  shown  by  pouring  it  into 
a  light  jar  attached  to  a  balance,  and  counterpoised  by  a  weight  in  the  opposite  scale 

(fig.  66). 


EFFECT  OF  CARBONIC  ACID  GAS  ON  FLAME. 


75 


rfjjl*™' 


Another  favourite  illustration  consists  in  floating  a  soap-bu"bble  on  the  surface  of  a 
layer  of  the  gas  generated  in  the  large  jar  (fig.  67),  by  pouring  diluted  sulphuric  acid 
upon  a  few  ounces  of  chalk  made  into  a  thin  cream  with  water. 

If  a  small  balloon,  made  of  collodion,  be 
placed  in  the  jar  A  (fig.  68),  it  will  ascend  on 
the  admission  of  carbonic  acid  gas  through  the 
tube  B. 

If  smouldering  brown  paper  be  held  at  the 
mouth  of  a  jar,  like  that  in  fig.  68,  the  smoke 
will  float  upon  the  surface  of  the  carbonic  acid 
gas,  and  will  sink  with  it  on  removing  the 
stopper. 

The  power  which  carhonic  acid  gas 
possesses  of  extinguishing  flame  is  very 
important,  and  has  received  practical 
application  in  the  case  of  burning  mines 
which  must  otherwise  have  been  flooded 
with  water.*  Many  attempts  have  also  been  made  from  time  to  time  to 
employ  this  gas  for  subduing  ordinary  conflagrations,  but  their  success  has 
hitherto  been  very  partial.  It  will  be  remembered  that  pure  nitrogen  is 
also  capable  of  extinguishing  the  flame  of  a  taper,  but  a  large  proportion 


Fig.  67. 


Fig.  68. 


Fig.  69. 


of  this  gas  may  be  present  in  air  without  affecting  the  flame,  whereas  a 
taper  is  extinguished  in  air  containing  one-eighth  of  its  volume  of  car- 
bonic acid  gas,  and  is  sensibly  diminished  in  brilliancy  by  a  much 
smaller  proportion  of  the  gas. 

The  power  of  extinguishing  flame,  conjoined  with  the  high  density  of  carbonic 
acid  gas,  admits  of  some  very  interesting  illustrations. 

Carbouic  acid  gas  may  be  poured  from  some  distance  upon  a  candle,  and  will  extin- 
guish it  at  once.  By  employing  a  gutter,  made  of  thin  wood  or  stifi"  paper,  to  conduct 
the  gas  to  the  flame,  it  may  be  extinguished  from  a  distance  of  several  feet. 

A  large  torch  of  blazing  tow  may  be  plunged  beneath  the  surface  of  the  carbonic 
acid  gas  in  the  jar  (fig.  67). 

*  All  gases  which  take  no  part  in  combustion  may  extinguish  flame,  even  in  the  presence 
of  air,  by  absorbing  heat  and  reducing  the  temperature  below  the  burning  pomt. 


76 


EFFECT  OF  CARBONIC  ACID  GAS  ON  ANIMAXS. 


Carbonic  acid  gas  maj'  be  raised  in  a  class  bucket  (fig.  69)  from  a  large  jar,  and 
poured  into  another  jar,  the  air  in  which  has  been  previously  tested  with  a  taper. 

A  wire  stand  with  several  tapers  fixed  at  different  levels  may  be  placed  in  the  jar 
A  (fig.  70),  and  carbonic  acid  gas  gradually  admitted 
through  a  flexible  tube  connected  with  the  neck  of 
the  jar,  from  the  cistern  B,  a  hole  in  the  cover  of 
which  allows  air  to  enter  it  as  the  gas  flows  out ; 
the  flame  of  each  taper  will  gradually  expire  as  the 
surface  of  the  gas  rises  in  the  jar. 

A  jar  of  oxygen  may  be  placed  over  a  jar  of  carbonic 
acid  gas,  as  shown  in  fig.  53,  and  a  taper  let  down 
through  the  oxygen,  in  which  it  will  burn  brilliantly, 
into  the  carbonic  acid  gas,  which  extinguishes  it,  and 
if  it  be  quickly  raised  again  into  the  oxygen,  it  will 
rekindle  with  a  slight  detonation.  This  alternate 
extinction  and  rekindling  may  be  repeated  several 
times. 

On  account  of  this  extinguishing  power  of 
carbonic  acid  gas,  a  taper  cannot  continue  to 
burn  in  a  confined  portion  of  air  until  it  has 
exhausted  the  oxygen,  but  only  until  its  com- 
bustion has  produced  a  sufficient  quantity  of 
Fig.  70.  carbon  dioxide  to  extinguish  the  flame.* 

To  demonstrate  this,  advantage  may  be  taken  of  the  circumstance  that  phosphorus 
will  continue  to  burn  in  spite  of  the  presence  of  carbonic  acid  gas.  Upon  the  stand 
A  (tig.  71)  a  small  piece  of  phosphorus  is  placed,  and  a 
taper  is  attached  to  the  stand  by  a  wire.  The  cork  B 
fits  air-tight  into  the  jar,  and  carries  a  piece  of  copper 
wire  bent  so  that  it  may  be  heated  by  the  flame  of  the 
taper.  A  little  water  is  poured  into  the  plate  to  prevent 
the  entrance  of  any  fresh  air.  If  the  taper  be  kindled, 
and  the  jar  placed  over  it,  the  flame  will  soon  die  out ; 
and  on  moving  the  jar  so  that  the  hot  wire  may  touch 
the  phosphorus,  its  combustion  will  show  that  a  con- 
siderable amount  of  oxygen  still  remain.?. 

In  the  same  manner,  an  animal  can  breathe  a 
confined  portion  of  air  only  until  he  has  charged  it  with  so  much  carbonic 
acid  gas  that  the  hurtful  effect  of  this  gas  begins  to  be  felt,  a  considerable 
quantity  of  oxygen  still  remaining. 

If  the  air  contained  in  the  jar  A  (fig.  72),  standing  over  water,  be  breathed  two  or 
three  times  through  the  tube  B,  a  painful  sense  of  opjiression  will  soon  be  felt  in 
consequence  of  the  accumulation  of  carbonic  acid  gas.  The  air  may  thus  be  charged 
with  10  volumes  of  carbonic  acid  gas  in  100  volumes,  the  oxygen  becoming  reduced 
to  about  one-half  its  original  quantity.  By  immersing  a  deflagrating  spoon  C, 
containing  a  piece  of  burning  phosphorus,  and  having  a  lighted  taper  attached,  it 
may  be  shown  that  although  there  is  enough  carbonic  acid  gas  to  extinguish  the 
taj)er,  the  oxygen  is  not  exhausted,  for  the  phosphorus  continues  to  burn  rapidly. 

Carbonic  acid  gas  is  not  poisonous  when  taken  into  the  stomach,  but 
acts  most  injuriously  when  breathed,  by  offering  an  obstacle  to  that  escape 
of  carbonic  acid  gas,  by  diffusion,  from  the  blood  of  the  venous  circu- 
lation in  the  lungs,  and  its  consequent  replacement  by  the  oxygen  neces- 
sary to  arterial  blood.  Any  hindrance  to  this  interchange  must  impede 
respiration,  and  such  hindrance  would,  of  course,  be  afforded  by  carbonic 
acid  gas  present  in  the  air  inhaled,  in  proportion  to  its  quantity.  The 
difference   in   constitution  and   temperament   in    individuals   makes   it 


Fig.  71. 


*  When  the  taper  is  extinguished,   the  air  contains  in  100  volumes  18|  volumes  of 
oxygeu  aud  2^  volumes  of  carbonic  acid  gas. 


PKINCIPLES  OF  VENTILATION. 


77 


Fig.  72. 


impossible  that  any  exact  general  rule  should  be  laid  down  as  to  tbe 
precise  quantity  of  carbonic  acid  gas  which  may  be  present  in  air  without 
injury  to  respiration,  but  it  may  be  safely  asserted  that  it  is  not  advisable 
to  breathe  for  any  length  of  time  in  air  containing  more  than  y^^-jyth  (0"1 
per  cent.)  of  its  volume  of  carbonic 
acid  gas.  The  air  of  a  room  contains 
too  much  carbonic  acid  gas,  if  half  a 
measured  ounce  of  lime-water  becomes 
turbid  when  shaken  in  a  half-pint 
bottle  of  the  air. 

There  appears  to  be  no  immediate 
danger,  however,  until  the  carbonic 
acid  gas  amounts  to  ^^th  (0'5  per 
cent.),  when  most  persons  are  attacked 
by  the  languor  and  headache  attending 
the  action  of  this  gas.  A  larger 
proportion  of  carbonic  acid  gas  pro- 
duces insensibility,  and  air  containing 
J^th  of  its  volume  causes  suffocation. 
The  danger  in  entering  old  wells, 
cellars,  and  other  confined  places,  is 
due  to  the  accumulation  of  this  gas, 
either  exhaled  from  the  earth  or  pro- 
duced by  decay  of  organic  matter.  The  ordinary  test  applied  to  such 
confined  air  by  introducing  a  candle  is  only  to  be  depended  upon  if  the 
candle  burns  as  brightly  in  the  confined  space  as  in  the  external  air ; 
should  the  flame  become  at  all  dim,  it  would  be  unsafe  to  enter,  for 
experience  has  shown  that  combustion  may  continue  for  some  time  in  an 
atmosphere  dangerously  charged  with  carbonic  acid  gas. 

The  accidents  from  choke  damp  and  after  damp  in  coal  mines,  and 
from  the  accumulation,  in  brewers'  and  distillers'  vats,  of  the  carbonic 
acid  gas  resulting  from  fermentation,  are  also  examples  of  its  fatal  effect. 

The  air  issuing  from  the  lungs  of  a  man  at  each  expiration  contains 
from  3"5  to  4  volumes  of  carbonic  acid  gas  in  100  volumes  of  air,  and 
could  not,  therefore,  be  breathed  again  Avithout  danger.  The  total  amount 
of  carbonic  acid  gas  evolved  by  the  lungs  and  skin  amounts  to  about  0*7 
cubic  foot  per  hoiir.  In  order  that  it  may  be  breathed  again  without 
inconvenience,  this  should  be  distributed  through  at  least  140  cubic  feet 
of  fresh  air,  or  a  space  measuring  5*2  feet  each  way.  Hence  the  necessity 
for  a  constant  supply  of  fresh  air  by  ventilation,  to  dilute  the  carbonic 
acid  gas  to  such  an  extent  that  it  may  cease  to  impede  respiration.  This 
becomes  the  more  necessary  where  an  additional  quantity  of  carbonic 
acid  gas  is  supplied  by  candles  or  gas-lights.  An  ordinary  gas  burner 
consumes  at  least  3  cubic  feet  of  gas  per  hour,  and  produces  about 
1  -7  cubic  foot  of  carbonic  acid  gas.  Fortunately^  a  natural  provision  for 
ventilation  exists  in  the  circumstance  that  the  processes  of  respiration  and 
combustion,  which  contaminate  the  air,  also  raise  its  temperature,  thus 
diminishing  its  specific  gravity  by  expansion,  and  causing  it  to  ascend 
and  give  place  to  fresh  air.  Hence  the  vitiated  air  always  accumulates 
near  the  ceiling  of  an  apartment,  and  it  becomes  necessary  to  afford  it  an 
outlet  by  opening  the  upper  sash  of  the  window,  since  the  chimney 
ventilates  immediately  only  the  lower  part  of  the  room. 


78 


PRINCIPLES  OF  VENTILATION. 


These  principles  may  be  illustrated  by  some  very  simple  experiments. 
Two  quart  jars  (fig.  73)  are  filled  with  carbonic  acid  gas,  and  after  being  tested  with 
a  taper,  a  4  oz.  flask  is  lowered  into  each,  one  flask  containing  cold  and  the  other  hot 

water.  After  a  few  minutes  the  jar  with 
the  cold  flask  will  still  contain  enough 
carbonic  acid  gas  to  extinguish  the  taper, 
whilst  the  air  in  the  other  jar  will  support 
combustion  brilliantly. 

A  tall  stoppered  glass  jar  (fig.  74)  is 
placed  over  a  stand,  upon  which  three 
lighted  tapers  are  fixed  at  different  heights. 
The  vitiated  air,  rising  to  the  top  of  the 
jar,  will  extinguish  the  uppermost  taper 
first,  and  the  others  in  succession.  By 
quickly  removing  the  stopper  and  raising 
the  jar  a  little  before  the  lowest  taper  has 
expired,  the  jar  will  be  ventilated  and  the 
taper  revived, 

A  similar  jar  (fig.  75),  with  a  glass  chimney  fixed  into  the  neck  through  a  cork  or 
piece  of  vulcanised  tubing,  is'  placed  over  a  stand  with  two  tapers,  one  of  which  is 
near  the  top  of  the  jar,  and  the  other  beneath  the  aperture  of  the  chimney  ;  if  a 


Fig.  73. 


I-Fig.  74. 


Fig.  75. 


crevice  for  the  entrance  of  air  be  left  between  the  jar  and  the  table,  the  lower  taper 
will  continue  to  burn  indefinitely,  whilst  the  upper  one  will  soon  be  extinguished  by 
the  carbonic  acid  gas  accumulating  around  it. 

In  ordinary  apartments,  the  incidental  crevices  of  the  doors  and  windows 
are  depended  upon  for  the  entrance  of  fresh  air,  whilst  the  contaminated 
air  passes  out  by  the  chimney ;  but  in  large  buildings  special  provision 
must  be  made  for  the  two  air  currents.  In  mines  this  becomes  the  more 
necessary,  since  the  air  receives  much,  additional  contamination  by  the 
gases  (marsh-gas  and  carbon  dioxide)  evolved  from  the  workings,  and  by 
the  smoke  occasioned  in  blasting  with  gunpowder.  Mines  are  generally 
provided  with  two  shafts  for  ventilation,  under  one  of  which  (the  upcast 
shaft)  a  fire  is  maintained  to  produce  the  upward  current,  which  carries  off 
the  foul  air,  whilst  the  fresh,  air  descends  by  the  other  [downcast  shaft). 
The  current  of  fresh  air  is  forced  by  wooden  partitions  to  divide  itself, 
and  to  pass  through  every  portion  of  the  workings. 

The  operation  of  such  provisions  for  ventilation  is  easily  exhibited. 

A  tall  jar  (fig.  76)  is  fitted  with  a  ring  of  cork,  carrying  a  wide  glass  chimney  (A). 
If  this  be  placed  over  a  taper  standing  in  a  plate  of  water,  the  accumulation  of  vitiated 
air  will  soon  extinguish  the  taper  ;  but  if  a  second  chimney  (B),  supported  in  a  wire 
ring,  be  placed  within  the  wide  chimney,  fresh  air  will  enter  through  the  interval 
between  the  two,  and  the  smoke  from  a  piece  of  brown  paper  will  demonstrate  the 
existence  of  the  two  currents,  as  shown  by  the  arrows. 


EFFERVESCING  DRINKS. 


79 


A  small  box  (fig.  77)  is  provided  with  a  glass  chimney  at  each  end.  In  one  of  these 
(B)  representing  the  ujicast  shaft,  a  lighted  taper  is  suspended.  A  piece  of  smoking 
brown  paper  may  be  held  in  each  chimney  to  show  the  direction  of  the  current.  On 
closing  A  with  a  glass  plate,  the  taper  in  B  will  be  extinguished,  the  entrance  of  fresh 
air  being  prevented.  By  breathing  gently  into  A  the  taper  will  also  be  extinguished. 
The  experiment  may  be  varied  by  pouring  carbon  dioxide  and  oxygen  alternately  into 
A,  when  the  taper  will  be  extinguished  and  rekindled  by  turns.  ^ 


Fig.  76. 


Fig.  77. 


A  pint  bell-jar  (fig.  78)  is  placed  over  a  taper  standing  in  a  tray  of  water.  If  a 
chimney  (a  common  lamp-glass)  be  placed  on  the  top  of  the  jar,  the  flame  of  the 
taper  will  gradually  die  out,  because  no  provision  exists  for  the  establishment  of  the 
two  currents,  but  on  dropping  a  piece  of  tin-plate  or  card-board  into  the  chimney 
so  as  to  divide  it,  the  taper  will  be  revived,  and  the  smoke  from  the  brown  paper  will 
distinguish  the  upcast  from  the  downcast  shaft. 

If  a  little  water  be  poured  into  a  wide-moutlied  bottle  of  carbonic 
acid  gas,  and  the  bottle  be  then  firmly  closed  by  the  palm  of  the  hand,  it 
will  be  found,  on  shaking  the  bottle  violently,  that  the  gas  is  absorbed, 
and  the  palm  of  the  hand  is  sucked  into  the  bottle.  The  presence  of 
carbonic  acid  in  the  solution  may  be  proved  by 
pouring  it  into  lime-water,  in  which  it  will  produce 
a  precipitate  of  calcium  carbonate,  redissolved  by  a 
further  addition  of  the  solution  of  carbonic  acid. 

One  pint  of  water  shaken  in  a  vessel  containing 
carbonic  acid  gas,  at  the  ordinary  pressure  of  the  atmo- 
sphere, will  dissolve  about  one  pint  of  the  gas,  equal 
in  weight  to  nearly  16  grains.  If  the  gas  be  confined 
in  the  vessel  under  a  pressure  equal  to  twice  or  thrice 
that  of  the  atmosphere — that  is,  if  twice  or  thrice  the 
quantity  of  gas  be  compressed  into  the  same  space, 
the  water  will  still  dissolve  one  pint  of  the  gas,  but 
the  weight  of  this  pint  will  now  be  twice  or  thrice  that 
of  the  pint  of  uncompressed  gas,  so  that  the  water  will 
have  dissolved  32  or  48  grains  of  the  gas,  accordingly 
as  the  pressure  had  been  doubled  or  trebled.  As  soon,  however,  as  the 
pressure  is  removed,  the  compressed  carbonic  acid  gas  will  resume  its 
former  state,  with  the  exception  of  that  portion  Avhich  the  water  is 
capable  of  retaining  in  solution  under  the  ordinary  pressure  of  the  'atmo- 
sphere.   Thus  if  the  water  had  been  charged  with  carbonic  acid  gas  under 


Fig.  78. 


80  LIQUEFACTION  OF  CARBONIC  ACID  GAS. 

a  pressure  equal  to  thrice  that  of  the  atmosphere,  and  had  therefore 
absorbed  48  grains  of  the  gas,  it  would  only  retain  16  grains  "when  the 
pressure  was  taken  off,  allowing  32  grains  to  escape  in  minute  bubbles, 
producing  the  appearance  known  as  effervescence.  This  affords  an  ex- 
planation of  the  properties  of  soda-water,  which  is  prepared  by  charging 
water  ^^th  carbonic  acid  gas  under  considerable  pressure,  and  rapidly 
confining  it  in  strong  bottles.  As  soon  as  the  resistance  offered  by  the 
cork  to  the  expansion  of  the  gas  is  removed,  the  excess  above  that  which 
the  water  can  hold  in  solution  at  the  ordinary  pressure  of  the  air,  escapes 
with  effervescence.  In  a  similar  manner  the  waters  of  certain  springs 
become  charged  with  carbonic  acid  gas,  under  high  pressure,  beneath  the 
surface  of  the  earth,  and  when,  upon  their  rising  to  the  surface,  this 
pressure  is  removed,  the  excess  escapes  with  effervescence,  giving  rise  to 
the  sparkling  appearance  and  sharp  flavour  which  renders  spring  water 
so  agreeable.  On  the  other  hand,  the  waters  of  lakes  and  rivers  are 
usually  flat  and  insipid,  because  they  hold  in  solution  so  small  a  quantity 
of  carbonic  acid  gas. 

The  solution  of  carbon  dioxide  in  water  is  believed  by  many  chemists 
to  contain  the  true  carbonic  acid  HgCOg,  for  COg  +  HgO  =  HgCOg,  but 
tliere  is  no  direct  evidence  in  support  of  this  view. 

The  sparkling  character  of  champagne,  bottled  beer,  &c.,  is  due  to  the 
presence  in  these  liquids  of  a  quantity  of  carbonic  acid  gas  which  has  been 
generated  by  fermentation,  subsequent  to  bottling,  and  has  therefore  been 
retained  in  the  liquid  under  pressure.  In  the  case  of  Seidlitz  powders 
and  soda-water  powders,  the  effervescence  caused  by  dissolving  them 
in  water  is  due  to  the  disengagement  of  carbonic  acid  gas,  by  the  action 
of  the  tartaric  acid,  which  composes  one  of  the  powders,  upon  the 
bicarbonate  of  soda,  producing  tartrate  of  soda  and  carbonic  acid  gas. 
In  the  dry  state  these  powders  may  be  mixed  without  any  chemical 
change,  but  the  addition  of  water  immediately  causes  the  effervescence. 
Baking  powders  are  mixtures  of  this  kind,  being  used  for  imparting 
lightness  and  porosity  to  bread  and  cakes,  by  distending  the  dough  with 
bubbles  of  carbonic  acid  gas. 

The  solubility  of  carbonic  acid  in  water  is  of  great  importance  in  the 
chemistry  of  nature ;  for  this  acid,  brought  down  from  the  atmosphere 
dissolved  in  rain,  is  able  to  act  chemically  upon  rocks,  such  as  granite, 
which  contain  alkalies — the  carbonic  acid  attacking  these,  and  thus 
slowly  disintegrating  or  crumbling  down  the  rock,  an  effect  much  assisted 
by  the  mechanical  action  of  the  expansion  of  freezing  water  in  the  inter- 
stices of  the  rock.  It  appears  that  soils  are  thus  formed  by  the  slow 
degradation  of  rocks,  and  when  these  soils  are  capable  of  supporting 
plants,  the  solution  of  carbonic  acid  is  again  of  service,  not  oidy  as  a 
direct  food,  by  providing  the  plant  with  carbon  through  its  roots,  but  as 
a  solvent  for  certain  portions  of  the  mineral  food  of  the  plant  (such  as 
calcium  phosphate),  which  pure  water  could  not  dissolve,  and  which  the 
})lant  cannot  take  up  except  in  the  dissolved  state. 

59.  Although  carbon  dioxide  retains  the  state  of  gas  under  all  tem- 
peratures and  pressures  to  which  it  is  commonly  exposed,  it  is  capable  of 
assuming  the  liquid  and  even  the  solid  state. 

At  about  the  ordinary  temperature  (63°  F.)  carbonic  acid  gas  is  con- 
densed, by  a  pressure  of  54  atmospheres  (800  lbs.  per  square  inch),  to  a 


LIQUEFACTION  OF  CARBONIC  ACID  GAS. 


81 


colourless  liquid  of  sp.  gr.  0'83  (water  =1),  and  at  a  temperature  of 
-  70°  ¥.  (70°  below  the  zero,  or  102°  below  the  freezing-point  ¥.)  becomes 
a  transparent  mass  of  solid  carbon  dioxide  resembling  ice. 

If  the  temperature  of  the  gas  be  reduced  to  32°  F.  a  pressure  of  35 
atmospheres  only  will  suffice  to  liquefy  it. 

The  experiments  of  Andrews  upon  the  liquefaction  of  carbon  dioxide  show  that,  in 
causing  the  liquefaction  of  gases,  increase  of  pressure  is  not  always  equivalent  to 
reduction  of  temperature,  but  that  there  exists  a  particular  temperature  for  each  gas 
above  which  no  amount  of  pressure  is  able  to  liquefy  it,  and  at  this  particular  tempera- 
ture, the  critical  point,  the  gas  is  wavering  between  the  gaseous  and  the  liquid  state, 
so  that  "  the  gaseous  and  liquid  states  are  only  widely  separated  forms  of  the  same 
condition  of  matter,  and  may  be  made  to  pass  into  one  another  by  a  series  of  grada- 
tions so  gentle,  that  the  passage  shall  nowhere  present  any  interruption  or  breach  of 
continuity."  It  was  found  to  be  impossible  to  liquefy  carbon  dioxide  above  a  tem- 
perature of  88°  F. ,  even  b}'  a  pressure  of  109  atmospheres  ;  but,  at  this  high  pressure 
the  gas  ceased  to  obey  the  law  that  the  volume  of  a  ga-s  is  inversely  as  the  pressure, 
for  instead  of  occupying  ^iw  of  its  original  volume,  it  had  been  reduced  to  -f^.  On 
cooling  the  gas  thus  compressed,  it  liquefied  suddenly,  and  not  gradually  as  in  the 
case  of  a  vapour  under  ordinary  pressure.  The  gas  iu  this  condition,  when  subjected 
to  very  small  variations  of  temperature  or  pressure,  exhibits  curious  flickering  move- 
ments, resembling  the  edect  produced  by  the  ascent  of  coluanns  of  heated  air  through 
colder  strata. 

Even  at  55°  F. ,  a  pressure  of  48 "89  atmospheres  reduced  the  gas  (not  to  -^^  but)  to 
^V  of  its  original  volume  without  liquefying  it,  but  at  this  point  an  additional  pressure 
of  only  tjV  atmosphere  suddenly  liquefied  one  half  of  the  gas. 

A  small  specimen  of  liquid  carbon  dioxide  is  easily  prepared.  A  strong  tube  of  green 
glass  (A,  fig.  79)  is  selected,  about  12  inches  long,  ^  iuch  diameter  in  the  bore,  and 
tV  inch  thick  in  the  walls. 

With  the  aid  of  the  blowpipe  a  

flame  this  tube  is  softened 
and  drawn  off  at  about  an 
inch  from  one  end,  as  at  B, 
which  is  thus  closed  (C). 
This  operation  should  be  per- 
formed slowly,  in  order  that 
the  closed  end  may  not  be 
much  thinner  than  the  walls 
of  the  tube.  When  the  tub;- 
has  cooled,  between  30  and 
40  grs.  of  powdered  bicar- 
bonate of  ammonia  (ordinary 
sesquicarbonate  which  hits 
crumbled  down)  are  tightly 
rammed  into  it  with  a  glass 
rod.  This  part  of  the  tube  is 
then  surrounded  with  a  few 
folds  of  wet  blotting-paper  to 
keep  it  cool,  and  the  tube  is 
bent,  just  beyond  the  carbon- 
ate of  ammonia,  to  a  somewhat 
obtuse  angle  (D).  The  tube 
is  then  softened  at  about  an 
inch  from  the  open  end,  and 

drawn  out  to  a  narrow  neck  (E),  through  which  a  measured  drachm  of  oil  of  vitriol 
is  poured  down  a  funnel-tube,  so  as  not  to  soil  the  neck,  which  is  then  carefully 
drawn  out  and  sealed  by  the  blowpipe  flame,  as  at  F.  The  empty  space  in  the  tube 
should  not  exceed  J  cubic  inch. 

When  the  tube  is  thoroughly  cold,  it  is  suspended  by  strings  in  such  a  position 
that  the  operator,  having  retired  behind  a  screen  at  some  distance,  may  reverse  the 
tube,  allowing  the  acid  to  flow  into  the  limb  containing  the  carbonate  of  ammonia  ; 
or  the  tube  may  be  fixed  in  a  box  which  is  shut  up,  and  reversed  so  as  to  bring  the 
tube  into  the  required  position. 

If  the  tube  be  strong  enough  to  resist  the  pressure,  it  will  be  found,  after  a  few 


( 

-1 

n 

5 ^=^- 

fl 

c<- 

a 

Fig.  79. 


82 


LIQUEFACTION  OF  CARBONIC  ACID  GAS. 


hours,  that  a  layer  of  liquid  carbon  dioxide  has  been  formed  upon  the  surface  of  the 
solution  of  ammonium  sulphate.  By  cooliufj  the  empty  limb  in  a  mixture  of  pounded 
ice  and  salt,  or  of  hydrochloric  acid  and  sodium  sulphate,  the  li(juid  can  be  made  to 
distil  itself  over  into  this  limb,  leaving  the  ammonium  sulphate  in  the  other. 

Fig.  80  represents  Thilorier's  apparatus  for  the  preparation  of  several  pints  of 
liquid  carbon  dioxide,  g  is  a  strong  wroicgM-iron  generator  of  gas  in  whicli  2  lbs.  of 
bicarbonate  of  soda  are  well  stirred  with  4  pints  of  water  at  ]  00°  F.  Half  a  pint  of 
oil  of  vitriol  is  poured  into  a  brass  tube  which  is  dropped  upright  into  the  generator, 
as  shown  by  the  dotted  Hues  in  the  figure,  which  also  indicate  the  level  of  the  liquid 
in  the  generator.  The  head  of  the  generator  is  then  firmly  screwed  on,  with  the  help 
of  the  spannei-s  represented  in  the  figure,  and  the  stopcock  *  firmly  closed  by  turning 
tlie  wheel  w.  The  generator  is  then  turned  over  and  over  on  its  tninnions  resting 
upon  the  stand  s,  for  ten  minutes,  so  that  the  whole  of  the  sulphuric  acid  may  be 
mixed  with  the  solution  of  bicarbonate  of  soda.  The  generator  is  then  connected,  by 
tlie  copper  tube  t,  with  the  strong  wrought-iron  receiver  r,  the  stopcock  of  which 
is  attached  to  a  tube  pa&*ing  down  to  the  bottom  of  the  vessel.  The  stopcock  of  the 
receiver  is  then  opened,  by  turning  the  wheel  v,  and  afterwards  that  of  the  generator. 

The  condensed  gas  then  passes  over  into  the  receiver.  After  two  or  three  minutes 
the  stopcocks  are  again  closed,  the  generator  detached,  the  waste  gas  blown  out 
through  the  stopcock,  the  head  unscrewed,  and  the  generator  emj>tied  and  recharged. 
After  the  operation  has  been  repeated  three  times,  the  pressure  in  the  receiver  will 


Fig.  80. — Liquefaction  of  carbonic  acid. 

be  found  to  have  liquefied  some  of  the  carbon  dioxide,  and  after  seven  charges,  the 
receiver  is  nearly  filled  with  the  liquid  acid.  The  tube  t  is  then  unscrewed  from  the 
receiver,  and  replaced  by  the  nozzle  n.  If  the  stopcock  be  then  slightly  opened,  a 
stream  of  the  liquid  will  be  forced  up  the  tube,  and,  issuing  into  the  air,  will  congeal 
by  its  own  evaporation  into  an  opaque  white  spray  of  solid  carbon  dioxide. 

In  order  to  collect  the  solid,  the  box  shown  as  b  is  employed.  This  is  made  of 
brass,  and  furnished  with  strong  flanges  by  which  the  cover  is  secured  to  it.  The 
handles  of  the  box  are  made  of  wood  or  gutta-percha,  and  are  hollow,  with  brass  tubes 
passing  through  them  to  allow  of  the  escape  of  the  gas,  the  ends  of  the  tubes  within 
the  box  being  covered  by  perforated  plates  which  prevent  the  escape  of  the  solid. 
The  box  and  its  cover  having  been  fitted  together,  the  nozzle  of  the  receiver  r  is 
inserted  into  a  short  tube  projecting  from  the  side  of  the  box,  and  whilst  one  operator 
liolds  the  box  firmly  by  the  handles,  another  gradually  opens  the  stopcock  by  turning 

*  These  stopcocks  are  steel  screws  with  conical  points  fitting  into  gun-metal  sockets. 
Leaden  washers  are  employed  to  secure  the  tightness  of  the  joints  between  the  iron  vessels 
and  their  heads,  which  are  made  of  gun-metaL 


SOLIDIFIED  CARBONIC  ACID  GAS. 


83 


Fis.  81. 


the  wheel  v.     A  stream  of  the  liquid  is  at  once  forced  into  the  box,  where  it  strikes 

against  a  curved  brass  plate  arranged  so  as  to  force  it  to  pass  all  around  the  inside  of 

the  box  ;  about  seven-eighths  of  it  evaporate  as  gas,  which  rushes  out  through  the 

tubular  handles,  and  the  rest  is  found  in  the  box  in  a  solid  state 

resembling  snow.     It  should  be  quickly  shaken  on  to  a  sheet  of 

paper,  ami  emptied  into  a  beaker  placed  within  a  larger  beaker, 

the  interval  being  filled  up  by  flannel.     By  covering  the  beaker 

with  a  dial  glass,  the  solid  may  be  kept  for  some  time.     The 

box  becomes  intensely  cold,  and  condenses  the  moisture  of  the 

air  to  a  thick  layer  of  hoar  frost,  and  if  it  be  dipped  into  water 

it  becomes  coated  with  ice. 

The  solid  carbon  dioxide  evaporates  without  melting,  for  its 
melting  point  is  -85°  F.,  and  its  own  evaporation  keeps  it  at 
-  125°  F.  It  produces  a  sharp  sensation  of  cold  when  placed  upon 
the  hand,  and  if  pressed  into  actual  contact  with  the  skin,  causes 
a  painful  frost-bite.  Its  rapid  evaporation  may  be  shown  by 
placing  a  few  fragments  on  the  surface  of  water  in  the  globe 
(fig.  81),  which  has  a  tube  passing  down  to  the  bottom,  through 
which  the  pressure  of  the  carbonic  acid  gas  forces  the  water  to 
a  considerable  height. 

The  solid  carbon  dioxide  is  soluble  in  ether,  and  it  evaporates 
from  this  solution  far  more  rapidly,  because  the  liquid  is  a  better 
conductor  of  heat  than  the  highly  porous  solid,  and  abstracts 
heat  more  rapidly  from  surrounding  objects. 

If  a  layer  of  ether  be  poured  upon  water,  and  some  solid 
carbon  dioxide  be  thrown  into  it,  the  water  is  covered  with  a 
layer  of  ice. 

On  immersing  the  bulb  of  a  thermometer  into  the  solution  of  solid  carbon  dioxide 
in  ether,  the  mercury  becomes  solid,  and  the  bulb  maj''  be  hammered  out  into  a  disk. 

By  placing  a  piece  of  filter-paper  in  an  evaporating  dish,  pouring  a  pound  or  so  of 
mercury  into  it,  immersing  a  wire  turned  into  a  flat  spiral  at  the  end,  covering  the 
mercury  with  ether,  and  throwing  in  some  solid  carbon  dioxide,  the  mercury  may 
soon  be  frozen  into  a  cake.  If  this  be  suspended  by  the  wire  in  a  vessel  of  water, 
the  mercury  melts,  descending  in  silvery  streams  to  the  bottom  of  the  vessel,  leaving 
a  cake  of  ice  on  the  wire,  with  icicles  formed  during  the  descent  of  the  mercury. 
This  experiment  is  rendered  more  effiective  by  using  an  inverted  gas-jar,  to  the 
ni?ck  of  which  is  attached,  by  a  perforated  cork,  a  test-tube  to  catch  the  mercuiy. 
The  round  lid  of  a  cardboard  box  gives  a  nice  disk  of  frozen  mercury. 

Even  in  a  rod  hot  vessel,  with  prompt  manipulation,  the  mercury  may  be  solidified 
by  the  solution  of  solid  carbon  dioxide  in  ether.  For  this  purpose  a  platinum  dish 
is  heated  to  redness  over  a  large  Bunsen  burner,  a  few  lumps  of  carbon  dioxide  are 
thrown  into  it,  upon  these  is  held  a  copper  or  platinum  dish  containing  the  mercury, 
in  which  is  also  held  a  wire  to  serve  as  a  handle  for  withdrawing  the  mercury.  Some 
more  carbon  dioxide  is  thrown  upon  the  mercury,  and  ether  is  spirted  on  to  it  from 
a  small  washing-bottle.  One  or  two  additions  of  the  carbon  dioxide  and  ether 
alternately  will  freeze  the  mercury,  which  may  be  withdrawn  from  the  flames  by  the 
wire  handle. 

The  temperature  produced  by  the  evaporation  of  the  solid  carbon  dioxide  dissolved 
in  ether  is  estimated  at  -  150°  F. 

60.  Carbonic  acid  gas  may  be  separated  from  most  other  gases  by  the 
action  of  potash,  which  absorbs  it,  forming  potassium  carbonate.  The 
proportion  of  carbonic  acid  gas  is  inferred,  either  from  the  diminution  in 
volume  suffered  by  the  gas  when  treated  with  potash,  or  from  the  increase 
of  weight  of  the  latter. 

In  the  former  case  the  gas  is  carefully  measured  over  mercury  (fig.  82),  with  due 
attention  to  temperature  and  barometric  pressure,  and  a  little  concentrated  solution 
of  potash  is  thrown  up  through  a  curved jni^ette  or  syringe,  introduced  into  the  orifice 
of  the  tube  beneath  the  surface  of  the  mercury.  The  tube  is  gently  shaken  for  a 
few  seconds  to  promote  the  absorption  of  the  gas,  and,  after  a  few  minutes'  rest,  the 
diminution  of  volume  is  read  off.  Instead  of  solution  of  potash,  damp  potassium 
hydrate  in  the  solid  state  is  sometimes  introduced,  in  the  form  of  small  sticks  or 
balls  attached  to  a  wire.     To  determine  the  weight  of  carbonic  acid  gas  in  a  gaseous 


84 


ANALYSIS  OF  ORGANIC  SUBSTANCES. 


mixture,  the  latter  is  passed  through  a  bulb-apparatus  (C,  fig.  83),  containing  a  strong 
solution  of  potash,  and  weighed  before  and  after  the  passage  of  the  gas.  When  the 
proportion  of  carbonic  acid  in  the  gas  is  small,  it  is  usual  to  attach  to  the  bulb-appa- 

ratas  a  little  tube,  containing  solid 
potash,  or  calcium  chloride,  or  pumice- 
stone  moistened  with  sulphuric  acid,  for 
the  purpose  of  retaining  any  vapour  of 
water  which  the  large  volume  of  unab- 
sorbed  gas  might  carry  away  in  passing 
through  the  solution  of  potash, 

6 1 .  Ultimate  (rrfjanic  analysis.  — 
It  is  necessary  to  determine  in  the 
above  manner  the  weight  of  car- 
bonic acid  "gas,  in  order  to  ascertain 
the  proportion  of  carbon  present 
in  organic  substances.  For  tliis 
purpose  an  accurately  weighed 
quantity  (usually  from  7  to  10 
grains)  of  the  organic  substance  is 
very  carefully  mixed  with  some 
compound  from  which  it  can  obtain 
oxygen  at  a  high  temperature,  such 
as  copper  oxide  (CuO)  or  lead  chromate  (PbCrO^),  care  being  taken  to 
employ  a  large  excess  of  the  oxidising  agent.  The  mixture  is  introduced 
into  a  combustion-tube  of  German  glass  (which  is  free  from  lead  and  noted 
for  its  infusibility)  of  the  form  shown  in  A  (fig.  83).  This  tube  is 
provided  with  a  small  tube  B,  containing  calcium  chloride,  which 
is  connected  by  a  tube  of  caoutchouc  with  the  potash  bulbs  C.  On 
gradually  heating  the  tube  in  a  charcoal  furnace,  or  over  a  properly 
constructed  gas-burner,  the  hydrogen  and  carbon  contained  in  the 
organic  substance  are  converted  respectively  into  water  and  carbonic 
acid  gas,  by  the  oxygea  derived   from   the  lead  chromate    or   copper 


Fig.  82. 


Fig.  83.  — Apparatus  for  organic  analysis. 

oxide.  The  water  is  absorbed  by  the  calcium  chloride  in  B,  and 
the  increase  of  weight  in  this  tube  will  indicate  the  quantity  of  water 
formed  in  the  combustion,  whilst  that  of  the  potash  bulbs  will  show  the 
■weight  of  the  carbonic  acid  gas.  When  the  whole  length  of  the  tube 
is  red  hot,  and  no  more  gas  passes  through  the  bulbs,  the  sealed  point  D 
of  the  tube  is  broken  off,  and  air  drawn  tiirough  by  applying  suction  at  E, 
in  order  to  sweep  out  the  last  traces  of  water  and  carbonic  acid  gas  into 
the  calcium  chloride  and  potash.  Sometimes  the  organic  substance  'is 
heated  in  a  little  platinum  tray,  placed  within  a  glass  tube,  through  which 
a  stream  of  pure  oxygen,  is  passed,   the  products  of  combustion  being 


EMPIRICAL  AND  EATIONAL  FORMULAE.  85 

afterwards  made  to  pass  over  red  hot  copper  oxide,  to  convert  any 
carbonic  oxide  into  carbon  dioxide,  and  collected  for  weighing  as 
before. 

"When  the  organic  substance  contains  carbon,  hydrogen,  and  oxygen, 
the  weight  of  this  last  is  inferred  by  subtracting  the  weights  of  the  carbon 
and  hydrogen  from  that  of  the  substance.  As  an  example  of  the  ultimate 
analysis  of  an  organic  substance,  the  results  of  an  analysis  of  oxalic  acid 
are  here  given — 

10  grs.  of  oxalic  acid,  dried  at  212°  F.,  gave  9-78  grs.  of  carbon  dioxide 
and  2-00  avs.  of  water. 


CO2 

C 

CO2 

44 

:     12     :  : 

9-78 

:     X 

x  = 

=  2'67  grs.  of  carbon  in 

10  grs.  c 

>f  oxalic 

acid. 

H2O 

H2 

H2O 

18 

:       2     :   : 

2 -00 

:   y 

y  = 

=  0-22  gr.  of 

hydrogen  in  10  grs. 

of  oxalic  acid. 

It  having  been  ascertained  by  preliminary  experiments  that  oxalic  acid 
contains  only  carbon,  hydrogen,  and  oxygen,  10  (oxalic  acid)  mimis  2 '89 
(carbon  and  hydrogen)  =  7'11  grs.  of  oxygen  in  10  grs.  of  oxalic  acid. 
It  appears,  therefore,  that 

10     grs.  of  oxalic  acid  contain 
2*67     „     carbon, 
0'22     ,,     hydrogen,  and 
7*11     „     oxygen. 

Empirical  and  rational  formula'. — In  order  to  deduce  from  these  num- 
bers the  chemical  formula  for  oxalic  acid,  that  is,  the  formula  expressing 
the  number  of  atoms  of  each  element,  it  will  be  necessary,  of  course,  to 
divide  the  Aveight  of  each  element  by  the  number  representing  its  atomic 
M' eight. 

Thus  2*67  -^  12  =  0*22  atomic  proportion  of  carbon; 
0-22  -^     1  =  0-22         „  „         hydrogen; 

7*11  ^  16  =  044         „  ,,         oxygen. 

Dividing  these  numbers  by  0*22,  the  formula  of  oxalic  acid  might  be 
written  CH02-  This,  however,  is  only  an  empiHcal  formula  for  oxalic 
acid,  that  is,  a  formula  which  represents  its  composition  only,  without 
reference  to  its  co?istitution,  i.e.,  to  the  absolute  number  of  atoms  pre- 
sent, and  to  the  mode  in  which  they  are  grouped  or  arranged  within  the 
compound.  A  formula  professing  to  give  such  information  would  be 
termed  a  rational  formula,  and  can  only  be  arrived  at  by  the  careful  study 
of  the  relation  of  the  substance  under  examination  to  others  of  wliich  the 
combining  w^eights  are  certainly  known.  Thus,  it  is  found  that  one 
molecule  ^56  parts)  of  caustic  potash  (KHO)  requires  45  parts  of  dry 
oxalic  acid  to  neutralise  it  and  form  the  potassium  oxalate.  Hence  it  is 
reasonable  to  regard  45  as  the  molecular  weight  of  dry  oxalic  acid.  This 
is  the  quantitj'  which  would  be  expressed  by  the  formida  CHO2.  The 
action  of  oxalic  acid  upon  caustic  potash  would  then  be  represented 
by  the  equation  KHO  +  CHO.,  -  H.^O  +  CKO^  (potassium  oxalate).  But 
there  is  another  oxalate  which  has  the  formula  C2KHO4  (hydropotassic 


se 


SALTS  FORMED  BY  CABBONIC  ACID. 


oxalate)  in  which  only  cue  half  of  the  hydrogen  is  displaced  hy  potassium. 
Hence  there  mtist  be  2  atoms  of  hydrogen  in  the  molecule  of  oxalic  acid, 
and  its  formula  is  C.jH.jO^.  In  determining  whether  this  formula 
represents  only  one  grouping  of  the  elements,  or  whether  it  contains  two 
or  more  groups  in  combination,  the  chemist  is  guided  by  the  residts  of  a 
more  minute  study  of  the  decompositions  which  the  compound  undergoes 
under  varied  conditions./' 

62.  Stilts  formed  hy  carbonic  acid. — Although  so  ready  to  combine  with 
the  alkalies  and  alkaline  earths  (as  shown  in  its  absorption  by  solution 
of  potash  and  by  lime-water),  carbonic  acid  must  be  classed  among  the 
weaker  acids.  It  does  not  neutralise  the  alkalies  completely,  and  it  may  be 
displaced  from  its  salts  by  most  other  acids.  Its  action  upon  the  colouring 
niatter  of  litmus  is  feeble  and  transient.  If  a  solution  of  carbonic  acid  be 
added  to  blue  infusion  of  litmus,  a  M'ine-red  liquid  is  produced,  which 
becomes  blue  again  when  boiled,  losing  its  carbonic  acid  ;  whilst  litmus 
reddened  by  sulphuric,  hydrochloric,  or  nitric  acid,  acquires  a  brighter 
red  colour,  which  is  permanent  on  boiling. 

With  each  of  the  alkalies  carbonic  acid  forms  two  well-defined  salts, 
the  carbonate  and  bicarbonate.  Thus,  the  carbonates  of  potassium  and 
sodium  are  represented  by  the  formulae,  K0CO3  and  XaoCOg,  whilst  the 
bicarbonates  are  KHCO,  and  JS^aHCOg.  The  existence  of  the  latter  salts 
would  favour  the  belief  in  the  existence  of  the  compound  HoCOg,  although 
no  such  combination  ha.s  yet  been  obtained  in  the  separate  stata  Perfectly 
dry  carbonic  acid  gas  is  not  absorbed  hj  pure  quicklime  (CaO),  but 
when  a  little  water  is  added,  combination  at  once  takes  place.  This 
supports  the  view  entertained  by  some  chemists,  that  COg  is  not  an  acid 
until  it  is  associated  with  water,  and  they  therefore  speak  of  it  as 
carbonic  anhydride,  reserving  the  name  carbonic  acid  for  the  as  yet 
undiscovered  compound  HgO.COg  (or  H.^COg). 

Opposed  to  this  view,  however,  is  the  fact  that  quicklime  wiU  absorb 
carbonic  acid  gas  when  heated  to  a  certain  point. 

Two  hard  glass  tubes  closed  at  one  end,  and  bent  as 
in  fig.  84,  are  perfectly  dried,  and  filled,  over  mercury, 
with  well-dried  carbonic  acid  gas.  Fragments  of  lime 
are  taken,  whilst  red  hot,  out  of  a  crucible,  cooled  under 
the  mercury,  inserted  into  the  tubes,  and  transferred 
to  the  upper  end.  Xo  absorption  of  the  gas  takes  place, 
though  the  tubes  be  left  for  some  days  ;  but  if  one  of 
them  be  heated  by  a  Bunsen  buiner,  the  absorption  of 
carbonic  acid  gas  takes  place  rapidly,  and  the  mercury 
is  forced  up  into  the  tube. 

The  carbonates  may  be  expressed  either  by  additive 
formulae,  showing  the  bases  which  combine  with  car- 
bonic acid  to  produce  them,  or  by  substitutive  formulae, 
in  which  they  are  represented  as  fonued  from  the 
Mfpothetical  H  jCOg  by  the  substitution  of  metals  for  the 
hydrogen.  In  the  latter  formulae  the  existence  of  CO, 
is  lost  sight  of  altogether. 

The  formula  HjCOj  represents  carbonic  acid  as  a 
dibasic  acid,  that  is,  an  acid  containing  two  atoms  of 
hydrogen  which  may  be  replaced  by  metals. 
Carbonates  may  be  normal,  acid,  or  basic.     A  normal  carbonate  is  one  in  which  all 
the  iiydrogen  in  H^COj  is  replaced  by  a  metal  or  metals. 

An  acid  carbonate  is  one  in  which  only  half  of  the  hydrogen  is  replaced  by  a  metal. 
A  basic  carbonate  is  a  normal  carbonate  in  combination  with  a  hydrate  of  the  metal. 


Fig.  84. 


CARBONATES. 


87 


The  following  are  some  of  the'  principal  carbonates  which  are  found  in 
nature  or  employed  in  the  arts  : — 


Chemical  Name. 


Potassium     car- 
bonate. 

Hydropotassic 
carbonate. 

Sodium    carbon- 
ate. 

Hydrosodic    car- 
bonate. 

Ammonium   ses- 
quicaibouate. 

Calcium  carbon- 
ate. 
Basic  ma(;nesium 

carbonate. 
Ferrous    carbon- 
ate. 
i  Zinc  carbonate. 
Ba.sic  copper  car- 
bonate. 
Basic    lead    car- 
bonate. 
Carbonate  of  cal- 
cium and  mag- 
nesium. 


Common  Name. 


>  Potashes,  Pearl-ash. 

1^  Bicarbonate        of 
)      potash. 
\  Alkali.  I 

I  Washing  soda.         ) 

[  Bicarbonate  of  soda. 

l  Smelling  salts.         ) 
)  Preston  sails.  f 

\  Carbonate   of  am-  ^ 
(      monia.  ) 

\  Limestone,  chalk. 
/  Marble. 
i  Macjiiesia  alba. 
\  Magnesia, 

I  Spathic  iron  ore. 

Calamine. 

>  Malachite. 

I  White  lead. 

I  Dolomite. 

<  Magnesian  lime-      /• 

(      stone.  ) 


Additive  Formula. 


K,O.CO., 
K2O.H2O.2CO., 
Naj,O.H20.2C02 
NagO.H2O.2CO2 

4NH3.3H.,0.3C02 

CaO.COa 

5(MgO.C02) 
2(MgO.H20) 

FeO.COg 

ZnO.COj, 

CuO.CO., 

CuO.H.,0 

2(PbO.C02) 

PbO.H.p 

CaO.MgO.2CO2 


Substitutive  Formula, 


K^COs 
KHCO3 
Na^HCOa 
NaHCOa 

(NH,)4H.,(C03)3 

CaCOs 

5MgC03.2Mg(HO), 

FeCOs 
ZnCOs 
CuC03.Cu(HO)2 

2PbC03.pb(HO)., 
MgCa2C03 


63.  Anahjtical  proof  of  the  composition  of  carbonic  aci'c?  .705.— Lavoisier  appears  to 
have  been  the  first  to  prove  that  carbonic  acid  gas  was  formed  when  carbon  combined 
with  oxygen,  but  its  composition  was  first  analytically  demonstrated  by  Smithson 
Tennant,  who  heated  carbonate  of  lime  with  phosphorus  in  a  sealed  glass  tube,  and 
obtained  phosphate  of  lime  ami  carbon,  the  latter  having  parted  with  its  oxygen  to 
convert  the  phosphorus  into  phosphoric  acid. 


Fig.  85. 

A  far  easier  method  of  demonstrating  the  composition  of  carbonic  acid  gas  consists 
in  introducing  a  pellet  of  potassium  into  a  bulb  tube,  through  wliich  a  current  of  car- 
bonic acid  gas  (dried  by  passing  through  oil  of  vitriol,  or  over  cliloride  of  calcium)  is 
flowing,  and  applying  the  heat  of  a  spirit-lamp  to  the  bulb.  The  metal  will  soon 
burn  in  the  gas,  which  it  robs  of  its  oxygen,  leaving  tlie  carbon  as  a  black  mass  iu 
the  bulb  (fig.  85).     The  potash  produced  by  the  oxidation  of  the  potassium  enters 


88 


CARBONIC  OXIDE  IN  FIRES  AND  FURNACES. 


into  combination  with  another  portion  of  the  carbonic  acid  gas,  forming  a  white  mass 
of  potassium  carbonate,  3C0j,+ K4  =  2KgC03+C.  If  slices  of  sodium  be  arranged  in 
a  test-tube  in  alternate  layers  with  dried  chalk  (calcium  carbonate),  and  strongly 
heated  with  a  spirit-lamp,  vivid  combustion  will  ensue,  and  much  carbon  will  be 
separated  (CaCOa  +  Na^  =  CaO  +  2NajO  +  C). 

When  the  action  of  the  sodium  upon  carbonic  acid  gas  is  moderated  by  employing 
it  in  the  form  of  a  mixture  with  pure  dry  sand,  and  by  keeping  the  temperature  below 
the  boiling  point  of  mercury,  sodium  oxalate  is  produced  by  the  combination  of 
the  sodium  Avith  the  elements  of  the  carbon  dioxide  ;  Na^  +  2CO2  =  NajjC204  (sodium 
oxalate). 

64.  Carbonic  oxide  (CO  =  28  parts  by  weight  =  2  volumes). — Other 
metals,  which  are  not  endowed  with  so  powerful  an  attraction  for  oxygen, 
do  not  carry  the  decomposition  of  carbon  dioxide  to  its  final  limit;  thus, 
iron  and  zinc*  at  a  high  temperature  Avill  only  deprive  the  gas  of  one  half 
of  its  oxygen,  a  result  which  may  also  be  brought  about  at  a  red  heat  by 
carbon  itself.  If  an  iron  tube  filled  with  fragments  of  charcoal  be  heated 
to  redness  in  a  furnace  (fig.  9),  a/id  carbonic  acid  gas  be  transmitted 
through  it,  it  will  be  found,  on  collecting  the  gas  which  issues  from  the 
other  extremity  of  the  tube,  that  it  has  no  longer  the  properties  of  carbonic 
acid,  but  that,  on  the  approach  of  a  taper,  it  takes  lire,  and  burns  with  a 
beautiful  blue  lambent  iiame,  similar  to  that  which  is  often  observed  to 
play  over  the  surface  of  a  clear  fire.  Both  flames,  in  fact,  are  due  to  the 
same  gas,  and  in  both  cases  this  gas  results  from  the  same  chemical 
change,  for,  in  the  tube,  the  carbonic  acid  gas  yields  half  of  its  oxygen  to 
the  char  ;oal,  both  becoming  converted  into  carbonic  oxide  ;  COg  +  C  = 
2C0.  In.  the  fire  the  carbonic  acid  gas  is  formed  by  the  combustion  of 
the  carboa  of  the  fuel  in  the  oxygen  of  the  air  entering  at  the  bottom  of 
the  grate;  and  this  carbonic  acid  gas  in  passing  over  the  layer  of  heated 
carbon  in  the  upper  part  of  the  fire^  is  partly  converted  into  carbonic  oxide, 
which  inflames  when  it  meets  with  the  oxygen  in  the  air  above  the  surface 
of  the  fuel,  and  burns  with  its  characteristic  blue  flame,  reproducing 
carbon  dioxide.  The  carbonic  oxide  occupies  twice  the  volume  of  the 
carbon  dioxide  from  which  it  was  produced. 

This  conversion  of  carbon  dioxide  into  carbonic  oxide  is  of  great  import- 


Fig  86. — Reverberatory  furnace  foi  copper  smelting. 

ance  on  account  of  its  extensive  application  in  metallurgic  operations.  It 
is  often  desirable,  for  instance,  that  a  flame  should  be  made  to  play  over 
the  surface  of  an  ore  placed  on  the  bed  or  hearth  of  a  reverberatory  fur- 
nace (fig.  '^^).  This  object  is  easily  attained  when  the  coal  affords  a  large 
quantity  of  inflammable  gas  ;  but  with  anthracite  coal,  which  burns  with 

*  Magnesium  also  reduces  carbon  dioxide  to  carbonic  oxide. 


PROPERTIES  OF  CARBONIC  OXIDE.  89 

very  little  flame,  and  is  frequently  employed  in  such  furnaces,  it  is  neces- 
sary to  pile  a  high  column  of  coal  upon  the  grate,  so  that  the  carbon 
dioxide  formed  beneath  may  be  converted  into  carbonic  oxide  in  passing 
over  the  heated  coal  above^  and  when  this  gas  reaches  the  hearth  of  the 
furnace,  into  which  air  is  admitted,  it  burns  with  a  flame  which  spreads 
over  the  surface  of  the  ore.  The  temperature  of  the  flame  of  carbonic 
oxide  burning  in  air  is  estimated  at  about  2050°  C. 

The  attraction  of  carbonic  oxide  for  oxygen  is  turned  to  account  in 
removing  that  element  from  combination  with  iron  in  its  ores,  as  will  be 
seen  hereafter. 

Carbonic  oxide  is  a  gas  of  so  poisonous  a  character  that,  according  to 
Lebhiuc,  1  volume  of  it  difi"used  through  100  volumes  of  air  totally 
unfits  it  to  sustain  life  ;  and  it  appears  that  the  lamentable  accidents 
which  too  frequently  occur  from  burning  charcoal  or  coke  in  braziers  and 
chafing-dishes  in  close  rooms,  result  from  the  poisonous  effects  of  the 
small  quantity  of  carbonic  oxide  which  is  produced  and  escapes  combus 
tion,  since  the  amount  of  carbonic  acid  gas  thus  diffused  through  the  air 
is  not  sufficient,  in  many  cases,  to  account  for  the  fatal  result.  The 
carbonic  oxide  formed  in  cast-iron  stoves  diffuses  through  the  hot  metal 
into  the  air  of  a  room. 

65.  The  knowledge  of  the  poisonous  character  of  carbonic  oxide  gave 
rise  a  few  years  since  to  considerable  apprehension,  when  it  was  proposed 
to  employ  this  gas  in  Paris  for  purposes  of  illumination.  The  character 
of  the  flame  of  carbonic  oxide  would  appear  to  afford  little  promise  of  its 
utility  as  an  illuminating  agent;  but  that  it  is  possible  so  to  employ  it  is 
easily  demonstrated  by  kindling  a  jet  of  the  gas  which  has  been  passed 
through  a  wide  tube  containing  a  little  cotton  moistened  with  rectified 
coal  naphtha  (benzene),  when  it  will  be  found  to  burn  with  a  very  luminous 
flame.  The  carbonic  oxide  destined  to  be  employed  for  illuminating  pur- 
poses was  prepared  by  passing  steam  over  red  hot  coke  or  charcoal,  when 
a  highly  inflammable  gas  was  obtained,  containing  carbon  dioxide,  carbonic 
oxide  and  hydrogen  ;  4H2O  +  Cg  =  COg  +  2C0  +  H3 . 

Since  neither  hydrogen  nor  carbonic  oxide  burns  with  a  luminous  flame, 
this  gas  was  next  passed  into  a  vessel  containing  red  hot  coke,  over  which 
melted  resin  Avas  allowed  to  trickle.  The  action  of  heat  upon  the  resin 
gave  rise  to  the  production  of  vapours  similar  to  that  of  the  benzene  em- 
ployed in  the  above  experiment,  and  which,  in  like  manner,  conferred 
considerable  illuminating  power  upon  the  gas. 

The  decomposition  of  steam  by  red  hot  carbon  is  also  taken  advantage 
of  in  order  to  procure  a  flame  from  anthracite  coal  when  employed  for 
heating  boilers.  The  coal  being  burnt  on  ^fish-bellied  bars,  beneath  which 
a  quantity  of  water  is  placed,  the  radiated  heat  converts  the  water  into 
steam,  which  is  carried  by  the  draught  into  the  fire,  Avhera  it  furnishes 
carbonic  oxide  and  hydrogen,  both  capable  of  burning  with  flame  under 
the  bottom  of  the  boiler.  The  temperature  of  the  bars  is  also  thus  re- 
duced, so  that  they  are  not  so  much  injured  by  the  intense  heat  of  the 
glowing  fuel. 

66.  Carbonic  oxide,  unlike  carbon  dioxide,  is  nearly  insoluble  in  water. 
It  is  even  lighter  than  air,  its  specific  gravity  being  0"967.  In  its 
chemical  relations  it  is  an  indifferent  oxide,  that  is,  it  has  neither  acid  nor 
basic  properties.  It  has  been  liquefied  b}'  the  cold  produced  by  its  own 
expansion  under  a  compression  of  300  atmospheres  at  -  29°  C. 


90 


PREPARATION  OF  CARBONIC  OXIDE. 


67.  A"  very  instnictive  process  for  obtaining  carbonic  oxide,  consists  in  heating 
cry.itallised  oxalic  acid  with  three  times  its  weight  of  oil  of  vitriol.  If  the  gas  be 
collected  over  water  (fig.  87),  and  one  of  the  jars  be  shaken  with  a  little  lime-water, 
the  milkiness  imparted  to   the  latter  will    indicate  abundance  of  carbon  dioxide  ; 

whilst,  on  removing  the  glass 
plate,  and  ap))lying  a  light, 
the  carbonic  oxide  will  burn 
with  its  charactistic  blue  flame. 
The  gas  thus  obtained  is  a 
mixture  of  equal  volumes  of 
carbonic  oxide  and  carbonic  acid 
gases.  Crystallised  oxalic  acid 
is  represented  by  the  formula 
C2Hij04.2Aq.,  and  if  the  water 
of  crystallisation  be  left  out  of 
consideration,  its  decomposition 
may  be  represented  by  the  equa- 
tion— 

C2H2O4  =  H^O  -(-  CO  -f  CO,, 

the  change  being  determined  by 
the  attraction  of  the  oil  of  vitriol 
for  water.     To  obtain  pure  car- 
bonic oxide,  the  mixture  of  gases  must  be  passed  through  a  bottle  containing  solution 
of  potash,  to  absorb  the  carbonic  acid  gas  (fig.  88). 

But  pure  carbonic  oxide  is  much  more  easily  obtained  by  the  action  of  sulphuric 
acid   upon   crystallised  potassium   ferrocyanide   (yellow  prussiate   of  potash)  at  a 


Fig.  87. 


';^4^ 


-r'— 


Fig.  88. — Preparation  of  carbonic  oxide. 

moderate  heat.  Since  the  gas  contains  small  quantities  of  sulphurous  and  carbonic 
aciil  gases,  it  must  be  passed  through  solution  of  potash  if  it  be  required  perfectly 
pure.     The  chemical  change  which  occurs  in  this  process  is  expressed  thus  : — 


K4CfiN«Fe  +  6H.p  -t-  6H.,S04 
Potassinm 
ferrocyanide. 


6C0  +  2K,S04  -f  3(NH4)2S04  -f  FeSG4 
Potassium         Ammonium  Ferions 

sulpliate.  sulpiiate.  sulplmte. 


Ten  grammes  of  crystallised  ferrocyanide,  with  135  grammes  of  sulphuric  acid 
(sp.  gr.  1-84)  and  13  grammes  of  watei-,  will  give  about  3^  litres  of  carbonic  oxide. 

If  the  boiling  is  continued  after  the  evolution  of  CO  has  ceased,  much  sulphurous 
acid  gas  is  disengaged  (2FeS04-f  2H.^S04=Fe.^(S04)3-f  2HiO-f-S02). 

68.  To  demonstrate  the  production  of  carbonic  acid  gas  during  the  combustion  of 
carbonic  oxide,  a  jar  of  the  gas  is  closed  with  a  glass  plate,  and  after  placing  it  upon 


CARBONIC  OXIDE.  91 

the  table,  the  plate  is  slipped  aside  and  a  little  lime-water  quickly  poured  into  the 
jar.  On  shaking,  no  niilkiuess  indicative  of  carbonic  acid  gas  should  be  perceived. 
The  plate  is  then  removed  and  the  gas  kindled.  On  replacing  the  plate  and  shaking 
the  j,\i;  an  abundant  precipitation  of  calcium  carbonate  will  take  place. 

When  carbonic  oxide  is  passed  through  a  red  hot  porcelain  tube,  a  portion  of  it  is 
decompose  1  into  carbonic  acid  gas  and  carbon ;  and  when  the  experiment  is  conducted 
without  special  arrangements,  the  carbonic  oxide  is  reproduced  as  the  temperature  of 
the  gas  falls.  But  by  passing  through  the  centre  of  the  porcelain  tube  a  brass  tube, 
through  which  cold  water  is  kept  running,  the  decomposition  has  been  demonstrated 
by  the  deposition  of  carbon  upon  the  cooled  tube,  and  by  collecting  the  carbonic  acid 
gas  formed. 

Carbonic  acid  gas  is  also  decomposed  by  intense  heat  into  carbonic  oxide  and 
oxygen  ;  but  if  these  gases  be  allowed  to  cool  down  slowly  in  contact,  they  recombine. 
The  gas  drawn  from  the  hottest  region  of  a  blast-furnace  (see  Iron),  and  rapidly 
cooled,  so  as  to  prevent  recombination,  was  found  to  contain  laoth  carbonic  oxide  and 
oxygen. 

According  to  Brodie,  carbonic  acid  gas  is  partially  decomposed  into  carbonic  oxide 
and  oxygen  by  electric  inductive  discharge  (p.  54),  and  |  of  the  oxygen  assumes  the 
form  of  ozone. 

By  passing  a  pellet  of  phosphorus  up  into  carbonic  acid  gas,  over  mercury,  in  a 
eudiometer,  and  passing  electric  sparks  for  some  days,  the  gas  has  been  entirely 
decomposed,  au  equal  volume  of  carbonic  oxide  being  left. 

The  reducing  action  of  carbonic  oxide  upon  metallic  oxides,  at  high  temperatures, 


Fig.  89. — Reduction  of  oxide  of  copper  by  carbonic  oxide. 

may  be  illustrated  by  passing  the  pure  gas  from  a  bag  or  gas-holder,  first  through 
bottle  of  lime-water  (B,  fig.  89),  to  prove  the  absence  of  carbonic  acid  gas,  then  over 
oxide  of  copper,  contained  in  the  tube  0,  and  afterwards  again  through  lime-water 
in  D.  When  enough  gas  had  been  passed  to  expel  the  air,  heat  may  be  apydied  to 
the  tube  by  the  gauze-burner  E,  when  the  formation  of  carbonic  acid  gas  will  be  im- 
mediately shown  by  the  second  portion  of  lime-water,  and  the  black  oxide  of  copper 
will  be  reduced  to  red  metallic  copper. 

If  precipitated  psroxide  of  iron  be  substituted  for  oxide  of  copper,  iron  in  the  state 
of  black  powder  will  be  left,  and  if  allowed  to  cool  in  the  stream  of  gas,  will  take  fire 
when  it  is  shaken  out  into  the  air,  becoming  reconverted  into  the  peroxide  {iron 
jyyrophoims). 

69.  Comjxmfion  by  volume  oj  carbonic  oxide  and  carbon  dioxide. — 
AVhen  carbon  burns  in  oxygen,  the  volume  of  the  carbon  dioxide  produced 
is  exactly  equal  to  that  of  the  oxygen,  so  that  one  volume  of  oxygen  fur- 
nishes one  volume  of  carbonic  acid  gas,  or  a  molecule  (two  volumes,  see 
p.  2)  of  carbonic  acid  gas  contains  two  volumes  of  oxygen. 

When  one  volume  of  carbonic  acid  gas  (containing  one  volume  of 
oxygen)  is  passed  over  heated  carbon,  it  yields  two  volumes  of  carbonic 
oxide  ;  hence  two  volumes,  or  one  molecule,  of  this  gas  contain  one 
volume  of  oxygen. 

Specific  gravity  (to  H)  of  COg,  i.e.,  weight  of  one  volume,  .         22 

Specific  gravity  (to  H)  or  weight  of  one  volume,  of  0,  .         .         16 

Weight  of  carbon  in  one  volume  of  CO.,,     .....  6 


92 


ACETYLENE. 


Hence,  a  molecule,  two  volumes  or  44  parts  by  weight,  of  COj,  contains  12  parts 
by  weight  of  carbon. 


Specific  gravity  (to  H),  or  weight  of  one  volume,  of  CO,  =  14 
Weight  of  two  volumes  of  CO,        ..... 
,,  one  volume  ot  0, 


28 
16 


12 


Weight  of  carbon  in  two  volumes  (or  one  molecule)  of  CO, 

70.  The  atomic  iceifjht  of  carbon  is  taken  as  12,  since  this  is  the 
.smallest  weight  of  carbon  which  can  be  found  in  two  volumes  of  any  of 
its  gaseous  compounds. 


Compounds  of  Carbon  and  Hyduogen. 

71.  No  two  other  elements  are  capable  of  occurring  in  so  many  different 
forms  of  combination  as  carbon  and  hydrogen.  The  lnjdrccarhons,  as 
their  compounds  are  generally  designated,  include  most  of  the  inflammable 
gases  wliieh  are  commonly  met  with,  and  a  great  number  of  the  essential 
oils,  naplithas,  and  other  useful  substances.  There  is  reason  to  believe 
tliat  all  these  bodies,  even  such  as  are  found  in  the  mineral  kingdom, 
have  been  originally  derived  from  vegetable  sources,  and  their  history 
belongs,  therefore,  to  the  department  of  organic  chemistry.  The  three 
simplest  examples  of  such  compounds  will,  however,  be  brought  forward 
in  this  place  to  afford  a  general  insight  into  the  mutual  relations  of  these 
two  important  elements.     Their  names  and  composition  are — 


Foi-mulse. 
(2  volumes.) 

Parts  by  Weight 

Acetylene, 
Marsh  gas,     . 
Olefiant  gas,  . 

C,H, 
CH^ 
C,H, 

C 

24 

12 
24 

H 

2 

4 
4 

72.  Acetylene* — When  very  intensely  heated,  carbon  is  capable  of 
combining  with  hydrogen  to  form  acetylene.  The  required  temperature 
is  procured  hy  means  of  a  powerful  galvanic  battery,  to  the  terminal  wires 
of  which  two  pieces  of  dense  carbon  are  attached,  and  the  voltaic  discharge 
is  allowed  to  take  place  between  them  in  an  atmosphere  of  hydrogen. 
The  experiment  possesses  little  practical  importance,  because  but  little 
acetylene  is  formed  in  proportion  to  the  force  employed,  but  its  theoretical 
interest  is  very  great,  since  it  is  the  first  step  in  the  production  of  organic 
substances  by  the  direct  synthesis  of  mineral  elements ;  acetylene  (CgHg) 
being  convertible  into  olefiant  gas  (CgH^),  this  last  into  alcohol  (C.2HgO), 
and  alcohol  into  a  very  large  number  of  organic  products. 

Acetylene  is  constantly  found  among  the  products  of  the  incomplete 
corabustiou  and  destructive  distillation  of  substances  rich  in  carbon  ; 
hence  it  is  always  present  in  small  quantity  in  coal  gas,  and  may  be  pro- 
duced in  abundance  by  passing  the  vapour  of  ether  through  a  red  hot 
tube.     The  character  by  which  acetylene  is  most  easily  recognised  is  that 

*  T.oug  known  as  Mumene,  having  been  obtained  in  1836  by  the  action  of  water  upon  a 
ioniiioun<l  contiining  carbon  and  potassium,  produced  during  the  preparation  of  that 
metal.  The  name  acetylene  is  derived  from  the  hypothetical  radial  acetyle  (C2H3),  to 
which  acetylene  bears  the  same  relation  as  ethylene  (CjHj)  does  to  ethyle  (CjHs). 


PREPARATION  OF  ACETYLENE. 


93 


of  producing  a  fine  red  precipitate  in  an  ammoniacal  solution  of  cuprous 
chloride  (subcliloride  of  copper). 

The  most  convenient  process  for  preparing  a  quantity  of  this  precipitate,  is  tliat 
in  wliicli  the  acetylene  is  produced  by  the  imperfect  combustion  taking  place  when 
a  jet  of  atmospheric  air  is  allowed  to  burn  in  coal  gas. 

An  adapter  (A,  fig.  90),  is  connected  at  its  narrow  end  with  the  pipe  supplying 
coal  gas.  The  wider  opening  is  closed  by 
a  bung  with  two  holes,  one  of  which 
receives  a  juece  of  brass  tube  (B)  about 
three-quarters  of  an  inch  wide  and  7  inches 
long,  and  in  the  other  is  inserted  a  glass 
tube  (C)  which  conducts  the  gas  to  the 
bottom  of  a  sejMrating  funnel  (D).  The 
lower  opening  of  the  brass  tube  B  is  closed 
with  a  cork,  through  which  passes  the 
glass-tube  E  connected  with  a  gas-holder 
or  bag  containing  atmospheric  air.  To 
commence  the  operation,  the  gas  is  turned 
on  through  the  tube  F,  and  when  all  air 
is  supposed  to  be  expelled,  the  tube  E  is 
withdrawn,  together  with  its  cork,  and  a 
light  is  applied  to  the  lower  opening  of 
the  brass  tube,  the  supply  of  coal  gas 
being  so  regulated  that  it  shall  burn  with 
a  small  liame  at  the  end  of  the  tube.  A 
feeble  current  of  air  is  then  allowed  to 
issue  from  the  tube  E,  which  is  passed  up 
through  the  flame  into  the  adapter,  where 
the  jet  of  air  continues  to  burn  in  the 
coal  gas,*  and  may  be  kept  burning  for 
hours  with  a  little  attention  to  the  pro- 
portions in  which  the  gas  and  air  are 
supplied.  A  solution  of  cuprous  chloride 
in  ammonia  is  poured  into  the  separating 
iunnel  through  the  lateral  opening  G,  so 
that  the  imperfectly  burnt  gas  may  pass 
through  it,  when  the  cuprous  acetylide 


Fig.  90. — Preparation  of  cuprous  acetylide. 


is  precipitated  in  abundance.  When  a  sufficient  quantity  has  been  formed,  or  the 
coppei'  solution  is  exhausted,  the  liquid  is  run  out  through  the  stopcock  (H)  on  to  a 
filter,  and  replaced  by  a  fresh  portion.  The  precipitate  may  be  rinsed  into  a  flask 
provided  with  a  funnel  tube  and  delivery  tube,  allowed  to  stibside,  the  water  decanted 
from  it,  and  some  strong  hydrochloric  acid  poured  in  through  the  funnel.  On  heating, 
the  acetylene  is  evolved,  and  may  be  collected,  either  over  water,  or  more  economically 
in  a  small  gas-bag,  or  in  a  mercurial  gas-holder.  To  obtain  a  pint  of  thft  gas,  as 
much  of  the  moist  cojjper  precipitate  is  required  as  will  measure  about  6  ounces  after 
settling  down.     Such  a  quantity  may  be  prepared  in  about  six  hours. 

A  solution  of  cuprous  chloride  suitable  for  this  experiment  is  conveniently  pre-, 
pared  in  the  following  manner: — 500  grains  of  black  oxide  of  copper  are  dissolved 
in  7  measured  ounces  of  common  hydrochloric  acid,  in  a  flask,  and  boiled  for 
about  twenty  minutes  with  400  grains  of  copper  in  filings  or  fine  turnings.  The 
brown  solution  of  cuprous  chloride  in  hydrochloric  acid,  thus  obtained,  is  poured  into 
about  3  pints  of  water  contained  in  a  bottle ;  the  white  precipitate  (cuprous 
chloride)  is  allowed  to  subside,  the  water  drawn  off"  with  a  siphon,  and  the  precipitate 
rinsed  into  a  20-ounce  bottle,  wliich  is  then  quite  filled  with  water  and  closed 
with  a  stopper.  When  the  precipitate  has  again  subsided,  the  water  is  drawn  off, 
and  4  ounces  of  powdered  chloride  of  ammonium  are  introduced,  the  bottle  being 
again  filled  up  with  water,  closed  and  shaken.  The  cuj)rous  chloride  is  entirely 
dissolved  by  the  chloride  of  ammonium,  but  would  be  precipitated  if  more  water 
were  added.  When  required  for  the  precipitation  of  acetylene,  the  solution  may  be 
mixed  with  about  one-tenth  of  its  bulk  of  strong  ammonia  ('880),  which  may  be 
poured  into  the   separating  funnel  (D)  before  the   copper  solution   is  introduced. 

*  It  is  advisable  to  attach  a  piece  nf  thin  platinum  wire  to  the  mouth  of  the  glass  tube 
to  render  the  flame  of  the  air  more  visible. 


94:  PR0PEETIE8  OF  ACETYLENE. 

Four  measured  ounces  of  the  solution  are  sufficient  for  oue  charge,  and  yield,  in 
three  hours,  about  3  measured  ounces  of  the  moist  precipitate.  The  blue  solution 
of  amnioniacal  cupric  chloride,  filtered  from  the  red  precipitate,  may  be  rendered 
serviceable  again  by  being  shaken,  in  a  stoppered  bottle,  with  precipitated  copper, 
prepared  by  reducing  a  solution  of  sulphate  of  copper,  acidulated  with  hydrochloric 
acid,  with  a  plate  of  zinc. 

The  red  precipitate  is  called  cnpros-ethenyle  hydrate,  and  its  formation 
is  explained  by  tlie  equations  (1)  C2H2  +  CugClg  +  NHy  =  CgHCu.jCl 
+  NH.Cl ;  (2)  C2HCU2CI  +  NH3  +  H^O  =  C^HCu.^OH  +  NH^CL 

If  the  acetylene  copper  precipitate  be  collected  on  a  filter,  washed,  and 
dried  either  by  mere  exposure  to  the  air,  or  over  oil  of  vitriol,  it  will  be 
found  to  explode  with  some  violence  when  gently  heated,  and  it  is  said 
that  the  accidental  formation  of  this  compound  in  copper  or  brass  pipes, 
through  which  coal  gas  passes,  has  occasionally  given  rise  to  explosions. 

When  acetylene  is  passed  through  solution  of  nitrate  of  silver,  a  white  curdy  pre- 
cipitate is  formed,  resembling  chloride  of  silver  in  appearance,  but  insoluble  in 
ammonia  (which  turns  it  yellow)  as  well  as  in  nitric  acid.  It  may  be  obtained  by 
allowing  the  imperfectly  burnt  gas  from  the  apparatus  in  fig.  90  to  pass  through 
nitrate  of  silver. 

It  may  be  more  easily  prepared  by  suspending  a  funnel  over  a  Bunsen  burner  which 
has  caught  fire  inside  the  tube,  and  drawing  the  products  of  imperfect  combustion,  by 
means  of  an  aspirator,  through  a  solution  of  silver  nitrate.  This  precipitate  may 
also  be  used  for  the  preparation  of  acetylene,  by  heating  it  with  hydrochloric  acid. 

When  this  precipitate  is  washed  and  allowed  to  dry,  it  is  violently  explosive  if 
heated  or  struck.*  A  minute  fragment  of  it  placed  on  a  glass  plate,  and  touched 
with  a  red  hot  wire,  detonates  loudly  and  shatters  the  glass  like  fulminate  of  silver. 
The  explosive  silver  compound  is  the  argent-etJi€7ii/le  hydrate,  CjHAgjOH,  the  chloride 
corresponding  to  it  (C^HAgjCl)  being  precipitated  when  acetylene  is  passed  through 
a  solution  of  chloride  of  silver  in  ammonia.  In  a  solution  of  hyijosulphite  of  gold 
and  sodium,  acetylene  gives  a  yellowish  very  explosive  precipitate. 

When  potassium  or  sodium  is  heated  in  excess  of  acetylene,  it  is  said  that  one- 
half  of  the  hydrogen  is  displaced  by  the  metal,  forming  acetylide  of  potassium 
(CjHK)  or  of  sodium  (CjjHNa),  a  portion  of  the  acetylene  being  converted  into  olefiant 
gas  (C.2H4)  by  combination  with  the  displaced  hydrogen.  When  heated  to  dull  red- 
ness, sodium  completely  decomposes  acetylene,  CgNa.^  lieing  obtained.  Both  these 
sodium  compounds  are  violently  decomposed  by  water,  acetylene  being  reproduced. 

The  copious  formation  of  acetylene  during  the  imperfect  combustion  of  ether,  is 
very  readily  shown  by  introducing  a  few  drops  of  ether  into  a  test-tube,  adding  a 
little  amnioniacal  solution  of  cuprous  chloride,  kindling  the  ether-vapour  at  the 
mouth  of  the  tube,  and  inclining  the  latter  so  as  to  expose  a  large  surface  of  the 
copper  solution,  when  a  large  quantity  of  the  red  cuprous  acetylide  is  produced.  If 
nitrate  of  silver  be  substituted  for  the  copper  solution,  the  white  precipitate  of  oxide 
of  argent-ethenyle  is  formed  abundantly. 

Acetylene  has  been  found  accompanying  the  vapour  of  hydrocyanate  of  ammonia 
produced  by  the  action  of  ammonia  on  red  hot  charcoal. 

It  has  also  been  prepared  by  distilling  ethene  dibromide  with  alcoholic  solution  of 
potash;  CjH4Br2  +  2KHO  =  C2Ha  +  2KBr  +  2H40;  and  by  the  action  of  sodium  on 
chloroform  ;  2CHCI3  +  Nag = 6Na01  +  C^Hj. 

Acetj^lene  is  a  colourless  gas  having  a  peculiar  odour,  recalling  that  of 
the  geranium,  which  is  always  perceived  where  coal  gas  is  undergoing 
imperfect  combustion.  It  burns  with  a  very  bright  smoky  flame.  Its 
most  remarkable  property  is  that  of  inflaming  spontaneously  when  brought 
in  contact  with  clilorine.  If  a  jet  of  the  gas  be  allowed  to  pass  into  a 
bottle  of  chlorine,  it  will  take  fire  and  burn  with  a  red  flame,  depositing 
much  carbon.  When  chlorine  is  decanted  up  into  a  cylinder  containing 
acetylene  standing  over  water,  a  violent    explosion  immediately  takes 

*  If  the  precipitate  is  prepared  from  a  slightly  ammoniacal  solution  of  nitrate  of  silver, 
it  is  more  sensitive  to  a  blow. 


OLEFIANT  GAS. 


95 


place,  attended  with  a  vivid  flash,  and  separation  of  a  large  amount  of 
carbon ;  C0H2  +  Cl^  =  Cg  +  2HC1 . 

When  acetylene  is  passed  into  water,  it  is  absorbed  in  sufficient  quan- 
tity to  impart  a  strong  smell  to  the  water,  and  to  yield  a  decided  precipi- 
tate with  ammoniacal  cuprous  chloride  and  with  silver  nitrate. 

The  action  of  heat  upon  acetylene  is  very  remarkable  and  instructive, 
since  it  results  in  the  formation  of  a  complex  body  from  one  which  is  less 
complex  in  composition.  When  heated  in  a  glass  tube  for  half  an  hour 
to  the  point  at  which  the  glass  began  to  soften,  it  was  found  to  be  reduced 
to  one-fifth  of  its  original  volume,  the  greater  portion  of  it  having  been 
converted  into  a  liquid  hydrocarbon,  ethenyle  -  benzene  or  styrolene, 
C^Hj.CgH^,  hitherto  obtained  from  the  vegetable  gum-resin  known  as 
storax.  The  remaining  gas  was  chiefly  hydrogen  (a  little  carbon  having 
separated)  with  a  little  olefiant  gas.  Benzene  (CgHg)  has  been  formed,  in 
a  similar  way,  from  three  molecules  of  acetylene.  When  heated  in  contact 
with  coke  or  iron,  the  bulk  of  the  acetylene  is  decomposed  into  its 
elements. 

By  suspending  the  acetylene  copper  precipitate  in  solution  of  ammonia, 
and  heating  with  a  little  granulated  zinc,  Berthelot  has  induced  the 
acetylene  to  combine  with  the  {nascent)  hydrogen  to  form  olefiant  gas 
(C,H,). 

When  a  mixture  of  acetylene  with  nitrogen  is  acted  on  by  a  succession 
of  electric  sparks,  hydrocyanic  or  prussic  acid  (HCN)  is  produced  by  their 
direct  union. 

73.  Olefiant  gas  or  ethylene  (C2H^  =  28  parts  by  weight  =2  volumes). — 
This  gas  is  found  in  larger  quantity  than  acetylene,  among  the  products 
of  the  action  of  heat  upon  coal 
and  other  substances  rich  in 
carbon,  and  it  is  one  of  the  most 
important  constituents  of  the 
illuminating  gases  obtained  from 
such  materials. 

Olefiant  gas  may  readily  be 
prepared  by  the  action  of  strong 
sulphuric  acid  (oil  of  vitriol, 
HqSO^)  upon  alcohol  (spirit  of 
wine,  C,H,0). 

Two  measures  of  oil  -of  vitriol  are 
introduced  into  a  flask  (fig.  91),  and 
one  measure  of  alcohol  is  gradually 
poured  in,  the  flask  being  agitated 
after  each  addition  of  the  acid;  much 
heat  is  evolved,  and  there  would  be  danger  in  mixing  large  volumes  suddenly.*  On 
applying  a  moderate  heat,  the  liquid  will  darken  in  colour,  effervescence  will  take 
place,  and  the  gas  may  be  collected  in  jars  flUed  with  water.  When  the  mixture  has 
become  thick,  and  the  evolution  of  tlie  gas  is  slow,  the  end  of  the  tube  must  be 
removed  from  the  water  and  the  lamp  extinguished.  Three  measured  ounces  of  spirit 
of  wine  generally  give  about  500  cubic  inches  of  olefiant  gas. 

The  gas  will  be  found  to  have  a  very  peculiar  odour,  in  which  that  of  ether  and  of 
sulphurous  acid  gas  are  perceptible.  One  of  the  jars  may  be  closed  with  a  glass  plate, 
and  placed  upon  the  table  with  its  mouth  upwards ;  on  the  approach  of  a  flame,  the 
gas  will  take  tire,  burning  with  a  bright  white  flame  characteristic  of  olefiant  gas.  and 


Fig.  91.- — Preparation  of  olefiant  gas. 


*  If  methylated  spirit  be  employed,  the  mixture  will  have  a  dark  red-brown  colour. 


96 


OLEFIANT  GAS. 


Fiff.  92. 


seen  to  best  advantage  when,  after  kindling  the  gas,  a  stream  of  water  is  poured 

down  into  the  jar  in  order  to  displace  the  gas  (fig.  92). 

Another  jar  of  the  gas  may  be  well  washed  by 
transfening  it  repeatedly  from  one  jar  to  another 
under  water,  a  little  solution  of  potash  may  then  be 
poured  into  it,  and  the  jar  violently  shaken,  its 
mouth  being  covered  with  a  glass  plate;  the  potash 
will  remove  all  the  sulphurous  acid  gas,  and  the  gas 
will  now  exhibit  the  peculiar  faint  odour  which 
belongs  to  olefiant  gas. 

The  purified  gas  may  be  transferred,  under  water, 
to  another  jar,  kindled  and  allowed  to  burn  out;  if 
a  little  lime-water  be  then  shaken  in  the  jar,  its 
turbidity  will  indicate  the  presence  of  carbonic  acid 
gas,  which  is  produced  together  with  water,  when 
olefiant  gas  burns  in  air:  C3H4  +  Oj  =  2CO, +  2HjO. 

Ethylene  has  been  liquefied  by  a  pressure  of  63 
atmospheres  at  10°  C. 

On  comparing  the  composition  of  olefiant 
gas  (CgH^)  with  that  of  alcohol  (CgHgO),  it  is 
evident  that  the  former  may  be  supposed  to 
be  produced  from  the  latter  by  the  abstraction 
of  a  molecule  of  water  (HgO)  which  is  removed 
by  the  sulphuric  acid,  though  other  secondary 
changes  take  place,  resulting  in  the  separation 
of  carbonaceous  matter  and  the  production  of 
sulphurous  acid  gas.  A  more  complete  explanation  of  the  action  of 
sulphuric  acid  upon  alcohol  must  be  reserved  for  the  chemical  history  of 
this  compound. 

Olefiant  gas  derives  its  name  from  its 
property  of  uniting  with  chlorine  and 
bromine  to  form  oily  liquids,  a  circum- 
stance which  is  applied  for  the  determina- 
tion of  the  proportion  of  this  gas  present 
in  coal  gas,  upon  which  great  part  of  the 
illuminating  value  of  coal  gas  depends. 
The  compound  with  chlorine  (CgH^Clg)  is 
known  as  Dutch  liquid,  having  being 
discovered  by  Dutch  chemists,  and  is 
remarkable  for  its  resemblance  to  chloro- 
form in  odour. 

When  etheue-dibromide  (CgH^Brj)  is 
heated  with  an  alcoholic  solution  of  pot- 
ash, it  yields  acetylene. 

To  exhibit  the  formation  of  Dutch  liquid,  a 

quart  C3'linder  (fig.  93)  is  half  tilled  with  olefiant 

gas,   and  half  with  chlorine,   which  is   rapidly 

passed  up  into  it,  from  a  bottle  of  the  gas,  under 

water.     The  cylinder  is  then  closed  with  a  glass 

plate,  and  supported  with  its  mouth  downwards 

under  water  in   a  se2)araiing  ftmncl  furnished 

with  a  glass  stopcock.     The  volume  of  the  mixed 

gases  begins  to  diminish  immediately,  drops  of 

fig.  yd,  ^j^  being  formed  upon  the  side  of  the  cylinder 

and  the  surface  of  the  water.     As  the  drops  increase,  they  fall  to  the  bottom  of  the 

funnel.     Water  must  be  poured  into  the  funnel  to  replace  that  which  rises  into  the 

cylinder,  and  when  the  whole  of  the  gas  has  disappeared,  the  oil  may  be  drawn  out  of 


OLEFIANT  GAS. 


97 


fl 


the  funnel  through  th&  stopcock  into  a  test-glass,  in  which  it  is  shaken  with  a  little 
potash  to  absorb  any  excess  of  chlorine.  The  fragrant  odour  of  the  Dutch  liquid  will 
then  be  perceived,  especially  on  pouring  it  out  into  a  shallow  dish. 

In  applying  this  principle  to  the  measurement  of  the  illuminating 
hydrocarbons  in  coal  gas,  daylight  must  be  excluded,  or  an  error 
would  be  caused  by  the  union  of  the  free  hydrogen  with  the  chlorine 
or  bromine.  The  hrmnine  test  may  be  applied  in  the  tube  repre- 
sented in  fig.  94.  The  gas  to  be  examined  is  measured  over  water 
in  the  divided  limb  a,  with  due  attention  to  temperature  and 
pressure ;  the  tube  being  held  perpendicularly,  the  limb  b  will  remain 
tilled  with  water,  so  that  gas  cannot  escape  nor  air  enter.  A  drop 
or  two  of  bromine  is  poured  into  this  limb,  which  is  then  depressed 
beneath  the  water  in  the  pneumatic  trough,  and  closed  by  the 
stopper  c.  On  shaking  the  gas  with  the  water  and  bromine,  the 
latter  will  absorb  the  illuminating  hydrocarbons;  and  if  the  tube 
be  again  opened  under  water,  the  volume  of  the  gas  in  a  \yill  be  found 
to  have  diminished,  and  the  diminution  gives  an  approximate  esti- 
mate of  the  olefiant  gas  and  other  illuminating  hydrocarbons. 

A  very  instructive  experiment  consists  in  tilling  a  three-pint 
cylinder  one-third  full  of  olefiant  gas,  then  rapidly  filling  it  up, 
under  water,  with  two  pints  of  chlorine,  closing  its  mouth  with  a 
glas^  plate,  shaking  it  to  mix  the  gases,  slipping  the  plate  aside  and 
applying  a  light,  when  the  mixture  burns  with  a  red  flame  which 
passes  gradually  down  the  cylinder,  and  is  due  to  the  combination  of 
the  hydrogen  with  the  chlorine,  the  whole  of  the  carbon  being 
separated  in  the  solid  state — 

C2H4  +  Cl4  =  4HCl  +  C2. 

"When  olefiant  gas  is  subjected  to  the  action  of  high  temperatures,  as 
by  passing  through  heated  tubes,  one  portion  is  decomposed  into  marsh 
gas  (CH^)  with  separation  of  carbon,  whilst  another  portion  yields 
acetylene  (CgHg)  and  hydrogen  ;  these  decompositions  will  be  found  to 
be  of  great  importance  in  the  manufacture  of  coal  gas. 

The  action  of  heat  upon  olefiant  gas  is  most  conveniently  shown  by  exposing  it  to 
the  spark  from  an  induction-coil. 

The  gas  is  confined  in  a  tube  (A,  fig.  95)  which  is  placed  in  a  cylindrical  jar  (B) 
containing  mercury.  Through  the  mercury  passes  a  copper 
wire  (C)  thrust  through  a  glass  tube  (D)  to  insulate  it  from 
the  mercury ;  this  wire  is  connected  with  one  of  the  wires 
(E)  from  the  induction-coil,  whilst  the  other  (F)  is  allowed 
to  dip  into  the  mercury  contained  in  the  cylinder.  On 
putting  the  coil  in  action  (with  two  or  three  cells  of  Grove's 
battery),  the  spark  will  pass  between  the  extremity  (C)_of  the 
insulated  copper  wire  and  the  surface  of  the  mercury  in  the 
tube,  decomposing  the  olefiant  gas  in  its  passage,  and  causing 
a  separation  of  carbon,  which  sometimes  forms  a  conducting 
communication,  and  allows  the  current  to  pass  without  a 
spark.  This  may  be  obviated  by  reversing  the  current,  or 
by  gently  shaking  the  tube. 

The  olefiant  gas  will  expand  to  nearly  twice  its  former 
volume,  so  that  the  tube  will  gradually  rise  in  the  mercury, 
but  the  same  distance  may  always  be  maintained  for  the 
passage  of  the  spark. 

To  show  the  production  of  acetylene,  another  arrangement 
will  be  found  convenient  (fig.  96).  A  globe  with  four  necks 
is  employed;  tlu'ough  two  of  these  necks  are  passed,  air- 
tight with  perforated  corks,  the  copper  wires  connected  with  the  induction-coil.  A 
third  neck  receives  a  tube,  conveying  olefiant  gas  from  a  gas-holder,  whilst  from  the 
fourth  proceeds  a  tube  dipping  to  the  bottom  of  a  small  cylinder.  When  the  whole 
of  the  air  has  been  displaced  by  olefiant  gas,  a  solution  of  cuprdtis  chloride  in  ammonia 
is  poured  into  the  cylinder,  and  the  gas  allowed  to  bubble  through  it,  when  the 
absence  of  acetylene  will  be  shown  by  there  being  no  red  compound  formed.  As  soon, 
however,  as  the  spark  is  passed,  the  red  precipitate  will  appear,  and,  in  a  very  few 

G 


Fig.  95. 


98 


PREPARATION  OF  MARSH  GAS. 


minutes,  a  large  quantity  will  be  deposited.     Coal  gas  may  be  employed  instead  of 
olefiant  gas,  but  of  course  less  of  the  copper  compound  will  be  obtained. 

74.  Marsh  gas  or  light  carhuretted  hydrogen  (CH4  =  16  parts  by  weight 
=  2   volumes). — This  hydrocarbon  is  found   in  nature,  being  produced 

wherever  vegetable  matter 
is  undergoing  decomposition 
in  the  presence  of  moisture. 
The  bubbles  rising  from 
stagnant  pools,  when  col- 
lected and  examined,  are 
found  to  contain  marsh  gas 
mixed  with  carbonic  acid 
gas,  and  there  is  reason  to 
believe  tbat  these  two 
gases  represent  the  principal 
forms  in  which  the  hydro- 
gen and  oxygen  respectively 
were  separated  from  wood 
during  the  process  of  its 
conversion  into  coal.  This 
would  account  for  the  con- 
stant presence  of  this  gas  in 
the  coal  formations,  where 
it  is  usually  termed  fire- 
damp. It  is  occasionally 
found  pent  up  under  pres- 
sure between  the  layers  of 
coal,  and  the  pores  of  the 
latter  are  sometimes  so  full 


Fig.  96.  — Preparation  of  cuprous  acetylide  from 
olefiant  gas. 


of  it  that  it  may  be  seen  rising  in  bubbles  when  the  freshly  hewn  coal  is 
thrown  into  water.  Perhaps  a  similar  origin  is  to  be  ascribed  to  the  liquid 
hydrocarbons  chemically  similar  to  marsh  gas,  which  are  found  so  abund- 
antly in  Pennsylvania  and  Canada,  and  are  known  by  the  general  name 
of  petroleum.  From  certain  gas-springs  in  Pennsylvania,  marsh  gas, 
olefiant  gas,  and  ethyle  hydride,  CgHg,  are  discharged  at  very  high  pressure, 
and  are  employed  for  heating  and  lighting. 

Marsh  gas  is  obtained  artificially  by  the  following  process  : — 

500  grains  of  dried  sodium  acetate  are  finely  powdered  and  mixed  in  a  mortar,  with 
200  grains  of  solid  potash,  and  300  grains  of  powdered  quicklime  (or  with  500  grains 
of  the  mixture  of  calcium  hydrate  and  sodium  hydrate,  which  is  sold  as  soda-lime). 
The  mixture  is  heated  in  a  Florence  flask  (or  better  a  copper  tube,  for  the  alkali  cor- 
rodes the  glass)  and  the  gas  collected  over  water  (fig.  97). 

The  decomposition  will  be  evident  from  the  following  equation  : — 

NaCaHsOa     +     NaHO     =     NagCOs     +     CH4 
Sodium  acetate.       Caustic  soda.    Sodium  carbonate. 

The  marsh  gas  will  be  easily  recognised  by  its  burning  with  a  pale 
illuminating  flame,  far  inferior  in  brilliancy  to  those  of  olefiant  gas  and 
acetylene,  but  unattended  with  smoke. 

Tlie  properties  of  this  gas  deserve  a  careful  study,  on  account  of  the 
frequent  fatal  explosions  to  which  it  gives  rise  in  coal-mines,  where  it  is 
<iften  found  accumulated  under  pressure,  and  discharging  itself  with  con- 
siderable force  from  the  fissures  or  blowers  made  in  hewing  the  coal. 


PEOPERTIES  OF  MARSH  GAS. 


99 


Marsh  gas  has  no  characteristic  smell  like  coal  gas,  and  the  miner  thence 
receives  no  timely  warning  of  its  presence ;  it  is  much  lighter  than  air 
(sp.   gr,  0-5596),  and  therefore  very  readUy  diffuses*  itself  (page    18) 


Fig.  97. — Preparation  of  marsh  gas. 

through  the  air  of  the  mine,  with  which  it  forms  an  explosive  mixture  as 
soon  as  it  amounts  to  one-eighteenth  of  the  volume  of  the  air.  The  gas 
issuing  from  the  blower  would  burn  quietly  on  the  application  of  a  light, 
since  the  marsh  gas  is  not  explosive  unless  mixed  with  the  air,  when  a 
large  volume  of  the  gas  is  burnt  in  an  instant,  causing  a  sudden  evolution 
of  a  great  deal  of  heat,  and  a  consequent  sudden  expansion  or  explosion 
exerting  great  mechanical  force.  The  most  violent  explosion  takes  place 
when  1  volume  of  marsh  gas  is  mixed  with  2  volumes  of  oxygen,  since 
this  quantity  is  exactly  sufficient  to  effect  the  complete  combustion  of 
the  carbon  and  hydrogen  of  the  gas,  and  therefore  to  evolve  the  greatest 
amount  of  heat :  CH^  +  0^  =  CO,  +  2H2O.  The  calculated  pressure 
exerted  by  the  exploding  mixture  of  marsh  gas  and  oxygen  amounts  to 
37  atmospheres,  or  555  lbs.  upon  the  square  inch.  Since  air  contains 
one-fifth  of  its  volume  of  oxygen,  it  would  be  necessary  to  employ  10 
volumes  of  air  to  1  volume  of  marsh  gas  in  order  to  obtain  perfect  com- 
bustion, but  the  explosion  will  be  much  less  violent  on  account  of  the 
presence  of  the  8  "volumes  of  inert  nitrogen,  the  calculated  pressure 
exerted  by  the  explosion  being  only  14  atmospheres,  or  210  lbs.  on  the 
square  inch.  Of  course,  if  more  air  is  employed,  the  explosion  will  be 
proportionally  weaker,  until,  when  there  are  more  than  18  volumes  of 
air  to  each  volume  of  marsh  gas,  the  mixture  will  be  no  longer  explosive, 
but  will  bum  with  a  pale  flame  around  a  taper  immersed  in  it.  The  car- 
bonic acid  gas  resulting  from  the  explosion  is  called  by  miners  the  after- 
damp, and  its  effects  are  generally  fatal  to  those  who  may  have  escaped 
death  from  the  explosion  itself. 

Fortunately,  marsh  gas  requires  a  much  higher  temperature  to  inflame 
it  than  most  other  inflammable  gases ;  a  solid  body  at  an  ordinary  red 
heat  does  not  kindle  the  gas  unless  kept  in  contact  with  it  for  a  consider- 
able period ;  contact  with  flame,  or  with  a  body  heated  to  whiteness, 
being  required  to  ignite  it  instantaneously. 

*  AnselVs  fire-damp  indicator  is  an  apparatus  in  which  the  high  rate  of  diffusion  of 
marsh  gas  is  taken  advantage  of  in  order  to  detect  its  presence  in  the  air  of  mines.  Tlie 
apparatus  represented  in  fig.  14  illustrates  its  principle. 


100 


EXPLOSION  OF  MABSH  GAS  WITH  AIE. 


Fig.  98. 


If  two  strong  gas  cylinders  be  filled,  respectively,  with  mixtures  of  2  volumes 
hydrogen  with  1  volume  oxygen,  and  of  1  volume  marsh  gas  and  2  volumes  oxygen, 
it  will  be  found,  on  holding  them  with  their  mouths  downwards,  and  inserting  a  red 

hot  iron  bar  (fig.  98),  that  the  marsh  gas  mixture 
will  not  explode,  but  if  the  bar  be  transferred  at 
once  to  the  hydrogen  mixture,  explosion  will  take 
place.  A  lighted  taper  may  then  be  used  to 
explode  the  marsh  gas  and  oxygen. 

Coal  gas,  although  answering  very  well  for 
many  illustrations  of  the  properties  of  marsh 
gas,  cannot  be  used  in  this  experiment,  since 
some  of  its  constituents  inflame  at  a  far  lower 
temperature. 

In  consequence  of  the  high  temperature 
required  to  inflame  the  mixture  of  marsh 
gas  and  air,  it  is  necessary  that  the  mixture 
be  allowed  to  remain  for  an  appreciable  time  in  contact  with  the  flame 
before  its  particles  are  raised  to  the  igniting  point.  It  was  on  this 
principle  that  Stephenson's  original  safety  lamp  was  constructed,  the 
flame  being  surrounded  with  a  tall  glass  chimney,  the  rapid  draught 
through  which  caused  the  explosive  mixture  to  be  hurried  past  the  flame 
without  igniting. 

To  illustrate  this,  a  copper  funnel  holding  about  two  quarts  (fig.  99)  is  employed, 
the  neck  of  which  has  an  opening  of  about  J  inch  in  diameter.  The  funnel  being 
placed  mouth  downwards  in  the  pneumatic  trough,  the  orifice  is  closed  with  the 
finger,  and  a  half-pint  of  coal  gas  passed  up  into  the  funnel.  The  latter  is  now 
raised  from  tUe  water,  so  that  it  may  become  entirely  filled  with  air.  By  depressing 
the  funnel  to  a  considerable  depth  in  the  water,  the  aperture  being  still  closed  by 
the  finger,  the  mixture  will  be  confined  under  considerable  pressure,  and  if  a  lighted 
taper  be  held  to  the  aperture,  and  the  finger  removed,  it  will  be  found  that  the 


Fig.  9it, 


i-. 


mixture  sweeps  past  the  flame  without  exploding,  until  the  water  has  reached  the 
same  level  in  the  funnel  as  in  the  trough,  when  the  gas  cotnes  to  rest  and  explodes 
with  great  violence. 

Davy's  safety  lamp  (fig.  100)  is  an  application  of  the  principle  that 
ignited  gas  {flame)  is  extinguished  by  contact  with  a  large  surface  of  a 
good  conductor  of  heat,  such  as  copper  or  iron. 

If  a  thin  copper  wire  be  coiled  round  into  a  helix,  and  carefully  placed  over  the 
wick  of  a  burning  taper  (fig.  101),  the  flame  will  be  at  once  extinguished,  its  heat 
lifiiig  so  rapidly  transmitted  along  the  wire  that  the  temperature  falls  below  the 
point  at  which  the  combustible  gases  enter  into  combination  with  oxygen,  and  therefore 
the  combustion  ceases.     If  the  coil  be  heated  to  redness  in  a  spiiit-lamp  flame  before 


PBINCIPLE  OF  SAFETY  LAMPS. 


101 


Fiff.  101. 


placing  it  over  the  wick,  it  will  not  absti-act  the  heat  so  readily,  and  will  not  extin- 
guish the  flame.     If  a  copper  tube  were  substituted  for  the  coiled  wire,  the  same  result 

Mould  be  obtained,  and  by  employing  a  number  of  tubes 

of  ver}'  s)nall  diameter,  so  that  the  metallic  surface  may  /fif) 

be  very  large  in  proportion  to  the  volume  of  ignited  gas,  n^, 

the  most  energetic  combustion  may  be  ai'rested,  as  in  the 

case  of  Heni'niings  safety  jet,  which  consists  of  a  brass 

tube  tightly  stuffed  with  thin  copper  wires  so  as  to  leave 

very  narrow  passages,  thus  rendering  it  impossible  for 

the  oxyhydrogen  flame  at  the  jet  to  pass  bacji  and  ignite 

the  mixture  in  the  reservoir.     It  is  evident   that   the 

exposure  of  a  large  extent  of  cooling  surface  to  the  action 

of  the  flame  may  be  efl"ected  either  by  increasing  the 

length  or  by  diminishing  the  width  of  the  metallic  tubes, 
so  that  wire  gauze,  which  may  be  regarded  as  a  collection  of  very  short  tubes,  will 
form  an  effectual  barrier  to  flame,  provided  that  it  has  a  sufficient  number  of  meshes 
to  the  inch. 

If  a  piece  of  iron  wire  gauze,  containing  about  400  meshes  to  the  square  inch,  be 
depressed  upon  a  flame,  it  will  extinguish  that  portion  with  which  it  is  in  contact, 
and  the  combustible  gas  which  escapes  through  the  gauze  may  be  kindled  by  a  lighted 
match  held  on  the  upper  side.  By  holding  the  gauze  2  or  3  inches  above  a  gas  jet, 
the  gas  may  be  lighted  above  it  without  communicating  the  flame  to  the  burner  itself. 
When  blazing  spirit  is  poured  upon  a  piece  of  wire  gauze  (fig.  102),  the  flame  will 
remain  upon  the  gauze,  and  the  extinguished  spirit  will  pass  through.  A  little 
benzene  or  turpentine  may  be  added  to  the  spirit, 
so  that  its  flame  may  be  more  visible  at  a  flistance. 

The  safety  lamp  (fig.  100)  is  an  oil  lamp, 
the  flame  of  which  is  surrounded  by  a  cage 
of  iron  wire  gauze,  having  700  or  800 
meshes  in  the  square  inch,  and  made 
double  at  the  top  where  the  heat  of  the 
flame  chiefly  plays.  This  cage  is  protected 
by  stout  iron  wires  attached  to  a  ring  for 
suspending  the  lamp.  A  brass  tube  passes 
up  through  the  oil  reservoir,  and  in  this 
there  slides,  with  considerable  friction,  a  wire  bent  at  the  top,  so  that  the 
wick  may  be  trimmed  without  taking  off"  the  cage. 

If  this  lamp  be  suspended  in  a  large  jar,  closed  at  the 
top  with  a  perforated  wooden  cover  A  (fig.  103),  and 
having  an  aperture  (B)  below,  through  which  coal  gas  is 
allowed  to  pass  slorvvly  into  the  jar,  the  flame  will  be 
seen  to  waver,  to  elongate  itself  very  considerably,  and 
will  be  ultimately  extinguished,  when  the  wire  cage  will 
be  seen  to  be  filled  with  a  mixture  of  coal  gas  and  air 
burning  tranquilly  mthin  the  gauze,  which  prevents  the 
flame  from  passing  to  ignite  the  explosive  atmosphere 
surrounding  the  lamp  ;  that  an  explosive  mixture  really 
fills  the  jar  may  be  readily  ascertained  by  introducing, 
through  an  aperture  (C)  in  the  cover,  the  unprotected 
flame  of  a  taper,  when  an  explosion  will  take  place. 

This  experiment  illustrates  the  action  of  the  Davy 
lamp  in  a  mine  which  contains  fire-damp,  and  makes  it 
evident  that  this  lamp  would  afford  complete  protection 
if  carefully  used.  It  would  obviously  be  unsafe  to  allow 
the  lamp  to  remain  in  the  explosive  mixture  when  the  cage  is  filled  with  flame,  for 
the  gauze  would  either  become  sufficiently  heated  to  kindle  the  surrounding  gas  or 
would  be  oxidised  and  eaten  into  holes,  which  would  allow  the  passage  of  the  flume. 
Ifor  should  the  lamp  be  exposed  to  a  very  strong  current,  which  might  possibly  be 
able  to  carry  the  flame  through  the  meshes. 

The  great  defect  of  the  Davy  lamp  is  that  it  does  not  afford  more 


Fig.  102. 


Fig.  103. 


102  USE  OF  THE  DAVY  LAMP. 

than  a  glimmering  light,  so  that  even  if  the  miners  were  prohibited 
from  employing  any  candles,  they  would  (and  experience  has  proved 
that  they  do)  remove  the  wire  cage  at  all  risks.  The  lamp  has  been 
modified  so  as  partially  to  remove  this  defect,  by  substituting  glass  or 
talc  for  some  portions  of  the  wire  gauze.  It  is  now  usual,  however,  to 
employ  the  Davy  lamp  merely  in  order  to  test  the  state  of  the  air  in  the 
different  parts  of  the  mine  ;  for  this  purpose  the  firemen  descend  before 
the  commencement  of  work  every  morning,  and  examine  with  their 
safety  lamps  every  portion  of  the  mine,  giving  warning  to  the  miners 
not  to  approach  those  parts  in  which  any  accumulation  of  fire-damp 
(or  technically,  "  sulphur ")  is  perceived.  The  miners  then  work  with 
naked  candles,  and  it  appears  to  be  not  unusual  to  see  a  blue  flame  (or 
corpse  light)  playing  around  the  candles,  so  that  the  miners  may  become 
accustomed  to  regard  with  little  concern  the  very  indication  which  shows 
that  the  quantity  of  fire-damp  is  only  a  little  below  that  required  to 
form  an  explosive  mixture.  Whenever  naked  flames  are  used  in  the 
mine,  there  must  always  be  great  risk ;  in  most  seams  of  coal  there  are 
considerable  accumulations  of  fire-damp  ;  when  a  fissure  is  made,  the 
gas  escapes  very  rapidly  from  the  blower,  and  the  air  in  its  vicinity  may 
soon  become  .  converted  into  an  explosive  mixture.  In  mines  where 
small  quantites  of  fire-damp  are  known  to  be  continually  escaping  from 
the  coal,  ventilation  is  depended  upon  in  order  to  dilute  the  gas  with 
80  large  a  volume  of  air  that  it  is  no  longer  explosive,  and  finally  to 
sweep  it  out  of  the  mine;  but  it  has  occasionally  happened  that  the 
ventilation  has  been  interfered  with  by  a  door  having  been  left  open  in 
one  of  the  galleries,  or  by  a  passage  having  been  obstructed  through  the 
accidental  falHng  in  of  a  portion  of  the  coal,  and  an  explosive  mixture 
has  then  been  formed. 

Galloway  has  shown  that  the  presence  of  fine  dust  of  coal  in  the  air 
of  the  mine  greatly  increases  the  liability  to  explosion.  Most  combustible 
substances  mixed  in  a  finely  divided  state  with  air,  burn  so  rapidly  as 
to  produce  effects  of  explosion.  Flour  mills  have  been  destroyed  from 
this  cause  in  very  dry  weather. 

If  some  lycopodium  be  placed  in  a  glass  funnel,  the  stem  of  which  has  been  lightly 
stopped  with  wool,  and  has  two  or  three  feet  of  wide  vulcanised  tubing  attached  to 
it,  the  lycopodium  may  be  blown  out  in  a  cloud  by  a  sudden  puff  of  air,  and  if  a 
lighted  taper  be  held  in  the  cloud,  an  immense  volume  of  flame  will  be  formed. 

(Lycopodium  is  the  seed  of  the  club  moss, — Lycopodium  clavatum, — and  is  used 
for  theatrical  lightning.) 

An  ingenious  fire-damp  indicator  has  been  constructed  of  two  platinum  wires, 
which  are  heated  by  a  magneto-electric  current.  One  wire  is  sheltered  from  the  fire- 
damp, and  the  other,  being  exposed  to  it,  glows  more  strongly  on  account  of  the  slow 
combustion  of  the  fire-damp  at  the  surface  of  the  platinum  (see  Platinum).  By  a 
careful  comparison  of  the  two  wires,  it  is  said  that  *25  per  cent,  of  marsh  gas  in  air 
may  be  detected,  whilst  the  Davy  lamp  will  not  indicate  less  than  2  per  cent. 

Structure  of  Flame. 

75.  The  consideration  of  the  structure  and  properties  of  ordinary 
flames  is  necessarily  connected  with  the  history  of  olefiaut  gas  and  marsh 
gas.  Flame  may  be  defined  as  gaseous  matter  heated  to  the  temperature 
at  which  it  becomes  visible,  or  emits  light.  Solid  particles  begin,  for  the 
most  part,  to  emit  light  when  heated  to  about  1000°  F.  ;  but  gases,  on 
account  of  their  lower  radiating  power,  must  be  raised  to  a  far  higher 


ILLUMINATING  FLAMES.  103 

temperature,  and  hence  the  point  of  visibility  is  seldom  attained,  except 
by  gases  which  are  themselves  combustible,  and  therefore  capable  of 
producing,  by  their  own  combination  with  atmospheric  oxygen,  the  requi- 
site degree  of  heat.  The  presence  of  a  combustible  gas  (or  vapour), 
therefore,  is  one  of  the  conditions  of  the  existence  of  flame ;  a  diamond, 
or  a  piece  of  thoroughly  carbonised  charcoal,  will  burn  in  oxygen  with 
a  steady  glow,  but  without  flame,  since  the  carbon  is  not  capable  of  con- 
version into  vapour,  while  sulphur  burns  with  a  voluminous  flame,  in 
consequence  of  the  facility  with  which  it  assumes  the  vaporous  condition. 
It  will  be  observed,  moreover,  that  in  the  case  of  a  non-volatile  combus- 
tible, the  combination  with  oxygen  is  confined  to  the  surface  of  contact, 
Avliilst  in  the  flame  of  a  gas  or  vapour  the  combustion  extends  to  a  con- 
siderable depth,  the  oxygen  intermingling  with  the  gaseous  fuel. 

Flames  may  be  conveniently  spoken  of  as  simple  or  co7npou7id,  accord- 
ingly as  they  involve  one  or  more  phenomena  of  combustion ;  thus,  for 
example,  the  flames  of  hydrogen  and  carbonic  oxide  are  simple,  whilst 
those  of  marsh  gas  and  olefiant  gas  are  compound,  since  they  involve  both 
the  conversion  of  hydrogen  into  Avater  and  of  carbon  into  carbon  dioxide. 

It  is  obvious  that  simple  flames  must  be  hollow  in  ordinary  cases, 
such  as  that  of  a  gas  issuing  from  a  tube  into  the  air,  the  hollow  being 
occupied  by  the  combustible  gas  to  which  the  oxygen  does  not  penetrate. 

All  the  flames  which  are  ordinarily  turned  to  useful  account  are  com- 
pound flames,  and  involve  several  distinct  phenomena.  Before  examining 
these  more  particularly,  it  will  be  advantageous  to  point  out  the  conditions 
which  regulate  the  luminosity  of  flames. 

In  order  that  a  flame  may  emit  a  brilliant  light,  it  is  essential  that  it 
should  contain  particles  whiph,  either  from  their  own  nature,  or  from  the 
conditions  under  which  they  are  placed,  do  not  admit  of  indefinite  ex- 
pansion by  the  heat  of  the  flame,  but  are  capable  of  being  heated  to 
mcandescence.  Thus  the  flame  of  the  oxyhydrogen  blowpipe  (p.  39)  emits 
a  very  pale  light,  but  if  the  mixture  of  oxygen  and  hydrogen  be  restrained 
from  expanding  when  fired,  as  in  the  Cavendish  eudiometer  (p.  34),  it 
gives  a  bright  flash  ;  or  if  the  flame  be  directed  upon  some  solid  body 
little  afiected  by  the  heat,  such  as  lime,  the  light  is  very  intense. 

Phosphorus  and  arsenic  burn  with  very  luminous  flames,  in  consequence 
of  the  formation  of  very  dense  vapours  of  phosphoric  and  arsenious  oxides 
during  the  combustion ;  the  density  of  the  vapours  being  here  attended 
with  the  same  result  as  that  produced  by  the  restrained  expansion  of  the 
steam  formed  in  the  Cavendish  eudiometer. 

It  is  not  necessary  that  the  incandescent  matter  should 
be  a  product  of  the  combustion  ;  any  extraneous  solid  in 
a  finely-divided  state  Avill  confer  illuminating  power  upon 
a  flame.  Thus  the  flame  of  hydrogen  may  be  rendered 
highly  luminous  by  blowing  a  little  very  fine  charcoal 
powder  into  it,  from  the  bottle  represented  in  fig.  104. 

The  luminosity  of  all  ordinary  flames  is  due  to  the 
presence  of  highly  heated  carbon  in  a  state  of  very 
minute  division,  and  it  remains  to  consider  the  changes 
by  which  this  finely-divided  carbon  is  separated  in  the  Fig.  104. 

flame. 

A  candle,  a  lamp,  and  a  gas  burner,  exhibit  contrivances  for  procuring 
light  artificially  in  different  degrees  of  complexity,  the  candle  being  the 


104 


STRUCTURE  OF  FLAME. 


most  complex  of  the  three.  When  a  new  candle  is  lighted,  the  first 
portion  of  the  wick  is  burnt  away  until  the  heat  reaches  that  part  which 
is  saturated  with  the  wax  or  tallow  of  which  the  candle  is  composed ; 
this  wax  or  tallow  then  undergoes  destructive  distillation,  yielding  a 
variety  of  products,  among  which  defiant  gas  is  found  in  abundance. 
The  flame  furnished  by  the  combustion  of  these  products  melts 
the  fuel  around  the  base  of  the  wick,  through  which  it  then 
mounts  by  capillary  attraction,  to  be  decomposed  in  its  turn, 
and  to  furnish  fresh  gases  for  the  maintenance  of  the  flame. 
In  a  lamp,  the  fuel  being  liquid  at  the  commencement,  the 
process  of  fusion  is  dispensed  with  ;  and  in  a  gas  burner,  where 
the  fuel  is  supplied  in  a  gaseous  form,  the  process  of  destructive 
distillation  has  been  already  carried  on  at  a  distance.  It  will 
be  seen,  however,  that  the  final  result  is  similar  in  all  three 
cases,  the  flame  being  maintained  by  such  gases  as  acetylene, 
marsh  gas,  and  olefiant  gas  arising  from  the  destructive  distilla- 
tion of  wax,  tallow,  oil,  coal,  &c. 

On  examining  an  ordinary  flame,  that  of  a  candle,  for  instance, 

Fig  105      ^^  ^^  ®®^^  ^'^  consist  of  three  concentric  cones  (fig.   105),  the 

innermost  around  the  wick,  appearing  almost  black,  the  next 

emitting  a  bright  white  light,  and  the  outermost  being  so  pale  as  to  be 

scarcely  visible  in  broad  daylight. 

The  dark  innermost  cone  consists 
merely  of  the  gaseous  combustible  to 
which  the  air  does  not  penetrate,  and 
which  is  therefore  not  in  a  state  of 
combustion. 

The  nature  of  this  cone  is  easily  shown  by 
experiment  :  a  strip  of  cardboard  held  across 
the  flame  near  its  base  will  not  burn  in  the 
centre  where  it  traverses  the  innermost  cone  ; 
a  piece  of  wre  gauze  depressed  upon  the  flame 
near  the  wick  (tig.  106)  will  allow  the  passage 
of  the  combustible  gas,  which  may  be  kindled 
above  it.  The  gas  may  be  conveyed  out  of  the 
flame  by  means  of  a  glass  tube,  inserted  into 

the  innermost  cone,  and  may  be  kindled  at  the  other  extremity  of  the  tube,  which 

should  be  inclined  downwards  (fig.  107). 


Fig.  106. 


Fig.  107. 

A  piece  of  phosphorus  in  a  small  spoon  held  in  the  interior  of  the  flame  of  a  spirit- 
lamp  will  jnelt  and  boil,  but  will  not  burn  unless  it  be  removed  from  the  flame,  and 
may  then  be  extinguished  by  replacing  it  in  the  flame. 


■EXPERIMENTS  ON"  FLAME. 


105 


The  combustible  gas  from  tbe  interior  of  a  flame  may  be  collected  in  a  flask  (fig. 
108)  furnished  with  two  tubes,  one  of  which  (A)  is  drawn  out  to  a  point  for  insertion 
into  the  flame,  whilst  the  other  (B),  which  passes  to  the 
bottom  of  the  flask,  is  bent  over  and  prolonged  by  a  piece 
of  vulcanised  tubing  so  that  it  may  act  as  a  siphon.  The 
flask  is  filled  up  with  water,  the  jet  inserted  into  the  interior 
of  a  flame,  and  the  siphon  set  running  by  exhausting  it  with 
the  mouth.  As  the.  water  flows  out  through  the  siphon,  the 
gas  is  drawn  into  the  flask,  and  after  removing  the  tube 
from  the  flame,  the  gas  may  be  expelled  by  blowing  down 
the  siphon  tube,  and  may  be  burnt  at  the  jet.  When  a 
candle  is  used  for  this  experiment,  some  solid  products  of 
destructive  distillation  will  be  found  condensed  in  the  flask. 


Fig.  108. 


In  the  second  or  luminous  cone,  combustion  is 
taking  place,  but  it  is  bj  no  means  perfect,  being 
attended  by  the  separation  of  a  quantity  of  carbon,  which  confers  himi- 
nosity  upon  this  part  of  the  flame.  The  presence  of  free  carbon  is  shown 
by  depressing  a  piece  of  porcelain  upon  this  cone,  when  a  black  film  of 
soot  is  deposited.  The  liberation  of  the  carbon  is  due  to  the  decomposi- 
tion of  the  olefiant  gas  and  similar  hydrocarbons  by  the  heat,  which 
separates  the  carbon  from  the  hydrogen,  and  this  latter  undergoing 
combustion  evolves  sufficient  heat  to  raise  the  separated  carbon  to  a  white 
heat,  the  supply  of  air  which  penetrates  into  this  portion  of  the  flame 
being  insufficient  to  effect  the  combustion  of  the  whole  of  the  carbon. 

Some  very  simple  experiments  will  illustrate  the  nature  of  the  luminous  portion  of 
flame. 

Over  an  ordinary  candle  flame  (fig.  109)  a  tube  may  be  adjusted  so  as  to  convey 
the  finely  divided  carbon  from  the  luminous  part  of  the  flame  into ,  the  flame  of 


Fig.  109.  Fig.  110.  .  Fig.  111. 

hydrogen,  which  will  thus  be  rendered  as  luminous  as  the  candle  flame,  the  dark 
colour  of  the  carbon  being  apparent  in  its  passage  through  the  tube. 

A  bottle  furnished  with  two  straight  tubes  (fig.  110)  is  connected  with  a  reservoir 
of  hydrogen.  One  of  the  tubes  is  provided  with  a  small  piece  of  wider  tube  contain- 
ing a  tuft  of  cotton  wool.  On  kindling  the  gas  at  the  orifice  of  each  tube,  no  differ- 
ence will  be  seen  in  the  flames  until  a  drop  of  benzene  (C^H^)  is  placed  upon  the 
cotton,  when  its  vapour,  mingling  with  the  hydrogen,  will  furnish  enough  carbon  to 
render  the  flame  brilliantly  luminous. 

Fig.  Ill  shows  a  more  convenient  apparatus  for  the  same  purpose  ;  the  hydrogen 


106 


EXPERIMENTS  ON  FLAME. 


being  passed  in  through  c,  burns  from  the  tube  a  with  non-luminous  flame,  and 
from  the  tube  b,  after  passing  over  a  piece  of  cotton  moistened  with  benzene,  with  a 
luminous  flame. 

The  pale  outermost  cone,  or  mantle,  of  the  flame,  in  which  the  separated 
carbon  is  finally  consumed,  may  be  termed  the  cone  of  perfect  combustion, 
and  is  much  thinner  than  the  luminous  cone,  the  supply  of  air  to  this 
external  shell  of  flame  being  unlimited,  and  the  combustion  therefore 
speedily  effected. 

The  mantle  of  the  flame  may  be  rendered  more  visible  by  burning  a  little  sodium 
near  the  flame,  when  the  mantle  is  tinged  strongly  yellow. 

By  means  of  a  siphon  about  one-third  of  an  inch  in  diameter  (fig.  112),  the  nature 
of  the  dift'ereut  portions  of  an  ordinary  candle  flame  may  be  very  elegantly  .shown. 
If  the  orifice  of  the  siphon  be  brought  just  over  the 
extremity  of  the  wick,  the  combustible  gases  and 
vapours  will  pass  through  it,  and  may  be  collected  in  a 
small  flask,  where  they  can  be  kindled  by  a  taper. 
On  raising  the  orifice  into  the  luminous  portion  of  the 
flame,  voluminous  clouds  of  black  smoke  will  pour  over 
into  the  flask,  and  if  the  siphon  be  now  raised  a  little 
above  the  point  of  the  flame,  carbonic  acid  gas  can  be 
collected  in  the  flask,  and  may  be  recognised  by  shaking 
with  lime-water. 

The  reciprocal  nature  of  the  relation  between  the 
combustible  gas  and  the  air  which  supports  its  combus- 
tion, may  be  illustrated  in  a  striking  manner  by  buniing 
a  jet  of  air  in  an  atmosphere  of  coal  gas, 
A  quart  glass  globe  with  three  necks  is  connected  at  A  (fig.  113)  with  the  gas-pipe 
by  a  vulcanised  tube.     The  second  neck  (B),  at  the  upper  part  of  the  globe,  is  con- 
nected by  a  short  piece  of  vulcanised  tube  with  a  piece  ol  glass  tube  about  J  inch 
wide,  from  which  the  gas  may  be  burnt.     Into  the  third  and  lowermost  neck   is 


Fig.  113. — Air  burning  in 
coal  gas. 


Fig.  114. — To  make  a  three-necked  flask. 


inserted,  by  means  of  a  cork,  a  thin  brass  tube  C  (an  old  cork-borer),  about  J  inch 
in  diameter.  When  the  gas  is  turned  on,  it  may  be  lighted  at  the  upper  neck  ;  and 
if  a  lighted  match  be  then  quickly  thrust  up  the  tube  C,  the  air  which  enters  it  will 
take  fire,  and  bum  inside  the  globe. 

A  very  inexpensive  apparatus  for  this  purpose  may  be  constructed  from  a  common 
Florence  oil  flask.  By  applying  a  blowpipe  flame  at  A  (fig.  114),  so  as  to  heat  to 
whiteness,  a  spot  as  large  as  a  threepenny-piece,  and  quickly  blowing  into  the  neck 
of  the  flask,  the  heated  portion  of  the  glass  may  be  made  to  bulge  out.  A  similar 
protuberance  is  then  to  be  formed  at  B.  A  sharp-pointed  flame  is  directed  upon  A, 
and  the  glass  burst  by  blowing  into  the  flask  whilst  it  is  still  exposed  to  the  flame. 
By  fusing  the  edges  of  the  hole  thus  produced,  and  turning  them  outwards  with  the 
t'lul  of  a  tile,  a  short  neck  may  be  formed  capable  of  receiving  a  cork.  When  t\m  is 
cool,  it  is  closed  with  a  cork,  and  a  second  similar  neck  is  produced  at  B. 


GAS  BURNERS. 


107 


Fi^.  115. — Argand  burner. 


From  this  review  of  tlie  structure  of  flame,  it  is  evident  that,  in  order 
to  secure  a  flame  which  shall  be  useful  for  illumination,  attention  must 
be  paid  to  the  supply  of  oxygen  (or  air),  and  to  the  composition  of  the 
fuel  employed.  The  use  of  the  chimney  of  an  Argand  burner  (fig.  115) 
affords  an  instance  of  the  necessity  for  attention 
to  the  proper  supply  of  air.  Without  the 
chimney,  the  flame  is  red  at  the  edges,  and 
smoky,  for  the  supply  of  air  is  not  sufficient  to 
consume  the  whole  of  the  carbon  which  is 
separated,  and  the  temperature  is  not  competent 
to  raise  it  to  a  bright  white  heat,  defects  which 
are  remedied  as  soon  as  the  chimney  is  placed 
over  it  and  the  rapidly-ascendiug  heated  column 
of  air  draws  in  a  liberal  supply  beneath  the 
burner,  as  indicated  by  the  arrows. 

By  using  two  chimneys,  and  causing  the  air 
to  pass  down  between  them,  so  as  to  be  heated 
to  about  500°  F.  before  reaching  the  flame,  an 
equal  amount  of  light  may  be  obtained  from  a 
much  smaller  supply  of  gas. 

The  smokeless  gas  burners  employed  in  laboratories  and  kitchens  exhibit 
the  result  of  mixing  the  gas  with  a  considerable  proportion  of  air  before 
burning  it,  the  luminous  part  of  the  flame  then  entirely  disappearing,  with 
great  augmentation  of  the  temperature  of  the  flame, 
since  the  carbon  is  burnt  simultaneously  with  the 
hydrogen,  and  the  size  of  the  flame  is  diminished. 

The  most  efficient  burner  of  this  kind  {BunserCs  burner, 
fig.  116)  is  that  in  which  the  gas  is  conveyed  through  a 
narrow  jet  into  a  wide  tube,  at  the  base  of  which  there  are 
four  large  holes  for  the  admission  of  air.  When  a  good 
supply  of  gas  is  turned  on,  a  quantity  of  air,  about  twice  the 
volume  of  the  gas,  is  drawn  in  through  the  lower  apertures, 
and  the  mixture  of  air  and  gas  may  be  kindled  at  the  orifice 
of  the  wide  tube,  its  rapid  motion  jireventing  the  flame  from 
passing  down  within  the  tube.  This  tube  is  sometimes 
surmounted  by  a  rosette  burner  to  distribute  the  flame, 
with  the  fingers,  a  luminous  flame  is  at  once  produced. 

The  luminosity  of  the  flame  may  also  be  destroyed  by  supplying  nitrogen  instead 
of  air  to  the  Bunsen  burner,  when  the  diminution  of  light  is  due  partly  to  the 
increased  area  of  the  flame  and  partly  to  the  cooling  efiect  of  the  nitrogen. 

The  temperature  of  the  Bunsen  flame  is  estimated  to  be  1200°  C.  in  the  inner  blue 
flame,  and  1350°  C.  in  the  outer  layer  or  mantle  of  the  flame. 

The  gauze  burner  (fig.  117)  consists  of  an  open  cylinder 
surmounted  by  wire  gauze.  When  this  is  placed  over  the 
gas  burner,  a  supply  of  air  is  drawn  in  at  the  bottom  by  the 
ascending  stream  of  gas,  and  the  mixture  burns  above  the 
gauze  with  a  very  hot  smokeless  flame,  the  metallic  meshes 
preventing  the  flame  from  passing  down  to  the  gas  below. 

The  luminosity  of  a  flame  is  materially  aff"ected 
by  the  pressure  of  the  atmosphere  in  which  it  burns, 
a  diminution  of  pressure  causing  a  loss  of  illuminat- 
ing power.  If  the  light  of  a  given  flame  burning 
in  the  air  when  the  barometer  stands  at  30  inches 
be  represented  by  100,  each  diminution  of  one 
inch  in  the  height  of  the  barometer  will  reduce  the  luminosity  by  five ; 


Fig.  116. — Bunsen's 
burner. 

By  closing  the  air-holes 


Fig.  117.— Gauze 
burner. 


108 


COMPOSITION^  OF  ILLUMINATING  FUEL. 


and  conversely,  when  the  barometer  rises  one  inch,  the  luminosity 
will  be  increased  by  five.  This  is  not  due  to  any  difference  in  the  rate 
of  burning,  which  remains  pretty  constant,  but  to  the  more  complete 
interpenetration  of  the  rarefied  air  and  the  gases  composing  the  flame; 
this  gives  rise  to  the  separation  of  a  smaller  quantity  of  incandescent 
carbon.  In  air  at  a  pressure  of  120  inches  of  mercury,  the  flame  of 
elcohol  is  highly  luminous,  the  high  density  of  the  air  discouraging  the 
intermixture  of  the  flame  gases  with  it,  and  thus  allowing  the  separation 
of  a  portion  of  carbon. 

In  considering  the  influence  exerted  by  the  composition  of  the  fuel 
upon  the  character  of  its  flame,  it  wiU  be  necessary  to  bear  in  mind  that 
some  kinds  of  fuel  consist  of  carbon  and  hydrogen  only,  whilst  others 
contain  a  considerable  proportion  of  oxygen. 

The  following  table  exhibits  the  composition  of  some  of  the  principal 
substances  concerned  in  producing  ordinary  illuminating  flames  : — 


Fuel. 

Formula. 

Carbon. 

Hydrogen. 

Oxygen. 

Marsh  gas,    . 

CH4 

30 

10 

Olefiant  gas, 

C,^4 

60 

10 

Paraffin, 

^1«"34 

30 

10 

Turpentine,  . 

CloHig 

75 

10 

Benzene,       .         ... 

•      Cett, 

120 

10 

Wax,    .... 

C46H92O2* 

60 

10 

3-5 

Stearine, 

CsrHiioOg 

62  1 

10 

87 

Oleine,           .         .         . 

^B7^iofie 

65-8 

10 

9-2 

Alcohol,         .          .          ; 

CaHgO 

40 

10 

27 

Wood  naphtha,     . 

CH4O 

30 

10 

40 

It  may  be  stated  generally  that  when  the  number  of  atoms  of  carbon  is 
less  than  one-third  that  of  hydrogen,  the  flame  will  be  free  from  smoke, 
as  in  the  case  of  marsh  gas.  When  there  is  more  carbon  than  this,  the 
flame  is  very  liable  to  smoke,  unless  managed  with  great  judgment. 
Those  hydrocarbons  which  contain,  like  turpentine,  benzene,  and  the 
paraffin  oils,  a  very  large  proportion  of  carbon, 
always  burn  with  much  smoke,  and  require  special 
contrivances  to  render  them  applicable  for  illumin- 
ating purposes,  such  as  lamps  with  tall  narrow 
chimneys  of  peculiar  construction  to  afford  a  strong 
current  of  air.  Benzene  (coal  naphtha)  vapour 
must  be  mixed  with  air  if  it  is  required  to  burn 
with  a  smokeless  flame. 

If  a  piece  of  cotton  wool,  moistened  Avith  benzene,  he 
placed  in  a  flask  provided  with  two  tubes  (tig.  118),  it  will 
be  found,  on  gently  warming  the  fla-sk  by  dipping  it  into 
hot  water,  and  blowing  through  one  of  the  tubes,  that  the 
mixture  of  benzene  vapour  and  air  issuing  from  the  other 
tube  will  burn  with  a  smokeless  bright  flame. 


Fig.  118. 


If  coal  gas,  which  is  essentially  a  mixture  of  hydrogen,  marsh  gas,  and 
olefiant  gas,  and  generally  contains  rather  too  much  hydrogen  in  propor- 

*  Tliis  is  the  composition  of  myricine,  which  forms  the  greater  part  of  bees'  wax. 


THE  BLOWPIPE  FLAME.  109 

tion  to  its  carbon,  be  enriclied  with,  carbon  by  passing  over  benzene  (ligbt 
coal  naphtlia),  or  naptbalene,  it  bums  with  a  far  more  luminous  flame 
(naphthalised  gas). 

When  the  fuel  contains  oxygen,  the  carbon  may  exist  in  larger  propor- 
tion to  the  hydrogen  without  giving  rise  to  the  production  of  smoke,  since 
this  oxygen  will  dispose  of  a  portion  of  the  carbon  during  the  combustion. 
Thus,  wax  is  much  less  liable  to  smoke  than  olefiant  gas,  although  con- 
taining the  same  projiortion  of  carbon  to  hydrogen,  whilst  stearine  (the 
chief  part  of  tallow)  and  oleine  (forming  the  bulk  of  oils)  may  be  burnt 
in  ordinary  candles  and  lamps,  although  still  richer  in  carbon,  because 
they  contain  more  oxygen  also. 

Alcohol  yields  a  flame  of  no  illuminating  value,  although  it  contains 
more  carbon  in  proportion  to  its  hydrogen  than  is  present  in  marsh  gas, 
because  its  oxygen  helps  to  consume  the  carbon  during  the  combustion, 
and  prevents  it  from  separating  in  the  incandescent  state.  By  adding 
about  one-tenth  of  its  bulk  of  benzole  or  turpentine,  however,  alcohol  may 
be  made  to  burn  with  a  brilliant  flame. 

76.  The  blowpipe  fiame. — The  principles  already  laid  down  will  render 
the  structure  of  the  blowpipe  flame  easily  intelligible.  It  must  be 
remembered  that  in  using  the  blowpipe,  the  stream  of  air  is  not  propelled 
from  the  lungs  of  the  operator  (where  a  great  part  of  its  oxygen  would 
have  been  consumed),  but  simply  from  the  mouth,  by  the  action  of  the 
muscles  of  the  cheeks.  The  first  apparent  effect  upon  the  flame  is 
entirely  to  destroy  its  luminosity,  the  free  supply  of  air  affecting  the 
immediate  combustion  of  the  carbon.  The  size  of  the  flame,  moreover,  is 
much  diminished,  and  the  combustion  being  concentrated  into  a  smaller 
space,  the  temperature  must  be  much 
higher  at  any  given  point  of  the 
flame.  In  structure,  the  blowpipe 
flame  is  similar  to  the  ordinary  flame, 
consisting  of  three  distinct  cones,  the 
innermost  of  which  (A,  fig.  119)  is 
filled  with  the  cool  mixture  of  air  and 
combustible  gas.  The  second  cone, 
especially  at  its  point  (E),  is  termed  Yig.  119.— Blowpipe  flame, 

the  reducing  flame,  for  the  supply  of 

oxygen  at  that  part  is  not  sufficient  to  convert  the  carbon  into  carbon 
dioxide,  but  leaves  it  as  carbonic  oxide,  which  speedily  reduces  almost  all 
metallic  oxides  placed  in  that  part  of  the  flame  to  the  metallic  state. 
The  outermost  cone  (0)  is  called  the  oxidising  flame,  for  there  the  supply 
of  oxygen  from  the  surrounding  air  is  unlimited,  and  any  substance  prone 
to  combine  Avith  oxygen  at  a  high  temperature  is  oxidised  Avhen  exposed 
to  the  action  of  that  portion  of  the  flame  ;  the  hottest  point  of  the  blow- 
pipe flame,  where  neither  fuel  nor  oxygen  is  in  excess,  appears  to  be  a 
very  little  in  advance  of  the  extremity  of  the  second  (reducing)  cone. 
The  difference  in  the  operation  of  the  two  flames  is  readily  shown  by 
placing  a  little  red  lead  (oxide  of  lead)  in  a  shallow  cavity  scooped  upon 
the  surface  of  a  piece  of  charcoal  (fig.  120),  and  directing  the  flames  upon 
it  in  succession ;  the  inner  flame  will  reduce  a  globule  of  metallic  lead, 
which  may  be  reconverted  into  oxide  by  exposing  it  to  the  outer  flame.* 

*  By  directing  the  reducing  flame  upon  the  metallic  oxide  in  the  cavity,  and  allowing 


110 


HOT-BLAST  BLOWPIPE. 


The  immense  service  rendered  by  this  instrument  to  the  chemist  and 
mineralogist  is  well  known. 

By  forcing  a  stream  of  oxygen  through  a  flame,  from  a  gas-holder  or 
bag,  an  intensely  hot  blowpipe  flame  is  obtained,  in  which  pipeclay  and 
platinum  may  be  melted,  and  iron  bums  with  great  brilliancy. 


Hot-blast  blowpipe. 


Fig.  120. — Reduction  of  metals  on  charcoal. 
Fletcher's  hot-blast  blowpipe  (fig.  121)  produces  a  much  higher  temperature  than 
the  ordinary  blowpipe.     Coal  gas  is  supplied  through  the  tube  g,  and  is  kindled  at 

the  Bunsen  burners  b  b  and  at  the  orifice  /,  the 
supply  to  the  former  being  regulated  by  the  stop- 
cock c,  and  to  the  latter  by  the  stopcock  d.  The 
flames  of  the  Bunsen  burners  heat  the  spiral  copper 
tube  e  to  redness,  so  that  the  air  blown  in  through 
the  flexible  tube  a  is  strongly  heated  before  being 
projected  into  the  flame  through  a  blowpipe  jet 
at  /.  Thin  platinum  wires  melt  easily  in  this 
flame,  and  thin  iron  wires  burn  away  rapidly. 

77.  Determination  of  the  composition  of 
gases  containing  carbon  and  hydrogen. — In 
order  to  ascertain  the  proportions  of  carbon 
and  hydrogen  present  in  a  gas,  a  measured 
volume  of  the  gas  is  mixed  with  an  excess  of 
oxygen,  the  volume  of  the  mixture  carefully  noted,  and  explosion  deter- 
mined by  passing  the  electric  spark ;  the  gas  remaining  after  the  explosion 
is  measured  and  shaken  with  potash,  which  absorbs  the  carbonic  acid  gas 
from  the  volume  of  which  the  proportion  of  carbon  may  be  calculated. 
For  example, 

0"4  cubic  inch  of  marsh  gas,  mixed  with 
1  '0  „  oxygen,  and  exploded,  left  \ 

0'6  „  gas  ;  shaken  with  potash,  it  left 

0-2  „  oxygen, 

showing  that  0'4  cubic  inch  of  carbonic  acid  gas  had  been  produced.  This 
quantity  of  carbonic  acid  would  contain  0*4  cubic  inch  of  oxygen.  De- 
ducting this  last  from  the  total  amount  of  oxygen  consumed  (0'8  cubic 
inch),  we  have  0*4  cubic  inch  for  the  volume  of  oxygen  consumed  by  the 
hydrogen.  Now,  0'4  cubic  inch  of  oxygen  would  combine  with  0-8  cubic 
inch  of  hydrogen,  which  represents  therefore  the  amount  of  hydrogen  in 
the  marsh  gas  employed.  It  has  thus  been  ascertained  that  the  marsh 
gas  contains  twice  its  volume  of  hydrogen. 

Sp.  gr.  (to  H)  or  weight  of  1  volume  of  marsh  gas,        .         .         =     8 

weight  of  2  volumes  (one  molecule),    .         .         =16 

2  volumes  of  marsh  gas  contain  4  volumes  H,  weighing  4 

2  volumes  of  marsh  gas  contain  x  volume  C,  weighing         .  12 

the  oxidising  flame  to  sweep  over  the  surface  of  the  charcoal,  as  shown  in  the  figure,  a 
vt'llow  incrustation  of  oxide  of  lead  is  formed  upon  the  surface  of  the  charcoal,  which 
affords  additional  evidence  of  the  nature  of  the  metal. 


PRODUCTS  OF  DISTILLATION  OF  COAL. 


Ill 


^F^ 


Fig.  122. 
Siphon  eudiometer. 

The  volume  of  residual 


For  the  purpose  of  illustration,  the  analysis  of  mareh  gas  may  be  effected  in  a  lire's 
eudiometer  (fig.  122),  but  a  considerable  excess  of  oxygen  should  be  added  to  mode- 
rate the  explosion.  The  eudiometer  having  been  filled 
with  water,  O'l  cubic  inch  of  marsh  gas  is  introduced 
into  it,  as  described  at  p.  36,  and  having  been  transferred 
to  the  closed  limb  and  accurately  measured  after  equal- 
ising the  level  of  the  water,  the  open  limb  is  again  filled 
up  with  water,  the  eudiometer  inverted  in  the  trough, 
and  1'2  cubic  inch  of  oxygen  added;  this  is  also  trans- 
ferred to  the  closed  limb  and  carefully  measured.  The 
electric  spark  is  passed  through  the  mixture  (see  p. 
36),  the  open  limb  being  closed  by  the  thumb.  The 
level  of  the  water  in  both  limbs  is  then  equalised,  and 
the  volume  of  gas  measured.  The  open  limb  is  filled 
up  with  a  strong  solution  of  potash,  and  closed  by  the 
thumb,  so  that  the  gas  may  be  transferred  from  the 
closed  to  the  open  limb  and  back,  until  its  volume  is 
no  longer  diminished  by  the  absorption  of  carbon  dioxide, 
oxygen  having  been  measured,  the  calculation  is  effected  as  above  described. 

The  results  are  more  exact  when  the  eudiometer  is  filled  with  mercury  instead  of 
water. 

Coal  Gas, 

78.  The  manufacture  of  coal  gas  is  one  of  the  most  important  appli- 
cations of  the  principle  of  destructive  distillation,  and  affords  an  excellent 
example  of  the  tendency  of  this  process  to  develop  new  arrangements 
of  the  elements  of  a  compound  hody.  The  action  of  heat  upon  coal,  in 
a  vessel  from  which  air  is  excluded,  gives  rise  to  the  production  of  a  very 
large  number  of  compounds  containing  some  two  or  more  of  the  five 
elements  of  the  coal,  in  different  proportions,  or  in  different  forms  of 
arrangement.  Although  no  clue  has  yet  been  obtained  to  indicate  the 
true  arrangement  of  these  elements  in  the  original  coal  (or,  as  it  is  termed, 
the  constitution  of  the  coal),  it  is  certain  that  these  various  compounds  do 
not  exist  in  it  before  the  application  of  heat,  but  are  really  the  results  of 
its  action;  that  they  are  indeed  products  and  not  educts. 

The  most  important  forms  assumed  by  the  carbon  and  hydrogen  when 
coal  is  strongly  heated,  are, — 


Gases 


(-Hydrogen, 
I  Marsh  gas, 
defiant  gas, 
Acetylene, 
i  Butylene, 


CH4 
C2H4 
CgHg 
C^Hfl 


Liquids 


\  Benzene, 
I  Toluene, 


CsHg 

CyHg 


I     .   [  Jfaphthalene, 
j  3  J  Anthracene, 
I  "3  1  Paraflin, 


CioHj 
C14H 
CjgH 
C 


34 


The  nitrogen  of  the  coal  reappears  in  the  forms  of — 
Gases      \  Nitrogen, 

(  Ammonia,      .         .     NHj        ) 
Aniline,  .         .     CgH^N    V  Alkaline. 

Liquids  <  Quinoline,      .         .     C9H7N    ) 
(  Hydrocyanic  acid,  .     CHN 

The  oxygen  contributes  to  the  production  of 
p         J  Carbonic  oxide,    .    CO 
^^^^^  ^  Carbon  dioxide,    .    CO. 


(  Water,  ,     H2O 

Liquids  <  Acetic  acid,  .     CgHjC^ 
(  Carbolic  acid,    CgHgO 


Sulphur  is  found  among  the  products  as, 

Sulphuretted  hydrogen  gas,      H^S  I  (very  voktile)  i  ^'^rbon  disulphide,  CS., . 

The  illuminating  gas  obtained  from  coal  consists  essentially  of  free  hydro- 
gen, marsh  gas,  olefiant  gas,  and-  carbonic  oxide,  with  small  quantities  of 


112 


COMPOSITION  OF  COAL  GAS. 


acetylene,   benzene   vapour,   and    some   other   substances.     Its    specific 
gravity  is  about  0"4,  and  varies  inversely  as  its  illuminating  value. 

A  fair  general  idea  of  its  composition  is  given  by  the  following  table : — 

Gasfrcnn  Cannel  Coal. 


Hydrogen,       ... 

45*847  volumes. 

Marsh  gas 

40-948 

Carbonic  oxide, 

4-167 

Olefiaut  gas,    ..... 

5-504 

Carbonic  acid  gas,  .... 

1-950 

Nitrogen, 

1-445 

Oxygen, 

0-139 

100-0 

The  only  constituents  which  contribute  directly  to  the  illuminating 
value  of  the  gas  are  the  marsh  gas,  olefiant  gas,  and  similar  hydrocarbons, 
acetylene,  and  benzene  vapour. 

The  most  objectionable  constituent  is  the  sulphur  present  as  sulphur- 
etted hydrogen  and  bisulphide  of  carbon,  for  this  is  converted  by  com- 
bustion into  sulphuric  acid,  which  seriously  injures  pictures,  furniture, 
&c.  The  object  of  the  manufacturer  of  coal  gas  is  to  remove,  as  far  as 
po.^sible,  everything  from  it,  except  the  constituents  mentioned  as  essential, 
and  at  the  same  time  to  obtain  as  large  a  volume  of  gas  from  a  given 
weight  of  coal  as  is  consistent  with  good  illuminating  value. 

The  mode  of  purifying  the  gas  and  the  general  arrangements  for  its 
manufacture,  will  be  described  in  a  later  part  of  the  work. 


Fig.  1 23.  —Destructive  distillation  of  coal. 

The  destructive  distillation  of  coal  may  be  exhibited  with  the  arrangement  repre- 
sented in  fig.  123.  The  solid  and  liquid  products  (tar,  ammoniacal  liquor,  &c.)  are 
condensed  in  the  globular  receiver  (A).  The  first  bent  tube  contains,  in  one 
limb  (B),  a  piece  of  red  litmus  paper  to  detect  ammonia;   and  in  the  other  (C) 

a  piece  of  paper  impregnated  with  lead  acetate,  which 
will  be  blackened  by  the  sulphuretted  hydrogen. 
The  second  bent  tube  (D)  contains  enough  lime-water 
to  fill  the  bend,  which  will  be  rendered  milky  by  the 
carbonic  acid  gas.  The  gas  is  collected  over  water, 
in  the  jar  E,  which  is  funiished  with  a  jet  from 
which  the  gas  may  be  burnt  when  forced  out  by 
depressing  the  jar  in  water. 

The  presence  of  acetylene  in  coal  gas  may  be 
shown  by  passing  the  gas  from  the  supply-pij)e  (A, 
tig.  124),  first  through  a  bottle  (B)  containing  a  little 
ammonia,  then  through  a  bent  tube  (C)  with  enough 
water  to  fill  the  bend,  and  a  piece  of  bright  sheet 
copper  immersed  in  the  water  in  each  limb.  After  a  short  time  the  bright  red  flakes 
of  the  copper  acetylide  will  be  seen  in  the  water. 


Fig.  124. 


QUARTZ — SAND — FLINT.  113 


SILICON. 

79.  In  many  of  its  chemical  relations  to  other  bodies,  this  element 
will  be  found  to  bear  a  great  resemblance  to  carbon;  but  whilst  carbon  is 
remarkable  for  the  great  variety  of  compound  forms  in  which  it  is  met 
with  in  nature,  silicon  is  always  found  in  combination  with  oxygen,  as 
silica  (SiO.,),  either  alone  or  as  silicates. 

Silica  (SiOa  =  60  parts  by  weight). — The  purest  natural  variety  of  silica 
is  the  transparent  and  colourless  variety  of  quartz  known  as  rock  crystal, 
the  most  widely  diffused  ornament  of  the  mineral  world,  often  seen 
crystallised  in  beautiful  six-sided  prisms,  terminated  by  six-sided  pyra- 
mids (fig.  125),  which  are  

always  easily  distinguished  ^^^^^^^^^;=^^=-^^^^^^g,   --^^^ 

by    their   great    hardness,    ^rff~^^L_^^^^^^^^^^^^^^^^^^^^k 
scratching  almost  as  Q^^'^SI^/SKI^^^K^^^^^^t^ti^^^^^ 

readily    as    the    diamond.    /  '-^    '   '  '•  ^^^^^^BBi^^^^^^^^^^^^^ 
Coloured     of     a    delicate    \  r^^___  :^^^^B^?a^^^^a=^^^--^^^^r 
purple,  probably  by  a  little     ^^^^^^■^-■■■(^■■■■■^■■•BHi^^^ 
organic  matter,  these  crys-  Fig.  125.— Crystal  of  quartz, 

tals  are  known  as  ame^/i?/s^; 

and  when  of  a  brown  colour,  as  Cairngorm  stones  or  Scotch  pebbles  Losing 
its  transparency  and  crystalline  structure,  we  meet  with  silica  in  the  form 
of  chalcedony  and  of  carnelian,  usually  coloured,  in  the  latter,  with  oxide 
of  iron. 

Hardly  any  substance  has  so  great  a  share  in  the  lapidary's  art  as  silica, 
for  in  addition  to  the  above  instances  of  its  value  for  ornamental  purposes, 
we  find  it  constituting /os^jjer,  agate,  cat's  eye,  onyx,  so  much  prized  for 
cameos,  opal,  and  some  other  precious  stones.  In  opal  the  silica  is  com- 
bined with  water. 

Sand,  of  which  the  whiter  varieties  are  nearly  pure  silica,  appears  to 
have  been  formed  by  the  disintegration  of  siliceous  rocks,  and  has  generally 
a  yellow  or  brown  colour,  due  to  the  presence  of  oxide  of  iron. 

The  resistance  offered  by  silica  to  aU  impressions  has  become  proverbial 
in  the  case  of  flint,  which  consists  essentially  of  that  substance  coloured 
with  some  impurity.  Flints  are  generally  found  in  compact  masses,  distri- 
buted in  regular  beds  throughout  the  chalk  formation  ;  their  hardness, 
which  even  exceeds  that  of  quartz,  formerly  rendered  them  useful  for 
striking  sparks  with  steel,  by  detaching  small  particles  of  the  metal,  which 
are  so  heated  by  the  percussion  as  to  continue  to  burn  (see  p.  29)  in  the 
air,  and  to  inflame  tinder  or  gunpowder  upon  which  they  are  allowed  to 
fall. 

The  part  taken  by  silica  in  natural  operations  appears  to  be  chiefly  a 
mechanical  one,  for  which  its  stability  under  ordinary  influences  peculiarly 
fits  it,  for  it  is  found  to  constitute  the  great  bulk  of  the  soil  which  serves 
as  a  support  and  food  reservoir  of  land  plants,  and  enters  largely  into  the 
composition  of  the  greater  number  of  rocks. 

But  that  this  substance  is  not  altogether  excluded  from  any  share  in 
life,  is  shown  by  its  presence  in  the  shining  outer  sheath  of  the  stems  of 
the  grasses  and  cereals,  particularly  in  the  hard  external  coating  of  the 
Dutch  rush  used  for  polishing;  and  this  alone  would  lead  to  the  inference 
that  silica  could  not  be  absolutely  insoluble,  since  the  capillary  vessels 
of  plants  are  known  to  be  capable  of  absorbing  only  such  substances  as  are 

H 


114  SILICA  RENDERED  SOLUBLE. 

in  a  state  of  solution.  Many  natural  waters  also  present  us  with  silica  in 
a  dissolved  state,  and  often  in  considerable  quantity,  as,  for  example,  in 
the  Geysers  of  Iceland,  which  deposit  a  coating  of  sUica  upon  the  earth 
around  their  borders. 

Pure  water,  however,  has  no  solvent  action  upon  the  natural  varieties 
of  silica.  The  action  of  an  alkali  is  required  to  bring  it  into  a  soluble 
form. 

To  eflTect  this  upon  the  small  scale,  a  few  crystals  of  common  washing- 
soda  (sodium  carbonate)  may  be  powdered  and  dried;  a  little  of  the  dried 
powder  is  placed  upon  a  piece  of  platinum  foil  slightly  bent  up  (fig.  126), 
and  is  fused  by  directing  the  flame  of  a  blowpipe  upon  the  under  side  of 
the  foil  As  soon  as  the  carbonate  of  soda  is  perfectly  liquefied,  a  small 
quantity  of  very  finely  powdered  white  sand  is  thrown  into  it,  when  brisk 
efiervescence  will  be  observed,  and  the  particles  of  sand  will  dissolve ; 
fresh  portions  of  sand  may  now  be  added  as  long  as  they  produce  eff'er- 
vescence,  which  is  due  to  the  escape  of  the  carbonic  acid  gas.  The  piece 
of  platinum  foil,  when  cool,  may  be  placed  in  a  little  warm  water,  and 


Fig.  126. — Fusion  on  platinum  foiL 

allowed  to  soak  for  some  time,  when  the  melted  mass  will  gradually 
dissolve,  forming  a  solution  of  sodium  silicate.  This  solution  will  be 
found  decidedly  alkaline  to  test-papers. 

If  a  portion  of  the  solution  of  sodium  silicate  in  water  be  poured  into 
a  test-tube,  and  two  or  three  drops  of  hydrochloric  acid  added  to  it,  with 
occasional  agitation,  efiervescence  will  be  produced  by  the  expulsion  of 
any  carbonic  acid  gas  still  remaining,  and  the  solution  will  be  converted 
into  a  gelatinous  mass  by  the  separation  of  silicic  acid.  But  if  another 
portion  of  the  solution  be  poured  into  an  excess  of  dilute  hydrochloric 
acid  (i.e.,  into  enough  to  render  the  solution  distinctly  acid),  the  silicic 
acid  will  remain  dissolved  in  the  water,  together  with  the  sodium  chloride 
formed. 

In  order  to  separate  the  sodium  chloride  from  the  silicic  acid,  the 
process  of  dialysis  *  must  be  resorted  to. 

Dialysis  is  the  separation  of  dissolved  substances  from  each  other  by 
taking  advantage  of  the  different  rates  at  which  they  pass  through  moist 
diaphragms  or  septa. 

If  the  mixed  solution  of  sodium  chloride  and  silicic  acid  were  poured 
upon  an  ordinary  paper  filter,  it  would  pass  through  without  alteration ; 
but  if  parchment  paper  be  employed,  which  is  not  pervious  to  water, 
although  readily  moistened  by  it,  none  of  the  liquid  will  pa«s  through. 

.*,  From  StoXiJw,  to  part  asunder. 


DIALYSED  SILICA.  115 

If  the  cone  of  parchment  paper  he  supported  upon  a  vessel  filled  with 
distilled  water  (fig.  127),  so  that  the  water  may  be  in  contact  with  the 
outer  surface  of  the  cone,  the  hydrochloric  acid  and  the  sodium  chloride 
will  pass  through  the  substance  of  the  parchment  paper,  and  the  water 
charged  with  them  may  be  seen  descending  in  dense 
streams  from  the  outside  of  the  cone.  After  a  few  hours, 
especially  if  the  water  be  changed  occasionally,  the  whole 
of  the  hydrochloric  acid  and  sodium  chloride  will  have 
passed  through,  and  a  pure  solution  of  silicic  acid  in  water 
will  remain  in  the  cone. 

This  solution  of  silicic  acid  is  very  feebly  acid  to  blue 
litmus  paper,  and  not  perceptibly  sour  to  the  taste.  It 
has  a  great  tendency  to  set  into  a  jelly  in  consequence  of 
the  sudden  separation  of  silicic  acid.  If  it  be  slowly 
evaporated  in  a  dish,  it  soon  solidifies;  but,  by  conducting 
the  evaporation  in  a  flask  so  as  to  prevent  any  drying  of  pj^  j27. 
the  silicic  acid  at  the  edges  of  the  liquid,  it  may  be 
concentrated  until  it  contains  14  per  cent,  of  silicic  acid.  When  this 
solution  is  kept,  even  in  a  stoppered  or  corked  bottle,  it  sets  into  a  trans- 
parent gelatinous  mass,  which  gradually  shrinks  and  separates  from  the 
water.  When  evaporated,  in  vacuo,  over  sulphuric  acid,  it  gives  a  trans- 
parent lustrous  glass  which  is  composed  of  22  per  cent  of  water  and  78 
per  cent,  of  silica  (HgO.SiOg). 

This  hydrate  of  silica  cannot  be  redissolved  in  water,  and  is  only  soluble 
to  a  slight  extent  in  hydrochloric  acid.  If  it  be  heated  to  expel  the  water, 
the  silica  which  remains  is  insoluble  both  in  water  and  in  hydrochloric 
acid,  but  is  dissolved  when  boiled  with  solution  of  potash  or  soda,  or  their 
carbonates. 

Silica  in  the  naturally  crystallised  form,  as  rock  crystal  and  quartz, 
is  insoluble  in  boiling  solutions  of  the  alkalies,  and  in  all  acids  except 
hydrofluoric  ;  but  amorphous  silica  (such  as  that  found  at  Farnham)  is 
readily  dissolved  by  boiling  alkalies.  These  represent,  in  fact,  two  dis- 
tinct modifications  of  silica.  A  transparent  piece  of  rock  crystal  may  be 
heated  to  bright  redness  without  change,  but  if  it  be  powdered  previously 
to  being  heated,  its  specific  gravity  is  diminished  from  2 '6  to  24,  and  it 
becomes  soluble  in  boiling  alkalies,  having  been  converted  into  the  amor- 
phous modification. 

Crystals  of  quartz  have  been  obtained  artificially  by  the  prolonged 
action  of  water  upon  glass  at  a  high  temperature  under  pressure.  Wheni 
fused  with  the  oxy hydrogen  blowpipe,  silica  does  not  crystallise,  being 
thus  converted  into  the  amorphous  variety  of  sp.  gr.  2*3. 

To  prepare  the  amorplious  modification  of  silica  artificially,  white  sand  in  very 
fine  powder  may  be  fused,  in  a  platinum  crucible,  with  six  times  its  weight  of  a  mix- 
ture of  equal  weights  of  the  potassium  and  sodium  carbonates,  the  mixture  being 
more  easily  fusible  than  either  of  the  carbonates  separately.  The  crucible  may  be 
heated  over  a  gas  burner  supplied  with  a  mixture  of  gas  and  air,  or  may  be  placed  in 
a  little  calcined  magnesia  contained  in  a  fireclay  crucible,  which  may  be  covered  up 
and  introduced  into  a  good  fire.  The  platinum  crucible  is  never  heated  in  direct 
contact  with  fuel,  since  tlie  metal  would  become  brittle  by  combining  with  carbon, 
silicon,  and  sulphur  derived  from  the  fuel.  The  magnesia  is  used  to  protect  the 
platinum  from  contact  with  the  clay  crucible.  When  the  action  of  the  silica  upon 
the  alkaline  carbonates  is  completed,  which  will  be  indicated  by  the  cessation  of  the 
effervescence,  the  platinum  crucible  is  allowed  to  cool,  placed  in  an  evaporating  dish, 
and  soaked  ibr  a  night  in  water,  when  the  mass  should  be  entirely  dissolved.    Hydro- 


116 


ACID  CHARACTER  OF  SILICA. 


Fig.  128. 


chloric  aciil  is  then  added  to  the  solution,  with  occasional  stirring,  until  it  is  distinctly 
acid  to  litmus  paper.  Ou  evaporating  the  solution,  it  will,  at  a  certain  point,  solidify 
to  a  gelatinous  mass  of  hydrated  silica,  which  would  be 
spirted  out  of  the  dish  if  evaporation  over  the  flame  were 
continued.  To  prevent  this,  the  dish  is  placed  over  an 
empty  iron  saucepan  (tig.  128)  so  that  the  heat  from  the 
flame  may  be  equally  distributed  over  the  bottom  of  the 
dish.  When  the  mass  is  quite  dry,  the  dish  is  allowed  to 
cool,  and  some  water  is  poured  into  it,  which  dissolves 
the  chlorides  of  potassium  and  sodium  (fonned  by  the 
action  of  the  hydrochloric  acid  upon  the  silicates),  and 
leaves  the  silica  in  white  flakes.  These  may  be  collected 
upon  a  filter  (fig.  129),  and  washed  several  times  with 
distilled  water.  The  filter  is  then  carefully  spread  out 
upon  a  hot  iron  plate,  or  upon  a  hot  brick,  and  allowed 
to  dry,  when  the  silica  is  left  as  a  dazzling  white  powder, 
which  must  be  strongly  heated  in  a  porcelain  or  platinum 
crucible  to  expel  the  last  traces  of  water.  It  is  remarkable  for  its  extreme  lightness, 
especially  when  heated,  the  slightest  current  of  air  easily  blowing  it  away. 

80.  For  effecting  such  fusions  as  that 
just  described,  an  air-gas  blowpipe  (A,  fig. 
130)  supplied  with  air  from  a  double  action 
bellows  (B),  worked  by  a  treadle  (C),  will 
be  found  most  convenient.  Where  gas  is 
not  at  hand,  the  fusion  may  be  effected 
in  a  small  furnace  (fig.  131),  surmounted 
with  a  conical  chimney,  and  fed  with 
charcoal. 

81.  Silicates. — The  acid  proper- 
ties of  silicic  acid  are  so  feeble  that 
it  is  a  matter  of  great  difficulty  to 
determine  the  proportion  of  any  base 
which  is  required  to  react  with  it  in 
order  to  form  a  chemically  neutral 
salt.  Like  carbonic  acid,  it  does  not 
destroy  the  action  of  the  alkalies 
upon  test-papers,  and  we  are  there- 
fore deprived  of  this  method  of 
ascertaining  the  proportion  of  alkali 
which  neutralises  it  in  a  chemical 
sense.  In  attempting  to  ascertain 
the  quantity  of  alkali  with  which  silica  combines,  from  that  of  the  carbon 
dioxide  which  it  expels  when  heated  with  an  alkaline  carbonate,  it  is 
found  that  the  proportion  of  carbon  dioxide  expelled  varies  considerably, 
according  to  the  temperature  and  the  proportion  of  alkaline  carbonate 
employed. 

By  heating  silica  with  sodium  hydrate  (NaHO),  it  is  found  that  60 
parts  of  silica  expel  36  parts  of  water,  however  much  sodium  hydrate  is 
employed,  and  the  same  proportion  of  water  is  expelled  from  barium 
hydrate  Ba(HO)o  when  heated  with  silica. 

The  formula  Si02  represents  60  parts  by  weight  of  silica,  and  36  parts 
represent  two  molecules  of  water.  Hence  it  would  appear  that  the  action 
of  silica  upon  sodium  hydrate  is  represented  by  the  equation,  4NaH0 
-f  Si02  =  Na^SiO^-l-2H.26;  and  that  upon  barium  hydrate  by  2Ba(HO)2 
-f  SiO.,  =  Ba.2SiO^  -1-  2H5,0 :  and  since  it  is  found  that  several  of  the  crystal- 
lised mineral  silicates  contain  a  quantity  of  metal  equivalent  to  H^,  it  is 


Fig.  129. — Washing  precipitate. 


SILICON. 


117 


usual  to  represent  silicic  acid  as  a  tetrahasic  acid,  H^SiO^.  containing 
4  atoms  of  hydrogen  which  may  be  replaced  by  metals. 

The  circumstance  that  silica  is  not  capable  of  being  converted  into 
vapour  at  a  high  temperature,  enables  it  to  decompose  the  salts  of  many 
acids  which,  at  ordinary  temperatures,  are  able  to  displace  silicic  acid. 

The  silicates  form  by  far  the  greatest  number  of  minerals.  The 
different  varieties  of  clay  consist  of  aluminium  silicate;  felspar  is  a  silicate 
of  aluminium  and  potassium;  meerschaum  is  a  silicate  of  magnesium. 

The  different  kinds  of  glass  are  composed  of  silicates  of  potassium, 
sodium,  calcium,  lead,  &c. 

None  but  the  silicates  of  the  alkali  metals  are  soluble  in  water. 

Scarcely  any  of  the  silicates  are  represented  by  formulae  which  express 
their  derivation  from  the  acid  H^SiO^ ;  they  are  mostly  irregular  com- 
binations of  metallic  oxides  with  SiOo  . 


Fig.  130. — Air-gas  blowpipe  table. 


Yis.  131. — Charcoal  furnace. 


82.  Silicon  or  silidum  (Si  =  28  parts  by  weight). — From  the  remarkably 
unchangeable  character  of  silica,  it  is  not  surprising  that  it  was  long  re- 
garded as  an  elementary  substance.  In  1813,  however,  Davy  succeeded  in 
decomposing  it  by  the  action  of  potassium,  and  in  obtaining  an  impure 
specimen  of  silicon.  It  has  since  been  produced,  far  more  easily,  by  con- 
verting the  silica  into  potassium  silico-fluoride  (K2SiFg),  and  decomposing 
this  at  a  high  temperature  with  potassium  or  sodium,  which  combines 
with  the  fluorine  to  form  a  salt  capable  of  being  dissolved  out  by  water, 
leaving  the  silicon  in  the  form  of  a  brown  powder  {amorphous  silicon), 
which  resists  the  action  of  all  acids,  except  hydrofluoric,  which  it  decom  poses, 
forming  silicon  fluoride,  and  evolving  hydrogen  (Si-f  4HF=  SiF^-t-H^). 
It  is  also  dissolved  by  solution  of  potash,  with  evolution  of  hydrogen,  and 
formation,  of  potassium  silicate.  It  burns  brilliantly  when  heated  in 
oxygen,  but  not  completely,  for  it  becomes  coated  with  silica  which  is 
fused  by  the  intense  heat  of  the  combustion.  When  heated  with  the 
blowpipe  on  platinum  foil,  it  eats  a  hole  through  the  metal,  with  which 
it  forms  the  fusible  platinum  silicide. 

If  potassium  silico-fluoride  be  fused  with  aluminium,  a  portion  of  the 


118  CHEMICAL  RELATIONS  OF  SILICON. 

latter  combines  with  the  fluorine,  and  the  remainder  combines  with  the 
silicon,  forming  ahiminium  silicide.  By  boiling  this  with  hydrochloric  and 
hydrofluoric  acids  in  succession,  the  aluminium  is  extracted,  and  crystalline 
scales  of  silicon,  with  a  metallic  lustre  resembling  black  lead,  are  left 
{fjraphitoid  silicon).  In  this  form  the  silicon  has  a  speciflc  gravity  of 
about  2*5,  and  refuses  to  burn  in  oxygen,  or  to  dissolve  in  hydrofluoric 
acid.  A  mixture  of  nitric  and  hydrofluoric  acids,  however,  is  capable  of 
dissolving  it.  Like  graphite,  this  variety  of  silicon  conducts  electricity, 
though  amorphous  silicon  is  a  non-conductor.  The  amorphous  silicon 
becomes  converted  into  this  incombustible  and  insoluble  form  under  the 
action  of  intense  heat.  It  is  worthy  of  remark  that  the  combustibility  of 
amorphous  carbon  (charcoal)  is  also  very  much  diminished  by  exposure 
to  a  high  temperature. 

Unlike  carbon,  however,  silicon  is  capable  of  being  fused  at  a  tempera-, 
ture  somewhat  above  the  melting-point  of  cast-iron  ;  on  cooling,  it  forms 
a  brilliant  metallic-looking  mass,  which  may  be  obtained,  by  certain  pro- 
cesses, crystallised  in  octahedra  so  hard  as  to  scratch  glass  like  a  diamond. 

In  their  chemical  relations  to  other  substances  there  is  much  resem* 
blance  between  silicon  and  carbon.  Silicon,  however,  is  capable  of 
displacing  carbon,  for  if  potassium  carbonate  be  fused  with  silicon,  the 
latter  is  dissolved,  forming  potassium  silicate,  and  carbon  is  separated. 
Silicon  also  resembles  carbon  in  its  disposition  to  unite  with  certain  metals 
to  form  compounds  which  still  retain  their  metallic  appearance.  Thus 
silicon  is  found  together  with  carbon  in  cast-iron,  and  it  unites  directly 
with  aluminium,  zinc,  and  platinum,  to  form  compounds  resembling 
metallic  alloys.  Nitrogen  enters  into  direct  union  with  silicon  at  a  high 
temperature,  though  it  refuses  to  unite  with  carbon  except  in  the  presence 
of  alkalies. 

Silicon  nitride  (SiN)  has  been  obtained  by  heating  silica  with  carbon  in  a  blast 
furnace,  and  treating  the  product  successively  with  hydrofluoric  acid  and  potash,  when 
the  nitride  is  left  as  a  green  infusible  powder  which  is  attacked  by  potash  at  a  red 
heat,  yielding  potassium  silicate,  hydrogen,  and  ammonia.  When  heated  in  chlorine, 
it  is  converted  into  a  white  substance  soluble  in  hydrofluoric  acid,  and  apparently 
containing  SisN^.  A  similar  body  is  also  formed  in  the  preparation  of  the  green 
nitride. 

In  their  relation  to  hydrogen,  carbon  and  silicon  are  widely  different, 
for  silicon  is  only  known  to  form  one  compound  with  hydrogen,  and  that 
of  a  very  unstable  character. 

The  silicon- hydride  has  been  found  to  have  a  composition  corresponding 
with  the  formula  SiH^.  It  derives  its  interest  chiefly  from  the  property 
of  taking  fire  spontaneously  in  contact  with  the  air,  in  which  it  burns 
with  a  brilliant  white  flame,  giving  off"  clouds  of  silica,  and  depositing  a 
brown  film  of  silicon  upon  a  cold  surface. 

Silicon  hydride  is  prepared  by  decomposing  magnesium  silicide  with  dilute  hydro- 
chloric acid.  The  magnesium  silicide  is  obtained  by  fusing  magnesium  chloride  (MgClj) 
with  sodium  silico-fluoride  (NagSiFg),  and  metallic  sodium,  when  the  latter  combines 
with  the  chlorine  and  fluorine,  leaving  the  magnesium  free  to  unite  with  the  silicon. 

The  magnesium  chloride  may  be  prepared  by  dissolving  ordinary  magnesium 
carbonate  in  hydrochloric  acid,  adding  three  parts  of  ammonium  chloride  for  each 
part  of  carbonate,  evaporating  to  dryness  in  a  porcelain  dish,  fusing  the  residue,  and 
pouring  it  out  on  to  a  clean  stone.  Being  very  deliquescent,  it  must  be  kept  in  a 
well-closed  bottle. 

Sodium  silico-fluoride  is  made  by  neutralising  hydro-fluosilicic  acid  with  sodium 
carbonate,  and  evaporating  to  dryness. 


HYDRIDE  OF  SILICON. 


119 


To  increase  the  fusibility  of  the  mixture,  some  fused  common  salt  will  be  required. 
Dried  salt  may  be  melted  in  a  fireclay  crucible,  at  a  bright  red  heat,  and  jjoured  out 
upon  a  clean  dry  stone. 

Eight  parts  of  the  magnesium  chloride,  7  of  sodium  silico-fluoride,  2  of  fused 
chloride  of  sodium,  and  4  of  sodium  in  slices,  are  raj)idly  weighed,  shaken  together 
in  a  dry  bottle,  and  thrown  into  a  red  hot  clay  crucible,  which  is  then  covered  and 
heated  as  long  as  the  yellow  flame  of  sodium  vapour  is  perceptible.  After  cooling, 
the  crucible  is  broken,  when  a  dark-coloured  layer  of  magnesium  silicide  will  be  found 
beneath  a  white  lajer  of  chloride  and  fluoride  of  sodium.  The  silicide  must  be 
rapidly  detached,  and  preserved  in  a  well-stopped  bottle.   . 

The  magnesium  silicide  is  coarsely  powdered,  and  introduced  into  a  Woulfe's 
bottle  (fig.  132)  provided  with  a  funnel  tube,  and  a  short  wide  tube  for  delivering 
the  gas.  The  bottle  is  filled  up  with  water  (previously 
boiled  to  expel  air,  and  allowed  to  cool),  and  placed  in 
the  pneumatic  trough  (containing  boiled  water),  so 
that  both  bottle  and  tubes  may  remain  filled  with 
water.  A  gas-jar,  filled  with  boiled  water,  having  been 
placed  over  the  delivery -tube,  some  strong  hydrochloric 
acid  is  added  through  the  funnel,  great  care  being  taken 
that  no  air  shall  enter.  The  silicon  hydride  is  at  once 
evolved,  and  must  be  allowed  to  stand  over  water  for 
some  little  time,  to  allow  the  froth,  caused  by  a  slight 
separation  of  silica,  to  subside.  The  gas  may  then  be 
transferred  to  a  capped  jar,  with  a  stopcock,  from  ^ 
which  it  may  be  allowed  to  pass  into  the  air  for  the  ^ 
examination  of  its  flame. 

When  cast-iron,  containing  silicon,  is  boiled  with 
hydrochloric  acid  until  the  whole  of  the  iron  is  dis- 
solved, a  grey  frothy  residue  is  left.  If  this  be  collected  on  a  filter,  well  washed  and 
dried,  it  is  found  to  consist  of  black  scales  of  graphite,  mixed  with  a  verj"  light 
white  powder.  On  boiling  it  with  potash,  hj^drogen  is  evolved  and  the  white  powder 
dissolves,  forming  a  solution  containing  potassium  silicate.  This  white  powder  appears 
to  be  identical  with  a  substance  obtained  by  other  processes,  and  called  leicconc* 
which  is  believed  to  have  the  composition  Si3H40g,  and  has  been  regarded  as  a 
hydrate  of  protoxide  of  silicon,  3SiO.2H.2O.  Its  action  upon  solution  of  potash  would 
be  explained  by  the  equation — 

SisH^Oj  -f  12KH0  =  3X^8104  +  Hg  +  5H2O . 
Leucone  is  slowly  converted  into  silicic  acid,  even  by  the  action  of  water,  hydrogen 
being  disengaged. 

Another  compound,  containing  silicon,  hydrogen,  and  oxygen,  has  been  named 
silicone.  It  is  a  yellow  substance,  the  general  characters  of  which  resemble  those  of 
the  compound  last  described.  When  exposed,  under  water,  to  the  action  of  sunlight, 
hydrogen  is  evolved,  and  the  yellow  body  becomes  converted  into  leucone. 


im.  132. 


BOROX. 

83.  Closely  allied  to  silicon  is  another  element,  boron,  which  has  at 
present  never  been  found  in  animal  or  vegetable  bodies,  but  appears  to 
be  entirely  confined  to  the  mineral  kingdom. 

Anhydrous  Boracic  Acid  (£203  =  69*8  parts  by  weight). — A  saline  sub- 
stance called  borax  {^?L.^^O,.\(i  Aq.)  has  long  been  used  in  medicine, 
in  working  metals,  and  in  making  imitations  of  precious  stones ;  this 
substance  Avas  originally  imported  from  India  and  Thibet,  where  it  was 
obtained  in  crystals  from  the  waters  of  certain  lakes,  and  came  into  this 
country  under  the  native  designation  of  tincal,  consisting  of  impure  borax, 
surrounded  with  a  peculiar  soapy  substance,  which  the  refiner  of  borax 
makes  it  his  business  to  remove. 

In  1702,  in  the  course  of  one  of  those  experiments  to  which,  though 
empirical  in  their  nature,  scientific  chemistry  is  now  so  deeply  indebted, 

*  AeuKos,  white. 


120 


BORON. 


Homberg  happened  to  distil  a  mixture  of  borax  and  green  vitriol  (ferrous 
sulphate),  when  he  obtained  a  new  substance  in  pearly  plates,  w-hich  was 
found  useful  in  medicine,  and  received  the  name  of  sedative  salt.  A 
quarter  of  a  century  later,  Lemery  found  that  this  substance  might  be 
separated  from  borax  by  employing  sulphuric  acid  instead  of  ferrous 
sulphate ;  but  another  quarter  of  a  century  elapsed  before  it  w^as  shown 
that  in  borax  these  pearly  crystalline  scales  were  combined  with  soda,  and 
were  possessed  of  acid  properties  which  entitled  them  to  receive  the  name 
horacic  add. 

Much  more  recently  this  acid  has  been  obtained  in  a  free  state  from 
natural  sources,  and  is  now  largely  imported  into  this  country  from  the 
volcanic  districts  in  the  north  of  Italy,  where  it  issues  from  the  earth  in 
the  form  of  vapour,  accompanied  by  violent  jets  of  steam,  which  are 
known  in  the  neighbourhood  as  soffi.oni.  It  would  appear  easy  enough, 
by  adopting  arrangements  for  the  condensation  of  this  steam,  to  obtain  the 
boracic  acid  which  accompanies  it,  but  it  is  found  necessary  to  cause  the 
steam  to  deposit  its  boracic  acid  by  passing  it  through  water,  for  which 
purpose  basins  of  brickwork  {laguves,  fig.  133)  are  built  up  around  the 
Boffioni,  and  are  kept  filled  with  water  from  the  neighbouring  springs  or 


Fig,  133. — Boracic  lagune  and  evaporating  pans. 

brooks ;  this  water  is  allowed  to  flow  successively  into  the  different  lagunes, 
which  are  built  upon  a  declivity  for  that  purpose,  and  it  thus  becomes 
impregnated  with  about  1  per  cent,  of  boracic  acid.  The  necessity  for. 
expelling  a  large  proportion  of  this  water,  in  order  to  obtain  the  boracic 
acid  in  crystals,  formed  for  a  long  time  a  great  obstacle  to  the  success  of 
this  branch  of  industry  in  a  country  where  fuel  is  very  expensive.  In 
1817,  however,  Larderello  conceived  the  project  of  evaporating  this  water 
by  the  steam  heat  afforded  by  the  soffioni  themselves,  and  several  hundred 
tons  of  boracic  acid  are  now  annually  produced  in  this  manner.  The 
evaporation  is  conducted  in  shallow  leaden  evaporating  pans  (A,  fig.  133), 
under  which  the  steam  from  the  soffioni  is  conducted  through  the  Hues  (F) 
constructed  for  that  purpose.  As  the  demand  for  boracic  acid  increased 
on  account  of  the  immense  consumption  of  borax  in  the  porcelain  manu- 
facture, the  experiment  was  made,  with  success,  of  boring  into  the  volcanic 
strata,  and  thus  producing  artificial  soffioni,  yielding  boracic  acid. 

The  crystals  of  boracic  acid,  as  imported  from  these  sources,  contain 
salts  of  ammonia  and  other  impurities.  They  dissolve  in  about  three 
times  their  weight  of  boiling  water,  and  crystallise  out  on  cooling,  since 


EORACIC  ACID,  121 

they  require  26  parts  of  cold  water  to  dissolve  them.  These  crystals  are 
represented  by  the  formula  SH^O.BgOg  (or  H3BO3).  If  they  are  sharply 
heated  in  a  retort,  they  partly  distil  over  unchanged,  together  with  the 
water  derived  from  the  decomposition  of  another  part ;  but  if  they  be 
heated  to  212°  F.  only,  they  effloresce,  and  become  converted  into 
HgO.  B.jOg.  When  this  is  further  heated,  the  whole  of  the  water  passes  off, 
carrying  with  it  a  little  boracic  acid,  and  the  BgOg  fuses  to  a  glass,  which 
remains  perfectly  transparent  on  cooling  [ntreous  boracic  acid).  This  is 
slowly  volatilised  by  the  continued  action  of  a  very  high  temperature.  It 
dissolves  very  slowly  in  water.  Boracic  acid  is  an  antiseptic,  i.e.,  it 
hinders  putrefaction,  and  is  applied  either  alone  or  in  combination  with 
glycerine,  for  the  preservation  of  milk,  meat,  and  other  foods.  It  is  also 
said  to  kill  grass. 

A  characteristic  property  of  boracic  acid  is  that  of  imparting  a  green 
colour  to  flames.  Its  presence  may  thus  be  detected  in  the  steam  issuing 
from  a  boiling  solution  of  boracic  acid  in  water  ;  for  if  a  spirit-lamp  flame 
or  a  piece  of  burning  paper  be  held  in  the  steam,  the  flame  will  acquire  a 
green  tint,  especially  at  the  edges. 

The  colour  is  more  distinctly  seen  when  the  crystallised  boracic  acid  is  heated  on 
platinum  foil  in  a  spirit-flame  or  an  air-gas  flame  ;  and  still  better  when  the  crystals 
are  dissolved  in  boiling  alcohol,  and  the  solution  burnt  on  a  plate.  The  presence  of 
boracic  acid  in  borax  may  be  ascertained  by  mixing  the  solution  of  borax  with  strong 
sulphuric  acid  to  liberate  the  boracic  acid,  and  adding  enough  alcohol  to  make  the 
mixture  burn.  Another  peculiar  property  of  boracic  acid  is  its  action  upon  turmeric. 
If  a  piece  of  turmeric  paper  be  dipped  in  solution  of  boracic  acid  and  dried  at  a  gentle 
heat,  it  assumes  a  fine  brown-red  colour,  which  is  changed  to  green  or  blue  by  potash 
or  its  carbonate.  In  applying  this  test  to  borax,  the  solution  is  slightly  acidified 
with  hydrochloric  acid,  to  set  free  the  boracic  acid,  before  dipping  the  paper. 

Borates. — Boracic  acid,  like  silicic,  must  be  classed  among  the  feeble 
acids.  It  colours  litmus  violet  only,  like  carbonic  acid,  and  does  not 
neutralise  the  action  of  the  alkalies  upon  test-papers.  At  high  tempera- 
tures, fused  boracic  anhydride  combines  with  the  alkalies  and  metallic 
oxides  to  form  transparent  glassy  borates,  which  have,  in  many  cases,  very 
brilliant  colours,  and  upon  this  property  depend  the  chief  uses  of  boracic 
acid  in  the  arts. 

Unlike  the  silicates,  the  borates  are  comparatively  rare  in  the  mineral 
world.  No  very  familiar  mineral  substance  contains  boracic  acid.  A 
double  borate  of  sodium  and  calcium,  called  horo-natrocalcite  (XagB^O;. 
CagBgOj^.lSHgO),  is  imported  from  Peru  for  the  manufacture  of  borax, 
and  the  mineral  known  as  horacite  is  a  magnesium  borate. 

In  determining  the  proportion  of  base  which  boracic  acid  requires  to 
form  a  chemically  neutral  salt,  the  same  difficulties  are  met  with  as  in  the 
case  of  silicic  acid  (p.  116);  but  since  it  is  found  that  69*8  parts  of 
boracic  anhydride  (the  weight  represented  by  B2O3)  displace  54  parts  of 
water  (three  molecules)  from  sodium  hydrate  and  from  barium  hydrate, 
both  employed  in  excess,  it  would  appear  that  the  boracic  acid  requires 
three  molecules  of  an  alkali  fully  to  satisfy  its  acid  character. 

The  action  of  B.,03  upon  an  excess  of  NaHO  would  be  represented  by 
the  equation  6NaH0  -I-  BgO^  =  2Xa3B03  -1-  3HoO.  Hence  boracic  acid  is 
a  tribasic  acid  *  represented  by  the  formula  H3BO3,  which  is  the  composi- 
tion of  the  crystallised  acid,  but  the  formulae  of  the  common  borates 
cannot  be  made  to  accord  with  this  view. 

*  A  tribasic  acid  is  one  which  contains  three  atoms  of  hydrogen  replaceable  by  metals. 


12'1  DIAaMOND  OF  BORON. 

84.  Boron  (B=  10'9  parts  by  weight). — It  was  in  the  year  1808  that 
Gay-Lussac  and  Thenard  succeeded,  by  fusing  boracic  anhydride  with 
potassium,  in  extracting  from  it  the  element  boron, ,  as  an  olive-green 
powder  {amorphous  boron),  which  has  a  general  resemblance  to  silicon, 
but,  unlike  that  element,  may  be  oxidised  by  nitric  acid.  It  also  requires 
a  higher  temperature  to  fuse  it  than  is  required  by  silicon.  The  brilliant 
copper-coloured  scales  obtained  by  a  process  similar  to  that  which  fur- 
nishes the  grapbitoid  silicon,  and  formerly  regarded  as  graphitoid  boron, 
consist  really  of  a  compound  of  boron  with  alumiidum  (AlBg). 

The  most  remarkable  form  of  boron  is  the  crystallised  variety  or  diamond 
of  boron,  which  is  obtained  by  very  strongly  heating  amorphous  boron 
with  aluminium,  and  afterwards  extracting  the  aluminium  from  the  mass 
with  hydrochloric  acid.  These  crystals  are  brilliant  transparent  octahedra, 
which  are  sometimes  nearly  colourless,  and  resemble  the  diamond  in  their 
power  of  refracting  light,  and  in  their  hardness,  which  is  so  great  that 
they  will  scratch  rubies,  and  will  even  wear  away  the  surface  of  the 
diamond.*  This  form  of  boron  cannot  be  attacked  by  any  acid,  but  is 
dissolved  by  fused  alkalies.  The  flame  of  the  oxyhydrogen  blowpipe  does 
not  fuse  it,  and  it  only  undergoes  superficial  conversion  into  boracic 
anhydride  when  heated  to  whiteness  in  oxygen.  When  heated  to  redness 
in  chlorine,  however,  it  burns,  forming  boron  trichloride.  Boron  closely 
resembles  silicon  in  its  chemical  relations  to  the  other  elementa  It  forms 
a  compoiind  with  hydrogen  which  is  a  spontaneously  inflammable  gas,  burn- 
ing with  a  green  flame,  and  obtained  by  heating  fused  boracic  anhydride 
with  magnesium  and  treating  the  mass  with  hydrochloric  acid.  Boron 
shows  greater  disposition  to  combine  with  nitrogen  than  is  manifested  by 
silicon.  It  absorbs  nitrogen  readily  when  heated  to  redness,  forming  a 
white  infusible  insoluble  powder,  the  ba)-on  nitride  (BN). 

85.  The  elements  carbon,  boron,  and  silicon  form  a  natural  group,  pos- 
sessing many  properties  in  common.  They  are  all  capable  of  existing  in 
the  amorphous  and  the  crystalline  forms  ;  all  incapable  of  being  converted 
into  vapour  ;  all  exhibit  a  want  of  disposition  to  dissolve  ;  all  form  feeble 
acid  oxides  by  direct  union  with  oxygen ;  and  all  unite  with  several  of 
the  metals  to  form  compounds  which  resemble  each  other.  Boron  and 
silicon  are  capable  of  direct  union  with  nitrogen,  and  so  is  carbon  if  an 
alkali  be  present.  Eecent  researches  attribute  to  silicon  the  power  of 
occupying  the  place  of  carbon  in  some  organic  compounds,  and  the 
formulae  of  leucone  and  silicone  (SijH^O^  and  SigHgO^)  strongly  remind, 
us  of  the  organic  compounds  of  carbon  with  hydrogen  and  oxygen.  In 
many  of  its  physical  and  chemical  characters  silicon  is  closely  allied  with 
the  metals,  and  it  will  be  found  that  tin  and  titanium  bear  a  particular 
resemblance  to  it  in  their  chemical  relations. 

NITROGEN. 

K  =  14  part^  by  weight  =  l  volume  ;  14  graius  =  467  cub.  in.  at  60°  F.  and  30' 
Bar.  ;  14  grammes  =  ll-2  litres  at  0°C.  and  760  mm.  Bar. 

86.  This  element,  which  has  already  been  referred  to  as  forming  four- 
fifths  of  the  volume  of  air,  is  elsewhere  found  in  nature  in  the  forms  of 
saltpetre   or  potassium   nitrate  (KNO3),  and  Chili  saltpetre  or   sodium 

*  The  author  has  known  them  to  cut  through  the  bottom  of  the  beaker-glass  used  in 
separating  them  from  the  aluminium. 


NITROGEl^. 


123 


nitrate  (NaNOo).  It  also  occurs  as  ammonia  (NHg)  in  the  atmospliere 
and  in  the  gaseous  emanations  from  volcanoes.  It  is  contained  in  the 
greater  number  of  animal,  and  in  many  vegetable,  substances,  and  therefore 
has  a  most  important  share  in  the  chemical  phenomena  of  life. 

Nitrogen  is  generally  obtained  by  burning  phosphorus  in  a  portion  of 
air  confined  over  water  (fig.  134).  The  phosphorus  is  floated  on  the  water 
in  a  small  porcelain  dish,  kindled,  and  covered  with  a  bell-jar.  The 
nitrogen  remains  mixed  with  clouds  of 
phosphoric  anhydride  (PgO^),  which  may 
be  removed  by  allowing  the  gas  to  stand 
over  water. 

When  nitrogen  is  required  in  larger 
quantity,  it  is  more  conveniently  prepared 
by  passing  air  from  a  gas-holder  over 
metallic  copper  heated  to  redness  in  a 
tube.  The  negative  properties  of  this 
gas,  however,  are  so  very  uninteresting, 
and  render  it  so  useless  for  most  chemical 
purposes,  that  it  will  be  unnecessary  to 
give  further  details  respecting  its  pre- 
paration. The  remarkable  chemical  in- 
activity of  free  nitrogen  has  been  alluded  to  in  the  article  on  atmospheric 
air.  It  has  been  seen,  however,  to  be  capable  of  combining  directly  with 
boron  and  silicon,  and  magnesium  and  titanium  unite  with  it  even  more 
readily  at  a  high  temperature.*  It  is  conspicuous  among  the  elements  for 
forming,  with  hydrogen,  a  powerful  alkali  (ammonia,  NHg),  whilst  the 
feeble  chemical  ties  which  hold  it  in  combination  with  other  elements, 
joined  to  its  character  of  a  permanent  gas,  render  many  of  its  compounds 
very  unstable  and  explosive,  as  is  the  case  with  the  so-called  chloride  and 
iodide  of  nitrogen,  gun-cotton,  the  fulminates  of  silver  and  mercury,  nitro- 
glycerine, &c. 

The  discovery  of  nitrogen  was  made  in  1872,  by  Rutherford  (Professor 
of  Botany  in  the  University  of  Edinburgh),  who  was  led  to  it  by  the 
observation  that  respired  air  was  still  unfit  to  support  life  when  all  the 
carbonic  acid  had  been  absorbed  from  it  by  a  caustic  alkali.  Hence  the 
name  azote  (a  priv.  and  ^wrj,  life)  formerly  bestowed  upon  this  gas. 

Nitrogen  has  been  liquefied  by  the  cold  produced  by  its  expansion  from 
a  compression  of  300  atmospheres  at  13°  C. 


Fig.  134. — Preparation  of  nitrogen. 


Ammonia. 

NH3  =  17  parts  by  weight  =  2  volumes. 

87.  The  proportion  of  ammonia  existing  in  atmospheric  air  is  so  small 
that  it  is  difficult  to  determine  it  with  precision ;  it  appears,  however,  not 
to  exceed  one-hundredth  of  a  grain  in  a  cubic  foot ;  for  although  ammonia 
is  constantly  sent  forth  into  the  air  by  the  putrefaction  of  animal  and 
vegetable  substances  containing  nitrogen,  it  is  soon  absorbed  by  water,  and 

*  Small  quantities  of  ammonia  have  recently  been  produced  by  the  combination  of 
nitrogen  with  hydrogen  under  the  influence  of  electric  discharges.  G.  S.  Johnson  has 
shown  that  if  any  substance  capable  of  absorbing  ammonia  be  present,  such  as  H2SO4,  a 
mixture  of  N  with  H3  may  be  entirely  converted  into  NH3  by  passing  the  induced  spark 
for  some  time. 


124 


PREPARATION  OF  AMMONIA. 


even  by  earth  and  other  porous  solids.  Plants  do  not  appear  to  be  capable 
of  absorbing  from  the  atmosphere  the  nitrogen  which  it  contains  so 
abundantly  in  the  uncombined  form,  but  to  derive  their  chief  supply  of 
that  element  from  the  ammonia,  and  nitrates  or  nitrites  contained  in  the 
air,  the  soil,  and  the  water.  During  the  life  of  an  animal,  it  restores  to  the 
air  the  nitrogen  which  formed  part  of  its  wasted  organs,  in  part  directly 
as  ammonia  in  the  breath  and  in  the  exhalation  from  the  skin,*  whilst 
another  portion  is  separated  as  urea  and  uric  acid  in  the  ■  urine,  to  be 
eventually  converted  into  ammonia  when  the  excretion  undergoes  putrefac- 
tion. Dead  animal  and  vegetable  matter,  when  putrefying,  restores  its 
nitrogen  to  the  air,  chiefly  in  the  forms  of  ammonia  and  substances  closely 
allied  to  it,  but  partly  also,  it  is  said,  in  the  free  state. 

The  liquor  ammoniiE,  or  solution  of  ammonia  in  water,  which  is  so  largely 
used  in  medicine  and  the  arts,  is  obtained  chiefly  from  the  ammoniacal 
liquor  resulting  from  the  destructive  distillation  of  coal  for  the  manufac- 
ture of  gas.  The  ammoniacal  liquor  of  the  gas-works  contains  ammonia 
in  combination  with  carbonic  and  hydrosulphuric  acid.  As  the  first  step 
towards  extracting  the  ammonia  in  a  pure  state,  the  liquor  is  neutralised 
with  hydrochloric  acid,  which  combines  with  the  ammonia,  expelling  the 
carbonic  and  hydrosulphuric  acid  gases.  Since  the  latter  has  a  very  bad 
smell  and  is  injurious  to  health,  the  neutralisation  is  generally  effected 
in  covered  vats  furnished  with  pipes,  which  convey 
the  gases  into  a  furnace  where  the  hydrosulphuric 
acid  is  burnt,  forming  water  and  sulphurous  acid 
gas.  The  solution  is  evaporated  to  expel  part  of 
the  water,  and  allowed  to  cool  in  wooden  vessels 
lined  with  lead,  where  ammonium  chloride  is 
deposited  in  crystals  which  contain  a  good  deal  of 
tarry  matter.  These  crystals  are  moderately  heated 
in  an  iron  pan  to  deprive  them  of  tar,  and  are 
finally  purified  by  sublimation,  that  is,  by  con- 
verting them  into  vapour  and  allowing  this  vapour 
to  condense  again  into  the  solid  form.  For  this 
purpose  the  crystals  are  heated  in  a  cylindrical 
iron  vessel  covered  with  an  iron  dome  lined  with 
fireclay.  The  ammonium  chloride  rises  in  vapour 
below  a  red  heat,  and  condenses  upon  the  dome  in 
the  form  of  the  fibrous  cake  known  in  commerce 
of  sal  ammoniac. 
To  obtain  ammonia  from  this  salt,  an  ounce  of  it  is  reduced  to  coarse 
powder,  and  rapidy  mixed  with  2  ounces  of  powdered  quicklime. 
The  mixture  is  gently  heated  in  a  dry  Florence  flask  (fig.  135),  and 
the  gas  being  little  more  than  half  as  heavy  as  air  (sp.  gr.  0*59)  may 
be  collected  in  dry  bottles  by  displacement  of  air,  the  bottles  being 
allowed  to  rest  upon  a  piece  of  tin  plate  which  is  perforated  for  the 
passage  of  the  tube.  To  ascertain  when  the  bottles  are  filled,  a  piece  of 
red  litmus  paper  may  be  held  at  some  little  distance  above  the  mouth, 
when  it  will  at  once  acquire  a  blue  colour  if  the  ammonia  escapes.  The 
bottles  should  be  closed  with  greased  stoppers. 


Fig.  135. — Preparation 
of  ammonia. 


*  Some  doubt  exists  as  to  the  exhalation  of  ammonia  from  the  Imigs  and  skin  of  man 
under  normal  conditions. 


PROPERTIES  OF  AMMONIA. 


125 


Fig.  136. 


The  action  is  explained  by  the  following  equation  : — 

2XH,C1  +  CaO  =  CaClg  +  H^O  +  2NH3 

Ammonium  Lime.        Chloride  of  Ammonia, 

chloride.  ^""c-  calcium. 

The  readiest  method  of  obtaining  gaseous  ammonia  for  the  study  of  its  properties 
consists  in  gently  heating  the  strongest  liquor  ammonm  in  a  retort  or  flask  provided 
with  a  bent  tube  for  collecting  the 
gas  by  displacement  (fig.  136).  The 
gas  is  evolved  from  the  solution  at  a 
very  low  temperature,  and  may  be 
collected  unaccompanied  by  steam. 

Ammonia  is  readily  distin- 
guished by  its  very  characteristic 
smell,  and  its  powerful  alkaline 
action  upon  red  litmus  and  tur- 
meric papers.  It  is  absorbed  by 
water  in  greater  proportion  by 
volume  than  any  other  gas,  one 
volume  of  water  absorbing  more 
than  700  volumes  of  ammonia 
at  the  ordina^j^  temperature,  and 
becoming  H  vjalumes  of  solution 
of  ammonia.  ;Xo  chemical  com- 
bination appears'  to"  take  place  between  the  water  and  ammonia,  for  the 
gas  gradually  lescapes  on  exposing  the  solution  to  the  air,  and  no  definite 
compound  of  the  two  has  been  noticed.  Moreover,  the  quantity  of 
ammonia  retained  by  the  water  is  dependent  upon  the  temperature  and 
pressure,  as  would  be  expected  if  the  ammonia  were  merely  dissolved  and 
not  combined  with  the  water.  The  escape  of  the  gas  from  the  solution 
is  attended  with  great  production  of  cold,  much 
heat  becoming  latent  in  the  conversion  of  the 
ammonia  from  the  liquid  to  the  gaseous  state. 

The  rapid  absorption  of  ammonia  by  water  is  well 
shown  by  filling  a  globular  flask  (fig.  137),  with  the 
gas,  placing  it  with  its  mouth  downwards  in  a  small 
capsule  of  mercury  which  is  placed  in  a  large  basin.  If 
this  basin  be  filled  with  water,  it  cannot  come  into 
contact  with  the  ammonia  until  the  mouth  of  the  flask 
is  raised  out  of  the  mercury,  when  the  water  will 
quickly  enter  and  fill  the  flask.  The  water  should  be 
coloured  with  reddened  litmus  to  exhibit  the  alkaline 
reaction  of  the  ammonia. 

That  the  amount  of  ammonia  in  solution  varies  with 
the  pressure,  may  be  proved  by  filling  a  barometer  tube, 
over  30  inches  long,  with  mercury  to  within  an  inch  of 
the  top,  filliug  it  up  with  strong  ammonia,  closing  the  mouth  of  the  tube,  and 
inverting  it  with  its  mouth  under  mercury;  on  removing  the  finger,  the  diminished 
pressure  caused  by  the  gravitation  of  the  column  of  mercury  in  the  tube  will  cause 
the  solution  of  ammonia  to  boil,  from  the  escape  of  a  large  quantity  of  the  gas,  which 
will  rapidly  depress  the  mercury.  If  the  pressure  be  now  increased  by  gi'adually 
depressing  the  tube  in  a  tall  cylinder  of  mercury  (tig.  138),  the  water  will  again 
absorb  the  ammoniacal  gas. 

To  exhibit  the  easy  expulsion  of  the  ammoniacal  gas  from  water  by  heat,  a 
moderately  thick  glass  tube  about  12  inches  long  and  \  inch  in  diameter,  may  be 
nearly  filled  with  niercur}-,  and  then  filled  up  with  strong  solution  of  ammonia  ;  on 
closing  it  with  the  thumb,  and  inverting  it  into  a  vessel  of  mercur)'  (fig.  139)  the 
solution  will,  of  course,  rise  above  the  mercury  to  the  closed  end  of  the  tube.  By 
grasping  this  end  of  the  tube  in  the  hand,  a  considerable  quantity  of  gas  may  be 


Fig.  137. 


126 


SPECIFIC  GRAVITY  OF  LIQUIDS  DETERMINED. 


expelled,  and  the  mercury  will  be  depressed.  If  a  little  hot  water  be  poured  over  the 
top  of  the  tube,  the  latter  will  become  filled  with  ammoniacal  gas,  which  will  be 
absorbed  again  by  the  water  when  the  tube  is  allowed  to  cool,  the  mercury  returning 
to  fill  the  tube. 

The  solution  of  ammonia,  which  is  an  article  of 
commerce,  may  be  prepared  by  conducting  the  gas 
into  water  contained  in  a  two-necked  bottle,  the 
second  neck  being  connected  with  a  tube  passing 
into  another  bottle  containing  water,  in  which  any 
escaping  ammon4a  may  be  condensed.  The  strength 
of  the  solution  is  inferred  from  its  specific  gravity, 
which,  is  lower  in  proportion  as  the  quantity  of 
ammonia  in  the  solution  is  greater.  .; 


Fig.  138 


Fig.  139. 


Thus,  at  57°  F.,  a  solution  of  sp.  gr.  0*8844  contains  36  parts  by  weight  of 
ammonia  in  100  parts  of  solution  {liquor  ammonicc  fortissimus) ;  the  sp.  gr.  0'8976 
indicates  30  per  cent.  ;  0-9106,  25  per  cent.  ;  0-9251,  20  per  cent.  ;  0-9414,  15  per 
cent.  ;  0-9593,  10  per  cent  {British  Pharmacopoeia) ;  0979,  5  per  cent.  The  specific 
gravity  is  ascertained  by  comparing  the  weights  of  equal  volumes  of  water  and  of  the 
solution  at  the  same  tempemture.  For  this  purpose  a  light  stop- 
pered bottle  is  provided,  capable  of  containing  about  two  ttuid 
ounces.  This  is  thoroughly  dried,  and  counterposed  in  a  balance 
by  placing  in  the  opposite  pan  a  piece  of  lead,  which  may  be  cut 
down  to  the  proper  weight.  The  bottle  is  then  filled  with  solution 
of  ammonia,  the  temperature  observed  with  a  thermometer  and 
recorded,  the  stopper  inserted,  and  the  bottle  weighed.  It  is  then 
well  rinsed  out,  filled  with  distilled  water,  the  temperature 
equalised  with  that  of  the  ammonia  by  placing  the  bottle  either  in 
warm  or  cold  water,  and  the  weight  ascertained  aa  before.  The 
specific  gravity  is  obtained  by  dividing  the  weight  of  the  solution  of 
ammonia  by  that  of  the  water.  The  ammonia  meter  (fig.  140)  is  a 
convenient  instrument  for  rapidly  ascertaining  the  specific  gravity 
of  liquids  lighter  than  water.  It  consists  of  a  hollow  glass  float 
with  a  long  stem,  weighted  with  a  bulb  containing  shot  or  mercury, 
so  that  when  placed  in  distilled  water  it  may  sink  to  1000°  of  the 
scale  marked  on  the  stem,  this  nuinl)er  representing  the  specific 
gravity  of  water.  When  placed  in  a  liquid  lighter  than  water,  it  must,  of  course, 
sink  lower  in  order  to  displace  more  liquid  (since  solids  sink  until  they  have  displaced 


Fig.  140, 


LIQUEFACTION  OF  AMMONIA. 


127 


their  own  weight  of  liquid).  By  trying  it  in  liquids  of  known  specific  gravities,  the 
mark  upon  the  scale  to  which  it  sinks  may  be  made  to  indicate  the  specific  gi'avity 
of  the  liquid.  The  ammonia  meter  generally  has  a  scale  so  divided  that  it  indicates 
at  once  the  percentage  weight  of  ammonia.  In  this  country  the  specific  gravity  of 
a  liquid  is  always  supposed  to  be  taken  at  60°  F. 

The  common  name  for  solution  of  ammonia,  spirit  of  harfs  horrid  is 
derived  from  the  circumstance  that  it  was  originally  obtained  for  medicinal 
purposes  by  distilling  shavings  of  that  materiaL 

"V\Tien  ammonia  is  exposed  to  a  temperature  of  —  40°  F.  (i.e.,  72°  below 
the  freezing-point),  or  to  a  pressure  of  6^  atmospheres  at  50°,  it  con- 
denses to  a  clear  liquid,  which  solidifies  at  a  temperature  of  - 103°  F. 
to  a  white  crystalline  mass.  The  comparative  ease  with  wiiich  it  may 
be  liquefied  has  led  to  its  application  in  Carre's  freezing  apparatus  (fig. 
141),  in  which  the  gas  generated  by  heating  a  concentrated  solution  of 
ammonia  in  a  strong  iron  boiler  (A)  is  liquefied  by  its  own  pressure  in  an 
iron  receiver  (B)  placed  in  cold  water.  When  the  boiler  is  taken  oif  the 
fire  and  cooled  in  water,  the  liquefied  ammonia  evaporates  very  rapidly 
from  the  receiver  back  into  the  boiler,  thereby  producing  so  much  cold  that 
a  vessel  of  water  (C)  placed  in  spirit  of  wine  contained  in  a  cavity  in  the 
receiver,  is  at  once  congealed  into  ice.  A  refrigerator  constructed  upon 
this  principle  is  employed  in  the  salt  gardens  of  the  south  of  France,  in 
order  to  render  their  crystallising  operations  independent  of  the  temperature 
of  the  air. 


Fig.  141.— Carre's  freezing  apparatus. 


Fig.  142. 


The  liquefaction  of  ammonia  is  very  easily  effected  by  heating  the  ammoniated 
silver  chloride  in  one  limb  of  a  sealed  tube,  the  other  limb  of  which  is  cooled  in  a 
freezing  mixture.  A  piece  of  stout  light  gi-een  glass  tube  (A,  fig.  142),  about  12 
inches  long  and  J  inch  in  diameter,  is  drawn  out,  at  about  an  inch  from  oue 
end,  to  a  narrow  neck.  About  300  grains  of  silver  chloi-ide  (dried  at  400°  F. )  are 
introduced  into  the  tube,  so  as  to  lie  loosely  in  it.  For  this  purpose  a  gutter  of  stiff" 
paper  (B)  should  be  cut  so  as  to  slide  loosely  in  the  tube,  the  silver  chloride 
placed  upon  it,  and  when  it  has  been  thrust  into  the  tube  (held  horizontally)  the 
latter  should  be  turned  upon  its  axis,  so  that  the  silver  chloride  may  fall  out  of 
the  paper,  which  may  be  tlien  withdi-awn.  The  tube  is  now  drawn  out  to  a  narrow 
neck  at  about  an  inch  from  the  other  end,  as  in  C,  and  afterwards  carefully  bent,  as 
in  D,  care  being  taken  that  none  of  the  chloride  falls  into  the  short  limb  of 
the  tube,  which  should  be  about  4  inches  long.  The  tube  is  then  supported  by 
a  holder,  so  that  the  long  limb  may  be  horizontal,  and  is  connected  by  a  tube  and 
cork  with  an  apparatus  delivering  dry  ammonia,  prepared  by  heating  1000  grains  of 
sal  ammoniac  with  an  equal  weight  of  quicklime  in  a  flask,  and  passing  the  gas,- 


128 


COMBUSTION  OF  AMMONIA. 


first  into  an  empty  bottle  (A,  fig  143)  standing  in  cold  water,  and  afterwards 
through  a  bottle  (B)  filled  with  lumps  of  quicklime  to  absorb  all  aqueous  vapour. 
The  long  limb  of  the  tube  must  be  surrounded  with  filtering  paper,  which  is  kept 
wet  with  cold  water.  The  current  of  ammonia  should  be  continued  at  a  moderate 
rate,  until  tlie  tube  and  its  contents  no  longer  increase  in  weight,  which  will  occupy 
about  three  hours — about  35  grains  of  ammonia  being  absorbed.     The  longer  limb 


Fig.  143. 

is  sealed  by  the  blowpipe  flame  whilst  the  gas  is  still  passing,  and  then,  as  quickly 
as  possible,  the  shorter  limb,  keeping  that  part  of  the  tube  which  is  occupied  by  the 
ainnioniated  silver  chloride  still  surrounded  by  wet  paper. 

When  the  shorter  limb  of  this  tube  is  cooled  (fig.  144),  in  a  mixture  of  ice 
and  salt  (or  of  8  ounces  of  sodium  sulphate  and  4  measured  ounces  of  common 
hydrochloric  acid),  whilst  the  longer  limb  is  "ently  heated  from  end  to  end  by  waving 
a  spirit-flame  beneath  it,  the  ammonia  evolved  by  the  heat  from  the  ammoniated 
silver  chloride,  which  partly  fuses,  will  condense  into  a  beautifully  clear  liquid 
in  the  cold  limb.  When  this  is  withdrawn  from  the  freezing  mixture,  and  the  tube 
allowed  to  cool,  the  liquid  ammonia  will  boil  and  gradually  disappear  entirely,  the 
gas  being  again  absorbed  by  the  silver  chloride,  so  that  the  tube  is  ready  to  be 
used  again. 


Fig.  144. — Liquefaction  of  ammonia.  Fig.  145. 

A  small  quantity  of  liquefied  ammonia  may  be  more  conveniently  obtained,  at 
lecture,  by  means  of  a  tube  prepared  as  above,  but  containing  about  twelve  inches  of 
fragments  of  well-dried  wood  charcoal  saturated  with  dried  ammonia  gas.  The  shorter 
limb  of  the  tube  should  be  drawn  out  to  a  long  narrow  point  before  sealing.  This 
limb  being  immersed  in  the  freezing  mixture,  the  other  is  placed  in  a  long  test-tube 
containing  water,  which  is  heated  to  boiling.  The  ammonia  soon  returns  to  the  char- 
coal when  the  tube  cools. 

Ammonia  is  feebly  combustible  in  atmospheric  air,  as  may  be  seen  by 
holding  a  taper  just  within  the  mouth  of  an  inverted  bottle  of  the  gas, 


DECOMPOSITION  OF  AMMONIA. 


129 


which  burns  with  a  peculiar  livid  flickering  light  around  the  flame,  but 
will  not  continue  to  burn  when  the  flame  is  removed.  During  its  com- 
bustion the  hydrogen  is  converted  into  water,  and  the  nitrogen  set  free. 
In  oxygen,  however,  ammonia  burns  with  a  continuous  flame. 

This  is  very  well  shown  by  surrounding  a  tube  delivering  a  stream  of  ammonia 
(obtained  by  heating  strong  solution  of  ammonia  in  a  retort)  with  a  much  wider 
cube  open  at  both  ends  (fig.  145) 
through  which  oxygen  is  passed  by 
holding  a  flexible  tube  from  a  gas-bag 
or  gas-holder  underneath  it.  On 
kindling  the  stream  of  ammonia  it 
will  give  a  steady  flame  of  10  or  12 
inches  long. 

A  similar  experiment  may  be  made 
with  a  smaller  supply  of  oxygen,  by 
lowering  the  tube  delivering  ammonia 
into  a  bottle  or  jar  of  oxygen,  and 
iipplying  a  light  to  it  just  as  it  enters 
the  mouth  of  the  jar  (fig.  146). 

The  elements  of  ammonia  are 
easily  separated  from  each,  other 
by  passing  the  gas  through  a  red 
hot  tube,  or  atill  more  readily  by  exposing  it  to  the  action  of  the  high 
temperature  of  the  electric  spark,  when  the  volume  of  the  gas  rapidly 
increases  until  it  is  exactly  doubled,  2  volumes  of  ammonia  being  decom- 
posed into  1  volume  of  nitrogen  and  3  volumes  of  hydrogen. 

For  this  experiment,  a  measured  volume  of  ammonia  gas  is  confined  over 
mercury  (fig.  147),  in  a  tube  through  which  platinum  wires  are  sealed  for  the 
passage  of  the  spark  from  an  induction-coil.     The  volume  of  the  gas  is  doubled  in 


Fig.  147. 


Fig.  148. 


a  few  minutes,  and  if  the  tube  be  furnished  with  a  stopcock  (A),  the  presence  of 
free  hydrogen  may  be  shown  by  filling  the  open  limb  with  mercury  and  kindling  the 
gas  as  it  issues  from  the  jet.* 

*  The  eudiometer  for  passing  electric  sparks  in  rapid  succession  must  have  the  platinum 
wires  passed  through  the  glass  as  shown  in  fig.  147,  or  it  will  be  cracked  by  the  heat  of  the 
sparks.  The  outlet  tube  B,  closed  by  a  small  screw  clamp  C,  pinching  a  caoutchouc  connec- 
tor, allows  the  mercury  to  be  drawn  off  when  necessary,  to  equalise  the  level  in  the  two  limbs. 


130  AMALGAM  OF  AMMONIUM. 

As  might  be  expected  from  its  powerfully  alkaline  character,  ammonia 
exhibits  a  strong  attraction  for  acids,  which  it  neutralises  perfectly.  If 
a  bottle  of  ammonia  gas,  closed  with  a  glass  plate,  be  inverted  over  a 
similar  bottle  of  hydrochloric  acid  ga.s,  and  the  glass  plates  withdrawn 
(fig  148),  the  gases  will  combine,  with  disengagement  of  much  heat, 
forming  a  white  solid,  ammonium  chloride  (NH^Cl),  in  which  the  acid 
and  alkali  have  neutralised  each  other.  Again,  if  ammonia  be  added  to 
diluted  sulphuric  acid,  the  latter  will  be  entirely  neutralised,  and  by 
evaporating  the  solution,  crystals  of  ammonium  sulphate  (^£^4)2804 
may  be  obtained. 

The  substances  thus  produced  by  neutralising  the  acids  with  solution 
of  ammonia  bear  a  strong  resemblance  to  the  salts  formed  by  neutralising 
the  same  acids  with  solutions  of  potash  and  soda,  a  circumstance  which 
would  encourage  the  idea  that  the  solution  of  ammonia  must  contain  an 
alkaline  hydrate  similar  to  KHO  or  NaHO. 

Berzelius  was  the  first  to  make  an  experiment  which  appeared  strongly 
to  favour  this  view  (commonly  spoken  of  as  the  ammonium  theory  of 
Berzelius).  The  negative  pole  of  a  galvanic  battery  was  placed  in  contact 
with  mercury  at  the  bottom  of  a  vessel  containing  a  strong  solution  of 
ammonia,  in  which  the  positive  pole  of  the  battery  was  immersed.  Oxygen 
was  disengaged  at  this  pole,  whilst  the  mercury  in  contact  with  the 
negative  pole  swelled  to  four  or  five  times  its  original  bulk,  and  became 
a  soft  solid  mass,  still  preserving,  however,  its  metallic  appearance.* 
So  far,  the  result  of  the  experiment  resembles  that  obtained  when 
potassium  hydrate  is  decomposed  under  similar  circumstances,  the  oxygen 
separating  at  the  positive  pole,  and  the  potassium  at  the  negative, 
where  it  combines  with  the  mercury.  Beyond  this,  however^  the 
analogy  does  not  hold ;  for  in  the  latter  case  the  metallic  potassium  can 
be  readily  separated  from  the  mercury,  whilst  in  the  former,  all  attempts 
to  isolate  the  ammonium  have  failed,  for  the  soft  solid  mass  resolves 
itself,  almost  immediately  after  its  preparation,  into  mercury,  ammonia 
(NH3),  and  hydrogen,  one  atom  of  the  latter  being  separated  for  each 
molecule  of  ammonia.  This  would  also  tend  to  support  the  conclusion 
that  a  substance  having  the  composition  NH3  +  H  or  NH^  had  united 
with  the  mercury ;  and  since  the  latter  is  not  known  to  unite  with  any  non- 
metallic  substance  without  losing  its  metallic  appearance,  it  would  be  fair  to 
conclude  that  the  soft  solid  was  really  an  amalgam  of  ammonium.  How- 
ever, the  increase  in  the  weight  of  the  mercury  is  so  slight,  and  the 
"  amalgam,"  whether  obtained  by  this  or  by  other  methods,  is  so  unstable, 
that  it  would  appear  safer  to  attribute  the  swelling  of  the  mercury  to  a 
physical  change  caused  by  the  presence  of  the  ammonia  and  hydrogen 
gases.  It  is  difficult  to  believe  that  the  solution  of  ammonia  does  really 
contain  ammonium  hydrate  (XHg  +  HgO  =  NH^HO),  when  we  find  it 
evolving  ammonia  so  easily ;  but  it  is  equally  difficult,  upon  any  other 
hypothesis,  to  explain  the  close  resemblance  between  the  salts  obtained  by 
neutralising  acids  with  this  solution  and  those  furnished  by  potash  and  soda. 

The  ordinary  mode  of  exhibiting  the  production  of  the  so-called  amalgam  of 
ammonium  consists  in  acting  upon  the  ammonium  chloride  (NH4CI),  with  sodium 

*  This  experiment  is  more  conveniently  made  with  a  strong  solution  of  ammonium 
sulphate  in  a  common  plate.  A  sheet  of  platinum  connected  with  the  positive  pole  of  the 
battery  (five  or  six  Grove's  cells)  is  immersed  in  the  solution,  a  piece  of  filter-paper  is  laid 
upon  it,  on  which  is  a  globule  of  mercury  into  which  the  negative  pole  is  plunged. 


ESTIMATION  OF  NITROGEN.  131 

amalgam.  A  little  pure  mercury  is  heated  in  a  test-tube,  and  a  pellet  of  sodium 
thrown  into  it,  when  combination  takes  place  with  great  energy.  When  the  amalgam 
is  nearly  cool  it  may  be  poured  into  a  larger  tube  containing  a  moderately  strong 
solution  of  ammonium  chloride  ;  the  amalgam  at  once  swells  to  many  times  its  former 
bulk,  forming  a  soft  solid  substance  lighter  than  the  water,  which  may  be  shaken  out 
of  the  tube  as  a  cylindrical  mass,  decomposing  rapidly  with  effervescence,  evolving 
ammonia  and  hydrogen,  and  soon  recovering  its  original  volume  and  liquid  con- 
dition. 

88.  Atomic  loeiglit  and  volume  of  nitrogen. — Two  volumes  (one 
molecule)  of  ammonia,  when  decomposed  by  a  succession  of  electric 
sparks,  yield  a  mixture  of  one  volume  (one  atom)  of  nitrogen,  and  three 
volumes  (three  atoms)  of  hydrogen.  22*4  litres  of  ammonia  would  yield 
11  "2  litres  of  nitrogen,  weighing  14  grammes,  and,  since  this  is  the 
smallest  weight  of  nitrogen  which  can  be  found  in  22 '4  litres  of  any  of 
its  gaseous  compounds,  14  is  taken  as  the  atomic  weight  of  nitrogen. 

89.  Determination  of  nitrogen  in  organic  substances. — An  exact  know- 
ledge of  the  composition  of  ammonia  is  of  great  importance,  because  the 
general  method  of  ascertaining  the  proportion  of  nitrogen  present  in  animal 
and  vegetable  substances  consists  in  converting  that  element  into  ammonia, 
Avliich,  being  collected  and  weighed,  furnishes  by  calculation  the  weight  of 
nitrogen  present. 

To  ascertain  the  proportion  of  nitrogen  present  in  an  organic  substance,  a  weighed 
quantity  of  it  is  mixed  with  a  large  proportion  of  soda-lime  (a  mixture  of  sodium 
hydrate  and  calcium  hydrate),  and 
introduced  into  a  tube  of  German 
glass  (A,  fig.  149)  to  which  is 
attached,  by  a  perforated  cork,  a 
bulb  apparatus  (B)  containing 
hydrochloric  acid.  On  heating 
the  tube  inch  by  inch  with  a 
charcoal  or  gas  furnace,  the  nitro- 
gen of  the  substance  is  evolved  in 

combination   with   the   hydrogen  t-,.      ,,„      t^  ,•      ,•        r     -x 

f  ,  V      I     ]    4-       •      i-v.     e  f  i  ig-  149. — iiStimation  01  nitrogen, 

or  the  hydrates,  in  the  form  of  °  ° 

ammonia,  which  is  absorbed  by  the  hydrochloric  acid  in  the  bulbs.     When  the 

whole  length  of  the  tube  has  been  heated,  the  point  (C)  is  nipped  off,  and  air  drawn 

through  by  applying  suction  to  the  orifice  (D)  of  the  bulb  apparatus,  so  that  all  the 

ammonia  may  be  carried  into  the  hydrochloric  acid.     Its  weight  is  then  ascertained, 

either  by  evaporating  the  liquid  in  a  weighed  dish  placed  over  a  steam  bath,  and 

weighing  the  ammonium  chloride,  or  more  accurately  by  converting  it  into  the  double 

chloride  of  platinum  and  ammonium.     Sometimes  a  solution  of  sulphuric  acid   of 

known  strength  is  substituted  for  the  hydrochloric  acid  in  the  bulbs,  and  the  weight 

of  the  ammonia  is  ascertained  by  determining  the  quantity  of  acid  which  has  been 

neutralised. 

To  illustrate  the  change  which  takes  place  when  the  organic  substance  is  heated 

with  the  hydrates,  let  it  be  supposed  that  urea  is  the  substance  submitted  to  analysis 

(urea)  0114^20 +  2NaHO  =  Na2C03  +  2NH3.     The  caustic  soda  alone  would   be  too 

fusible,  and  would  corrode  the  glass  too  rapidly. 

In  the  analysis  of  an  organic  substance  containing  carbon,  hydrogen, 
nitrogen,  and  oxygen,  the  proportions  of  carbon  and  hydrogen  having  been 
ascertained  by  the  method  described  at  p.  84,  and  that  of  nitrogen  by  the 
process  given  above,  the  sum  of  the  carbon,  hydrogen,  and  nitrogen  is 
deducted  from  the  entire  weight  of  the  svibstance,  to  obtain  the  proportion 
of  oxygen.  The  weights  thus  found  are  divided  by  the  atomic  weights 
of  the  several  elements  to  obtain  the  empirical  formula,  which  is  converted 
into  a  rational  formula  on  the  principle  illustrated  at  p.  85. 


132  OXIDATION  OF  AMMONIA. 

For  example,  10  p^rs.  of  urea  were  found  to  contain  2  grs,  of  caxbon,  0'66 
gr.  of  hydrogen,  and  4'67  grs.  of  nitrogen. 

10  grs.  of  urea  minus  7*33  (carbon,  hydrogen,  and  nitrogen)  =  2*67  grs. 
of  oxygen. 

Dividing  each  of  these  numbers  by  the  atomic  weight  of  the  element 
to  which  it  refei-s,  we  have — 


2  0 
0-66 
4-67 
2-67 


12  =  0'165  atomic  proportion  of  carbon, 

1  =  0*66         „  „  hydrogen, 

14  =  0'33         „  ,,  nitrogen, 

16  =  0*165      „  „  oxygen. 


leading  to  the  empirical  formula,  in  its  simplest  form,  CH^NgO,  for  urea. 
But  urea  is  an  organic  base,  capable  of  uniting  with  acids  to  fonn  salts, 
and  it  is  found  that  to  neutralise  one  molecular  weight  (36  "5  parts)  of 
hydrochloric  acid,  60  parts  of  urea  are  necessary.  This  quantity  would 
contain  1 2  parts  (one  atom)  of  carbon,  4  parts  (four  atoms)  of  hydrogen, 
28  parts  (two  atoms)  of  nitrogen,  and  16  parts  (one  atom)  of  oxygen,  so 
that  the  above  formula  would  correctly  represent  the  molecule  of  urea. 

90.  Formation  of  ammonia  in  the  rusting  of  iron. — Although  free 
nitrogen  and  hydrogen  can  only  with  difficulty  be  made  to  form 
ammonia  by  direct  combination,  this  compound  is  produced  when  the 
nitrogen  meets  with  hydrogen  in  the  nascent  state ;  that  is,  at  the  instant 
of  its  liberation  from  a  combined  form.  Thus,  if  a  few  iron  filings  be 
shaken  with  a  little  water  in  a  bottle  of  air,  so  that  they  may  cling  round 
the  sides  of  the  bottle,  and  a  piece  of  red  litmus  paper  be  suspended  be- 
tween the  stopper  and  the  neck,  it  will  be  found  to  have  assumed  a  blue 
colour  in  the  course  of  a  few  hours,  and  ammonia  may  be  distinctly 
detected  in  the  rust  which  is  produced.  It  appears  that  the  water  is 
decomposed  by  the  iron  in  the  presence  of  the  carbonic  acid  of  the  air 
and  water,  and  that  the  hydrogen  liberated  enters  at  once  into  combination 
with  the  nitrogen,  held  in  solution  by  the  water,  to  form  ammonia. 

If  a  few  inches  of  magnesium  tape  be  kindled  and  held  over  a  plate  to  collect  the 
product,  it  will  be  found  a  mixture  of  MgO  and  magnesium  nitride,  which  evolves 
NHj  when  boiled  with  water  ;  Mg3N2  +  3H20  =  3MgO  +  2NH3. 

In  his  experiments  on  the  electrolysis  of  distilled  water,  Davy  found  that  nitric 
acid  was  formed  around  the  positive  pole,  by  oxidation  of  the  nitrogen  of  the  air  con- 
tained in  the  water,  while  ammonia  was  formed  at  the  negative  pole  by  combination 
of  the  hydrogen  with  nitrogen. 

91.  Production  of  nitrous  andnitnc  acids  from  ammonia. — If  a  few 
drops  of  a  strong  solution  of  ammonia  be  poured  into  a  pint  bottle,  and 
ozonised  air  (from  the  tube  for  ozonising  by  induction,  fig.  48)  be  passed 
into  the  bottle,  thick  white  clouds  will  speedily  be  formed,  consisting  of 
ammonium  nitrite,  the  nitrous  acid  having  been  produced  by  the  oxida- 
tion of  the  ammonia  at  the  expense  of  the  ozonised  oxygen — 

2NH3   +    03    =    H,,0    +   NH4NO2 

Ammonium  nitrite. 

If  copper  filings  be  shaken  with  solution  of  ammonia  in  a  bottle  of  air, 
white  fumes  will  also  be  produced,  together  with  a  deep  blue  solution 
containing  copper  oxide  and  ammonium  nitrite ;  the  act  of  oxidation 
of  tlie  copper  appearing  to  have  induced  a  simultaneous  oxidation  of  the 
ammonia. 


OXIDATION  OF  AMMONIA. 


133 


Fig.  150. 


A  coil  of  thin  platinum  wire  made  round  a  pencil,  if  heated  to  redness 
at  the  lower  end  and  suspended  in  a  flask  (fig.  150)  with  a  little  strong 
ammonia  at  the  bottom,  will  contimie  to  glow  for  a 
great  length  of  time,  in  consequence  of  the  combina- 
tion of  the  ammonia  with  the  oxygen  of  the  air  taking 
place  at  its  surface,  attended  with  great  evolution  of 
heat.  Thick  white  clouds  of  ammonium  nitrite  are 
formed,  and  f requentl}^  red  vapour  of  nitrous  anhydride 
(N^O^)  itself.  A  coil  of  thin  copper  wire  acts  in  a 
si  miliar  manner. 

If  a  tube  delivering  oxygen  gas  be  passed  down  to  the  bottom 
of  the  flask  (tig.  151),  the  action  will  be  far  more  energetic,  the 
heat  of  the  platinum  rising  to  whiteness,  when  an  explosion 
of  the  mixture  of  ammonia  and  oxygen  will  ensue.     After  the 

explosion  the  action  will  recommence,  so  that  the  explosion  will  repeat  itself  as  often 
as  may  be  wished.     It  is  unattended  with  danger  if  the  mouth  of  the  flask  be  pretty 
large.*     By  regulating  the  stream  of  oxygen,  the  bubbles 
of  that  gas  may  be  made  to  burn  as  they  pass  through  the  f',  ;;s.  ^  -^ 

ammonia  at  the  bottom  of  the  flask. 

The  oxidation  of  ammonia  may  also  be  shown  by  the 
arrangement  represented  in  fig.  152.  Air  is  slowly  passed 
from  the  gas-bag  B,  through  very  weak  ammonia  in  the 
bottle  a,  into  a  hard  glass  tube  having  a  piece  of  red  litmus 
paper  at  b,  and  a  plug  of  platinised  asbestos  in  the  centre, 
heated  by  a  gas  burner  ;  a  piece  of  blue  litmus  paper  is 
placed  at  c,  and  the  tube  is  connected  with  a  large  globe  (rf). 
The  red  litmus  at  b  is  changed  to  blue  by  the  ammonia, 
whilst  the  blue  litmus  at  c  is  reddened  by  the  nitrous  acid 
produced  in  its  oxidation,  and  clouds  of  ammonium  nitrite 
accompanied  by  red  nitrous  fumes,  appear  in  d.  To  obtain 
all  the  results  in  perfection,  small  quantities  of  ammonia  must  be  successively 
introduced  into  a. 


Fig.  152. — Oxidation  of  ammonia. 

(The  burner  represented  in  the  figure  is  a  Bunsen  burner  (p.  107),  surmounted  by  a 
T-)iiece  with  several  holes.) 

When  hydrogen  or  coal  gas  burns  in  air,  small  quantities  of  nitrous  and  nitric  acids 
are  produced,  apparently  by  the  oxidation  of  atmospheric  nitrogen. 

In  the  presence  of  strong  bases,  and  of  porous  materials  to  favour  oxi- 
dation, ammonia  appears  to  be  capable  of  suffering  further  oxidation  and 
conversion  into  nitric  acid,  which  acts  upon  the  base  to  form  a  nitrate, 
thus — - 


2Is^H,   +    CaO    +    0, 


Calcium  nitrate. 


3H,0 . 


This  formation  of  nitrates  from  ammonia  is  commonly  referred  to  as 
nitrification,  and  appears  to  be  concerned  in  the  formation  of  the  natural 

*  It  is  advisable  to  surround  the  flask  with  a  cylinder  of  coarse  wire  gauze. 


134  COMPOUNDS  OF  NITROGEN  AND  OXYGEN. 

supplies  of  saltpetre  which  are  of  so  great  importance  to  the  arts.*  Recent 
investigations  indicate  that  the  presence  of  some  minute  fungus  or 
organised  ferment  plays  an  important  part  in  the  process. 

This  ferment  consists  of  minute  round  or  oval  corpuscles,  which  appear  to  propagate 
by  budding,  like  yeast.  It  is  abundant  in  soils,  in  sewage,  and  in  water  contami- 
nated with  organic  matter.  Feeble  alkalinity,  such  as  is  due  to  the  presence  of 
calcium  carbonate,  is  favourable  to  its  action. 

When  the  nitrification  of  ammonia  takes  place  in  cold  dilate  solutions,  in  the  dark, 
nitrates  only  are  formed  ;  but  in  the  case  of  strong  solutions,  or  at  higher  tempera- 
tures, or  under  exposure  to  light,  nitrites  are  produced.  The  formation  of  nitrites  or 
nitrates  seems  to  depend,  in  part,  upon  the  condition  of  the  ferment ;  in  some  cases, 
it  produces  nitrites  only,  even  if  light  be  excluded.  A  solution  of  potassium  nitrite 
may  be  converted  into  nitrate,  in  the  dark,  by  adding  a  little  solution  in  which 
nitrites  have  lately  changed  into  nitrates,  and  which  therefore  contains  the  nitrifying 
ferment,  t 

Compounds  op  Nitbogen  and  OyyoEK. 

92.  Though  these  elements  in  their  pure  state  exhibit  no  attraction  for 
each  other,  five  compounds,  which  contain  them  in  different  proportions, 
have  been  obtained  by  indirect  processes. 

When  a  succession  of  strong  electric  sparks  from  the  induction-coil  is 
passed  through  atmospheric  air  in  a  Hask  (especially  if  the  air  be  mixed 
with  oxygen),  a  red  gas  is  formed  in  small  quantity,  which 
is   either   nitrous   anhydride   (N2^3)   ^^   nitric   peroxide 
(NO,).l 

If  the  experiment  be  made  in  a  graduated  eudiometer  (fig.  153), 
standing  over  water  coloured  with  blue  litmus,  the  latter  will  very 
soon  be  reddened  by  the  acid  formed,  and  the  air  will  be  found  to 
diminish  very  considerably  in  volume,  evsntuallj-  losing  its  power 
of  supporting  combustion,  in  consequence  of  the  removal  of  oxygen. 
A  U-tube  having  one  limb  surmounted  by  a  stoppered  globe  into 
which  platinum  wires  are  sealed,  allows  the  air  to  be  tested  with 
a  small  taper  to  show  that  the  oxygen  has  been  removed. 

When  a  few  inches  of  magnesium  tape  are  burnt  in  a  gas-jar  of 
Fig.  153.  air,  red  fumes  may  be  perceived  on  looking  down  the  jar  at  the 

close  of  the  combustion,  and  the  presence  of  N2O3  or  NO^  may  be 
shown  by  drawing  the  residual  air  through  a  mixture  of  potassium  iodide  with  a 
little  starch  and  acetic  acid,  when  the  iodine  is  set  free  and  blues  the  starch.  This 
renders  it  probable  that  the  electric  spark  causes  the  combination  of  nitrogen  and 
oxygen  on  account  of  its  high  temperature. 

When  hydrogen  gas,  mixed  with  a  small  quantity  of  nitrogen,  is 
burnt,  the  water  collected  from  it  is  found  to  have  an  acid  taste  and 
reaction,  due  to  the  presence  of  a  little  nitric  acid,  resulting  from,  the 
combination  of  the  nitrogen  with  the  oxygen  of  the  air  under  the  in- 
fluence of  the  intense  heat  of  the  hydrogen  flame. 

Since  all  the  compounds  of  nitrogen  and  oxygen  are  obtained,  in  prac- 
tice, from  nitric  acid,  the  chemical  history  of  that  substance  must  jjrecede 
that  of  the  oxides  of  nitrogen. 

XiTRic  Acid. 

93.  This  most  important  acid  is  obtained  from  saltpetre,  which  is 
found  as  an  incrustation  upon  the  surface  of  the  soil  in  hot  and  dry 

*  The  charcoal  which  has  been  used  in  the  sewer  ventilators  (see  p.  67)  has  been  found 
to  contain  abundance  of  nitrates. 

t  Warington  on  Nitrification,  Jour.  Chem.  Soc,  1879. 

+  Brodie  lias  shown  that  perfectly  dry  air  yields  oxides  of  nitrogen  under  the  influence 
of  the  induction  tube  (p.  54). 


PREPARATION  OF  NITRIC  ACID. 


135 


Fig.  154. — Preparation  of  nitric  acid. 


climates,  as  in  some  parts  of  India  and  Peru.  The  salt  imported  into  this 
country  from  Bengal  and  Oude  consists  of  nitrate  of  potash  or  potassium 
nitrate  (KNO3),  whilst  the 
Peruvian  or  Chilian  saltpetre  is 
nitrate  of  soda  or  sodium  nitrate 
(NaNOg).  Either  of  these  will 
serve  for  the  preparation  of 
nitric  acid. 

On  the  small  scale,  in  the 
laboratory,  nitric  acid  is  pre- 
pared by  distilling  potassium 
nitrate  with  an  equal  weight  of 
concentrated  sulphuric  acid. 

In  order  to  make  the  experiment,  four  ounces  of  powdered  nitre,  thoroughly  dried, 
may  be  introduced  into  a  pint  stoppered  retort  (fig.  154)  and  two  and  a  half  mea- 
sured ounces  of  concentrated  sulphuric  acid  poured  upon  it.  As  soon  as  the  acid  has 
soaked  into  the  nitre,  a  gradually  increasing  heat  may  be  applied  by  means  of  an 
Argand  burner,  when  the  acid  will  distil  over.  It  must  be  preserved  in  a  stoppered 
bottle. 

AVhen  the  acid  has  ceased  distilling,  the  retort  should  be  allowed  to  cool,  and  filled 
with  water.  On  applying  a  moderate  heat  for  some  time,  the  saline  residue  will  be 
dissolved.  The  solution  may  then  be  poured  into  an  evaporating  dish,  and  evapo- 
rated down  to  a  small  bulk.  On  allowing  the  concentrated  solution  to  cool,  crystals 
of  bisulphate  of  potash  or  hydro-potassic  sulphate  (KHSO4)  are  deposited,  a  salt  which 
is  very  useful  in  many  metallurgic  and  analytical  operations. 

The  decomposition  of  potassium  nitrate  by  an  equal  weight  of  concen- 
trated sulphuric  acid  is  explained  by  the  equation — 

KNO3     +     H2SO,     =     H^Og     +     KHSO4. 

It  would  appear  at  first  sight  that  one-half  of  the  sulphuric  acid  might 
be  dispensed  with,  but  it  is  found  that  when  less  sulphuric  acid  is 
employed,  so  high  a  tem- 
perature is  required  to 
efiFectthe  complete  decom- 
position of  the  saltpetre 
(the  above  equation  then 
representing  only  the  first 
stage  of  the  action),  that 
much  of  the  nitric  acid  is 
decomposed  ;  and  the  nor- 
mal potassium  sulphate 
(K.,SO^)  which  would  be 
the  final  result,  is  not 
nearly  so  easily  dissolved 
out  of  the  retort  by  water 
as  the  bisulphate. 

For  the  preparation  of 
large   quantities    of   nitric 


Fig.  155. — Preparation  of  nitric  acid. 


acid,  sodium  nitrate   is  substituted   for   potassium  nitrate,  being  much 
cheaper,  and  furnishing  a  larger  proportion  of  nitric  acid. 

The  sodium  nitrate  is  introduced  into  an  iron  cylinder  (A,  fig.  155)  lined  with  fire- 
clay to  protect  it  from  the  action  of  the  acid,  and  half  its  weight  of  sulphuric  acid 
(oil  of  vitriol)  is  poured  upon  it.     Heat  is  then  applied  by  a  furnace,  into  which  the 


136  PROPERTIES  OF  NITRIC  ACID. 

cylinders  are  built  in  pairs,  when  the  nitric  acid  passes  off  jn  vapour,  and  is  con- 
densed in  a  series  of  stoneware  bottles  (B),  surrounded  with  cold  water. 

2NaX03   +    H0SO4   =    Na^SO^   +    2HNO3 

S?d'""'  oil  of  vitriol.  ,^°;l;"'P  Nitric  acid, 

nitrate.  sulphate. 

The  sodium  sulphate  left  in  the  retort  is  useful  in  the  manufacture  of  glass. 

In  the  preparation  of  nitric  acid,  it  will  be  observed  at  the  beginning 
and  towards  the  end  of  the  operation  that  the  retort  becomes  filled  with 
a  red  vapour.  This  is  due  to  the  decomposition  by  heat  of  a  portion  of  the 
colourless  vapour  of  nitric  acid,  into  water,  oxygen,  and  nitric  peroxide, — 

2HNO3  =  H2O  +  O  +  2NO2, 
this  last  forming  the  red  vapour,  a  portion  of  which  is  absorbed  by 
the  nitric  acid,  and  gives  it  a  yellow  colour.  The  pure  nitric  acid 
is  colourless,  but  if  exposed  to  sunlight  it  becomes  yellow,  a  portion 
suffering  this  decomposition.  In  consequence  of  the  accumulation  of  the 
oxygen  in  the  upper  part  of  the  bottle,  the  stopper  is  often  forced  out 
suddenly  when  the  bottle  is  opened,  and  care  must  be  taken  that  drops 
of  this  very  corrosive  acid  be  not  spirted  into  the  face. 

The  strongest  nitric  acid  (obtained  by  distilling  perfectly  dry  nitre 
with  an  equal  weight  of  pure  oil  of  vitriol,  and  collecting  the  middle 
portion  of  the  acid  separately  from  the  first  and  last  portions,  which  are 
somewhat  weaker)  emits  very  thick  grey  fumes  when  exposed  to  damp 
air,  because  its  vapour,  though  itself  transparent,  absorbs  water  very 
readily  from  the  air,  and  condenses  into  very  minute  drops  of  diluted 
nitric  acid  which  compose  the  fumes.  The  weaker  acids  commonly  sold 
in  the  shops  do  not  fume  so  strongly.  An  exact  criterion  of  the  strength 
of  any  sample  of  the  acid  is  afforded  by  the  specific  gravity,  which  may 
be  ascertained  by  the  methods  described  for  ammonia,  using  a  hydrometer 
adapted  for  liquids  heavier  than  water.  Thus,  the  strongest  acid  (HNO3) 
has  the  specific  gravity  1 '52  ;*  whilst  the  ordinary  agMo/b/^/'s  or"  diluted 
nitric  acid  has  the  sp,  gr.  1'29,  and  contains  only  46*6  per  cent,  of  HNO3. 
The  concentrated  nitric  acid  usually  sold  by  the  operative  chemist  {double 
aquafortis)  has  the  sp.  gr.  1*42,  and  contains  67"6  per  cent,  of  HNO3. 

A  very  characteristic  property  of  nitric  acid  is  that  of  staining  the  skin 
yellow.  It  produces  the  same  effect  upon  most  animal  and  vegetable 
matters,  especially  if  they  contain  nitrogen.  The  application  of  this  in 
dyeing  silk  of  a  fast  yellow  colour  may  be  seen  by  dipping  a  skein  of 
white  silk  in  warm  diluted  nitric  acid,  and  afterwards  immersing  it  in 
dilute  ammonia,  which  will  convert  the  yellow  colour  into  a  brilliant 
orange.  When  sulphuric  or  hydrochloric  acid  is  spilt  upon  the  clothes,  a 
red  stain  is  produced,  and  a  little  ammonia  restores  the  original  colour  ;  but 
nitric  acid  stains  are  yellow,  and  ammonia  intensifies  instead  of  removing 
them,  though  it  prevents  the  cloth  from  being  eaten  into  holes. 

JS^itric  acid  changes  most  organic  colouring  matters  to  yellow,  but,  unless 

very  concentrated,  it  merely  reddens  litmus.     If  solutions  of  indigo  and 

litmus  are  warmed  in  separate  flasks,  and  a  little  nitric  acid  added  to  each, 

the   indigo   will   become  yellow  and  the  litmus  red.     Here  the  indigo, 

(CgHgNO)  acquires  oxygen  from  the  nitric  acid,  and  is  convertedinto 

imtine  (CgHgNOg). 

*  It  is  extreme!}'  difficult  to  obtain  the  HNO3  free  from  any  extraneous  water,  as  it 
uiKleigoes  decomposition  not  only  when  vaporised  at  the  boiling-point,  but  even  at  ordinary 
temperatures. 


ACTION  OF  NITRIC  ACID  UPON  METALS.  137 

When  nitric  acid  is  heated,  it  begins  to  boil  at  184°  F.  (84°  C),  but  it 
cannot  be  distilled  unchanged,  for  a  considerable  quantity  is  decomposed 
into  nitric  peroxide,  oxygen,  and  water,  the  two  first  passing  oif  in 
the  gaseous  form,  whilst  the  water  remains  in  the  retort  with  the  nitric 
acid,  which  thus  becomes  gradually  more  and  more  diluted,  until  it  con- 
tains 68  per  cent,  of  HNO3,  when  it  passes  over  unchanged  at  the 
temperature  of  248°  F.  (120°  C.).  The  specific  gravity  of  this  acid  is  1-42, 
If  an  acid  weaker  than  this  be  submitted  to  distillation,  water  will  pass  off 
until  acid  of  this  strength  is  obtained,  when  it  distils  over  unchanged. 

The  specific  gravity  of  the  vapour  of  nitric  acid,  at  86°  C,  has  been 
determined  as  29 '6  (H  =  l),  which  is  sufficiently  near  to  half  of  63,  to 
show  that  the  molecule  HNO3  ^o^^d  occupy  exactly  two  volumes  if  it 
had  not  suffered  partial  decomposition  by  heat. 

The  facility  with  which  nitric  acid  parts  with  a  portion  of  its  oxygen, 
renders  it  very  valuable  as  an  oxidising  agent.  Comparativel3r  few  sub- 
stances which  are  capable  of  forming  compounds  with  oxygen  can  escape 
oxidation  w^hen  treated  with  nitric  acid. 

A  small  piece  of  phosphorus  dropped  into  a  porcelain  dish  containing 
the  strongest  nitric  acid  (and  placed  at  some  distance  to  avoid  danger), 
soon  begins  to  act  upon  the  acid,  generally  with  such  violence  as  to  burst 
out  into  flame,  and  sometimes  to  shatter  the  dish ;  the  result  of  this  action 
is  phosphoric  acid,  the  highest  state  of  oxidation  of  phosphorus. 

When  sulphur  is  heated  with  nitric  acid,  it  is  actually  oxidised  to  a 
greater  extent  than  when  burnt  in  pure  oxygen^  for  in  this  case  it  is  con- 
verted into  sulphurous  acid  gas  (SOg),  whilst  nitric  acid  converts  it  into 
sulphuric  acid  HgSO^. 

Charcoal,  which  is  so  unalterable  by  most  chemical  agents  at  the 
ordinary  temperature,  is  oxidised  by  nitric  acid.  If  the  strongest  nitric 
acid  be  poured  upon  finely  powdered  charcoal,  the  latter  takes  fire  at  once. 

Even  iodine,  which  is  not  oxidised  by  free  oxygen,  is  converted  into 
iodic  acid  (HIO3)  by  nitric  acid. 

But  it  is  especially  in  the  case  of  metals  that  the  oxidising  powers  of 
nitric  acid  are  called  into  useful  application. 

If  a  little  black  oxide  of  copper  be  heated  in  a  test-tube  with  nitric 
acid,  it  dissolves,  without  evolution  of  gas,  yielding  a  blue  solution,  which 
contains  copper  nitrate — 

2HNO3   -t-    CuO   =   HP    +    Cu(N03)2. 

But  when  nitric  acid  is  poured  upon  metallic  copper  (copper* turnings) 
very  violent  action  ensues,  red  fumes  are  abundantly   evolved,  and  the 
metal  dissolves  in  the  form  of  copper  nitrate,  nitric  oxide  being  formed — 
8HNO3   +    CU3   --=    3Cu(X03)2   +    4H2O    +    2X0. 

The  nitric  oxide  itself  is  colourless,  but  as  soon  as  it  comes  into  contact 
with  the  oxvgen  of  the  air^  it  is  converted  into  the  red  nitric  peroxide, 
NO  +  0  =  ^0.,. 

All  the  metals  in  common  use  are  acted  upon  by  nitric  acid,  except 
gold  and  platinum,  so  that  this  acid  is  employed  to  distinguish  and 
separate  these  metals  from  others  of  less  value.  The  ordinary  ready 
method  of  ascertaining  whether  a  trinket  is  made  of  gold,  consists  in 
touching  it  with  a  glass  stopper  wetted  with  nitric  acid,  which  leaves 
gold  untouched,  but  colours  base  alloys  blue,  from  the  formation  of 
copper   nitrate.      The    touch-stone   allows   this   mode    of   testing   to    be 


138  ACTION  OF  NITRIC  ACID  ON  ORGANIC  SUBSTANCES. 

applied  with  great  accuracy.  It  consists  of  a  species  of  black  basalt, 
obtained  chiefly  from  Silesia.  If  a  piece  of  gold  be  drawn  across  its  sur- 
face, a  golden  streak  is  left,  which  is  not  affected  by  moistening  with 
nitric  acid ;  whilst  the  streak  left  by  brass,  or  any  similar  base  alloy, 
would  be  rapidly  dissolved  by  the  acid.  Experience  enables  an  operator 
to  determine,  by  means  of  the  touch-stone,  pretty  nearly  the  amount  of 
gold  present  in  the  alloy,  comparison  being  made  with  the  streaks  left 
by  alloys  of  known  composition. 

Tliough  all  the  metals  in  common  use,  except  gold  and  platinum,  are  oxidised  by 
nitric  acid,  they  are  not  all  dissolved  ;  there  are  two  metals,  tin  and  antimony,  which 
are  left  by  the  acid  in  the  state  of  insoluble  oxides,  which  possess  acid  properties,  and 
do  not  unite  with  the  nitric  acid. 

If  some  concentrated  nitric  acid  be  poured  upon  tin  filings,  no  action  will  be 
observed  ;*  but  on  adding  a  little  water,  red  fumes  will  be  evolved  in  abundance, 
and  the  tin  will  be  converted  into  a  white  powder,  which  is  tbe  binoxide  of  tin  or 
stannic  oxide  (SnO^),  putty  powder. 

If  the  white  mixture  of  stannic  oxide  with  nitric  acid  be  made  into  a  paste  with 
slaked  lime,  the  smell  of  ammonia  will  be  exhaled ;  and  experiments  with  other 
metals  have  shown  it  to  be  a  general  principle,  that  when  any  metal  capable  of 
decomposing  water  is  dissolved  in  diluted  nitric  acid,  ammonia  is  always  formed,  its 
quantity  increasing  with  the  degree  of  dilution  of  the  nitric  acid  ;  of  course  the 
ammonia  combines  with  the  excess  of  acid  present  to  form  ammonium  nitrate,  and 
the  lime  was  added  in  the  above  experiment  in  order  to  displace  the  ammonia  from 
its  combination,  and  to  exhibit  its  odour.  This  conversion  of  nitric  acid  into 
ammonia  becomes  the  more  interesting  when  it  is  remembered  that  the  ammonia 
can  be  reconverted  into  nitric  acid  (p.  132). 

By  dissolving  zinc  in  very  diluted  nitric  acid,  a  very  large  quantity  of  ammonia 
may  be  obtained.  The  change  is  easily  followed  if  we  suppose  the  nascent  hydrogen, 
produced  by  the  action  of  the  zinc  upon  the  water,  to  act  upon  the  nitric  acid, 
converting  its  oxygen  into  water,  and  its  nitrogen  into  ammonia,  thus — HNO3  +  Hg 
=  3H20  +  NH.j.  The  exalted  attractions  possessed  by  substances  in  the  nascent 
state,  that  is,  at  the  instant  of  their  passing  from  a  state  of  combination,  are  very 
remarkable,  and  will  be  found  to  receive  frequent  application,  t 

Action  of  nitric  acid  upon  organic  substances. — The  oxidising  action 
of  nitric  acid  upon  some  organic  substances  is  so  powerful  as  to  be 
attended  with  inflammation ;  if  a  little  of  the 
strongest  nitric  acid  be  placed  in  a  porcelain 
capsule,  and  a  few  drops  of  oil  of  turpentine  be 
poured  into  it  from  a  test-tube  fixed  to  the  end 
of  a  long  stick,  the  turpentine  takes  fire  with 
a  sort  of  explosion.  By  boiling  some  of  the 
strongest  acid  in  a  test-tube  (fig.  156),  the 
mouth  of  which  is  loosely  stopped  with  a  plug 
of  raw  silk  or  of  horse-hair,  the  latter  may  be 
made  to  take  fire  and  -burn  brilliantly  in  the 
vapour  of  nitric  acid. 

In  many  cases  the  products  of  the  action  of 

*  It  is  a  fact  which  has  scarcely  been  explained  in  a  satisfactory  manner,  that  the  con- 
centrated nitric  acid  often  refuses  to  act  upon  metals  which  are  violently  attacked  by  the 
diluted  acid. 

+  When  a  solution  of  potassium  nitrate  is  mixed  with  a  strong  solution  of  caustic  potash, 
and  heated  with  granulated  zinc,  ammonia  is  abundantly  disengaged,  being  produced  from 
the  nitric  acid  by  the  nascent  hydrogen  resulting  from  the  action  of  the  zinc  upon  the 
caustic  potash. 

Recent  experiments  have  indicated  the  existence  of  substances  intermediate  between 
the  nitric  acid  and  the  ammonia  into  which  it  is  finally  converted.  One  of  these,  named 
hydroxylamine,  NH3O,  has  been  examined.  It  is  a  well-defined  base,  forming  crystalline 
salts  with  the  acids. 


ANHYDROUS  NITRIC  ACID.  139 

nitric  acid  exhibit  a  most  interesting  relation  to  the  substances  from 
which  they  have  been  produced,  one  or  more  atoms  of  the  hydrogen  of 
the  original  compound  having  been  removed  in  the  form  of  water  by  the 
oxygen  of  the  nitric  acid,  whilst  the  spaces  thus  left  vacant  have  been 
filled  up  by  the  nitric  peroxide  resulting  from  the  deoxidation  of  the  nitric 
acid,  producing  what  is  termed  a  nitro-suhstitution  compound.  A  very 
simple  example  of  this  displacement  of  H  by  NOg  is  afforded  by  the 
action  of  nitric  acid  upon  benzene.  A  little  concentrated  nitric  acid  is 
placed  in  a  flask,  and  "benzene  cautiou?ly  dropped  into  it;  a  violent  action 
ensues,  and  the  acid  becomes  of  a  deep  red  colour ;  if  the  contents  of 
the  flask  be  now  poured  into  a  large  vessel  of  water,  a  heavy  yellow  oily 
liquid  is  separated,  having  a  powerful  odour,  like  that  of  bitter  almond 
oil.  This  substance,  which  is  used  to  a  considerable  extent  in  perfumery 
under  the  name  of  essence  of  Mirbane,  is  called  nitro-henzeiie,  and  its 
formula,  CgH5(N02),  at  once  exhibits  its  relation  to  benzene,  CgHg.* 

But  the  change  does  not  stop  here,  for  by  continuing  the  action  of  the 
acid,  dinitro-henzene  CgH^(NOo)2  is  obtained,  in  which  two  atoms  of 
hydrogen  have  been  displaced  by  nitric  peroxide. 

It  is  by  an  action  of  this  description  that  nitric  acid  gives  rise  to  gun- 
cotton,  and  other  explosive  substances  of  the  same  class,  when  acting  upon 
the  different  varieties  of  woody  fibre,  as  cotton,  paper,  saw-dust,  &c. 

The  preparation  and  composition  of  gun-cotton  will  be  described  here- 
after. 

94.  The  oxidising  effects  of  nitric  acid  are  not  confined  to  the  free  acid, 
but  are  shared  to  some  extent  by  the  nitrates.  A  mixture  of  nitrate  of 
lead  with  charcoal  explodes  when  sharply  struck,  from  the  sudden  evolu- 
tion of  carbonic  acid  gas,  produced  by  the  oxidation  of  the  carbon.  If  a 
few  crystals  of  copper  nitrate  be  sprinkled  with  water  and  quickly  wrapped 
up  in  tin-foil,  the  latter  will,  after  a  time,  be  so  violently  oxidised  as  to 
emit  brilliant  sparks. 

But  in  the  case  of  the  nitrates  of  alkali  metals,  the  oxidation  takes 
place  only  at  a  high  temperature.  If  a  little  nitre  be  fused  in  an  earthen 
crucible  or  an  iron  ladle,  and,  when  it  is  at  a  red  heat,  some  powdered 
charcoal,  and  afterwards  some  flowers  of  sulphur,  be  thrown  into  it,  the 
energy  of  the  combustion  will  testify  to  the  violence  of  the  oxidation. 
In  this  manner  the  carbon  is  converted  into  potassium  carbonate  (KgCO^), 
and  the  sulphur  into  potassium  sulphate  (K2SOJ.     See  Gunpowder. 

95.  Anhydrous  nitric  acid  or  nitric  anhydride  (NgOg)  is  obtained  by  gently  heating 
silver  nitrate  in  a  slow  current  of  chlorine,  great  care  being  taken  to  exclude  every 
trace  of  water  ;  2 AgNOj  +  d.^  =  2AgCl  +  0  +  N.^Og. 

It  may  also  be  obtained  by  adding  anhydrous  phosphoric  acid  to  the  strongest 
nitric  acid  cooled  in  snow  and  salt,  and  carefully  distilling  at  as  low  a  temperature  as 
possible  into  a  receiver  cooled  in  snow  and  salt. 

The  anhydride  is  condensed  as  a  crystalline  solid.  It  forms  transparent  colourless 
prisms  which  liquefy  at  85°  F.,  and  boil  at  113°.  By  a  slightly  higher  temperature 
it  is  readily  decomposed  ;  and  it  has  been  said  to  decompose  even  at  the  ordinary 
temperature,  in  sealed  tubes,  which  were  shattered  by  the  evolved  gas. 

When  the  anhydride  is  brought  in  contact  with  water,  much  heat  is  evolved,  and 
nitric  acid  is  produced. 

The  specific  gravity  of  the  vapour  of  nitric  anhydride  being  unknown,  it  is  only  a 
surmise  that  its  molecule  is  represented  by  NjOg.     Its  formation  by  the  action  of 

*  CgHg     +     HXO,        =   CgHg  (NO.,)    +    H,0. 
CgHe      +     2(HN03)   =   CeH^lNO-Jj    +    2H,0. 


140 


NITROUS  OXIDE. 


chlorine  upon  silver  nitrate  appears  to  take  place  in  two  stages — (1)  Ag-NOjO  +  Clj 

=  AgCl  +  N0,C1  {azotyle  chloride)  +  0 ;  and  (2)  NOgCl  +  Ag.  NO^.  0  =  AgOl  +  NO^.  NO^.O 

(nitric  anhydride). 

The  disposition  of  HNO3  to  give  NOg  as  a  product  of  its  decomposition,  and  to 

exchange  it  for  the  hydrogen  of  organic  substances,  leads  to  the  belief  that  it  is  really 

H  ) 
formed  upon  the  type  of  a  molecule  of  water  tt  [  0,  in  which  half  the  hydrogen 

is   displaced  by   NO^.     The  relation   between   the  anhydride,   the   acid,   and   the 

nitrates,    would  then  be  a  very  simple  one  ;  nitric  anhydride  -j^q*  >   0 ;     nitric 


H 


0. 


acid,^Q   I  0  ;  saltpetre,  -v^q 

Nitrates. — Its  powerful  action  on  bases  places  nitric  acid  among  the 
strongest  of  the  acids,  though  the  disposition  of  its  elements  to  assume  the 
gaseous  state  at  high  temperatures,  conjoined  with  the  feeble  attraction 
existing  between  nitrogen  and  oxygen,  causes  its  salts  to  be  decomposed, 
without  exception,  by  heat. 

The  nature  of  the  decomposition  varies  with  the  metal  contained  in  the 
nitrate.  The  nitrates  of  alkali  metals  are  first  converted  into  nitrites  by 
the  action  of  heat  ;  thus  KNO3  gives  KNO,  and  0  ;  the  nitrites  them- 
selves being  eventually  decomposed,  evolving  nitrogen  and  oxygen,  and 
leaving  the  oxide  of  the  metal  The  nitrates  of  copper  and  lead  evolve 
nitric  peroxide  (NOg)  and  oxygen,  the  oxides  being  left.  The  nitrate  of 
mercury  leaves  red  oxide  of  mercury,  which  is  decomposed  at  a  higher  tem- 
perature into  mercury  and  oxygen. 

Nitric  acid  is  a  monobasic  acid,  because  it  contains  only  one  atom  of 
hydrogen  to  be  replaced  by  a  metal. 

Comparatively  few  of  the  nitrates  are  in  common  use ;  the  following 
table  contains  those  most  frequently  used : — 


Chemical  Name. 

Common  Name. 

Formula. 

Potassium  nitrate 
Sodium  nitrate 
Strontium  nitrate 
Basic  bismuth  nitrate 
Silver  nitrate 

Nitre,  saltpetre 
i  Cubic  nitre                               ) 
\  Peruvian  saltpetre                  \ 

Nitrate  of  strontian 
<  Trisnitrate  of  bismuth           ) 
1  Flake  white                              \ 

Lunar  caustic 

KNO3 

NaNOj 

Sr(N03)2 

Bi(N03)3  .  2Bi(OH)3 

AgNOa 

96.  Nitrous  oxide  or  laughing  gas  (N20  =  44  parts  by  weight  =  2 
volumes)  is  prepared  by  heating  ammonium  nitrate,  when  it  is  resolved 
into  water  and  nitrous  oxide  ;  *  NH4NO3  =  2H2O  +  NgO. 

Nitrate  of  ammonia  or  ammonium  nitrate  is  obtained  by  adding  fragments  of 
ammonium  carbonate  to  nitric  acid  t  diluted  with  an  equal  volume  of  water,  until  the 
(■arbonate  no  longer  effervesces  in  the  liquid,  which  is  then  evaporated  down  until  a 
drop  solidities  on  a  cold  surface,  when  the  whole  may  be  poured  out  upon  a  clean 
stone  and  the  mass  broken  up  and  preserved  in  a  well -stoppered  bottle,  because  it  is 
liable  to  attract  moisture  from  the  air.  To  obtain  the  nitrous  oxide,  an  ounce  of  the 
salt  may  be  gently  heated  in  a  small  retort,  when  it  melts,  boils,  and  gradually  dis- 
a])pears  entirely  in  the  forms  of  steam  and  nitrous  oxide.  The  latter  may  be  collected 
with  slight  loss  over  water.  Crystallised  ammonium  nitrate  may  be  employed  instead 
of  the  fused  salt. 

*  By  passing  the  mixture  of  nitrous  oxide  and  aqueous  vapour  over  hydrate  of  potash  at 
a  (lull  red  lieat,  nitric  acid  and  ammonia  are  reproduced. 
+  Which  must  remain  clear  when  tested  with  silver  nitrate,  showing  it  to  be  fi-ea  from 

chlorine. 


NITRIC  OXIDE. 


141 


In  the  preparation  of  nitrous  oxide,  if  the  temperature  be  too  high,  the  gas  may 
contain  nitric  oxide  and  nitrogen  ;  NH4N03  =  NO  +  N  +  2H20.  To  purify  the  gas,  it 
sliould  be  passed  through  a  strong  solution  of  ferrous  sulphate,  to  absorb  the  nitric 
oxide,  and  afterwards  through  potash  to  absorb  acid  vapours. 

Nitrous  oxide  is  perfectly  colourless,  but  lias  a  slight  odour  and  a 
sweetish  taste.  Its  characteristic  anaesthetic  property  is  well  known. 
It  accelerates  the  combustion  of  a  taper  like  oxygen  itself,  and  will 
even  kindle  into  flame  a  spark  at  the  end  of  a  match.  When  C  is  burnt 
into  CO2  by  2N2O,  it  evolves  40,400  more  units  of  heat  than  when  burnt 
in  0,  showing  that,  contrary  to  the  usual  law,  heat  is  evolved  in  the 
decomposition  of  the  N^O,  amounting  to  20,200  units  per  molecule. 
Xitrous  oxide  can  readily  be  distinguished  from  oxygen  by  shaking  it 
with  water,  which  absorbs,  at  the  ordinary  temperature,  about  three- 
fourths  of  its  volume  of  the  nitrous  oxide.  It  is  absorbed  in  larger 
quantity  by  alcohol.  It  is  also  much  heavier  than  oxygen,  its  specific 
gravity  being  1  '53,  and  is  liquefied  by  a  pressure  of  40  atmospheres  at 
45°  R,  and  solidified  at  -  150°  F.  It  is  now  sold  in  a  liquid  state  in 
wrought-iron  vessels  for  use  as  an  anaesthetic  in  dental  surgery. 

The  liquid  nitrous  oxide  possesses  properties  similar  to  those  of  liquid  carbon 
dioxide  with  respect  to  its  rapid  evaporation ;  but  it  may  be  drawn  into  test-tubes  in  3 
liquid  state  from  the  receiver.  A  lighted  match  thrown  into  the  liquid  burns  with 
great  brilliancy.  When  mixed  with  carbon  disulphide  and  evaporated  in  vacuo,  it 
produces  the  lowest  temperature  hitherto  obtained  -  220°  F. 

97.  Nitric  oxide  (NO  =  30  parts  by  weight  =  2  volumes)  is  usually 
obtained  by  the  action  of  copper  upon  diluted  nitric  acid  (see  page  137). 

300  grains  of  copper  turnings  or  clippings  are  introduced  into  a  retort,  and  3 
measured  ounces  of  a  mixture  of  concentrated  nitric  acid  with  an  equal  volume  of 
water  are  poured  upon  them.  A 
very  gentle  heat  may  be  applied 
to  assist  the  action,  and  the  gas 
may  be  collected  over  water  (see 
fig.  157),  which  absorbs  the  red 
fumes  (NO.,)  formed  by  the  union 
of  the  NO  with  the  oxj'gen  of  the 
air  contained  in  the  retort. 

Nitric  oxide  is  distinguish- 
ed from  all  other  gases  by  the 
production  of  a  red  gas,  when 
the  colourless  nitric  oxide  is 
allowed  to  come  in  contact 
with  uncombined  oxygen,  the 
presence  of  which,  in  mixtures 
of  gases,  may  be  readily  de- 
tected by  adding  a  little  nitric  oxide.  The  red  gas  consists  chiefly  of 
nitric  peroxide  (NO.,),  but  it  often  contains  also  some  (NgOg)  nitrous 
anhydride. 

The  combination  of  nitric  oxide  with  oxygen  may  be  exhibited  by  decanting  a  pint 
bottle  of  oxygen,  under  water,  into  a  tall  jar  filled  with  water  coloured  with  blue 
litmus,  and  adding  to  it  a  pint  bottle  of  nitric  oxide  (fig.  158).  Strong  red  fumes  are 
immediately  produced,  and  on  gently  agitating  the  cyUnder,  the  fumes  are  absorbed 
by  the  wate'r,  reddening  the  litmus.  The  oxygen  will  now  have  been  reduced  to  half 
its  volume,  and  if  another  pint  of  nitric  oxide  be  added,  the  remainder  of  the  oxygen 
will  be  absorbed,  showing  that  tivo  voluvics  of  nitric  oo:idc  combine  with  one  volume  of 
oxygen,  forming  the  nitric  peroxide  which  is  absorbed  by  the  water. 


142 


PROPERTIES  OF  NITRIC  OXIDE. 


The  addition  of  nitric  oxide  to  atmospheric  air  was  one  of  the  earliest 
methods  employed  for  removing  the  oxygen  in  order  to  determine  the 
composition  of  air ;  but  important  variations  were  observed  in  the  results, 
in  consequence  of  the  occasional  formation  of  NgOy  in  addition  to  the  NOg- 

The  rough  analysis  of  air  by  this  method  may  be  instructively  performed  with  two 
similar  gas  cylinders,  each  divided  into  ten  equal  volumes.  Into  one  are  introduced 
live  volumes  of  air,  and  into  the  other  five  volumes  of  nitric  oxide.  On  decanting 
the  air,  under  water,  into  the  nitric  oxide  (fig.  159),  the  red  nitric  peroxide  will  be 
formed  and  absorbed  by  the  water,  the  ten  volumes  of  gas  shrinking  to  seven,  showing 
that  three  volumes  have  been  absorbed,  of  which  one  volume  would  of  course  repre- 
sent the  oxygen  contained  in  the  five  volumes  of  air. 


Fig.  158. 


Fig.  159. 


The  nitric  oxide  prepared  by  the  action  of  copper  on  nitric  acid  generally  contains 
nitrous  oxide,  and  will  seldom  give  correct  results  in  the  above  experiment.  Pure 
nitric  oxide  may  be  obtained  by  heating  in  a  retort  100  grains  potassium  nitrate, 
1000  grains  of  ferrous  sulphate,  and  three  measured  ounces  of  diluted  .sulphuric  acid 
(containing  one  measure  of  acid  to  three  measures  of  water),  which  will  yield  above 
two  pints  of  gas. 

2KNO3  +  6FeS04  +  4H,jS04  =  K^SO^  +  3Fej(S04)3  +  2N0  +  iH^O . 
In  all  its  properties  nitric  oxide  is  very  different  from  nitrous  oxide. 
It  is  much  lighter,  having  almost  exactly  the  same  specific  gravity  as  air, 
viz.,  1  "04,  and  is  not  dissolved  to  an  important  extent  by  water.  It  is  more 
difficult  to  liquefy,  requiring  a  pressure  of  104  atmospheres  at  —  11°  C. 
"When  a  lighted  taper  is  immersed  in  nitric  oxide  it  is  extinguished, 
although  this  gas  contains  twice  as  much  oxygen  as  nitrous  oxide,  which 
so  much  accelerates  the  combustion  of  a  taper  ;  for  the  elements  are  held 
together  by  a  stronger  attraction  in  the  nitric  oxide,  so  that  its  oxygen  is 
not  so  readily  available  for  the  support  of  combustion.  (The  nitric  oxide 
prepared  from  copper  and  nitric  acid  soipetimes  contains  so  much  nitrous 
oxide  that  a  taper  burns  in  it  brilliantly.)  Even  phosphorus,  when  just 
kindled,  is  extinguished  in  nitric  oxide,  but  when  allowed  to  attain  to  full 
combustion  in  air,  it  burns  with  extreme  brilliancy  in  the  gas.  Indeed, 
nitric  oxide  appears  to  be  the  least  easy  of  decomposition  of  the  whole 
series  of  oxides  of  nitrogen,  which  accounts  for  it  being  the  most  common 
result  of  the  decompo.sition  of  the  other  oxides.  Nitrous  oxide  itself, 
when  passed  through  a  red  hot  tube,  is  partly  converted  into  nitric  oxide ; 
and  when  a  taper  burns  in  a  bottle  of  nitrous  oxide,  the  upper  part  of  the 
bottle  is  often  tilled  with  a  red  gas,  indicating  the  formation  of  nitric  oxide, 
iind  its  oxidation  by  the  air  entering  the  bottle. 


NITROUS  ANHYDRIDE, 


143 


by  their 
au  equal 


SQp- 


The  difference  in  the .  stability  of  the  two  gases  is  also  shown 
behaviour  with  hydrogen.  A  mixture  of  nitrous  oxide  with 
volume  of  hydrogen  explodes 
when  in  contact  with  flame,  yield- 
ing steam  and  nitrogen,  but  a 
mixture  of  equal  volume  of  nitric 
oxide  and  hydrogen  burns  quietly 
in  air,  the  hydrogen  nofc'  decon]- 
posing  the  nitric  oxide.  An  ex- 
cess of  hydrogen,  however,  is 
capable  of  decomposing  nitric 
oxide,  ammonia  and  water  being 
formed. 

If  two  volumes  of  nitric  oxide  be 
mixed  with  live  volumes  of  hydrogen 
and  the  gas  passed  through  a  tube 
having  a    bulb   filled  with   platinised  Fig.  160. 

asbestos  (fig.  160),*  the  mixture  issuing 

from  the  orifice  of  the  tube  will  produce  the  red  vapours  by  contact  with  the  aii', 
which  will  strongly  redden  blue  litmus  ;  but  if  the  platinised  asbestos  be  heated 
with  a  spirit-lamp,  the  hydrogen,  encouraged  by  the  action  of  the  platinum  (91)  will 
decompose  the  nitric  oxide,  and  strongly  alkaline  vapours  of  ammonia  will  be  produced, 
restoring  the  blue  colour  to  the  reddened  litmus;  NO  +  Hg  =  NH3-l-H20.  It  will 
be  remembered  that  when  oxygen  is  in  excess,  ammonia  is  converted,  under  the 
influence  of  platinum,  into  water  and  nitrous  acid  (91). 

Nitric  oxide  is  readily  absorbed  by  ferrous  salts  (salts  of  protoxide  of 
iron)  with  which  it  forms  dark  brown  solutions.  If  a  little  solution  of 
ferrous  sulphate  (FeSO^)  be  shaken  in  a  cylinder  of  nitric  oxide  closed 
with  a  glass  plate,  the  gas  will  be  immediately  absorbed  and  the  solution 
will  become  dark  brown.  On  applying  heat,  the  brown  compound  is 
decomposed.  A  compound  of  4FeS04  *^^  -^^  ^^^  been  obtained  in  small 
brown  crystals,  which  lose  all  their  nitric  oxide  in  vacuo. 

98.  Nitrous  anhydride  {^2^^?.  =  '^^  parts  by  weight). — Ammonium 
nitrite  is  said  to  exist  in  minute  quantity  in  rain  water,  and  nitrites  are 
occasionally  found  in  well-waters,  where  they  have  probably  been  formed 
by  the  oxidation  of  ammonia  (91).  Small  quantities  of  ammonium  nitrite 
appear  to  be  formed  by  the  combustion  in  air  of  gases  containing  hydro- 
gen, this  element  uniting  with  the  atmospheric  oxygen  and  nitrogen. 

Nitrous  anhydride  may  be  obtained  by  heating  starch  with  nitric  acid, 
but  the  most  convenient  process  consists  in  gently  heating  nitric  acid  (»p. 
gr.  rSo)  with  an  equal  weight  of  white  arsenic,  and  passing  the  gas,  first 
through  a  U-tube  (iig.  161)  surrounded  with  cold  water,  to  condense  uu- 
decomposed  nitric  acid,  then  through  a  similar  tube  containing  calcium 
chloride,  to  absorb  aqueous  vapour,  and  afterwards  into  a  U-tube  sur- 
rounded with  a  freezing  mixture  of  ice  and  salt.  Through  a  small  tube 
opening  into  the  bend  of  this  U-tube,  the  condensed  nitrous  anhydride 
drops  into  a  tube  drawn  out  to  a  narrow  neck,  so  that  it  may  be  drawn  olf, 
and  sealed  by  the  blowpipe — 

2HNO3  +  As.Og  +  2H2O  =  2H3AsO^  -f  N2O3 


Wliite  arsenic. 


Arsenic  acid. 


*  Asbestos  which  has  been  wetted  with  solution  of  platinic  chloride,  dried,  and  heated 
to  redness,  to  reduce  the  platinum  to  the  metallic  state. 


141 


NITROUS  ANHYDRIDE. 


Tilden  prepares  nitrous  anhydride  by  decomposing  the  acid  nitrosyle 
sulphate  (see  Aqna  Regia)  with  a  small  quantity  of  water — 
2NOHSO4  +  H2O  =2H2S04  +  N2O3. 
Nitrous  anhydride  is  a  blue  liquid  which  boils  below  32°  F.,  becoming 
converted  into  a  red  vapour,  and  partly  decomposed  into  NO  and  NOg. 
Water  at  about  32°  F.  dissolves  the  acid  without  decomposing  it,  yielding 
a  blue  solution,  which  is  decomposed,  as  the  temperature  rises,  into  nitric 
acid,  which  remains  in  the  liquid,  and  nitric  oxide  which  escapes  with 
effervescence,  SNgOg  +  HgO  =  2HNO3  +  4N0  . 

The  blue  solution  is  believed  to  contain  nitrous  acid,  HNOg,  resulting 
from  the  reaction  NgOg  +  HgO  =  2HNO2 ;  but  this  compound  has  not 
been  obtained  in  a  pure  state, 

A  very  dilute  solution  of  nitrous  acid  may  be  preserved  for  some  time 
aud  even  distilled  without  decomposition. 


Fig.  161. — Preparation  of  nitrous  anhydride. 

The  salts  of  nitrous  acid,  or  nitrites,  are  interesting  on  account  of  their 
production  from  the  nitrates  by  the  action  of  heat  (p.  1 40). 

If  potassium  nitrate  be  fused  in  a  fireclay  crucible  and  heated  to  redness,  it  will 
evolve  bubbles  of  oxygen,  and  slowly  become  converted  into  potassium  nitrite 
(KNO.j).  The  heat  may  be  continued  until  a  portion  removed  on  the  end  of  an 
iron  rod,  and  dissolved  in  water,  gives  a  strongly  alkaline  solution.  The  fused  mass 
may  then  be  poured  upon  a  dry  stone,  and  when  cool,  broken  into  fragments  and 
preserved  in  a  stoppered  bottle.  On  heating  a  fragment  of  the  nitrite  with  diluted 
sulphuric  acid,  red  vapours  will  be  disengaged,  but  these  contain  little  nitrous  acid, 
the  greater  part  of  this  being  decomposed  by  the  water  into  nitric  acid  and  nitric 
oxide. 

When  nitrous  acid  acts  upon  ammonia,  both  compounds  suffer  decomposition, 
water  and  nitrogen  being  the  results  ;  NH3  +  HN0.2  =  N2  +  2H.p. 

This  is  sometimes  taken  advantage  of  in  preparing  nitrogen  gas  by  boiling  mixed 
solutions  of  sal  ammoniac  and  potassium  nitrite  ;  NH4CI  +  KN02=  KCl  +  211.20  +  Ng. 

In  experiments  upon  organic  compounds,  nitrous  acid  is  sometimes  employed  as  a 
convenient  agent  for  effecting  simultaneously  the  removal  of  3  atoms  of  hydrogen 
from  a  compound,  and  the  insertion  of  1  atom  of  nitrogen. 

Wlien  solutions  of  nitrites  are  heated  in  contact  with  air,  they  gradually  absorb 
oxygen,  becoming  converted  into  nitrates. 

When  a  solution  of  sodium  nitrate,  NaNO.,,  is  acted  on  by  sodium  amalgam,  it  is 
iirst  reduced  to  sodium  nitrite,  NaNO^,  and  then  to  sodium  hyponitritc,  NaNO,  which 
gives  a  yellow  precipitate  of  silver  hyponitrite,  AgNO,  on  addition  of  silver  nitrate 
to  the  solution  after  neutralisation  with  nitric  acid.  The  sodium  salt  may  be  pre- 
pared in  large  quantity  by  fusing  sodium  nitrate  with  iron  filings  in  an  iron  crucible, 
when  the  iron  aljstracts  0  from  the  NaNOg,  and  converts  it  into  NaNO.     By  boiling 


PROPERTIES  OF  NITRIC  PEROXIDE.  14 

the  fused  mass  with  water,  filtering,  and  evaporating^  to  a,  small  bulk,  needle-shaped 
crystals  are  obtained  on  eoolino^,  which  have  the  formula  NaN0.3Aq. 

The  corresponding  acid,  HNO,  has  not  been  obtained,  the  attempts  to  prepare  it 
having  resulted  in  the  formation  of  nitrous  oxide  and  water  ;  2HNO  =  N20  +  H^G. 

99.  Nitric  peroxide  (NOg  =  46  parts  by  weight  =  2  volumes),  also 
called  hyponitric  acid  and  peroxide  of  nitrogen  or  pernitric  oxide :  for- 
merly known  as  nitrous  acid. — By  passing  a  mixture  of  nitric  oxide  with 
half  its  volume  of  oxygert,  free  from  every  trace  of  moisture,  into  a  per- 
fectly dry  tube  cooled  in  a  mixture  of  ice  and  salt,  the  dark  red  gas  is 
condensed  into  colourless  prismatic  crystals  which  melt  at  10°  F.  into 
a  nearly  colourless  liquid.  This  gradually  becomes  yellow  as  the  tempera- 
ture rises,  and  at  the  ordinary  temperature  has  a  deep  orange  colour. 
It  is  very  volatile,  boiling  at  71°  F.,  and  being  converted  into  a  red- 
brown  vapour,  which  was  long  mistaken  for  a  permanent  gas,  on  account 
of  the  great  difficulty  of  condensing  it  when  once  mixed  with  air  or 
oxygen.  Nitric  peroxide  is  also  obtained  mixed  with  one-fourth  of  its 
volume  of  oxygen,  by  heating  lead  nitrate  (fig.  162) ; 
Pb(X03)^  =  PbO  +  2XO2  +  0  . 

The  vapour  of  nitric  peroxide  is  much  heavier 
than  atmospheric  air. 

Its  specific  gravity  (compared  with  hydrogen  at  the  same 
temperature)  diminishes  as  the  temperature  rises.  At  275° 
F.  it  is  23  times  as  heavy  as  hydrogen,  showing  its  mole- 
cular weight  to  be  46.  This  variation  in  density,  in  con- 
junction with  the  other  changes,  with  increase  of  tempera- 
ture, lead  to  the  belief  that  the  molecule  of  nitric  peroxide 
at  low  temperatures  (in  its  liquid  state)  is  '^^0^,  and  becomes  -rig-  lo^-— ^Preparation 
decomposed  into  2NO2  at  high  temperatures.  °^  °""°  peroxide. 

Its  colour  varies  with  the  temperature,  becoming  very  dark  at  100°  F. 
The  smell  of  the  vapour  is  very  characteristic.  It  supports  the 
combustion  of  strongly  burning  charcoal  or  phosphorus,  and  oxidises 
most  of  the  metals,  potassium  taking  fire  in  it  spontaneously.  The 
nitric  peroxide  must,  therefore,  rank  as  a  powerful  oxidising  agent, 
and  it  is  the  presence  of  this  substance  in  the  red  fuming  nitric  acid 
that  imparts  to  it  higher  oxidising  powers  than  those  of  the  colourless 
nitric  acid. 

The  so-called  nitrous  acid  of  commerce  is  really  nitric  acid  holding  in 
solution  a  large  proportion  of  nitric  peroxide,  and  is  prepared  by  intro- 
ducing sulphur  into  the  retorts  containing  the  mixture  of  sodium  nitrate 
and  sulphuric  acid  employed  in  the  preparation  of  the  nitric  acid,  a  por- 
tion of  which  is  deoxidised  and  converted  into  nitric  peroxide.  Water 
in  excess  immediately  decomposes  the  nitric  peroxide  into  nitrous  acid 
and  nitric  acid  ;  2NO2  +  H^O  =  HNO3  +  HNOo . 

When  water  is  gradually  added  to  liquid  nitric  peroxide,  it  effervesces, 
from  escape  of  nitric  oxide,  and  becomes  green,  blue,  and  ultimately 
colourless ;  SXOo  -t-  H.^O  =  XO  +  2IIXO3.  If  the  red  nitric  acid  of  com- 
merce be  gradually  diluted  with  water,  it  will  be  found  to  undergo 
similar  changes,  always  becoming  colourless  at  last.  The  nitric  acid 
which  has  been  used  in  a  Grove's  battery  always  has  a  green  colour, 
from  the  large  amount  of  nitric  peroxide  which  has  accumulated  in  it,  in 
consequence  of  the  decomposition  of  the  acid  by  the  hydrogen  disengaged 
during  the  action  of  the  battery  ;  H  4-  HXO3  =  H^O  -I-  XO.,.  If  this 
green  acid  be  diluted  with  a  little  water  it  becomes  blue,  and  a  larger 

K 


146  GENERAL  SUMMARY  OF  OXIDES  OF  NITROGEN. 

quantity  of  water  renders  it  colourless,  causing  the  evolution  of  nitric 
oxide.  Similar  colours  are  obtained  by  passing  nitric  oxide  into  nitric 
acid  of  different  degrees  of  concentration,  apparently  because  nitric 
peroxide  is  formed  and  dissolved  by  the  acid. 

When  silver,  mercury,  and  some  other  metals  are  dissolved  in  cold  nitric 
acid,  a  green  or  blue  colour  is  often  produced,  leading  a  novice  to  suspect 
the  presence  of  copper,  the  colour  being  really  caused  by  the  solution,  in 
the  unaltered  nitric  acid,  of  the  nitric  peroxide  produced  by  the  deoxida- 
tion  of  another  portion. 

i!^itric  peroxide  was  formerly  believed  to  be  an  independent  acid 
capable  of  forming  salts.  It  is  true  that  its  vapours  have  a  strongly  acid 
reaction  to  test-papers,  but  when  brought  into  contact  with  alkalies,  it  pro- 
duces a  mixture  of  nitrate  and  nitrite — 

2NO2   +    2KH0   =    KXO3   -1-   KNO2   +   H2O. 

100.  General  review  of  the  oxides  of  nitrogen. — ^Nitric  oxide,  citrous 
acid,  and  nitric  peroxide,  are  very  remarkable  for  their  relations  to 
oxygen.  Nitric  oxide  is  one  of  the  very  few  substances  which  combine 
with  dry  oxygen  at  the  ordinary  temperature,  and  yet  the  nitric  peroxide 
which  is  thus  produced  is  very  ready  to  yield  its  oxygen  to  other  sub- 
stances. Nitrous  acid,  as  might  be  expected,  is  intermediate  in  this 
respect,  being  capable  of  acting  as  a  reducing  agent  upon  powerfully 
oxidising  substances,  and  as  an  oxidising  agent  upon  substances  having 
a  great  attraction  for  oxygen.  Thus  a  solution  of  potassium  nitrite 
acidified  with  sulphuric  acid  will  bleach  potassium  permanganate,  reducing 
the  permanganic  acid  tomanganous  oxide  (MnO);  whilst  if  added  to  ferrous 
sulphate,  the  nitrite  converts  the  ferrous  into  ferric  salt,  and  this  solution, 
which  was  capable  of  reducing  the  potassium  permanganate  before,  is  now 
found  to  be  without  effect  upon  it,  unless  an  excess  of  the  nitrite  has 
been  added. 

The  oxides  of  nitrogen,  as  illustrating  combination  in  multiple  propor- 
tions hy  weight  and  volume. — In  its  most  general  form,  the  Law  of  Multiple 
Proportions  may  be  thus  stated.  When  a  substance  (A)  combines  with 
another  substance  (B)  in  more  than  one  proportion,  the  quantities  of  B 
which  combine  with  a  constant  quantity  of  A,  are  multiples  of  the 
smallest  combining  quantity  of  B  by  some  whole  number. 

In  the  oxides  of  nitrogen  this  law  is  exemplified  in  the  simplest  form, 
since  the  quantities  of  oxygen  which  combine  with  a  constant  quantity  of 
nitrogen  are  multiples  of  the  least  combining  quantity  of  oxygen  by  2, 
o,  4,  and  5. 

Nitrous  oxide,     . 

Nitric  o-xide  (two  molecules), 

Nitrous  anhydride, 

Nitric  peroxide,  . 

Nitric  anhydride, 

It  was  shown  at  p.  131  that  there  is  ground  for  representing  th.e  atomic  weight  of 
nitrogen  as  =  14. 

When  nitrous  oxide  is  passed  through  a  red  hot  porcelain  tube,  its  volume  is 
increased  by  one-half,  and  the  resulting  gas  is  found  to  be  a  mixture  of  1  volume 
of  oxygen  and  2  volumes  of  nitrogen.  Hence  it  is  inferred  that,  in  nitrous  oxide, 
2  volumes  or  atoms  (28  parts)  of  nitrogen  are  united  with  1  volume  or  atom  (16  parts) 
of  oxygen,  to  form  2  volumes  or  one  molecule  of  nitrous  oxide  (representing  44  parts 
by  weight). 


N 

0 

.  N,0 

28 

16 

.  NjOa 

28 

16  X  2 

.  N..O3 

28 

16  X  3 

.    .  n;o. 

28 

16  X  4 

.    .  N,Os 

28 

16  X  5 

CHLORINE.  147 

AVhen  charnoal  is  strongly  heated  in  nitric  oxide,  the  volume  of  the  gas  remains 
unchanged  ;  but  it  is  found  on  analysis  to  have  become  converted  into  a  mixture 
of  equal  volumes  of  carbonic  acid  gas  and  nitrogen  (2N0  + 0  =  002  +  1^2).  Since 
1  volume  of  carbonic  acid  gas  contains  1  volume  of  oxygen  (page  91),  the  experiment 
proves  that  1  volume  of  oxygen  and  1  volume  of  nitrogen  exist  in  2  volumes  of 
nitric  oxide,  or  that  1  atom  of  nitrogen  (or  14  parts)  is  combined  with  1  atom  of 
oxygen  (16  parts)  in  2  volumes  (.one  molecule,  or  30  parts  by  weight)  of  nitric  oxide. 

The  direct  evidence  of  the  composition  of  nitrous  anhydride  is  not  so  satisfactory 
as  that  in  the  two  preceding  cases.  This  gas  has  been  obtained,  however,  by  the 
direct  union  of  1  volume  of  oxygen  with  4  volumes  of  nitric  oxide,  leading  to  the 
conclusion  that  it  contains  NgOg. 

Nitric  peroxide  has  been  analysed  by  passing  the  vapour  produced  from  a  known 
weight  of  the  liquid,  over  red  hot  metallic  copper,  which  absorbed  the  oxygen,  leaving 
the  nitrogen  to  be  collected  and  measured.  It  was  thus  found  that  14  parts  by  weight 
(one  atom  =1  volume)  of  nitrogen  were  combined  with  32  parts  by  weight  (two 
atoms  =  2  volumes)  of  oxygen,  a  result  which  is  confirmed  by  the  direct  union  of  2 
volumes  of  NO  ^one  molecule)  with  1  volume  of  oxygen  (one  atom)  to  form  NO2. 

Nitric  anhydride,  or  anhydrous  nitric  acid,  was  analysed  by  a  method  similar  to 
that  employed  for  nitric  peroxide,  and  was  found  to  contain  28  parts  by  weight 
(2  atoms)  of  nitrogen,  combined  with  80  parts  (5  atoms)  of  oxygen.  The  volume 
occupied  by  the  molecule  of  nitric  anhydride  in  the  state  of  vapour  has  not  been 
determined,  on  account  of  the  want  of  stability  of  this  compound. 

The  facility  with  which  nitrous  anhydride  and  nitric  peroxide  can  be  decomposed  with 
formation  of  nitric  oxide,  renders  it  probable  that  they  really  contain  that  compound. 
To  express  this,  they  may  plausibly  be  represented  as  formed  after  the  same  plan  as  a 

XT      \ 

molecule  of  water.     Just  as  in  tt   [  0,  the  two  atoms  of  hydrogen  are  linked  together 

^0  ) 

by  the  diatomic  oxygen,  so  in  nitrous  anhydride,  i^^  >  0,  two  molecules   of    nitric 

oxide  are  linked  together  by  the  atom  of  oxygen,  whilst  in  nitric  peroxide  (N2O4)  a 
molecule  of  NO  is  bound  up  with  a  molecule  of  NO.^  thus  -j^q   [  0.        If    nitric 

anhydride  be  represented  by  -j^q-  |  0,  it  is  easy  to  understand  the  behaviour  of 
these  three  oxides  with  the  alkalies.  Thus,  by  the  action  of  nitrous  anhydride  on 
caustic  potash,  we  obtain  potassium  nitrite  -^^  [  0,  whilst  nitric  acid  gives  potassium 

K     ) 

nitrate,    -^^   >  0,  and  nitric  peroxide  gives  a  mixture  of  both  salts. 

From  the  experiments  of  Berthelot,  it  appears  that  the  decomposition  of  all  the 
oxides  of  nitrogen  is  attended  by  evolution  of  heat,  which  is  greatest  for  nitric  oxide. 

chloei:n"e. 

Cl  =  35"5  parts  by  weight  =  1  volume  ;  35"5grs.  =467  cub.  in.  at  60°  F.  and  30"  Bar.  ; 
35  "5  grammes  =  11 '2  litres  at  0°  C.  and  760  mm.  Bar. 

•  101.  This  element  is  never  found  in  the  uncombined  state,  but  is  very 
abundant  in  the  mineral  world  in  the  forms  of  sodium  chloride  (common 
salt)  and  potassium  chloride.  In  these  forms  also  it  is  an  important  con- 
stituent of  the  fluids  of  the  animal  body,  but  as  it  is  not  found  in  sufficient 
proportion  in  vegetable  food,  or  in  the  solid  parts  of  animal  food,  a 
I  quantity  of  salt  must  be  added  to  these  in  order  to  form  a  wholesome 
diet.  Sodium  chloride  is  indispensable  as  a  raw  material  for  several  of 
the  most  useful  arts,  such  as  the  manufactures  of  soap  and  glass,  bleaching, 
&c. ;  in  fact,  it  is  the  source  of  three  of  the  most  generally  useful  chemical 
products,  viz.,  chlorine,  hydrochloric  acid,  and  soda. 

About  the  middle  of  the  17th  century,  a  GermJin  chemist  named 
Glauber  distilled  some  common  salt  with  sulphuric  acid,  and  obtained  a 
strongly  acid  liquid  to  which  he  gave  the  name  muriatic  acid  (from  nmria, 
brine),  and  which  was  proved  to  be  identical  with  the  acid  long  known  to 


148 


PREPARATION  OF  CHLORINE. 


the  alchemists  as  spirit  of  salt.  The  saline  mass  which  was  left  after  the 
experiment  was  then  termed  Glauber's  salt,  but  afterwards  received  its 
present  name  of  sodium  sulphate. 

It  was  undoubtedly  a  natural  inference  from  this  experiment  that  com- 
mon salt  was  composed  of  muriatic  acid  and  soda,  and  that  the  sulphuric 
acid  had  a  greater  attraction  for  the  soda  than  the  muriatic  acid,  which 
was  therefore  displaced  by  it.  In  accordance  with  this  view,  common 
salt  was  called  muriate  of  soda,  without  further  question,  until  the  year 
1810,  when  the  experiments  of  Davy  proved  that  it  was  really  composed 
of  the  two  elementary  substances,  chlorine  and  sodium,  and  must  there- 
fore be  styled,  as  it  now  is,  sodium  chloride,  and  represented  by  the 
formula  NaCl.  It  was  further  shown  by  Davy  that  the  muriatic  acid 
was  really  composed  of  chlorine  and  hydrogen,  and  that  it  was,  in  fact 
(HCl),  chloride  of  sodium  (NaCl),  in  which  the  sodium  had  been  dis- 
placed by  hydrogen. 

Preparation  of  chlorine. — In  order  to  extract  chlorine  from  common 
salt,  it  is  heated  with  black  oxide  of  manganese  and  diluted  sulphuric 
acid,  when  the  sulphates  of  sodium  and  manganese  are  left  in  solution, 
and  chlorine  escapes  in  the  form  of  gas — 

2]SraCl  +  MnOg  +  2H2SO4  =  mgSO^  +  MnSO^  +  2H2O  +  C\  . 

600  grains  of  common  salt  may  be  mixed  with  450  grains  of  binoxide  of  manganese, 
introduced  into  a  retort  (fig.  163),  and  a  cold  mixture  of  1^  oz.  by  measure  of  strong 
suljihuric  acid  with  4  oz.  of  water  poured  upon  it.     The  retort  having  been   well 


Fig.  163. — Preparation  of  chlorine. 

shaken,  to  wet  the  powder  thoroughly  with  the  acid,  a  very  gentle  heat  is  applied, 
and  the  gas  collected  in  bottles  filled  with  water  and  inverted  in  the  pneumatic 
trough.  When  the  bottles  are  filled,  the  stoppers,  previously  greased,  must  be 
inserted  into  them  under  water.  The  first  bottle  or  two  will  contain  the  air  from  the 
retort,  and  will  therefore  have  a  paler  colour  than  the  pure  chlorine  afterwards  col- 
lected. It  is  advisable  to  keep  a  jar  filled  with  water  standing  ready  on  the  shelf  of 
the  trough,  so  that  any  excess  of  chlorine  may  be  passed  into  it  instead  of  being 
allowed  to  escape  into  the  air,  causing  serious  inconvenience.  The  bottles  of  moist 
chlorine  must  always  be  preserved  in  the  <lark.  Chlorine  may  also  be  conveniently 
prepared  by  gently  heating  500  grains  of  binoxide  of  manganese  with  4  oz.  (measured) 
of  common  hydrochloric  acid — 

MnOa  +  4HC1  =  MnCla  -f-  2H2O  -f  C\^. 

Either  of  the  above  methods  will  furnish  about  five  pints  of  chlorine. 

as  a  carrier  of.9  -process  for  the  manufacture  of  chlorine,  the  manganese  is  made  to  act 

as  a  carrier  of  oxygen  from  the  atmosphere  to  the  hydrogen  of  the  hydrochloric  acid. 


•  LIQUEFACTION  OF  CHLORINE.  149 

setting  the  chlorine  free.  For  this  purpose  the  chloride  of  manganese  obtained  in 
the  above  process  is  decomposed  by  lime;  MnClj  +  CaO  =  CaClj  +  MnO.  By  mixing 
the  MnO  with  more  lime,  and  blowing  atmospheric  air  through  the  mixture,  MnO. 
is  reproduced,  and  may  be  employed  for  decomposing  a  fresh  quantity  of  HCl.  In 
Deacon's  process,  a  mixture  of  air  and  hydrochloric  acid  gas  is  passed  over  heated 
fire-brick  which  has  been  soaked  in  solution  of  copper  sulphate  and  sodium  sulphate, 
and  dried.  The  final  result  is  expressed  by  the  equation  2HC1  +  (N4  +  0)  =-  Up  +  Clj 
+  N4,  so  that  the  chlorine  obtained  is  mixed  with  twice  its  volume  of  nitrogen, 
which  is  stated,  however,  not  to  interfere  seriously  with  its  useful  application.  The 
action  of  the  copper-salt  has  not  been  clearly  explained,  but  it  appears  to  depend  upon 
the  instability  of  the  chlorides  of  copper  under  the  influence  of  heat  and  oxygen. 

*  Properties  of  chlonne. — The  physical  and  chemical  properties  of  chlorine 
are  more  striking  than  those  of  any  element  hitherto  considered.  Its 
colour  whence  it  derives  it  name  (;^A.wpos,  pale  green),  is  bright  greenish- 
yellow,  its  odour  insupportable.  It  is  twice  and  a  half  as  heavy  as  air 
(sp.  gr.  2*47),  and  may  be  reduced  to  the  liquid  state  by  a  pressure  of  only 
four  atmospheres  at  60°  F.  If  a  bottle  of  chlorine  be 
held  mouth  downAvards  in  water,  its  stopper  removed, 
one-third  of  the  chlorine  decanted  into  a  jar,  and  the 
rest  of  the  gas  shaken  with  the  water  in  the  bottle, 
the  mouth  of  which  is  closed  by  the  palm  of  the  hand 
(fig.  164),  the  water  will  absorb  nearly  twice  its 
volume  of  chlorine,  producing  a  vacuum  in  the  bottle, 
which  will  be  held  firmly  against  the  hand  by  atmo- 
spheric pressure.  If  air  be  then  allowed  to  enter,  and 
the  bottle  again  shaken  as  long  as  any  absorption 
takes  place,  a  saturated  solution  of  chlorine  (liquor  Mori,  chlorine  water) 
will  be  obtained.  By  exposing  this  yellow  solution  to  a  temperature 
approaching  32°  F.,  yellow  crystals  of  hydrate  of  chlorine  (Cl.SHgO)  are 
obtained,  the  liquid  becoming  colourless.  . 

When  the  water  in  the  pneumatic  trough,  over  which  chlorine  is  being  collected, 
happens  to  be  very  cold,  the  gas  is  often  so  foggy  as  to  be  quite  opaque,  in  conse- 
quence of  the  deposition  of  minute  crystals  of  the  hydrate.  On  standing,  the  gas 
becomes  clear,  crystals  of  the  hydrate  being  deposited  like  hoar-frost  upon  the  sides 
of  the  bottle  ;  the  gas  also  becomes  clear  when  the  bottles  are  slightly  warmed. 

The  hydrate  of  chlorine  affords  a  convenient  source  of  liquid  chlorine.  A  number 
of  bottles  of  saturated  solution  of  chlorine,  prepared  as  above,  are  exposed  on  a  cold 
winter's  day  until  the  hydrate  has  crystallised.  The  crystals  are  thrown  upon  a 
filter  cooled  to  nearly  32°,  allowed  to  drain,  and  rammed  into  a  pretty  strong  tube 
closed  at  one  end,  about  12  inches  long,  and  \  an  inch  in  diameter,  previously 
cooled  in  ice  or  snow.  The  tube  having  been  nearly  filled  with  the  crystals,  is  kept 
surrounded  with  snow,  whilst  its  upper  end  is  gradually  softened  in  the  blowpipe 
flame  and  drawn  ofi^  so  as  to  be  strongly  sealed.  When  this  tube  is  immersed  in 
water  at  100°  F. ,  the  chlorine  separates  from  the  water,  and  two  layers  of  liquid  are 
formed,  the  lower  one  consisting  of  amber-yellow  liquid  chlorine  (sp.  gr.  1'33),  and 
the  upper,  about  three  times  its  volume,  of  a  pale  yellow  aqueous  solution  of  chlorine. 
On  allowing  the  tube  to  cool  again,  the  crystalline  hydrate  is  reproduced,  even  at 
common  temperatures,  being  more  permanent  under  pressure.  It  may  even  be  sub- 
limed in  a  sealed  tube. 

Liquid  chlorine  may  also  be  obtained  in  a  state  in  which  it  can  be  preserved,  by 
disengaging  the  chlorine  in  a  sealed  tube  (as  in  the  liquefaction  of  ammonia)  from 
about  200  grains  of  platinic  chloride  previously  dried  at  400°  F.  The  chloride 
is  heated  with  a  spirit-lamp  in  one  limb  of  the  tube,  whilst  the  other  is  immersed 
in  a  freezing  mixture.  The  face  and  hands  of  the  operator  should  be  protected 
against  the  bursting  of  the  tube. 

The  most  characteristic  chemical  feature  of  chlorine  is  its  powerful 
attraction  for  many  other  elements  at  the  ordinary  temperature.  Among 
the  non-metals,  hydrogen,  bromine,  iodine,  sulphur,  selenium,  phosphorus, 


150 


EXPERIMENTS  WITH  CHLORINE: 


and  arsenic,  combine   spontaneously  with   chlorine,  and  nearly  aU  the 
metals  behave  in  the  same  way. 

If  a  piece  of  diy  phosphorus  be  placed  in  a  deflagrating  spoon,  and  immersed  in  a 
bottle  of  chlorine  (fig.  165),  it  will  take  fire  spontaneously,  combining  with  the  chlorine 

to  form  phosphorous  chloride  (PCI3).  A  tall  glass 
shade  may  be  placed  over  the  bottle,  which  should 
stand  in  a  plate  containing  water,  so  that  the 
fumes  may  not  escape  into  the  air. 

If  phosphorus  be  placed  in  a  bottle  of  oxygen  to 
which  a  small  quantity  of  chlorine  has  been  added, 
it  will  burst  out  after  a  minute  or  two  into  most 
brilliant  combustion. 

Powdered  antimony  (the  metal,  not  the  sulphide), 
sprinkled  into  a  bottle  of  chlorine  (fig.  166),  de- 
scends in  a  brilliant  shower  of  white  sparks,  the 
antimony  burning  in  the  chlorine  to  form  anti- 
monious  chloride  (SbC'lj).     A  little  water  should 
be  placed  at  the  bottom  of  the  bottle  to  prevent 
it  from  being  cracked,  and  the  fumes  should  be 
restrained  by  a  shade  standing  in  water. 
If  a  flask,  provided  with  a  stopcock  (fig.  167),  be  filled  with  leaves  of  Dutch  metal 
(an  alloy  of  copper  and  zinc  resembling  gold  leaf),  exhausted  of  air,  and  screwed  on 
to  a  capped  jar  of  chlorine  standing  over  water,  it  will  be  found,  on  opening  the 


Fig.  165. 


Fig.  166.  Fig.  167. 

stopcocks  so  that  the  chlorine  may  enter  the  flask,  that  the  metal  burns  with  a  red 
light,  forming  thick  yellow  fumes  containing  cupric  chloride  (CuClj)  and  zinc  chloride 
(ZnCl,).  If  a  gold  leaf  be  suspended  in  chlorine,  it  will  not  be  immediately  attacked, 
but  will  gradually  become  converted  into  auric  chloride  (AuClj). 

102,  The  most  important  useful  applications  of  chlorine  depend  upon 
its  powerful  chemical  attraction  for  hydrogen.  The  two  gases  may  he 
mixed  without  combining,  if  kept  in  the  dark  ;  but  when  the  mixture  is 
exposed  to  light,  they  combine  to  form  hydrochloric  acid  gas  (HCl),  with 
a  rapidity  proportionate  to  the  intensity  of  the  actinic  rays  (or  rays  capable 
of  inducing  chemical  change)  in  the  light  employed.  Exposed  to  gas-light 
or  ordinary  diftused  daylight,  the  hydrogen  and  chlorine  combine  slowly  ; 
but  direct  sunlight  causes  sudden  combination,  attended  with  explosion, 
resulting  from  the  expansion  which  the  hydrochloric  acid  formed  suffers 
by  the  heat  evolved  in  the  act  of  combination.  The  light  of  magnesium 
burning  in  air,  and  some  other  artificial  lights,  also  cause  sudden  com- 
bination. , 


SYNTHESIS  OF  HYDROCHLORIC  ACID. 


151 


Two  pint  gas-bottles  should  be  ground  so  that  their  mouths  may  be  fitted  accu- 
rately to  each  other,  and  filled  respectively  with  dry  hydrogen  and  dry  chlorine,  both 
gases  having  been  dried  by  passing  through  oil  of  vitriol,  and  collected,  the  hydrogen 
by  upward,  and  the  chlorine  by  downward,  displacement  of  air.  The  mouths  should 
be  slightly  greased  before  the  bottles  are  filled  with  gas,  and  afterwards  closed  with 
glass  plates.  On  placing  the  bottles  together,  and  removing  the  plates  so  that  the 
gases  may  come  in  contact  (see  hg.  148),  the  yellow  colour  of  the  chlorine  will  be 
permanent  as  long  as  the  mixture  is  kept  in  the  dark,  but  on  exposure  to  daylight 
the  colour  will  gradually  disappear,  the  hydrochloric  acid  gas  being  colourless.  If 
the  bottles  be  now  closed  with  glass  plates,  the  small  quantity  of  gas  which  escapes 
during  the  operation  will  be  seen  to  fume  strongly  in  air,  a  property  not  possessed 
either  by  hydrogen  or  chlorine  ;  and  when  the  necks  of  the  bottles  are  immersed  in 
water,  and  the  glass  plates  withdrawn,  the  water  will  gradually  absorb  the  gas,  and  be 
forced  into  the  bottles  so  as  to  fill  them,  with  the  exception  of  a  small  space  occupied 
by  the  air  accidentally  admitted,  showing  that  the  hydrochloric  acid  gas  possesses 
the  joint  volumes  of  the  hydrogen  and  chlorine.  If  the  water  be  tinged  with  blue 
litmus,  it  will  be  strongly  I'eddened  as  it  enters  the  bottles. 

The  sudden  union  of  the  gases  with  explosion  may  be  safely  exhibited  in  a  Flor- 
ence flask.  The  flask  is  filled  with  water,  which  is  then  poured  out  into  a  measure. 
Exactly  half  the  water  is  returned 
to  the  flask,  and  its  level  in  the 
latter  carefully  marked  with  a  dia- 
mond or  file.  The  flask  having  been 
again  filled  with  water,  is  closed  with 
the  thumb  and  inverted  in  the  pneu- 
matic trough,  so  that  hydrogen  may 
be  passed  up  into  it  to  displace  one- 
half  of  the  water.  A  short-necked 
funnel  is  then  inserted,  under  the 
water,  into  the  neck  of  the  flask, 
and  chlorine  rapidly  decanted  up 
from  a  gas-bottle  (fig.  168)  until  the 
rest  of  the  water  has  been  disjilaced. 
The  flask  is  now  raised  from  the 
water  and  quickly  closed  with  a  cork 
(fig.  169),  through  which  pass  two 
gutta-percha-covered    copper    wires, 

the  ends  of  which  have  been  stripped  and  brought  sufliciently  near  to  each  other 
to  allow  of  the  passage  of  the  electric  spark  within  the  flask.  The  ends  external  to 
the  flask  are  also  stripped  and 
bent  into  hooks,  for  convenient 
connexion  with  the  conducting 
wires.  The  flask  is  placed  upon 
the  ground,  and  covered  with  a 
wooden  box  to  prevent  the  pieces 
from  flying  about.  On  connecting 
the  copper  wires  with  the  con- 
ducting wires  from  an  induction- 
coil  or  on  electrical  machine,  it 
will  be  heard,  on  passing  the  spark, 
that  the  mixture  has  violently  ex- 
ploded ;  on  raising  the  box,  it  will 
be  found  filled  with  strong  fumes 
of  hydrochloric  acid,  and  a  heap  of 
small  fragments  of  glass  will  repre- 
sent the  flask. 

A  flask  filled  in  the  .same  way  with  the  mixture  of  hydrogen  and  chlorine  may  be 
attached  to  the  end  of  a  long  stick,  and  thrust  out  into  the  sunlight,  when  it  explodes 
with  great  violence. 

To  illustrate  the  direct  combination  of  hj'drogen  and  chlorine  under  the  influence 
of  artificial  light,  it  is  better  to  employ  the" mixture  of  exactly  equal  volumes  of  the 
two  gases  obtained  by  decomposing  hydrochloric  acid  by  the  galvanic  current.  The 
voltameter  (A,  fig.  170)  is  filled  with  concentrated  hydrochloric  acid,  and  its  con- 
ducting wires  (B)  connected  with  the  terminals  of  a  Grove's  battery  of  five  or  six 


Fig.  168. 


Fig.  169. 


152 


EXPLOSION  OF  CHLORINE  AND  HYDKOGEN. 


cells.  Chlorine  is  at  once  evolved  at  the  positive  pole  (or  that  connected  with  the 
platinum  in  the  battery),  and  hydrogen  at  the  negative  pole  (attached  to  the  zinc  of 
the  battery).  It  is  advisible  to  place  the  voltameter  in  a  vessel  of  cold  water,  to 
prevent  the  hydrochloric  acid  from  becoming  too  hot.  The  gas  evolved  during  the 
lirst  five  minutes  should  be  allowed  to  pass  into  a  waste-jar,  because,  until  the  liquid 

becomes  saturated  with  chlorine, 
the  evolved  gas  does  not  contain 
exactly  equal  volumes  of  the 
constituent  elements.  A  very 
thin  glass  bulb  (C),  about  2 
inches  in  diameter,  blown  upon 
a  stout  piece  of  tube,  the  ends  of 
which  have  been  drawn  out  to 
narrow  open  points  (fig.  171),  is 
then  connected  with  the  volta- 
meter by  means  of  a  caoutchouc 
tube.  A  similar  caoutchouc  tube 
is  attached  to  the  free  end  of  the 
bulb.  When  the  colour  of  the 
gas  in  the  bulb  (which  should  be 
shaded  from  sunlight)  shows  that  it  is  completely  filled, , the  caoutchouc  tubes  are 
well  closed  by  nipper-taps  (fig.  172),  and  the  bulb  detached  from  the  voltameter.  In 
this  condition  it  may  be  kept  in  the  dark  for  a  long  time  without  alteration  or  escape 
of  gas.  The  mixture  may  be  most  eifectively  exploded  by  exposing  it  to  the  flash  of 
light  evolved  by  firing  a  mixture  of  nitric  oxide  gas  with  vapour  of  carbon  disulphide.^^ 
For  this  purpose  a  cylinder  may  be  filled  with  nitric  oxide  (page  141)  over  water, 
closed  with  a  glass  plate,  and  placed  mouth  upwards  upon  the  table  :  the  glass  plate 
being  lifted  for  an  instant,  a  few  drops  of  bisulphide  of  carbon  are  poured  into  the 
cylinder,  which  is  then  shaken.  The  bulb  containing  the  explosive  mixture  is 
suspended  at  some  distance  from  the  operator,  and  the  gas  cylinder  is  placed  within 
a  few  inches  of  it  (fig.  173),     On  applying  a  light  to  the  cylinder,  the  flash  will  cause 


Fig.  170. 


Fig.  172.  Fig.  173. 

the  immediate  explosion  of  the  mixture  in  the  bulb,  with  production  of  strong  fumes 
of  hydrochloric  acid. 

If  the  bulb  be  thin,  no  injury  will  be  inflicted  by  the  pieces  of  glass,  or  the 
operator  may  easily  protect  his  face  by  a  screen. 

•  The  attraction  of  chlorine  for  hydrogen  enables  it  to  effect  the  decom- 
position of  water.  The  solution  of  chlorine  in  water  may  be  preserved 
in  the  dark  without  change ;  but  when  exposed  to  light,  it  loses  the 
smell  of  chlorine  and  becomes  converted  into  weak  hydrochloric  acid, 
the   oxygen   being  liberated;  H20  +  Cl2  =  2HCl  +  0.t     The  decomposi- 

*  A  mixture  of  equal  volumes  of  chlorine  and  hydrogen  may  be  exploded  in  a  strong 
cjilnder  by  the  light  of  a  piece  of  magnesium  tape.  The  cylinder  should  be  closed  with  a 
thin  plate  of  mica,  and  placed  on  the  table  with  its  mouth  upwards. 

t  A  portion  of  this  oxygen  combines  with  chlorine,  producing  hypochlorous  acid  and, 
as  recently  stated,  perchloric  acid. 


ACTIOX  OF  CHLOEINE  UPON  HYDROGEN  COMPOUNDS. 


153 


tion  takes  place  much  more  quickly  at  a  red  heat,  so  that  oxygen  is 
obtained  in  abundance  by  passing  a  mixture  of  chlorine  and  steam 
through  a  red  hot  tube. 

For  this  experiment  a  porcelain  tube  is  employed,  which  is  loosely  filled  with 
fragments  of  broken  porcelain,^  to  expose  a  large  heated  surface.  This  tube  is 
gradually  heated  to  redness  in  a  charcoal  furnace  (fig.  174).  One  end  of  it  receives 
the  mixture  of  chlorine  with  steam,  obtained  by  passing  the  chlorine  evolved  from 
hydrochloric  acid  and  manganese  dioxide  in  A,  through  a  flask  (B)  of  boiling  water. 
The  other  end  of  the  tube  is  connected  with  a  bottle  (C)  containing  solution  of 
potash,  to  absorb  any  excess  of  chlorine  and  the  hydrochloric  acid  formed  ;  from  this 
bottle  the  oxygen  is  collected  over  the  pneumatic  trough. 


Fig.  174. — Steam  decomposed  by  chlorine. 

Since  water  is  decomposed  by  chlorine,  it  is  not  surprising  that  most 
other  hydrogen  compounds  are  attacked  by  it.  Ammonia  (i!^H3)  is  acted 
upon  with  great  violence.  If  a  stream  of  ammonia  gas  issuing  from  a  tube 
connected  with  a  flask  in  which  solution  of  ammonia  is  heated  (see  fig.  146) 
be  passed  into  a  bottle  of  chlorine,  it  takes  fire  immediately,  burning 
with  a  peculiar  flame,  and  yielding  thick  white  clouds  of  ammonium 
chloride;  4XH3  +  CI3  =  SNH^Cl  +  K  A  piece  of  folded  filter-paper 
dipped  in  strong  ammonia,  and  immersed  in  a  bottle  of  chlorine,  will 
exhibit  the  same  effect.  When  the  chlorine  is  allowed  to  act  upon 
ammonium  chloride,  its  operation  is  less  violent,  and  one  of  the  most 
explosive  substances  is  produced,  which  was  formerly  believed  to  be  a 
chloride  of  nitrogen,  but  is  probably  a  compound  formed  by  the  removal 
of  a  part  of  the  hydrogen  from  ammonia,  and  the  introduction  of  chlorine 
in  its  stead. 

Many  of  the  compounds  of  hydrogen  with  carbon  are  also  decomposed 
with  violence  by  chlorine.  When  a  piece  of  folded  filter-paper  is  dipped 
into  oil  of  turpentine  (C^QlIjg),  and  afterwards  into  a  bottle  of  chlorine,  it 
bursts  into  a  red  flame,  liberating  voluminous  clouds  of  carbon  and 
hydrochloric  acid.  Acetylene  (CgHg)  was  found  to  explode  spontaneously 
with  chlorine  when  exposed  to  light  (page  94).  ThS"  striking  decomposi- 
tion of  olefiant  gas  (C.^H^)  by  chlorine  on  the  approach  of  a  flame  has 
already  been  noticed  (page  97).  When  a  lighted  taper  is  immersed  in 
pure  clilorine,  it  is  extinguished;  but  if  a  little  air  be  present,  it  continues  to 


154 


BLEACHING  BY  CHLORINE. 


l)urn  with  a  small  red  flame,  the  hydrogen  only  of  the  wax  comhining 
with  the  chlorine,  whilst  the  carbon  separates  in  black  smoke,  mixed 
AV'ith  the  hydrochloric  fumes.  When  chlorine  is  brought  in  contact  with 
the  flame  of  a  spirit-lamp,  it  renders  the  flame  luminous  by  causing  the 
separation  of  solid  particles  of  carbon  (page  105).  It  has  been  seen,  in 
the  case  of  olefiant  gas,  that  chlorine  sometimes  combines  directly  with 
the  hydrocarbons. 

When  marsh  gas  (CH^)  is  diluted  with  an  equal  bulk  of  carbon  dioxide 
to  prevent  violent  action,  and  4  volumes  of  chlorine  are  added  for 
each  volume  of  marsh  gas,  an  oily  liquid  is  gradually  formed  under  the 
influence  of  daylight.  This  oily  liquid  is  a  mixture  of  chloroform  and 
carbon  tetrachloride,  the  production  of  which  is  explained  by  the  follow- 
ing equations  : — 

CH4  +  Clg  =  3HC1  +  CHCI3  {Chloroform). 

CH4  +  Clg  =  4HC1  +  CCI4      {Carbon  tetrachloride). 

It  is  evident  from  these  equations  that  chlorine  is  capable,  not  only  of 
removing  hydrogen  from  a  compound,  but  also  of  taking  its  place,  atom 
for  atom — a  mode  of  action  which  gives  rise  to  a  very  large  number  of 
chlorinated  products  from  organic  substances. 

The  attraction  of  chlorine  for  hydrogen  enables  the  moist  gas  to  act  as 
an  oxidising  agent.  Thus,  if  marsh  gas  and  chlorine  be  mixed  in  the 
presence  of  water,  and  exposed  to  daylight,  the  water  is  decomposed,  its 
hydrogen  combining  with  the  chlorine,  and  its  oxygen  with  the  carbon 
of  the  marsh  gas  ;  CH^  +  2H2O  +  Clg  =  CO2  +  8HC1 .     .. 

103.  The  powerful  bleaching  effect  of  chlorine  upon  organic  colouring 
matters  is  now  easily  understood.  If  a  solution  of  chlorine  in  water  be 
poured  into  solution  of  indigo  {sulpliindigotic  acid),  the  blue  colour  of  the 
indigo  is  discharged,  and  gives  place  to  a  comparatively  light  yellow 
colour.  The  presence  of  water  is  essential  to  the  bleaching  of  indigo  by 
chlorine,  the  dry  gas  not  affecting  the  colour  of  dry  indigo.  The  indigo 
is  first  oxidised  at  the  expense  of  the  water  and  converted  into  isatine, 
which  is  then  acted  upon  by  the  chlorine  and  converted  into  chlorisatine^ 
having  a  brownish-yellow  colour — 

CgHgNO    (Indigo)    +H2O  +  CI2  =  C8H5NO2       (I'^^tine)  +    2HC1] 

C^B..^O ^U<^o-tim)  +  CI2  =   CgH^ClNOg  miorUatine)  +  HCl  . 

!N"early  all  vegetable  and  animal  colouring  matters 
contain  carbon,  hydrogen,  nitrogen,  and  oxygen, 
and  are  converted  by  moist  chlorine  into  products 
of  oxidation  or  chlorination  which  happen  to  be 
colourless,  or  nearly  so. 

That  dry  chlorine  will  not  bleach  may  be  shown  by 
shaking  some  oil  of  vitriol  in  a  bottle  of  the  gas  and 
allowing  it  to  stand  for  an  hour  or  two,  so  that  the  acid 
may  remove  the  whole  of  the  moisture.  If  a  piece  of 
crimson  paper  be  dried  at  a  moderate  heat  and  suspended 
in  the  bottle  while  warm,  it  will  remain  unbleached  for 
hours  ;  but  a  similar  piece  of  paper  suspended  in  a  bottle 
of  moist  chlorine  will  be  bleached  almost  immediately. 
If  characters  be  written  on  crimson  paper  with  a  wet 
brush,  and  the  paper  placed  in  a  jar  beside  a  bottle  of 
chlorine  (fig.   175),   it  will  be  found  on  removing  the 


Fig.  175. 


stopper  that  white  characters  soon  make  their  appearance  on  the  red  ground. 


CHLOJJIDE  OF  LIME.  155 

If  a  collection  of  coloured  linen  or  cotton  fabrics,  or  of  artificial  flowers,  be  exposed 
to  the  action  of  moist  chlorine  gas  or  of  chlorine  water,  those  which  are  dyed  with 
organic  colouring  matters  will  be  bleached  at  once,  whilst  the  mineral  colours  will  for 
the  most  part  remain  unaltered.  Green  leaves  immersed  in  chlorine  acquire  a  rich 
autumnal  brown  tint,  and  are  eventually  bleached.  All  flowers  are  very  readily 
bleached  by  this  gas. 

Chlorine  is  very  extensively  employed  for  bleaching  linen  and  cotton, 
the  gas  acting  upon  the  colouring  matter  without  affecting  the  fibre ;  but 
silk  and  wool  present  much  less  resistance  to  chemical  action,  and  would 
be  much  injured  by  chlorine,  so  that  they  are  always  bleached  by 
sulphurous  acid  gas. 

Xeither  chlorine  itself  nor  its  solution  in  water  can  be  very  conveniently 
employed  for  bleaching  on  the  large  scale,  on  account  of  the  irritating 
effect  of  the  gas,  so  that  it  is  usual  to  employ  it  in  the  form  of  chloride  oj 
lime,  from  which  it  can  be  easily  liberated  as  it  is  wanted. 
•>.  104.  Chloride  of  lime  or  bleaching  poicder  is  prepared  by  passing 
chlorine  gas  into  boxes  of  lead  or  stone  in  which  a  quantity  of  slaked 
I  lime  is  spread  out  upon  shelves.  The  lime  absorbs  nearly  half  its  weight 
of  chlorine,  and  forms  a  white  powder,  \srhich  has  a  very  peculiar  smell, 
somewhat  different  from  that  of  chlorine. 

The  formula  of  chloride  of  lime  is  generally  written  CaOClg. 

The  constitution  of  chloride  of  lime  appears  doubtful.  "When  the  calcium  hydrate 
Ca(H0)2,  is  acted  on  by  chlorine,  the  simplest  reaction  would  be  Ca(HO)2  +  Cl2 
=  0301(010) +  H,0,  according  to  which  the  chloride  of  lime  would  result  from  the 
replacement  of  one  of  the  HO  groups  by  01,  and  of  the  other  by  010 ;  but  this  would 
require  the  calcium  hydrate  to  absorb  neatly  an  equal  weight  of  chlorine,  whereas  the 
amount  never  exceeds  half  this  quantity. 

According  to  another  view,  the  chloride  of  lime  is  a  mixture  of  calcium  hypo- 
chlorite Ca(C10)2  with  calcium  oxvchloride  CajOgClg,  produced  bj'  the  reaction 
40a(HO).2  +  Cl4  =  0a(01O).^  +  0a3O201j  +  4H2O,  which  would  require  the  absorption  of 
nearly  half  its  weight  of  chlorine  by  the  calcium  hydrate.  A  more  recent  theoiy 
regards  the  chloride  of  lime  as  containing  calcium  chloride,  together  with  the 
compound  OaHOlOg,  resulting  from  the  substitution  of  CI  for  H  in  CaHoOj ;  but  since 
calcium  chloride  absorbs  water  and  becomes  wet  on  exposure  to  air,  whilst  good 
chloride  of  lime  remains  dry,  it  is  difficult  to  admit  the  correctness  of  this  view.  The 
analyses  which  support  this  theory  would  also  agree  equally  well  with  the  formula 
0a3(OH).2(O01)20l2,  which  would  explain  the  tendency  ot  chloride  of  lime  to  yield, 
among  the  products  of  its  decomposition,  calcium  chloride  CaCl^,  calcium  hypo- 
chlorite Ca(001).2  and  calcium  hydrate  Ca(0H)2. 

Practically,  the  constitution  of  chloride  of  lime  itself  is  of  less  importance  than 
that  of  the  solution  obtained  by  treating  it  with  water,  which  is  generally  admitted 
to  contain  calcium  hypochlorite  Oa(010)2  and  calcium  chloride  OaClj,  with  some 
calcium  hydrate  Oa(HO)2,  of  which  a  large  quantity  is  left  in  the  undissolved 
residue. 

Taking  each  of  the  three  views  above  mentioned,  the  action  of  water  upon  chloride 
of  lime  would  be  represented  by  one  of  the  following  equations:  (1)  20a01(010) 
=  OaOlj  +  Oa(C10)2 ;  (2)  Oa(010)2  +  Oa302Cl2  +  2H2O  =  Oa(OlO),  +  CaOl^  +  2Ca(HO)2 ; 
(3)  2CaHC102  +  CaOU  =  Oa(010)2  +  CaOL^  +  OaCHO).. 

If  the  solution  of  chloride  of  lime  be  added  to  blue  litmus,  it  will  be 
found  to  exert  little  bleaching  action ;  but  on  adding  a  little  acid  (sul- 
phuric, for  example),  the  blue  colour  will  be  discharged,  the  acid  setting 
free  the  chlorine,  which  acts  upon  the  colouring  matter. 

Ca(C10)2  -h   CaCl^  +  2H2SO4  =  2C^^0^  +  2B.^0  +  C\,. 

Solution  of  chloride  of  lime.  ^ 

Even  carbonic  acid  will  develop  the  bleaching  property  of  chloride  of 
lime,  so  that  the  above  mixture  may  be  decolorised  by  lareatbing  into  it 
through  a  glass  tube. 


156  DISINFECTION  BY  CHLORINE. 

When  chloride  of  lime  is  used  for  bleaching  on  the  large  scale,  the  stuGF 
to  be  bleached  is  first  thoroughly  cleansed  from  any  grease  or  weaver's  dress- 
^^*i7>  l>y  boiling  it  in  lime-water  and  in  a  weak  solution  of  soda,  and  is  then 
immersed  in  a  weak  solution  of  the  chloride  of  lime.  This,  by  itself,  how- 
ever, exerts  very  little  action  upon  the  natural  colouring  matter  of  the 
fibre,  and  the  stuff"  is  therefore  next  immersed  in  very  dilute  sulphuric 
acid,  when  the  colouring  matter  is  so  far  altered  as  to  become  soluble  in 
the  alkaline  solution  in  which  it  is  next  immersed,  and  a  repetition  of 
these  processes,  followed  up  by  a  thorough  rinsing,  generally  perfects  the 
bleaching. 

The  property  possessed  by  acids  of  liberating  chlorine  from  the  chloride 
of  lime  is  applied,  in  calico-printing,  to  the  production  of  white  patterns 
upon  a  red  ground.  The  stuff"  having  been  dyed  with  Turkey  red,  the 
pattern  is  imprinted  upon  it  with  a  discharge  consisting  of  an  acid  (tar- 
taric, phosphoric,  or  arsenic)  thickened  with  gum.  On  passing  the  fabric 
through  a  bath  of  weak  chloride  of  lime,  the  colour  is  discharged  only  at 
those  parts  to  which  the  acid  has  been  applied,  and  where,  consequently, 
chlorine  is  liberated. 

The  explanation  above  given  of  the  bleaching  eff"ect  of  chlorine  may 
probably  be  applied  also  to  its  so-called  dUdnfecting  properties.  The 
atmosphere,  in  particular  localities,  is  occasionally  contaminated  with 
poisonous  substances,  some  of  which  are  known  only  by  their  injurious 
eff"ects  upon  the  health,  their  quantity  being  so  small  that  they  do  not 
appear  in  the  results  of  the  analysis  of  such  air.  Since,  however,  these 
substances  appear  to  be  acted  upon  by  the  same  agents  which  are  usually 
found  to  decompose  organic  compounds,  they  are  commonly  believed  to 
be  bodies  of  this  class,  and  chlorine  has  been  very  commonly  employed  to 
combat  these  insidious  enemies  to  health,  since  Guy  ton  de  Morveau,  in 
the  latter  part  of  the  last  century,  made  use  of  it  to  destroy  the  odour 
arising  from  the  bodies  interred  in  the  vaults  beneath  the  cathedral  of  Dijon. 

Among  the  off"ensive  and  unhealthy  products  of  putrefaction  of  animal 
and  vegetable  matter,  sulphuretted  hydrogen,  ammonia,  and  bodies  simi- 
larly constituted,  are  found.  That  chlorine  breaks  up  these  hydrogen 
compounds  is  well  known,  and  hence  its  great  value  for  removing  the 
unwholesome  properties  of  the  air  in  badly-drained  houses,  (fcc. 

Chloride  of  lime  is  one  of  the  most  convenient  forms  in  which  to  apply 
chlorine  for  the  purposes  of  fumigating  and  disinfecting.  If  a  cloth 
saturated  with  the  solution  be  suspended  in  the  air,  the  carbonic  acid  gas 
in  the  latter  causes  a  slow  evolution  of  hypochlorous  acid,  which  is  even  a 
more  powerful  disinfectant  than  chlorine  itself.  In  extreme  cases,  where 
a  rapid  evolution  of  chlorine  is  required,  the  bleaching  powder  is  placed 
in  a  plate,  and  diluted  sulphuric  acid  is  poured  over  it,  or  the  pow-der  may 
be  mixed  with  half  its  weight  of  pow^dered  alum  in  a  plate,  when  a  pretty 
rapid  and  regular  escape  of  clilorine  will  ensue. 

105.  The  discovery  of  chlorine,  and  the  discussions  which  ensued  with 
respect  to  its  real  nature,  contributed  very  largely  to  the  advancement  of 
chemical  science.  About  the  year  1770,  the  Swedish  chemist  Scheele 
(who  afterwards  discovered  oxygen)  first  obtained  chlorine  by  heating 
manganese  ore  with  muriatic  acid. 

The  construction  which  Scheele  put  upon  the  result  of  this  experiment 
was  one  which  was  consistent  with  the  chemistry  of  that  date.     He  sup- 


PREPAEATION  OF  HYDEOCHLORIC  ACID. 


157 


posed  the  muriatic  acid  to  have  been  deprived  of  phlogiston,  and  hence 
chlorine  was  termed  by  him  depMogisticated  muriatic  acid.  This  phlo- 
giston had  long  been  a  subject  of  contention  among  philosophers,  having 
been  originally  assumed  to  exist  in  combination  with  all  combustible 
bodies,  and  to  be  separated  from  them  during  their  combustion.  To- 
wards the  decline  of  the  phlogistic  theory,  attempts  were  made  to  prove 
the  identity  of  this  imaginary  substance  with  hydrogen,  which  shows 
how  very  nearly  Scheele's  reasoning  approached  to  the  truth,  even  with 
the  very  imperfect  light  which  he  then  possessed.  Berthollet's  move- 
ment was  retrograde  when,  ten  years  afterwards,  he  styled  chlorine  oxj/- 
genised  muriatic  or  oxymuriatic  acid  ;  but  the  experiments  of  Gay-Lussac 
and  Th^nard,  and  more  particularly  those  of  Davy  in  1811,  proved  de- 
cisively that  hydrochloric  acid  was  composed  of  chlorine  and  hydrogen, 
and  that  the  etfect  of  the  black  oxide  of  manganese  in  Scheele's  experi- 
ment was  to  remove  the  hydrogen  in  the  form  of  water,  thus  setting  the 
chlorine  at  liberty. 

Hydrochloric  Acid. 

HCl  =  36  "5  parts  by  weight  =  2  volumes. 

106.  This  acid  is  found  in  nature  among  the  gases  emanating  from 
active  volcanoes,  and  occasionally  in  the  spring  and  river  waters  of  vol- 
canic districts.  For  use  it  is  always  prepared  autificially  by  the  action  of 
sulphuric  acid  upon  common  salt — 

NaCl  4-  H2SO4  =  HCl  -t-  NaHSO^ 

Common  salt.  Hydrosodic  sulphate. 

the  sodium  of  the  common  salt  changing  places  with  the  hydrogen  of  the 
sulphuric  acid. 

300  grains  of  common  salt  (pre- 
viously dried  in  an  oven)  are  intro- 
duced into  a  dry  Florence  tiask  (tig. 
176),  to  which  has  been  fitted,  bj' 
means  of  a  perforated  cork,  a  tube 
bent  twice  at  right  angles,  to  allow 
the  gas  to  be  collected  by  downward 
displacement.  Six  fluid  drachms  of 
strong  sulphuric  acid  are  poured 
upon  the  salt,  and  the  cork  having 
been  inserted,  the  flask  is  very 
gently  heated,  in  order  to  promote 
the  disengagement  of  the  hydro- 
chloric acid  gas,  which  is  collected 
in  a  perfectly  diy  bottle,  the  mouth 
of  which,  when  full,  may  be  covered 
with  a  glass  plate  smeared  with  a 
little  grease.  While  being  filled,  the 
bottle  may  be  closed  with  a  per- 
forated card. 


Fig.  176. — Preparation  of  hydrochloric  acid  gas. 


Common  salt  in  powder  sometimes  froths  to  a  very  inconvenient  extent  with  sul- 
phuric acid  ;  it  is  therefore  often  preferable  to  employ  fragments  of  rock  salt  or  of 
fused  salt,  prepared  by  fusing  the  common  salt  in  a  clay  crucible,  and  pouring  on  to 
a  clean  dr}'  stone. 

A  very  regular  supply  of  hydrochloric  acid  gas  is  obtained  from  1|  oz.  of  sal 
ammoniac  in  lumps,  and  1^  oz.  (measured)  of  sulphuric  acid.^^ 

The  bottle  mil  be  known  to  be  filled  with  gas  by  the  abundant  escape 
of  the  dense  fumes  which  hydrochloric  acid  gas,  itself  transparent,  pro- 
duces by  condensing  the  moisture  of  the  air ;  for  since  the  gas  is  much 


158 


HYDROCHLORIC  OR  MURIATIC  ACID. 


heavier  than  air  (sp.  gr.  1-247),  it  will  not  escape  in  any  quantity  from 
the  bottle  vntil  the  latter  is  fulL  The  odour  of  the  gas  is  veiy  suflFocat- 
iug,  but  not  nearly  so  irritating  as  that  of  chlorine.  The  powerful 
attraction  for  water  is  one  of  the  most  important  properties  of  hydrochloric 
acid  gas. 

If  a  jar  of  hydrochloric  acid  gas  be  closed  with  a  glass  plate  and  inverted  nnder 
water,  it  will  be  found  on  removing  the  plate  that  the  gas  is  absorbed  with  great 
rapidity,  the  water  being  forced  up  into  the  bottle  by  the  pressure  of  the  external  air 
in  proi)ortion  as  the  gas  is  absorbed. 

A  Florence  flask  is  more  convenient  than  a  gas-bottle  for  this  experiment.  It  most 
be  perfectly  dry,  and  thoroughly  well  filled  with  the  gas,  which  may  be  allowed  to 
escape  abundantly  from  the  mouth.  The  tube  delivering  the  hydrochloric  acid  gas 
must  be  slowly  withdrawn,  so  that  the  vacancy  may  be  filled  by  gas,  and  not  by  air. 
The  flask  is  then  closed  with  the  thumb,  and  opened  under  water,  which  will  enter  it 
with  great  violence.  The  experiment  may  also  be  made  as  in  the  case  of  ammonia 
(fig.  177,  see  page  125). 


Fig.  177. 


Fig.  178. — Preparation  of  solution  of 
hydrochloric  acid. 


The  liquid  hydrochloric,  or  muriatic  acid  of  commerce,  is  a  solution  of 
the  gas  in  water,  and  may  be  recognised  by  the  grey  fumes,  with  the 
peculiar  odour  of  the  acid,  which  it  evolves  when  exposed  to  the  air. 
One  pint  of  water  at  a  temperature  of  40°  F.,  is  capable  of  absorbing  480 
pints  of  hydrochloric  acid  gas,  forming  \\  pint  of  the  solution,  having  the 
specific  gravity  1-21.  The  strength  of  the  acid  purchased  in  commerce  is 
usually  inferred  from  the  specific  gravity,  by  reference  to  tables  indicat- 
ing the  weight  of  hydrochloric  acid  contained  in  solutions  of  different 
specific  gravities.  The  strongest  hydrochloric  acid  (sp.  gr.  1"21)  contains 
43  per  cent,  by  weight  of  the  gas.  At  -18°  C.  it  deposits  crystals  of 
HC1.4Aq,  The  common  acid  has  usually  a  bright  yellow  colour,  due 
to  the  accidental  presence  of  a  little  ferric  chloride  (FegClg). 

This  acid  is  produced  in  enormous  quantities  in' the  alkali  works,  where 
common  salt  is  decomposed  by  sulphuric  acid  in  order  to  convert  it  into 
sodium  sulphate,  aa  a  preliminary  step  to  the  production  of  sodium 
carlionate.  The  alkali  manufacturer  is  compelled  to  condense  the  gas,  for 
it  is  found  to  wither  up  the  vegetation  in  the  neighbourhood.  For  this 
purpose  the  hydrochloric  acid  gas  is  drawn  up  from  the  furnace  through 
vertical  cylinders  filled  with  coke,  over  which  streams  of  water  are  made 
to  trickle.     The  water  absorbs  the  acid,  and  is  drawn  off  from  below. 

In  preparing  a  pure  solution  of  the  acid  for  chemical  use  on  a  small  scale,  the 
gas  prepared  as  above  may  be  passed  into  a  small  bottle  containing  a  very  little  water, 


HYDEOCHLOEIC  ACID. 


159 


to  wash  the  gaSj'or  remove  any  sodium  sulphate  which  may  splash  over,  and  then  into 
a  bottle  about  two-thirds  filled  with  distilled  water,  the  tube  delivering  the  gas  pass- 
ing only  about  yV  "^°h  below  the  surface,  so  that  the  heavy  solution  of  hydrochloric 
acid  may  fall  to  the  bottom,  and  fresh'^water  may  be  presented  to  the  gas  (fig.  178). 
For  ordinary  use,  an  acid  of  suitable  strength  is  obtained  by  passing  the  gas  from  6 
ounces  of  common  salt  and  10  ounces  of  sulphuric  acid  into  7  (measur-id)  ounces  of 
water  until  its  bulk  has  increased  to  8  ounces.  The  bottle  containing  the  water 
should  be  surrounded  with  cold  water,  since  the  absorption  of  hydrochloric  acid  by 
water  is  attended  with  evolution  of  heat. 

Pure  solution  of  hydrochloric  acid  is  sometimes  prepared  on  the  large  scale  by 
allowing  concentrated  sulphuric  acid  to  run  into  the  common  hydrochloric  acid,  when 
the  gas  is  evolved,  which  is  washed  and  passed  into  water. 

When  the  concentrated  solution  of  hydrochloric  acid  is  heated  in  a  re- 
tort it  evolves  abundance  of  hydrochloric  acid  gas,  rendering  it  probable  that 
it  is  not  a  true  chemical  compound  of  water  with  the  acid.  The  evolution 
of  gas  ceases  when  the  remaining  liquid  contains  20  per  cent,  of  acid  (and 
has  a  sp.  gr.  of  1-10).  If  a  weaker  acid  than  this  be  heated,  it  loses 
water  until  it  has  attained  this  strength,  when  it  distils  unchanged* 

The  concentrated  solution  forms  a  very  convenient  source  from  which  to  procure 
the  gas.  It  may  be  heated  in  a  flask,  and  the  gas  dried  by  passing  through  a  bottle 
filled  with  fragments  of  pumice-stone  wetted  with  concentrated  sulphuric  acid,  being 
collected  over  the  mercurial  trough  (fig.  179). 


Fig.  179. 

The  avidity  with  which  water  absorbs  hydrochloric  acid  is  the  more 
remarkable,  because  this  gas  can  be  liquefied  only  under  a  very  high 
pressure,  amounting  at  the  ordinary  temperature  to  about  40  atmospheres. 

The  liquefied  hydrochloric  acid  has  comparatively  little  action  even 
upon  those  metals  which  decompose  its  aqueous  solution  with  great 
violence ;  quicklime  is  unaffected  by  it,  and  solid  litmus  dissolves  in  it 
with  a  faint  purple  colour,  instead  of  the  bright  red  imparted  by  the 
aqueous  hydrochloric  acid.  Dry  hydrochloric  acid  gas  is  not  absorbed  by 
calcium  carbonate. 

The  injurious  action  of  hydrochloric  acid  gas  upon  growing  plants  is 
probably  connected  with  its  attraction  for  water.  If  a  spray  of  fresh 
leaves  is  placed  in  a  bottle  of  hydrochloric  acid,  it  becomes  at  once  brown 
and  shrivelled. 

107.  Action  of  hydrocliloric  add  upon  metals. — Those  metals  Avhich 
have  the  strongest  attraction  for  oxygen  will  also  ""generally  have  the 

*  The  proportion  of  acid  thus  retained  by  the  water  varies  directly  with  the  atmospheric 
pressure  to  which  it  is  exposed  during  the  distillation. 


160  ACTION  OF  HYDROCHLORIC  ACID  ON  METALLIC  OXIDES. 

strongest  attraction  for  chlorine,  so  that  in  respect  to  their  capability  of 
decomposing  hydrochloric  acid,  they  may  be  ranked  in  pretty  nearly  the 
same  order  as  in  their  action  upon  water  (p.  11).  Since,  however,  the 
attraction  of  chlorine  for  the  metals  is  generally  superior  to  that  of  oxygen, 
the  metals  are  more  easily  acted  upon  by  hydrochloric  acid  than  by  water, 
the  metal  taking  the  place  of  the  hydrogen,  and  a  chloride  of  the  metal 
being  formed. 

Even  silver,  which  does  not  decompose  water  at  any  temperature,  is 
dissolved,  though  very  slowly,  by  boiling  concentrated  hydrochloric  acid, 
the  chloride  of  silver  formed  being  soluble  in  the  strong  acid,  though  it 
may  be  precipitated  by  adding  water. 

Gold  and  platinum,  however,  are  not  attacked  by  hydrochloric  acid ;  but 
if  a  little  free  chlorine  be  present,  it  converts  them  into  chlorides. 

Iron  and  zinc  decompose  the  acid  very  rapidily  in  the  cold,  forming 
ferrous  chloride  and  zinc  chloride,  and  liberating  hydrogen ;  Fe  +  2HC1 
=  FeCl2+H2. 

When  potassium  or  sodium  is  exposed  to  hydrochloric  acid  gas,  it  im- 
mediately becomes  coated  with  a  white  crust  of  chloride,  which  partly 
protects  the  metal  from  the  action  of  the  gas;  but  when  these  metals  are 
heated  to  fusion  in  hydrochloric  acid  gas,  they  burn  vividlv;  Na  +  HCl 
=  NaCl  +  H. 

The  composition  of  hydrochloric  acid  may  be  exhibited  by  confining  a 
measured  volume  of  the  gas  over  mercury  (see  fig.  82,  page  84),  and  passing 
up  a  freshly-cut  pellet  of  sodium.  On  gently  agitating 
the  tube,  the  gas  diminishes  in  volume,  and  after 
a  time  will  have  contracted  to  one-half,  and  will  be 
found  to  have  all  the  properties  of  hydrogen.  This 
result  confirms  that  obtained  by  synthesis,  as  de- 
scribed above,  that  2  volumes  of  hydrochloric  acid 
contain  1  volume  of  hydrogen  and  1  volume  of 
chlorine. 


The  electrolysis  of  hydrochloric  acid, is  exhibited  in   the 

V-tube  represented  in  fig.  180,  where  the  platinum  plate  ^  in 

the  closed  limb  o  is  connected  with  a  platinum  wire  sealed 

into  the  glass ;  the  other  limb  h  is  open.      If  the  closed  limb 

be  entirely  filled  with  strong  hydrochloric  acid,  and  connected 

with  the  negative  pole  of  a  battery  composed  of  five  or  six 

Grove's  or  iTunsen's  cells,  the  positive  pole  being  connected 

with  h,  hydrogen  will  rapidly  collect   in   the   closed   limb, 

whilst  the  odour  of  chlorine  will  be  perceived  in  the  open 

limb.     As  soon  as  the  liquid  fills  the  open  limb,  the  wire  h  is 

rig.  180.  withdrawn,  this  limb  closed  with  the  thumb,  and  the  hydrogen 

transferred  to  it  by  inclining  the  tube.     After  testing  the 

hydrogen  with  a  match,  the  poles  of  the  battery  may  be  reversed,  when  the  chlorine 

will  collect  as  gas  in  the  closed  limb,  as  soon  as  the  hydrochloric  acid  has  become 

saturated  with  it. 

108.  Action  of  hydrochloric  acid  %ipon  metallic  oxides. — As  a  general 
rule,  it  may  be  stated  that,  when  hydrochloric  acid  acts  upon  the  oxide  of 
a  metal,  the  results  are  water  and  a  chloride  of  the  metal,  in  which  each 
atom  of  oxygen  in  the  oxide  has  been  displaced  by  2  atoms  of  chlorine. 

Thus,  silver  oxide  acted  on  by  hydrochloric  acid  gas  gives  water  and 
silver  chloride ;  AggO  +  2HC1  =  H2O  +  2AgGl . 

Suboxide  of  copper  (cuprous  oxide)  yields  water  and  subchloride  of 
copper  (cuprous  chloride) ;  CugO  +  2HC1  =  HgO  +  Qu^\ . 


OXIDES  OF  CHLORINE.  161 

Ferric  oxide  gives  water  and  ferric  chloride  ;  re.203  +  6HC1  =  3HoO 
+  Fe,Cl,. 

"With  stannic  oxide,  vrater  and  "stannic  chloride  are  obtained ;  Sn02 
+  41101  =  2H20-f-SnCI^. 

Antimonious  oxide  is  converted  into  water  and  antimonious  chloride; 

Sb203   +    6HC1   =   SH^O    +    2SbCl3. 

109.  In  cases  where  the  corresponding  chloride  does  not  exist,  or  is  not 
stable  under  the  conditions  of  the  experiment,  a  chloride  is  formed  con- 
taining less  chlorine  than  is  equivalent  to  the  oxygen  in  the  oxide,  and 
the  balance  is  evolved  in  the  free  state.  Thus,  when  manganese  sesqui- 
oxide  and  dioxide  are  heated  with  hydrochloric  acid — 

Mn.Og      +      6HC1     =     SH^O      +      2MnCl2     +     Cl^; 
MnO^       4-      4HC1      =      2H,0      +        MnCl.^      +      Clg . 

Chromic  anhydride,  a  chloride  corresponding  to  which  is  not  known  to 
exist,  when  heated  with  hydrochloric  acid,  yields  chromic  chloride  and 
chlorine  ;  2Cr03  +  1 2HCI  =  6H,0  +  Cr.Clg  +  Clg . 

Every  metallic  oxide  containing  1  atom  of  oxygen  has  a  corresponding 
chloride  of  a  stable  character,  but  the  higher  oxides  less  frequently  form 
corresponding  chlorides  endowed  with  any  stability. 

Compounds  op  Chlobine  with  Oxygen. 

110.  It  is  worthy  of  notice,  that  whilst  chlorine  and  hydrogen  so  readily 
unite,  there  is  no  method  by  which  chlorine  can  be  made  to  combine  in  a 
direct  manner  with  oxygen,  all  the  compounds  of  these  elements  having 
been  hitherto  obtained  only  by  indirect  processes.  An  excellent  illustra- 
tion is  thus  afforded  of  the  fact,  that  the  more  closely  substances  resemble 
each  other  in  their  chemical  relations,  the  less  wiU  be  their  tendency  to 
combine;  for  chlorine  and  oxygen  are  both  highly  electro-negative  bodies, 
and  therefore,  having  both  a  powerful  attraction  for  the  electro-positive 
hydrogen,  their  attraction  for  each  other  is  of  a  very  low  order. 

111.  Hypoclilor oils  anhydride  (ClgO)  is  of  some  practical  interest  in 
connexion  with  chloride  of  lime,  chloride  of  soda,  and  other  bleaching 
compounds.  It  is  prepared  by  passing  dry  chlorine  gas  over  dry  preci- 
pitated mercuric  oxide,  and  condensing  the  product  in  a  tube  surrounded 
with  a  mixture  of  ice  and  salt;  HgO  +  Cl^  =  HgClg  +  CI2O  . 

The  hypochlorous  anhydride  is  thus  obtained  as  a  deep  red  liquid,  which 
boils  at  19°  F.,  evolving  a  yellow  vapour  twice  as  heavy  as  air,  and  having 
a  very  powerful  and  peculiar  odour.  This  vapour  is  remarkably  explosive, 
the  heat  of  the  hand  having  been  known  to  cause  its  separation  into 
its  constituents,  when  2  volumes  of  the  vapour  yield  2  volumes  of 
chlorine  and  1  volume  of  oxygen.  As  might  be  expected,  most  substances 
which  have  any  attraction  for  oxygen  or  chlorine  will  decompose  the  gas, 
sometimes  with  explosive  violence.  Even  hydrochloric  acid  decomposes 
it :  1  volume  of  hypochlorous  acid  gas  is  entirely  decomposed  by  2 
volumes  of  hydrochloric  acid,  yielding  water  and  chlorine  ;  C1.,0  +  2HC1 
=  H.,0-f-Cl^.  Hypochlorous  anhydride  is  a  powerful  bleaching  agent, 
both  its  chlorine  and  oxygen  acting  upon  the  colouring  matter  in  the 
manner  explained  at  page  154. 

Hypochlorous  anhydride  is  absorbed  in  large  quantity  by  water ;  the 
solution  is  supposed  to  contain  hypochlorous  acid,   HCIO,   for   H2O   -h 

L 


162  HYPOCHLOROUS  ACID. 

ClgO  =  2HC10  ;  but  HCIO  has  not  been  obtained  in  the  separate  state. 
The  sohitiou  may  be  very  readily  prepared  by  shaking  the  red  oxide  of 
inercury  with  water  in  a  bottle  of  chlorine  as  long  as  the  gas  is  absorbed. 
The  greater  part  of  the  mercuric  chloride  which  is  produced  combines 
with  the  excess  of  oxide  to  form  a  brown  insoluble  oxychloride,  whilst 
the  hypochlorous  acid  and  a  little  mercuric  chloride  remain  in  solution. 
This  solution  is  a  most  powerful  oxidising  and  bleaching  agent ;  it  erases 
writing  ink  immediately,  and  does  not  corrode  the  paper  if  it  be  carefully 
washed.  Printing  ink,  which  contains  lamp  black  and  grease,  is  not 
bleached  by  hypochlorous  acid,  so  that  this  solution  is  very  useful  for 
removing  ink  stains  from  books,  engravings,  &c. 

The  action  of  some  metals  and  their  oxides  upon  solution  of  hypo- 
chlorous acid  is  instructive.  Iron  seizes  upon  the  oxygen,  whilst  the 
chlorine  is  liberated  ;  copper  lakes  both  the  oxygen  and  chlorine ;  whilst 
silver  combines  with  the  chlorine,  and  liberates  oxygen.  Oxide  of  lead 
(PbO)  removes  the  oxygen,  becoming  peroxide  of  lead  (PbOg),  and  liber- 
ating chlorine,  but  oxide  of  silver  converts  the  chlorine  into  chloride  of 
silver,  and  liberates  the  oxygen  ;  AggO  +  ClgO  =  2AgCl  +  Oj . 

The  salts  of  hypochlorous  acid,  or  hypochlorites,  are  not  known  in  a 
pure  state,  but  are  obtained  in  solution  by  neutralising  the  solution  of 
hypochlorous  acid  with  bases.*  They  are  decomposed  even  by  carbonic 
acid,  with  liberation  of  hypochlorous  acid. 

When  the  solution  of  a  hypochlorite  is  boiled,  it  becomes  converted 
into  a  mixture  of  chloride  and  chlorate ;  thus — 


3KC10     = 

=       KCIO3 

+     2KC1 

Potassium 

Potassium 

Potassium 

hypochlorite. 

chlorate. 

chloride. 

This  change  is  turned  to  practical  account  in  the  manufacture  of  chlorate 
of  potash.  It  is  much  hindered  by  the  presence  of  an  excess  of  alkalL 
The  solution  of  hypochlorous  acid  itself,  when  exposed  to  light,  is 
decomposed  into  chloric  acid  and  free  chlorine  ;  5HC10  =  HCIO3  +  2H2O 
+  C1,. 

112.  Chloride  of  lime  (calx  chlorata,  see  p.  155)  is  the  most  important 
compound  formed  by  hypochlorous  acid.  Its  formula  has  already  been 
discussed  at  p.  155.  When  this  compound  is  distilled  with  a  small 
quantity  of  diluted  sulphuric  acid,  a  solution  of  hypochlorous  acid  is 
obtained ;  but  if  an  excess  of  acid  be  used,  free  chlorine  is  the  result. 

Bleaching  powder  is  liable  to  decomposition  when  kept,  evolving 
oxygen,  and  becoming  converted  into  calcium  chloride,  which  attracts 
moisture  greedily,  and  renders  the  bleaching  powder  deliquescent.  It  has 
been  known  to  shatter  the  glass  bottle  in  which  it  was  preserved,  in  con- 
sequence of  the  accumulation  of  oxygen  ;t  CaOCl.2  =  CaClg  -f-  0 . 

When  a  solution  of  a  salt  of  manganese  or  cobalt  is  added  to  solution 
of  chloride  of  lime,  a  black  precipitate  of  MnOg  or  C02O3  is  obtained.  If 
this  precipitate  be  boiled  with  an  excess  of  solution  of  chloride  of  lime,  it 
causes  a  rapid  disengagement  of  oxygen,  in  some  manner  that  has  not  yet 
been  clearly  explained.     Large  quantities  of  oxygen  are  easily  obtained 

*  Calcium  hypochlorite  has  been  obtained  in  crystals  of  the  formula  Ca(C10)2.4H.20 
liy  evaporating  solution  of  chloride  of  lime  in  vacuo  over  sulphuric  acid  and  potash 
( kingzett). 

f  When  rapidly  made  and  hastily  packed,  it  has  been  known  to  become  so  hot  as  to  set 

fire  to  the  casks. 


CHLORATE  OF  POTASH. 


163 


by  adding  a  few  drops  of  solution  of  cobalt  nitrate  to  solution  of  chloride 
of  lime,  and  applying  a  gentle  heat^ 

Old  chloride  of  lime  always  contains  calcium  chlorate ;  6CaOCl2 
=  5CaCl2  +  Ca(C103)2. 

Sodium  hypochlorite,  which  is  very  useful  for  removing  ink,  is  prepared 
in  solution  by  decomposing  solution  of  chloride  of  lime  with  solution  of 
sodium  carbonate,  and  separating  the  calcium  carbonate  by  filtration. 
The  solution  is  generally  called  "  chloride  of  soda  "  {liquor  sodm  chloratce). 

/  113.  Chloric  add  (HCIO3). — This  acid  is  appropriately  studied  here, 
since  its  salts  are  usually  obtained  by  the  decomposition  of  the  hypo- 
chlorites. The  only  chlorate  which  possesses  any  great  practical  importance 
is  potassium  chlorate  (KCIO3),  which  is  largely  employed  as  a  source  of 
oxygen,  as  an  ingredient  of  several  explosive  compositions,  and  in  the 
manufacture  of  lucifer  matches. 

Potassium  chlorate  or  chlorate  of  potash. — 
The  simplest  method  of  obtaining  this  salt 
consists  in  passing  an  excess  of  chlorine  rapidly 
into  a  strong  solution  of  potash  (fig.  181), 
when  the  liquid  becomes  hot  enough  to 
decompose  the  hypochlorite  first  formed  into 
potassium  chloride,  which  remains  in  solution, 
and  potassium  chlorate,  which  is  deposited  in 
tabular  crystals,  the  ultimate  result  being 
expressed  by  the  equation — 

6KH0  +  Clg  =  KCIO3  +  5KC1  +  3H2O.        ^ 

If  potassium  carbonate  or  a  weak  solution  of 
potash  be  employed,  the  liquid  will  require  Fig-  181. 

boiling  after  saturation  with  chlorine,  in  order  to  convert  the  hypochlorite 
into  chlorate. 

The  following  proportions  will  be  found  convenient  for  the  preparation  of  potassium 
chlorate  on  the  small  scale  as  a  laboratory  experiment.  300  grains  of  potassium 
carbonate  are  dissolved,  in  a  beaker,  with  2  measured  ounces  of  water.  600  grains  of 
common  salt  are  mixed  with  450  grains  of  binoxide  of  manganese,  and  very  gently 
heated  in  a  flask  (fig.  181)  with  a  mixture  of  1|  ounce  (measured)  of  strong  sulphuric 
acid  and  4  ounces  (measured)  of  water,  the  evolved  chlorine  being  passed  through  a 
rather  wide  bent  tube  into  the  solution  of  potassium  carbonate. 

At  first  no  action  will  appear  to  take  place,  although  the  solution  absorbs  the 
chlorine  ;  because  the  first  portion  of  that  gas  converts  the  potassium  carbonate  into 
a  mixture  of  potassium  hypochlorite,  potassium  chloride,  and  hydropotassic  carbonate, 
some  crystals  of  which  will  probably  be  deposited  — 

2K2CO3  +   CI2   +   HgO   =   KCl  +   KCIO   +   2KHCO3, 

On  continuing  to  pass  chlorine,  these  crystals  will  redissolve,  and  brisk  efferves- 
cence will  be  caused  by  the  expulsion  of  the  carbouic  acid  gas;  2KHC0,  +  0L  =  KC1 

+  KCIO  +  H2O  +  2CO2. 

When  this  eff'ervescence  has  ceased,  and  the  chlorine  is  no  longer  absorbed  by  the 
liquid,  the  change  is  complete,  the  ultimate  result  being  represented  by  the  equa- 
tion K2CO3  +  Cl2  =  KCl  +  KCIO +  CO2.  The  solution  (which  often  has  a  pink 
colour,  due  to  a  little  potassium  ferrate)  is  now  poured  into  a  dish,  boiled  for  two 
or  three  minutes,  filtered,  if  necessary,  from  any  impurities  (silica,  &c. ),  derived  from 
the  potassium  carbonate,  and  set  aside  to  crystallise.  The  ebi^ition  has  converted 
the  ]iotassium  hypochlorite  into  chlorate  and  chloride  of  potassium  ;  3KC10  =  KC103 

+  2KC1.  The  latter,  being  soluble  in  about  three  times  its  weight  of  cold  water,  is 
retained  in  the  solution,  whilst  the  chlorate,  which  would  require  about  sixteen  times 
its  weight  of  cold  water  to  hold  it  dissolved,  is  deposited  in  brilliant  rhomboidal 


164  PREPARATION  OF  CHLORATE  OF  POTASH. 

tables.  These  crystals  may  be  collected  on  a  filter,  and  purified  from  the  adheriag 
solution  of  potassium  chloride  by  pressure  between  successive  portions  of  filter-paper. 
If  they  be  free  from  chloride,  their  solution  in  water  will  not  be  changed  by  silver 
nitrate,  which  would  yield  a  milky  precipitate  of  silver  chloride  if  that  impurity  were 
present.  Should  this  be  the  case,  the  crystals  must  be  redissolved  in  a  small  quantity 
of  boiling  water,  and  recrystallised. 

The  above  processes  for  preparing  potassium  chlorate  are  far  from 
economical,  since  five-sixths  of  the  potash  are  converted  into  chloride, 
being  employed  merely  to  furnish  oxygen  to  convert  the  chlorine  into 
chloric  acid.  In  manufacturing  the  chlorate  upon  the  large  scale,  a  much 
cheaper  material,  lime,  is  used  to  furnish  the  oxygen,  one  molecule  of 
potassium  carbonate  being  mixed  with  six  molecules  of  slaked  lime  and 
the  damp  mixture  saturated  with  chlorine.  On  treating  the  mass  with 
boiling  water,  a  solution  is  obtained  which  contains  potassium  chlorate 
and  calcium  chloride  :  the  latter,  being  very  soluble,  remains  in  the  liquor, 
from  which  the  chlorate  crystallises  on  cooling.  The  ultimate  result  of 
the  action  of  chlorine  upon  the  mixture  of  potassium  carbonate  and  lime 
is  thus  expressed ;  K2CO3  +  6Ca(HO)2  +  Cl^a  =  2KCIO3  +  5CaCl2  +  CaCOg 
-I-  6H0O , 

A  still  cheaper  salt  of  potassium,  the  chloride,  has  recently  been  em- 
ployed with  great  economy  as  a  substitute  for  the  carbonata  Lime  is 
mixed  with  water,  and  saturated  with  chlorine  gas  in  close  leaden  tanks  ; 
2Ca(OH)2  (calcium  hydrate)  +  Cl4  =  Ca(OCl)2  (calcium  hypochlorite) 
+  CaCl2  (calcium  chloride)  -|-  2H2O.  The  liquid  is  boiled  down,  when 
the  calcium  hypochlorite  is  decomposed  into  calcium  chlorate  and  chloride  ; 
3Ca(OCl)2  =  2Ca(Cl03)2-f-CaCl2.  The  calcium  chlorate  is  now  decom- 
posed by  boiUng  with  potassium  chloride,  when  it  yields  calcium  chloride 
which  remains  in  solution,  and  potassium  chlorate  which  separates  in 
crystals  as  the  solution  cools  ;  Ca(C103)2  +  2KCI  =  CaClg  +  2KCIO3 . 

Chloric  acid  (HCIO3)  may  be  procured  by  decomposing  a  solution  of 
potassium  chlorate  with  hydrofluosilicic  acid,  when  the  potassium  is 
deposited  as  an  insoluble  silico-fluoride,  and  chloric  acid  is  found  in  the 
solution  * — 

2KCIO3  -f-  H2SiF6  =  2HCIO3  +  IS^SiF^ 

Hydroflaosilicic  acid. 

On  evaporating  the  solution  at  a  temperature  not  exceeding  100°  F., 
the  chloric  acid  is  obtained  as  a  yellow  liquid,  with  a  peculiar  pungent 
smell. 

In  its  chemical  characters,  chloric  acid  bears  a  very  strong  resemblance 
to  nitric  acid,  but  is  far  more  easily  decomposed.  It  cannot  even  be  kept 
unchanged  for  any  length  of  time,  and  at  temperatures  above  104°  F.  it  is 
decomposed  into  perchloric  acid,  chlorine,  and  oxygen ;  4HCIO3  =  2HCIO4 
-hH^O-t- 012-1-93. 

Chloric  acid  is  one  of  the  most  powerful  oxidising  agents  :  a  drop  of  it 
will  set  fire  to  paper,  and  it  oxidises  phosphorus  (even  the  amorphous 
variety)  with  explosive  violence. 

Chlorates. — Chloric  acid,  like  nitric,  is  monobasic,  containing  only 
one  atom  of  hydrogen  replaceable  by  a  metaL  The  chlorates  resemble  the 
nitrates  in  their  oxidising  pwwer,  but  generally  act  at  lower  temperatures, 
in  consequence  of  the  greater  facility  with  which  the  chlorates  part  with 
their  oxygen. 

*  440  grain  measures  of  hydrofluosilicic  acid  of  sp.  gr.  1078  will  decompose  100  grains 
of  the  chlorate. 


DETONATING  COMPOSITIONS. 


165 


A  grain  or  two  of  potassium  chlorate,  rubbed  in  a  mortar  with  a  little  sulphur,  for 
example,  detonates  violently,  evolving  a  powerful  odour  of  chloride  of  sulphur.     Potas- 
sium chlorate  and  sulplmr  were  used  in  some  of  the  first  per- 
cussion caps,  but  being  found  to  corrode  the  nipple  of  the  gun, 
they  gave   place  to  the  anticorrosive  caps  containing  mercuric 
fulminate. 

If  a  little  powdered  chlorate  be  mixed  on  a  card  with  some 
black  antimony  sulphide,  and  wrapped  up  in  paper,  the  mixture 
will  detonate  when  struck  with  a  hammer. 

A  mixture  of  this  description  is  employed  in  the  friction  tubes 
used  for  firing  cannon.  These  are  small  tubes  (A,  fig.  182)  of 
sheet  copper  (for  military)  or  of  quill  (for  naval  use),  filled  with 
gunpowder :  in  the  upper  part  of  the  tube  a  small  copper  rasp 
(B)  is  tightly  fixed  across  it,  and  on  each  side  of  the  rasp  a  pellet 
is  placed  containing  12  parts  of  potassium  chlorate,  12  of  antimony 
sulphide,  and  1  of  sulphur,  these  ingredients  being  worked  up 
into  a  paste  with  a  solution  of  an  ounce  of  shellac  in  a  pint  of 
spirit  of  wine.  The  friction  tube  is  fixed  in  the  vent  of  the  gun, 
and  the  copper  rasp  quickly  withdrawn  by  a  cord  in  the  hands 
of  the  gunner,  when  the  detonating  pellets  explode  and  fire  the 
powder. 

The  earliest  lucifer  matches  were  tipped  with  a  mixture  of 
potassium  chlorate,  antimony  sulphide,  and  starch,  and  were 
kindled  by  drawing  them  briskly  through  a  doubled  piece  of  sand- 
pajier. 

At  high  temperatures  the  chlorates  act  violently  upon  combustible 
bodies.  A  little  potassium  chlorate  sprinkled  upon  red  hot  coals  causes  a 
very  violent  deflagration.  If  a  little  of  the  chlorate 
be  melted  in  a  deflagrating  spoon,  and  plunged  into 
a  bottle  or  flask  containing  coal  gas  (fig.  183),  the  salt 
burns  with  great  brilliancy,  its  oxygen  combining 
with  the  carbon  and  hydrogen  in  the  gas,  which 
Ijecomes  in  this  case  the  supporter  of  combustion. 
The  flask  may  be  conveniently  filled  with  coal  gas 
by  inverting  it,  and  passing  a  flexible  tube  from  the 
gas  pipe  up  into  it. 

Potassium  chlorate  is  much  used  in  the  manu- 
facture of  fireworks,  especially  as  an  ingredient  of 
coloured  fire  compositions,  which  generally  consist  of 
potassium  chlorate  mixed  with  sulphur,  and  with 
some  metallic  compound,  to  produce  the  desired 
colour  in  the  flame.  They  are  not  generally  made  of 
the  best  quality  on  the  small  scale,  from  want  of  attention  to  the  very 
finely-powdered  state  of  the  ingredients,  the  absence  of  all  moisture,  and 
the  most  intimate  mixture. 

If  these  precautions  be  attended  to,  the  following  prescription  will  give  very  good 
coloured  fires  : — 

Red  fire. — 40  grains  of  nitrate  of  strontia,  thorouglily  dried  over  a  lamp,  are  mixed 
with  10  grains  of  chlorate  of  potash,  and  reduced  to  the  finest  possible  powder.  In 
another  mortar  13  grains  of  sulphur  are  mixed  with  4  grains  of  black  sulphide  ot 
antimony  (crude  antimony).  The  two  powders  are  then  placed  upon  a  sheet  of 
paper,  and  very  intimately  mixed  with  a  bone  knife,  avoiding  any  great  pressure. 
A  little  heap  of  the  mixture  touched  with  a  red  hot  iron  ought  to  burn  with  a  uniform 
red  flame,  the  colour  being  due  to  the  strontium.  ^t. 

Blue  fire. — Ifi  grains  of  chlorate  of  potash  are  mixed  with  10  grains  of  nitrate  of 
potash  and  30  grains  of  oxide  of  copper,  in  a  mortar.  The  finely-powdered  mixture 
is  transferred  to  a  sheet  of  paper,  and  mixed,  by  a  bone  knife,  with  15  grains  of 
sulphur.     The  colour  of  the  fire  is  given  cliiefly  by  the  copper. 


166  COLOURED  FIRES. 

Green  fire. — 10  grains  of  chlorate  of  baryta  are  mixed  with  10  grains  of  nitrate  of 
bartyta  in  a  mortar,  and  afterwards  on  paper  with  12  grains  of  sulphur.  The  barium 
is  the  cause  of  the  bright  green  colour  of  the  flame. 

These  compositions  are  rather  dangerous  to  keep,  since  they  are  liable  to  spon* 
taneous  combustion. 

White  gunpowder  is  a  mixture  of  two  parts  of  chlorate  of  potash  with  one  part  of 
dried  yellow  prussiate  of  potash,  and  one  part  of  sugar,  which  explodes  very  easily 
under  friction  or  percussion. 

The  decomposition  of  potassium  chlorate  by  heat  into  oxygen  and 
potassium  chloride  is  attended  with  evolution  of  heat,  unlike  most  cases 
of  chemical  decomposition,  in  which  heat  is  generally  absorbed.  If  the 
chlorate  be  heated  to  the  point  at  which  it  begins  to  decompose,  and  a 
little  ferric  oxide  be  thrown  into  it,  enough  heat  will  be  evolved  to  bring 
the  mass  to  a  red  heat,  although  the  ferric  oxide  is  not  oxidised.  Experi- 
ment has  shown  that  one  part  of  chlorate  evolves,  during  decomposition, 
nearly  39  units  of  heat,  or  enough  heat  to  raise  39  parts  of  water  through 
1°  C.  This  anomalous  evolution  of  heat  must  of  course  contribute  to 
increase  the  energy  of  explosive  mixtures  containing  the  chlorate,  and 
may  be  accounted  for  on  the  supposition  that  the  heat  evolved  by  the 
combination  of  the  potassium  with  the  chlorine  to  form  potassium  chloride 
exceeds  that  which  is  absorbed  in  effecting  the  chemical  disintegration  of 
\  the  chlorate. 

114.  Perchloric  acid  (HCIO^)  is  obtained  by  evaporating  down,  at  a 
boiling  heat,  the  solution  of  chloric  acid  obtained  by  decomposing 
potassium  chlorate  with  hydrofluosilicic  acid  (see  p.  164),  when  the 
chloric  acid  is  decomposed  into  perchloric  acid,  chlorine,  and  oxygen ; 
4HCIO3  =  2HCIO4  +  H2O  +  CI2  +  O3  . 

When  the  greater  part  of  the  water  has  been  boiled  off,  the  liquid  may  be  intro- 
duced into  a  retort  and  distilled.  After  the  remainder  of  the  water  has  passed  over, 
it  is  followed  by  a  heavy  oily  liquid,  which  is  HCIO4.2H2O.  If  this  be  mixed  with 
four  times  its  volume  of  strong  sulphuric  acid  and  again  distilled,  the  pure  per- 
chloric acid  (HCIO4)  first  passes  over  as  a  yellow  watery  liquid.  If  the  distillation 
be  continued  the  oily  HCIO4.2H2O,  distils  over,  and  if  this  be  mixed  with  the  former 
and  cooled,  it  yields  silky  crystals  containing  HC104.H.^0,  which  are  decomposed  at 
230°  F.  into  HCIO4,  which  may  be  distilled  off,  and  HCIO4.2H2O,  which  is  left  in 
the  retort;  2(HC104.H20)  =  HC104  +  HC104.2H20. 

The  pure  perchloric  acid  is  a  colourless,  very  heavy  liquid  (sp.  gr. 
1"782),  which  soon  becomes  yellow  from  decomposition.  It  cannot  be 
kept  for  any  length  of  time.  When  heated,  it  undergoes  decomposition, 
often  with  explosion.  In  its  oxidising  properties  it  is  more  powerful 
than  chloric  acid.  It  burns  the  skin  in  a  very  serious  manner,  and  sets 
fire  to  paper,  charcoal,  &c.,  with  explosive  violence.  This  want  of  stability, 
however,  belongs  only  to  the  pure  acid.  If  water  be  added  to  it,  heat 
is  evolved,  and  a  diluted  acid  of  far  greater  permanence  is  obtained. 
Diluted  perchloric  acid  does  not  even  bleach,  but  reddens  litmus  in  the 
ordinary  way. 

Perchloric  acid  is  monobasic.  The  perchlorates  are  decomposed  by 
heat,  evolving  oxygen,  and  leaving  chlorides  ;  thus — KCIO^^  KCl  +  0^. 

The  potassium  perchlorate  is  always  formed  in  the  first  stage  of 
the  decomposition  of  potassium  chlorate  by  heat;  2KC103  =  KC104 
+  KCI  +  O2. 

If  a  few  crystals  of  potassium  chlorate  be  heated  in  a  test-tube,  they  first  melt  to 
a  perfectly  clear  liquid,  which  soon  evolves  bubbles  of  oxygen.  After  a  time  the 
liquid  becomes  pasty,  and  if  the  contents  of  the  tube,  after  cooling,  be  dissolved  by 


CHLORIC  PEROXIDE.  167 

boiling  with  water,  the  latter  will  deposit,  as  it  cools,  crystals  of  potassium  per- 
chlorate.  These  are  readily  distinguished  from  chlorate  by  their  not  yielding  a  yellow 
gas  (ClOj)  when  treated  with  strong  sulphuric  acid.  The  perchlorate  is  remarkable 
as  one  of  the  least  soluble  of  the  potassium  salts,  requiring  150  times  its  weight  of 
cold  water  to  dissolve  it.  Neither  perchloric  acid  nor  any  of  its  salts  is  applied  to 
any  useful  purpose. 

115.  Chloric  peroxide  or  peroxide  of  chlorine  (ClOj)  is  dangerous  to  prepare  and 
examine  on  account  of  its  great  instability  and  violently  explosive  character.  It  is 
obtained  by  the  action  of  strong  sulphuric  acid  upon  potassium  chlorate — 

3KCIO3   +   2H2SO4  =   KCIO4  +   2KHSO4   +   2CIO3  +   HjO. 

It  is  a  bright  yellow  gas,  with  a  chlorous  and  somewhat  aromatic  smell,  and  sp.  gr. 
2  •32;  condensible  at  -4°  F.  to  a  red,  very  explosive  liquid.  The  gas  is  gradually 
decomposed  into  its  elements  by  exposure  to  light,  and  a  temperature  of  140°  F. 
causes  it  to  decompose  with  violent  explosion  into  a  mixture  of  chlorine  and  oxygen, 
the  volume  of  which  is  one-third  greater  than  that  of  the  compound. 

On  a  small  scale,  chloric  peroxide  may  be  prepared  with  safety  by  pouring  a  little 
strong  sulphuric  acid  upon  one  or  two  crystals  of  potassium  chlorate,  in  a  test-tube 
supported  in  a  holder.  The  crystals  at  once  acquire  a  red  colour,  which  gradually 
diffuses  itself  through  the  liquid,  and  the  bright  yellow  gas  collects  in  the  tube.  If 
heat  be  applied,  the  gas  will  explode,  and  the  colour  and  odour  of  chloric  peroxide 
will  be  exchanged  for  those  of  chlorine.  If  the  chlorate  employed  in  this  experiment 
contains  potassium  chloride,  explosion  often  takes  place  in  the  cold,  since  the  hydro- 
chloric acid  evolved  by  the  action  of  the  acid  upon  that  salt  decomposes  a  part  of  the 
chloric  peroxide,  and  thus  provokes  the  decomposition  of  the  remainder. 

Chloric  peroxide  is  easily  absorbed  by  water,  and  the  solution  has- 
powerful  bleaching  properties.  Combustible  bodies,  such  as  sulphur 
and  phosphorus,  decompose  the  gas,  as  might  be  expected,  with  great 
violence. 

This  powerful  oxidising  action  of  chloric  peroxide  upon  combustible  sub- 
stances appears  to  be  the  cause  of  the  property  possessed  by  mixtures 
of  such  substances  with  potassium  chlorate,  to  inflame  when  touched  with 
strong  sulphuric  acid. 

If  a  few  crystals  of  potassium  chlorate  be  thrown  into  a  glass  of  water  (fig.  184), 
one  or  two  small  fragments  of  phosphorus  dropped  upon  them,  and  some  strong 
sulphuric  acid  poured  down  a  funnel  tube  to  the  bottom  of 
the  glass,  the  chloric  peroxide  will  inflame  the  phosphorus 
with  bright  flashes  of  light  and  slight  detonations. 

Powdered  sugar  mixed  with  potassium  chlorate  on  paper, 
will  burn  brilliantly  when  touched  with  a  glass  rod  dipped  in 
strong  sulphuric  acid.  Matches  may  be  prepared,  which 
inflame  when  moistened  with  sulphuric  acid,  by  dipping  the 
ends  of  splinters  of  wood  in  melted  sulphur,  and,  when  cool, 
tipping  them  with  a  mixture  of  5  grains  of  sugar  and  15  grains 
of  potassium  chlorate  made  into  a  paste  with  4  drops  of  water. 
When  dry,  they  may  be  fired  by  dipping  them  into  a  bottle 
containing  asbestos  moistened  with  strong  sulphuric  acid. 
These  matches,  under  the  names  of  Eupyrion  and  Vesta 
matches,  were  used  before  the  introduction  of  phosphorus  into 
general  use.  The  Promethean  light  was  an  ornamental  scented 
paper  si>ill,  one  end  of  which  contained  a  small  glass  bulb  of 
sulphuric  acid  surrounded  with  a  mixture  of  chlorate  and 
sugar,  which  inflamed  when  the  end  of  the  spill  was  struck  Fig.  184. 

or  squeezed,  so  as  to  break  the  bulb  containing  the  sulphuric 

acid.  The  paper  was  waxed  in  order  to  make  it  inflame  more  easily.  Percussion 
fuzes,  &c.,  have  been  often  constructed  upon  a  similar  principle. 

Chloric  peroxide  used  to  be  called  hypochloric  acid;  but,  like  nitric 
peroxide,  it  appears  to  have  no  claim  to  be  considered  a  true  acid,  since, 
in  contact  with  the  alkalies,  it  vields  mixtures  of  chlorites  and  chlorates; 
thus— 2CIO2  +  2KH0  =  KCIO2  +  KCIO3  -1-  H.p . 


168 


CHLOROUS  ACID. 


Euchlorine,  the  deep  yellow,  dangerously  explosive  gas  evolved  by  the 
action  of  strong  hydrochloric  acid  upon  potassium  chlorate,  appears  to 
be  a  mixture  of  chloric  peroxide  with  free  chlorine.  It  is  resolved  by 
explosion  into  CI  and  0.  Mercurous  chloride  absorbs  CI  from  it, 
leaving  ClOj.  Hence  its  production  may  be  explained  by  the  equation, 
4KCIO3  +  12HC1  =  4KC1  +  6H2O  +  3CIO2  +  Clg . 

116.  Chlorous  anhydride  (ClgOg)*  is  another  unstable  and  dangerously 
explosive  gas,  obtained  by  the  action  of  a  very  gentle  heat  upon  a  mix- 
ture of  3  parts  of  white  arsenic,  4  of  potassium  chlorate,  and  16  of  diluted 
nitric  acid  (sp.  gr.  1  '24) — 

2KCIO3  +  2HNO3  +  AS2O3  +  2H2O  =  2KNO3  +  2H3ASO4  +  CI2O3 

Arsenic  acid. 

Chlorous  anhydride  is  a  deep  yellowish-green  heavy  gas  (sp.  gr.  2 "65) 
which  is  absorbed  by  water,  and  decomposed  even  more  easily  than  the 
chloric  peroxide.  The  solution  is  supposed  to  contain  chlorous  acid, 
HCIO2;  for  CI2O3 -I- H2O  =  2HCIO2,  but  this  has  not  been  obtained  in 
the  separate  state.  It  is  a  weak  acid,  its  salts,  the  chlorites,  being  decom- 
posed even  by  carbonic  acid.  A  mixture  of  ice  and  salt  does  not  liquefy 
chlorous  anhydride,  but  an  intense  cold  condenses  it  to  a  red  liquid,  of  sp. 
gr.  1  -33,  which  boils  at  a  little  above  the  melting-point  of  ice,  and  explodes 
at  a  somewhat  higher  temperature. 

117.  General  review  of  the  oxides  of  chlorine. — Several  points  of  resem- 
blance will  have  been  noticed  between  the  series  of  oxides  of  chlorine  and 
those  of  nitrogen,  but  the  former  are  much  less  stable  than  the  latter. 
Chlorous  anhydride  {CI2O3),  like  nitrous  anhydride  (N2O3),  yields  a  weak 
acid  when  dissolved  in  water ;  chloric  peroxide  (ClOg)  gives,  with  alkalies, 
chlorites  and  chlorates,  just  as  nitric  peroxide  (NU2)  gives  nitrites  and 
nitrates.  Chloric  acid  (HCIO3)  is  a  powerful  oxidising  agent,  like  nitric 
acid  (HXO3),  ^°^  *'^®  chlorates  resemble  the  nitrates  in  their  solubility  in 
water  and  their  oxidising  power.  The  composition  by  volumes  of  those 
oxides  of  chlorine  which  are  known  in  the  separate  state  is  exhibited  in 
the  following  table  : — 


=     Fonnuia.         ^0^^ 

Molecular 
Volume. 

By  Volume. 

Hypochlorous  anhydride, 
Chlorous                  ,, 
Chloric  peroxide, 

C1,0 
01,0, 
CIO, 

87 
119 
67-5 

2 
S 
2 

CI 
2 
2 
1 

0 
1 
3 

2 

Chlorides  of  Carbox. 

118.  It  has  already  been  seen  that  chlorine  has  no  direct  attraction  for  carbon, 
the  two  elements  not  being  known  to  enter  into  direct  combination  ;  but  several 
clilorides  of  carbon  may  be  obtained  b)'  the  action  of  chlorine  upon  other  compounds 
of  carbon.  Thus,  if  Dutch  liquid  (C2H4CI2),  produced  by  the  combination  of  olefiant 
gas  with  chlorine  (p.  96),  be  acted  upon  with  an  excess  of  chlorine  in  sunlight,  the 
whole  of  its  hydrogen  is  removed  in  the  form  of  hydrochloric  acid,  and  an  equivalent 
amount  of  chlorine  is  substituted  for  it,  yielding  the  trichloride,  formerly  called 
scsquichloride  of  carbon  (C^Cl^)  ;  CjH4Cl2  +  Cl8=C,Clj  +  4HCl. 

*  This  gas  occupies  three  times  the  volume  of  an  atom  of  hydrogen,  instead  of  twice 
that  volume,  as  usual. 


CHLOEIDES  OF  CAEBON. 


169 


Carbon  trichloride  is  a  white  crystalline  vsolid,  with  an  aromatic  odour,  rather 
like  that  of  carajihor.  It  fuses  at  320°  F.,  and  boils  at  360°,  subliming  unchanged. 
It  is  not  dissolved  by  water,  but  is  soluble  in  alcohol  and  ether. 

When  the  vapour  of  carbon  trichloride  is  passed  through  a  tube  containing 
fragments  of  glass  heated  to  redness,  it  is  decomposed  into  chlorine  and  a  colourless 
liquid,  which  is  the  dichloride,  formerly  called  protochloriAe  of  carbon  (CgCl^).  It 
has  an  aromatic  odour,  and  boils  at  248°  F.  ;  is  heavier  than  water  (sp.  gr.  1'5), 
which  does  not  dissolve  it,  and  is  soluble  in  alcohol  and  ether. 

By  passing  the  vapour  of  this  carbon  dichloride  through  tubes  heated  to  bright 
redness,  it  is  decomposed  into  chlorine  and  monochloride,  formerly  called  suhchloride 
of  carbon  (CgClg),  which  forms  silky  crystals  almost  free  from  odour,  insoluble  in 
water,  but  soluble  in  ether,  and  capable  of  being  sublimed  unchanged  at  a  high 
temperature.     It  burns  in  air  with  a  red  smoky  flame. 

Carbon  tetrachloride  (CCl^)  has  been  mentioned  (p.  154)  as  the  final 
result  of  the  action  of  chlorine  upon  marsh  gas  (CHJ  and  upon  chloroform 
(CHClg).  It  is  easily  obtained  in  large  quantity,  by  passing  chlorine 
(dried  by  passing  through  a  tube  containing  pumice  wetted  with  strong 
sulphuric  acid)  (fig.  185)  through  a  bottle  containing  bisulphide  of  carbon, 
and  afterwards  through  a  porcelain  tube  wrapped  in  sheet  copper,  and 
filled  with  fragments  of  broken  porcelain,  maintained  at  a  red  heat  by  a 
charcoal  or  gas  furnace,  and  condensing  the  products  in  a  bottle  surrounded 


Fig.  185. — Preparation  of  carbon  tetrachloride. 

by  ice.  A  mixture  of  carbon  tetrachloride  and  sulphur  chloride  is  thus 
obtained  ;  CSg  +  Clg  =  CCI4  +  SgClg.  By  shaking  this  mixture  with  potash, 
the  sulphur  chloride  is  decomposed  and  dissolved,  whilst  the  carbon 
tetrachloride  separates  and  falls  to  the  bottom.  The  upper  layer  having 
been  poured  ofl^,  the  tetrachloride  may  be  purified  by  distillation. 

Another  method  of  preparing  CCI4  consists  in  distilling  carbon 
disulphide  with  antimonic  chloride. 

Carbon  tetrachloride  is  a  colourless  liquid,  much  heavier  than  water 
(sp.  gr.  1-6),  having  a  peculiar  odour,  and  boiling  at  172°  F.  It  may  be 
solidified  at  -  9°  F.  The  tetrachloride  is  insoluble  in  water,  but  dissolves 
in  alcohol  and  ether.  v.. 

By  the  action  of  chlorine  on  naphthalene  (C^QlIg),  Laurent  obtained,  as 
the  ultimate  result,  a  crystalline  chloride  of  carbon  containing  C^qCIs,  to 
which  he  gave  the  name  chlona^phthaliae. 


170 


CHLORIDES  OF  CARBON. 


It  will  be  noticed  that  each  of  the  compounds  of  chlorine  with  carbon,  except  the 
trichloride,  has  its  parallel  in  the  compounds  of  hydrogen  with  carbon;*  thus— 
Acetylene     CjH2  corresponds  to  the  monochloride  €2012 , 
Olefiant  gas  C2H4  ,,  dichloride        C2CI4, 

Marsh  gas    CH4  ,,  tetrachloride   CCI4. 

The  history  of  carbon  trichloride  affords  an  instructive  instance  of  the  influence 
of  the  molecular  weight  of  a  compound  upon  its  properties.  By  passing  the  vapour 
of  carbon  tetrachloride  through  a  tube  heated  to  dull  redness,  a  liquid  is  obtained 
which  is  found  by  analysis  to  contain  precisely  the  same  proportions  of  carbon  and 
chlorine  as  the  solid  trichloride  above  described,  but  the  specific  gravity  of  its  vapour 
(H  =  l)  is  only  59*25,  which  is  half  that  of  the  vapour  of  solid  carbon  trichloride, 
showing  that  in  the  liquid  compound  the  same  proportions  of  carbon  vapour  and 
chlorine  are  condensed  into  a  volume  twice  as  large  as  in  the  solid  trichloride,  and 
it  must  be  represented  by  the  formula  CCI3 . 

The  following  table  exhibits  the  composition  of  the  chlorides  of  carbon  : — 

Chlorides  of  Carbon. 


Molecular 
Form  ul  88. 

Molecular 
Volume. 

Moleculai* 
Weight. 

Monochloride, 

C2CI2 

2? 

95-0 

Dichloride,      .... 

C2CI4 

2 

166-0 

Trichloride  (solid),  . 

C2CI6 

2 

237-0 

(liquid), 

CCI3 

2 

118-5 

Tetrachloride, 

CCI4 

2 

154-0 

119.  Oxyehloride  of  carbon,  carbonyle  chloride,  or  phosgene  gas,  is  produced  by  the 
direct  combination  of  equal  volumes  of  carbonic  oxide  and  chlorine  gases  under  the 
influence  of  sunlight  (whence  its  last  name),  when  the  mixture  condenses  to  half  its 
volume  of  a  colourless  gas,  condensable  by  cold,  having  a  very  peculiar  pungent 
smell,  and  fuming  strongly  when  exposed  to  moist  air,  decomposing  the  moisture 
and  producing  hydrochloric  acid;  CO.Cl2  +  H20  =  C02  +  2HCl.t  It  is  decomposed 
by  alkalies,  producing  chlorides  and  carbonates.  It  is  sometimes  found  useful  in 
chemical  research  for  removing  hydrogen  from  organic  compounds,  and  introducing 
carbonic  oxide,  or  its  elements,  into  its  place.  Its  action  on  ammonia  afi"ords  an 
example  of  this — 

4NH3  +  CO.CI2  =  COH4N2  +  2NH4CI 

ITrpa  Ammonium 

^^^^-  chloride. 

in  which  two  molecules  of  NH3  have  been  decomposed,  two  atoms  of  the  hydrogen 
having  been  removed  in  the  form  of  hydrochloric  acid,  and  replaced  by  CO. 

COCIj  may  also  be  prepared  by  passing  a  mixture  of  equal  volumes  of  CO  and 
CI  through  a  long  tube  filled  with  granulated  animal  charcoal,  which  favours  the 
combination  of  the  gases  ;  or  by  passing  dried  carbonic  oxide  through  antimony 
pentachloride  ;  SbClg  +  CO  =  COClg  +  SbClj . 

120.  Silicon  tetracliloride,  unlike  the  chlorides  of  carbon,  may  be  formed 
by  the  direct  union  of  silicon  with  chlorine  at  a  high  temperature ;  but  it 
is  best  prepared  by  passing  dry  chlorine  over  a  mixture  of  silica  and 
charcoal,  heated  to  redness  in  a  porcelain  tube  connected  with  a  receiver 
kept  cool  by  a  freezing  mixture.  Neither  carbon  nor  chlorine  separately 
will  act  upon  the  silica,  but  when  they  are  employed  together,  the 
carbon  removes  the  oxygen  and  the  chlorine  combines  with  the  silicon ; 
S1O2  +  (^2  +  CI4  =  SiCl4  +  2C0. 

*  When  vapour  of  carbon  dichloride  is  mixed  with  liydrogen,  and  passed  through  a  red 
hot  tube,  olefiant  gas  and  hydrochloric  acid  are  produced.  The  tetrachloride,  under  similar 
circumstances,  yields  marsh  gas. 

f  Phosgene  gas  has  also  been  obtained  by  heating  carbon  tetrachloride  with  phosphoric 
anhydride,  in  a  sealed  tube  ;  3CCl4  +  Ps05=2POCl3+3COCl2. 


CHLOEIDE  OF  NITROGEN.  171 

The  tetrachloride  is  a  colourless  hjpavy  liquid  (sp.  gr.  1*52),  which 
is  volatile  (boiling-point,  138°  F.),  and  fumes  when  exposed  to  air,  the 
moisture  of  which  decomposes  it,  yielding  hydrochloric  acid  and  silica — 

SiCi^   +   2H2O   =   SiOg  +   4HC1. 

Although  it  has  received  no  practical  application  on  a  large  scale,  it  is 
valuable  to  the  chemist  as  a  convenient  source  of  compounds  of  silicon, 
which  could  not  easily  be  procured  from  the  very  unchangeable  silica. 

By  passing  hydrochloric  acid  over  silicon  heated  to  redness,  a  very  remarkable 
liquid  is  obtained,  which  is  much  more  volatile  than  the  chloride  of  silicon  (boiling- 
point,  108°  F.),  and,  unlike  most  chlorine  compounds,  is  inflammable,  burning  with 
a  greenish  flame,  and  producing  silica  and  hydrochloric  acid.  It  fumes  strongly  in 
air,  and  is  decomposed  by  water,  yielding  hydrochloric  acid,  and  the  substance  termed 
leucone.  The  composition  of  this  liquid  appears  to  be  Si3H4Cljo,  and  its  production 
would  be  represented  by  the  equation  Sis -l-10HCl  =  Si3H4Clio-l-H5.  Its  decomposi- 
tion by  water  would  be  explained  by  the  equation — 

SisH^Cljo  +  5H2O  =  SisH^Og  +  lOHCl. 
Leucone. 

The  boron  tricMoHde  (BCI3)  is  similar  in  its  general  character  to  the 
silicon  tetrachloride,  and  is  prepared  by  a  similar  process,  but  it  is  a  gas 
instead  of  a  liquid  at  ordinary  temperatures. 

121.  Chloride  of  nitrogen  is  the  name  usually  given  to  the  very  explo- 
sive compound  before  referred  to  as  being  produced  by  the  action  of 
chlorine  on  sal  ammoniac.  Its  composition  is  somewhat  uncertain ;  its 
explosive  character  rendering  its  exact  analysis  very  difficult.  Some 
chemists  regard  it  as  NCI3,  that  is  ammonia  in  which  all  the  hydrogen 
has  been  displaced  by  chlorine,  ■\rhilst  others  believe  it  to  contain  hydrogen, 
regarding  it  as  derived  from  two  molecules  of  ammonia  (NH3.NH3), 
by  the  substitution  of  five  atoms  of  chlorine  for  five  of  hydrogen  (NCI3. 
NHCy. 

It  is  a  yellow,  heavy,  oily  liquid  (sp.  gr.  1  -GS),  which  volatilises  easily, 
yielding  a  vapour  of  very  characteristic  odour,  which  affects  the  eyes. 
When  heated  to  about  200°  F.  it  explodes  with  great  violence,  emitting  a 
loud  report  and  a  flash  of  light.*  Its  instability  is,  of  course,  attributable 
to  the  feeble  attraction  which  holds  its  elements  together ;  and  the  violence 
of  the  explosion,  to  the  sudden  expansion  of  a  small  volume  of  the  liquid 
into  a  large  volume  of  nitrogen,  chlorine,  and  perhaps  hydrochloric  acid. 
As  might  be  expected,  its  explosion  is  at  once  brought  about  by  contact 
with  substances  which  have  an  attraction  for  chlorine,  such  as  phosphorus 
and  arsenic ;  the  oils  and  fats  cause  its  explosion,  probably  by  virtue  of 
their  hydrogen;  oil  of  turpentine  explodes  it  with  greater  certainty  than 
the  fixed  oils.  Alkalies  also  decompose  it  violently ;  whilst  acids,  having 
no  action  upon  the  chlorine,  are  not  so  liable  to  explode  it.  At  160°  F. 
this  substance  has  actually  been  distilled  without  explosion. 

Although  practically  unimportant,  the  violent  explosive  properties  of 
this  substance  render  it  so  interesting  that  it  may  be  well  to  give  some 
directions  for  its  safe  preparation. 

Fifty  grains  of  red  oxide  of  mercury  are  very  finely  powdered,  and  thrown  into 
a  pint  bottle  of  chlorine  together  with  J  oz.  (measured)  of  w^ter.  The  stopper  is 
replaced,  and  the  bottle  well  shaken,  loosening  the  stopper  occasionally,  as  long  as 

*  It  is  said  to  absorb  38478  gramme-degrees  of  heat  per  equivalent,  in  the  process  of 
formation,  and  would  therefore  disengage  that  amount  of  heat  in  the  act  of  decomposition. 


172  AQUA  REGIA. 

the  chlorine  is  absorbed.  The  solution  of  hypochlorous  acid  thus  produced  is 
filtered  from  the  residual  mercuric  oxychloride,  and  poured  into  a  clean  thumb-glass 
(fig.  186).  A  lump  of  sal  ammoniac  weighing  20  grains  is  then  dropped  into  the 
solution,  and  the  glass  is  placed  under  a  stout  wooden  box.  After  the 
lapse  of  twenty  minutes,  the  chloride  of  nitrogen  may  be  exploded  by 
inserting  through  a  hole  in  the  box  a  stick  dipped  in  turpentine,  fixed 
at  right  angles  to  a  longer  stick.  The  glass  will  be  shattered  into  very 
small  fragments. 

122.  Aqzia  regia. — This  name  has  been  bestowed  upon  the 
Fig.  186.  mixture  of  1  measure  of  nitric,  and  3  measures  of  hydro- 
chloric acid  (nitromwiatic  add),  which  is  employed  for  dis- 
solving gold,  platinum,  and  other  metals  which  are  not  soluble  in  the 
separate  acids.  If  a  little  gold  leaf  be  placed  in  hydrochloric  and  nitric 
acids  contained  in  separate  glasses,  the  metal  will  remain  unaflfected  even 
on  warming  the  acids ;  but  if  the  contents  of  the  glasses  be  mixed,  the 
gold  will  be  immediately  dissolved  by  the  chlorine,  which  is  liberated  in 
the  action  of  the  acids  upon  each  other — • 

HNO3   +   3HC1   =    2H2O   +   NOCl  +   CI2. 

The  nitrosyle  chloride  (NOCl)  is  a  red  gas,  condensable  in  a  freezing  mixture 
to  a  dark  red  liquid,  which  boils  at  1 8°  F.  It  has  a  very  peculiar  odour,  and  is 
decomposed  by  contact  with  water.  Nitrosyle  chloride  is  also  produced  by  mixing 
2  volumes  of  nitric  oxide  with  1  volume  of  chlorine  ;  it  condenses  to  a  red  liquid  at 
0°  F.  When  nitrosyle  chloride  is  passed  into  oil  of  vitriol  cooled  to  32°  F. ,  ciystals 
of  the  acid  nitrosyle  sulphate  are  deposited ;  N0C1  +  H2S04=HC1  +  N0HS04. 

BEOMINE. 

Br  =  80  parts  by  weight. 

123,  It  generally  happens  that  elements  between  which  any  strong 
family  likeness  exists  are  found  associated  in  nature.  This  remark  par- 
ticularly applies  to  the  three  elements — chlorine,  bromine,  and  iodine — all 
of  which  are  found  in  sea  water,  though  the  first  predominates  to  such 
an  extent  that  the  others  for  a  long  time  escaped  notice.  Bromine  was 
brought  to  light  in  the  year  1826  by  Balard  in  the  examination  of  bittern, 
which  is  the  liquid  remaining  after  the  sodium  chloride  and  some  other 
salts  have  been  made  to  crystallise  by  evaporing  sea  water,  which  contains 
only  about  1  grain  of  bromine  per  gallon  in  the  forms  of  bromide  of 
magnesium  and  bromide  of  sodium.  It  is  also  extracted  from  the  waters 
of  certain  mineral  springs,  as  those  of  Kreuznach  and  Kissingen,  which 
contain  much  larger  quantities  of  bromine,  combined  with  potassium, 
sodium,  or  magnesium.  During  the  last  few  years  much  bromine  has 
been  obtained  from  the  mother-liquors  of  the  salt-works  at  Stassfurth, 
and  from  saline  springs  in  the  United  States. 

In  extracting  the  bromine  from  these  waters,  advantage  is  taken  of  the 
circumstance  that  chlorine  is  capable  of  displacing  bromine  from  its 
combinations  with  the  metals.  After  most  of  the  other  salts,  such  as 
sodium  chloride,  sodium  sulphate,  and  magnesium  sulphate,  which  are 
less  soluble  than  the  bromides,  have  been  separated  from  the  water 
by  evaporation  and  crystaUisation,  the  remaining  liquid  is  subjected  to  the 
action  of  chlorine  gas,  when  it  acquires  an  orange  colour,  due  to  the 
liberation  of  the  bromine;  KBr -I- CI  =  KCl -1- Br.  The  bromine  thus 
set  free  exists  now  diffused  through  a  large  volume  of  water,  which  can- 
not be  separated  from  it  in  the  usual  way,  by  evaporation,  because  bromine 
is  itself  very  volatile.     An  ingenious  expedient  is  therefore  resorted  to,  of 


EXTRACTION  OF  BROMINE.  173 

shaking  the  orange  liquid  briskly  with  ether,  which  has  a  greater  solvent 
power  for  bromine  than  is  possessed  by  water,  and  therefore  abstracts  it 
from  the  aqueous  solution  :  since  ether  does  not  mix  to  any  great  extent 
with  water,  it  now  rises  to  the  surface  of  the  liquid,  forming  a  layer  of  a 
beautiful  orange  colour,  due  to  the  bromine  which  it  holds  in  solution. 
This  orange  layer  is  carefully  separated,  and  shaken  with  solution  of 
potash,  which  inmiediately  destroys  the  colour  by  removing  the  bromine, 
leaving  the  ether  to  rise  to  the  surface  in  a  pure  state,  and  fit  to  be 
employed  for  abstracting  the  bromine  from  a  fresh  portion  of  the  water. 
The  action  of  the  bromine  upon  potash  is  precisely  similar  to  that  of 
chlorine;  6KH0  +  Br^  =  5KBr  +  KBrOg  +  3H2O. 

Potassium       Potassium 
bromide.  bromate. 

After  the  solution  of  potash  has  been  several  times  shaken  with  the 
ethereal  solution  of  bromine,  and  has  become  highly  charged  with  this 
element,  it  is  evaporated  so  as  to  expel  the  water,  leaving  a  solid  residue 
containing  the  potassium  bromide  and  bromate.  This  saline  mass  is 
strongly  heated  to  decompose  the  bromate,  and  convert  it  into  bromide  ; 
KBrOg  =  KBr  +  O3. 

From  this  salt  the  bromine  is  extracted  by  distilling  it  with  manganese 
dioxide  and  sulphuric  acid,  when  the  potassium  is  oxidised  at  the  expense 
of  the  manganese  dioxide,  and  the  bromine  is  liberated  and  condensed  in  a 
receiver  kept  cold  by  iced  water — 

2KBr  +  Mn02  +  2H2SO^  =  KgSO^  +  MnSO^  +  2H2O  +  Bt^  . 

The  aspect  of  the  bromine  so  produced  is  totally  diffierent  from  that  of 
any  other  element,  for  it  distils  over  in  the  liquid  condition,  and 
preserves  that  form  at  ordinary  temperatures,  being  the  only  liquid  non- 
metallic  element.  Its  dark  red-brown  colour,  and  the  peculiar  orange 
colour  of  the  vapour  which  it  exhales  continually,  are  also  characteristic ; 
but,  above  all,  its  extraordinary  and  disagreeable  odour,  |rom  which  it 
derives  its  name  (/Jpw/Aos,  a  stench),  leaves  no  doubt  of  its  identity.  The 
odour  has  some  slight  resemblance  to  that  of  chlorine,  but  is  far  more 
intolerable,  often  giving  rise  to  great  pain,  and  sometimes  even  to  bleeding 
at  the  nose. 

Liquid  bromine  is  thrice  as  heavy  as  water  (sp.  gr.  2  "96),  and  boils  at 
63°  C,  yielding  a  vapour  5|  times  as  heavy  as  air  (sp.  gr.  5'54).  It 
may  be  frozen  at  -  7°  C.  to  a  brown  crystalline  solid.  It  requires  33 
times  its  weight  of  cold  water  to  dissolve  it,  and  is  capable  of  forming  a 
crystalline  hydrate  (Br. 5 H2O)  corresponding  to  chlorine  hydrate. 

In  its  bleaching  power,  its  aptitude  for  direct  combination,  and  its 
other  chemical  characters,  it  very  closely  resembles  chlorine,  so  closely, 
indeed,  that  it  is  difficult  to  distinguish,  in  many  cases,  between  the  com- 
pounds of  chlorine  and  bromine  with  other  substances,  unless  the  elements 
themselves  be  isolated.  A  necessary  consequence  of  so  great  a  similarity 
is,  that  very  little  use  has  been  made  of  bromine,  since  the  far  more 
abundant  chlorine  fulfils  nearly  all  the  purposes  to  which  bromine  might 
otherwise  be  applied.  In  the  daguerreotype  and  photographic  arts,  how- 
ever, some  special  applications  of  bromine  have  been  discovered,  and  for 
some  chemical  operations,  such  as  the  determination  of  the  illuminating 
hydrocarbons  in  coal  gas,  bromine  is  sometimes  preferred  to  chlorine.  It 
has  also  been  used  in  America  as  a  disinfectant.  The  bromides  of  potas- 
sium and  ammonium  are  frequently  employed  in  medicine.     Bromide  of 


174 


HYDBOBROMIC  ACID. 


cadmium  is  used  in  photograpliy.  In  the  composition  of  their  compounds 
chlorine  and  bromine  exhibit  great  analogy. 

Hypohromoiis  acid  (HBrO)  has  been  obtained  in  solution  by  shaking 
mercuric  oxide  with  water  and  bromine.  The  solution  is  very  unstable, 
decomposing,  especially  when  heated,  with  liberation  of  bromine  and  for- 
mation of  bromic  acid.  The  action  of  bromine  upon  diluted  solutions  of 
the  alkalies,  and  upon  the  alkaline  earths,  produces  bleaching  liquids 
similiar  to  those  formed  by  chlorine. 

Bromic  acid  (HBrOg)  can  be  prepared  in  a  similar  manner  to  chloric 
acid,  to  which  it  has  a  great  general  resemblance,  the  bromates  being  also 
similar  to  the  chlorates. 

124.  Hydrohromic  acid  (HBr  =  81  parts  by  weight  =  2  volumes). — 
The  inferiority  of  bromine  to  chlorine  in  chemical  energy  is  well  exemplified 
in  its  relations  to  hydrogen ;  for  the  vapour  of  bromine  mixed  with  hydro- 
gen will  not  explode  under  the  action  of  flame  or  of  the  electric  spark, 
like  the  mixture  of  chlorine  and  hydrogen.  Direct  combination  may, 
however,  be  slowly  induced  by  contact  with  heated  platinum. 

When  it  is  attempted  to  prepare  this  acid  by  distilling  bromide  of 
sodium  or  potassium  with  sulphuric  acid  (as  in  the  preparation  of  hydro- 
chloric acid)  the  inferior  stability  of  hydrobromic  acid  is  shown  by  the 
decomposition  of  a  part  of  it,  the  hydrogen  being  oxidised  by  the  sulphuric 
acid,  and  the  bromine  set  free ;  2HBr  +  H2SO4  =  2H2O  +  SOg  +  Bv^ . 

If  a  strong  solution  of  phosphoric  acid  be  employed  instead  of  the 
sulphuric,  pure  hydrobromic  acid  may  be  obtained. 

But  the  most  instructive  method  of  obtaining 
hydrobomic  acid  consists  in  attacking  water 
with  bromine  and  phosphorus  simultaneously, 
when  the  phosphorus  takes  the  oxygen  of  the 
water,  forming  phosphoric  acid,  and  the 
bromine  combines  with  the  hydrogen  to  form 
hydrobromic  acid— 

3H2O  +  Brg  +  P  =  HPO3  4  5HBr 

Phosphoric  acid. 
The  experiment  may  be  made  in  a  W-formed  tube 
(fig.  187),  one  bend  of  which  contains  40  grains  of 
phosphorus  in  fragments  intermingled  with  glass 
moistened  with  water,  whilst  the  other  bend  contains 
240  grains  of  bromine  (about  1  drachm).  This  limb  of  the  tube  is  corked,  and  the 
other  furnished  with  a  delivery  tube,  so  that  the  gas  may  be  collected  either  by 
downward  displacement  or  over  mercury.  The  bromine  is  slightly  heated,  when  it 
distils  over  to  the  moist  phosphorus,  and  hydrobromic  acid  is  evolved.  A  moderate 
heat  should  afterwards  be  applied  to  the  moist  glass,  to  expel  part  of  the  h3'drobromic 
acid  from  the  water. 

Hydrobromic  acid  is  very  similar  to  hydrochloric  acid ;  it  liquefies  at 
-  92°  F.,  and  has  been  solidified  by  a  still  lower  temperature,  which  is  not 
the  case  with  hydrochloric  acid.  Like  that  gas,  it  is  very  soluble  in  water, 
and  the  solution  acts  upon  metals  and  their  oxides  in  the  same  manner 
as  hydrochloric  acid.  Chlorine  removes  the  hydrogen  from  hydrobromic 
acid,  liberating  bromine,  which  it  converts  into  chloride  of  bromine  if 
employed  in  excess. 

Bromide  of  nitrogen  has  been  obtained  by  the  action  of  bromide  of 
potassium  upon  chloride  of  nitrogen,  which  it  resembles  in  general 
character  and  explosive  properties. 


Fig.  187. — Preparation  of 
hydrobromic  acid. 


DISCOVERY  OF  IODINE.  175 

Carbon  tetrahromide,  CBr^,  is  obtained  by  heating  CCI4  with  aluminium 
bromide  in  a  sealed  tube  to  100°  C. 

CJiloride  of  bromine  is  a  very  volatile  yellow  liquid  of  pungent  odour. 
Its  composition  is  not  certainly  known.  That  chlorine  should  unite 
directly  with  bromine,  which  it  so  much  resembles  in  chemical  character, 
illustrates  its  great  tendency  to  direct  chemical  combination. 

IODINE. 

1  =  127  parts  by  weight. 
/  125.  Iodine  is  contained  in  sea  water  in  even  smaller  quantity  than 
bromine,  but  the  sodium  iodide  appears  to  constitute  a  portion  of  the 
necessary  food  of  certain  varieties  of  sea-weed,  which  extract  it  from  the 
sea  water,  and  concentrate  it  in  their  tissues.  The  ash  remaining  after 
sea- weed  has  been  burnt  was  long  used,  under  the  name  of  kelp,  in  soap- 
making,  because  it  contains  a  considerable  quantity  of  sodium  carbonate ; 
and  in  the  year  1811,  Courtois,  a  soap-boiler  of  Paris,  being  engaged  in 
the  manufacture  of  soda  from  kelp,  obtained  from  the  waste  liquors  a 
substance  which  possessed  properties  different  from  those  of  any  form  of 
matter  with  which  he  Avas  acquainted.  He  transferred  it  to  a  French 
chemist,  Clement,  who  satisfied  bimself  that  it  was  really  a  new  substance ; 
and  Gay-Lussac  and  Davy  having  examined  it  still  more  closely,  it  took 
its  rank  among  the  non-metallic  elementary  substances,  under  the  name 
of  iodine  (uoSt;?,  violet-coloured),  conferred  upon  it  in  allusion  to  the 
magnificent  violet  colour  of  its  vapour. 

This  history  of  the  discovery  of  iodine  affords  a  very  instructive  example 
of  the  advantage  of  training  persons  engaged  in  manufactures  to  habits  of 
accurate  observation,  and,  if  possible,  of  accurate  chemical  observation; 
for  had  Courtois  passed  over  this  new  substance  as  accidental,  or  of  no 
consequence,  the  community  would  have  lost,  at  least  for  some  time,  the 
benefits  derived  from  the  discovery  of  iodine. 

For  some  years  the  new  element  was  only  known  as  a  chemical 
curiosity,  but  an  unexpected  demand  for  it  at  length  arose  on  the  part  of 
the  physician,  for  it  had  been  found  that  the  efficacy  of  the  ashes  of 
sponge,  which  had  long  been  used  in  some  particular  maladies,  was  due 
to  the  small  quantity  of  iodine  which  they  contained,  and  it  was  of  course 
thought  desirable  to  place  this  remedy  in  the  hands  of  the  medical  pro- 
fession in  a  purer  form  than  the  ash  of  sponge,  where  it  is  associated  with 
very  large  quantities  of  various  saline  substances.  Much  more  recently, 
the  demand  for  this  element  has  greatly  increased  on  account  of  its  employ- 
ment in  photography,  and  large  quantities  of  it  are  annually  produced 
from  kelp,  the  collection  and  burning  of  which  affords  occupation  to  the 
very  poor  inhabitants  of  some  parts  of  the  coasts  of  Ireland  and  Scotland, 
who  would  otherwise  have  been  thrown  out  of  work  when  soda  began  to 
be  manufactured  from  common  salt,  and  the  demand  for  kelp  as  the  source 
of  that  alkali  had  ceased.  The  sea-weed*  is  spread  out  to  dry,  and  burnt 
in  shallow  pits  at  as  low  a  temperature  as  possible;  for  the  sodium  iodide 
is  converted  into  vapour  and  lost  if  the  temperature  be  very  high.  The 
ash,  which  is  left  in  a  half-fused  state,  is  broken  \^to  fragments  and 
treated  with  hot  water,  wliich  dissolves  about  half  of  it,  leaving  a  residue 
consisting  of  calcium  carbonate  and  sulphate,  sand,  &c.     The  whole  of  the 

*  The  Laminaria  digitata,  or  deep  sea  tangle,  coutains  most  iodine. 


176 


EXTRACTION  OF  IODINE. 


sodium  iodide  is  contained  in  the  portion  dissolved  by  the  water,  but  is 
mixed  with  much  larger  quantities  of  sulphate,  carbonate,  hyposulphite, 
sulphide  and  bromide  of  sodium,  together  with  sulphate  and  chloride  of 
potassium.  A  portion  of  the  water  is  expelled  by  evaporation,  when  the 
sulphate  and  carbonate  of  sodium  and  chloride  of  potassium,  being  far  less 
soluble  than  the  iodide  of  sodium,  crystallise  out.  In  order  to  decompose  the 

hyposulphite  and  sulphide 
of  sodium,  the  liquid  is 
mixed  with  an  eighth  of  its 
bulk  of  oil  of  vitriol,  which 
decomposes  these  salts, 
evolving  sulphurous  and 
hj'drosulphuric  acid  gases, 
with  deposition  of  sulphur, 
and  forming  sodium  sul- 
phate, which  is  deposited  in 
crystals.  The  liquor  thus 
prepared  is  next  mixed  with 
manganese  dioxide,  and 
heated  in  an  iron  still 
with  a  leaden  cover  (fig. 
188),  when  the  iodine  is 
evolved  as  a  magnificent 
purple  vapour,  which  con- 
denses in  the  globular  glass 
or  stoneware  receivers  in  the  form  of  dark  grey  scales  with  metallic  lustre, 
and  having  considerable  resemblance  to  black  lead.  The  liberation  of  the 
iodine  is  explained  by  the  following  equation — 2NaI  -|-  MnOg  +  2H2SO4 
=  Na^SO^  +  MnSO^  +  2H2O  + 12 . 

When  no  more  iodine  passes  over,  some  more  manganese  dioxide  is 
added,  and  the  bromine  then  distils.  The  quantity  of  bromine  obtained 
is  about  one-tenth  that  of  the  iodine. 


Fig.  188. — Extraction  of  iodine. 


Several  processes  have  been  devised  to  render  the  extraction  of  the  iodine  from  the 
concentrated  solution  of  kelp  easier  and  more  economical.  The  most  promising  is 
very  similar  to  that  employed  for  separating  bromine  (p.  172).  The  iodine  is 
liberated  by  chlorine,  and  extracted  from  the  liquid  by  shaking  it  with  benzene  ;  by 
treating  the  benzene  with  solution  of  potash,  the  iodine  is  converted  into  a  mixture 
of  potassium  iodide  and  iodate,  from  which  the  iodine  may  be  precipitated 
by  acidifying  with  hydrochloric  acid  —  6KH0  +  Ig  =  5KI  +  KIO3  -I-  3HjO  ; 
5K1  +  KI03  +  6HCI  =  6KC1  +  3H20  +  I5.  A  far  more  economical  process  for  the 
treatment  of  sea-weed  consists  in  distilling  it,  when  ammonia,  acetic  acid,  naphtha, 
tar,  and  illuminating  gas  are  obtained,  whilst  a  porous  charcoal  remains  in  the  retort, 
which  is  treated  with  water  in  order  to  extract  the  iodides  and  other  soluble  salts. 
This  charcoal  somewhat  resembles  animal  charcoal  in  character,  containing  much 
phosphate  and  carbonate  of  calcium  and  magnesium  ;  it  is  useful  as  a  decolorising 
and  deodorising  agent.  Iodine  is  now  extracted  from  the  deposits  of  nitrate  of  soda 
occurring  in  Chili,  which  contain  sodium  iodate  (NalOg). 

The  features  of  this  element  are  extremely  well  marked :  its  metallic 
lustre  and  peculiar  odour  sufficiently  distinguish  it  from  all  others,  and 
the  effect  of  heat  upon  it  is  very  striking,  in  first  easily  fusing  it  (at  225° 
F.),  and  afterwards  converting  it  (boiling-point,  347°  F.)  into  the  most 
exquisitely  purple  vapour,  which  is  nearly  nine  times  as  heavy  as  air  (sp. 
gr.  8  "72),  and  condenses  upon  a  cool  surface  in  shining  scales.     It  stains 


PROPERTIES  OF  IODINE.  177 

the  skin  intensely  brown  if  handled.  The  specific  gravity  of  solid  iodine 
is  4-95. 

When  iodine  is  shaken  with  cold  water,  a  very  small  quantity  is  dis- 
solved, forming  a  light  brown  solution.  Hot  water  dissolves  a  larger 
quantity,  but  alcohol  is  one  of  the  best  solvents  for  iodine,  producing  a 
dark  red-brown  solution  from  which  part  of  the  iodine  may  be  precipi- 
tated by  adding  water.  A  solution  of  potassium  iodide  also  dissolves 
iodine  freely  ( LugoVs  solution  ;  liquor  iodi).  Tincture  of  iodine  contains 
iodine  with  half  its  weight  of  potassium  iodide  dissolved  in  alcohol. 
Benzene  and  carbon  disulphide  dissolve  it  abundantly,  producing  fine 
violet-red  solutions,  which  deposit  the  iodine,  if  allowed  to  evaporate 
spontaneously,  in  minute  rhombic  octahedral  crystals  aggregated  into  very, 
beautiful  fern-like  forms.  If  an  extremely  weak  aqueous  solutioa  of 
iodine  be  shaken  with  a  little  carbon  disulphide,  the  latter  will  remove 
the  iodine  from  the  solution,  and  on  standing,  will  fall  to  the  bottom  of 
the  liquid,  having  a  beautiful  red  colour.  By  dissolving  a  large  quantity 
of  iodine  in  carbon  disulphide,  a  solution  is  obtained  which  is  perfectly 
opaque  to  rays  of  light,  though  it  allows  heat-rays  to  pass  freely,  and  is 
therefore  of  great  value  in  physical  experiments.  A  solution  of  iodine  in 
carbon  tetrachloride  is  also  used  for  the  same  purpose. 

Existing,  as  iodine  does,  in  very  minute  quantity  in  the  water  from 
various  natural  sources,  it  would  often  be  overlooked  if  the  chemical 
analyst  did  not  happen  to  possess  a  test  of  the  most  delicate  description 
for  it. 

Iodine,  in  the  uncombined  sfate,  dyes  starch  of  a  beautiful  blue  colour, 
as  may  be  proved  by  heating  a  grain  or  two  of  the  element  with  water, 
and  adding  to  the  cold  solution  a  little  thin  starch  (see  p.  55),  or  by 
placing  a  minute  fragment  of  iodine  in  a  stoppered  bottle,  and  suspend- 
ing in  it  a  piece  of  paper  dipped  in  thin  starcL  This  test,  however, 
though  sensitive  to  the  smallest  quantity  of  free  iodine,  gives  no  indica- 
tion whatever  with  iodine  in  combination,  as  it  always  exists  in  nature ; 
in  order,  therefore,  to  test  for  iodine,  a  little  starch -paste  is  added  to  the 
suspected  liquid,  and  then  a  drop  of  a  weak  solution  of  chlorine,  which 
will  set  free  the  iodine,  and  cause  the  production  of  the  blue  colour.  It 
is  necessary,  however,  carefully  to  avoid  adding  too  much  chlorine,  since 
it  would  immediately  destroy  the  colour  of  the  iodised  starch.  If,  then, 
a  very  little  sulphurous  acid  be  added,  the  blue  tint  returns,  and  is  again 
bleached  by  more  sulphurous  acid.*  Alkalies  also  bleach  it,  and  the 
colour  of  a  mixture  of  the  iodised  starch  with  water  is  removed  by  heat- 
ing, but  returns  in  great  measure  when  the  solution  cools.  The  starch 
appears  to  be  only  dj'ed  by  the  iodine,  and  not  combined  with  it ;  on 
shaking  the  blue  iodised  starch  for  some  time  with  CSg,  the  blue  colour 
is  removed,  and  the  red  solution  of  iodine  in  CSg  is  obtained. 

Though  very  closely  connected  with  chlorine  and  bromine  in  its  general 
chemical  relations,  there  are  several  points  in  the  history  of  iodine  which 
cause  it  to  stand  out  in  marked  contrast  by  the  side  of  these  elements. 
The  attraction  which  binds  it  to  hydrogen  and  the  metals  is  certainly 
weaker  than  that  exerted  by  chlorine  and  bromine,  so  that  either  of  these 
is  capable  of  displacing  it  from  its  compounds,  and  its  bleaching  properties 

*  The  following  equations  explain  these  changes  : — 

(1)  KI  +  C1  =  KCI  +  I;  (2)  I-!-.3H.20  +  Cl5  =  HI03  +  5HCl; 

(3)  2HI03  +  5H2S03=5H2S04+Io  +  HaO;        (4)  l2  +  H20-i-H2S03  =  2HI  +  H2S04. 

M 


178  IODIC  ACID. 

are  very  feeble.  On  the  other  hand,  it  exhibits  a  more  powerful  tendency 
to  unite  with  oxygen  ;  for  boiling  nitric  acid  converts  it  into  iodic  acid 
(HIO3),  though  this  oxidising  agent  would  not  affect  chlorine  or  bromine. 

Some  of  the  compounds  of  iodine  with  the  metals  are  remarkable  for  their  beautiful 
colours.  The  mercuric  iodide,  produced  by  mixing  solutions  of  j)otassium  iodide  and 
mercuric  chloride,  forms  a  fine  scarlet  precipitate,  which  dissolves  in  an  excess  of 
|>otassiuni  iodide  to  a  colourless  solution. 

If  the  mercuric  iodide  be  collected  on  a  filter,  washed  and  dried,  it  will  be  found, 
on  heating  a  portion  of  it  in  a  test-tube,  that  it  acquires  a  fine  yellow  colour,  and 
.sublimes  in  golden  yellow  crystals,  which  resume  the  original  red  colour  when  rubbed 
with  a  glass  rod.  If  it  be  spread  upon  paper  and  gently  heated,  the  scarlet  iodide 
becomes  yellow,  but  the  red  colour  returns  on  rubbing  it  with  the  thumb-nail.  These 
(.hangfs  of  colour  are  attended  by  an  alteration  in  crystalline  form,  but  not  in  the 
chemical  compo.sition  of  the  mercuric  iodide.  This  iodide  is  used  in  painting  under 
the  name  of  pure  scarlet  or  ioduie  scarlet,  but  the  colour  is  not  durable. 

Lead  iodide  has  a  bright  yellow  colour,  as  may  be  seen  by  precipitating  potassium 
iodide  with  a  solution  of  lead  acetate.  The  precijutate  is  dissolved  by  boiling  with 
water  (especially  on  adding  a  little  hydrochloric  acid),  forming  a  colourless  solution, 
from  which  the  lead  iodide  crystallises  in  very  brilliant  golden  scales  on  cooling. 
Silver  iodide  is  produced  as  a  yellow  precipitate  when  silver  nitrate  is  added  to 
])otassium  iodide.  The  bromide  and  chloride  of  silver  would  form  white  precipi- 
tates. Silver  iodide  is  more  stable  than  the  chloride  or  bromide ;  when  ex- 
posed to  light  it  appears  to  be  unchanged,  but  if  a  reducing  agent,  such  as  ferrous 
sulphate  or  pyrogallin,  be  afterwards  poured  over  it,  that  portion  of  the  iodide  which 
has  been  exposed  to  light  is  immediately  blackened,  from  the  separation  of  silver  in 
the  metallic  state.  This  is  the  principle  of  the  process  for  developing  the  negative 
j)hotograph  taken  on  a  collodion  film  rendered  sensitive  by  silver  iodide.  The 
iodides  of  potassium,  ammonium,  and  cadmium  are  also  used  in  photography. 

126.  Iodic  acid,  HIO3. — It  is  most  easily  prepared  by  boiling  iodine 
with  the  strongest  nitric  acid  in  a  long-necked  flask,  when  it  is  dissolved 
in  the  form  of  iodic  acid,  which  is  left,  on  evaporating  the  nitric  acid,  as 
a  white  mass.  This  may  be  purified  by  dissolving  in  water  and  crystal- 
lising, when  the  iodic  acid  forms  white  hexagonal  tables,  which  have  the 
composition  HI03.Aq.  Heated  to  266°  F.  they  become  HIO3,  ^^^  *^ 
360°  r.  the  iodic  acid  is  decomposed  into  water  and  iodic  anhydride, 
2HI03  =  H20-f  IgOy  This  last  is  decomposed  at  about  700°  F.  into 
iodine  and  oxygen.  The  iodic  anhydride  oxidises  combustible  bodies, 
but  not  with  any  great  violence.  The  acid  is  far  more  stable  than 
chloric  and  bromic  acids.  Its  solution  first  reddens  litmus  paper,  and 
afterwards  bleaches  it  by  oxidation.  Its  salts,  the  iodates,  are  less 
easily  soluble  in  water  than  the  chlorates  and  bromates,  which  they 
resemble  in  their  oxidising  action  upon  combustible  bodies.  They 
are  all  decomposed  by  heat,  evolving  oxygen,  and  sometimes  even  iodine, 
showing  how  much  inferior  this  element  is  to  chlorine  and  bromine 
in  its  attraction  for  metals.  The  iodates  exhibit  some  remarkable  irregu- 
larities in  their  composition. 

Periodic  acid,  HIO4,  is  obtained  from  the  basic  sodium  periodate  fonned  by  passing 
chlorine  through  a  mixture  of  sodium  iodate  and  sodium  hydrate,  when  the  latter  is 
decomposed,  its  sodium  being  abstracted  by  the  chlorine,  whilst  its  oxygen  converts 
the  iodic  acid  into  periodic  acid  ;  NaI03-f3NaHO-l-Cl2  =  2NaCl-l-NaI04.]SraHO.H20 
(basic  sodium  periodate). 

Tills  periodate  is  deposited,  being  sparingly  soluble  in  water,  a  most  unusual 
circumstance  with  sodium  salts.  By  dissolving  it  in  nitric  acid,  and  adding  silver 
nitrate,  a  basic  silver  periodate  is  obtained,  which  is  yellow  when  precipitated  from 
cold,  and  red  from  hot  solutions.  When  the  silver  salt  is  dissolved  in  nitric  acid,  it 
is  decomposed  into  silver  nitrate,  which  remains  in  solution,  and  normal  silver 
perioilate,  AglO^,  which  is  deposited  in  crystals.     When  this  is  boiled  with  water, 


HYDRIODIC  ACID, 


179 


it  again  yields  the  insoluble  basic  periodate,  and  periodic  acid  is  found  in  the  solu- 
tion. On  evaporating  the  solution,  the  periodic  acid  is  deposited  in  prismatic 
crystals  having  the  composition  H104.2Aq,  which  are  decomposed  at  about  320°  F., 
2HI04.2Aq=IaO-  +  3H20.  The  J.fi^  is  decomposed  into  I^Og  and  O,  at  400°  F. 
The  solution  of  periodic  acid,  of  course,  exhibits  oxidising  properties. 

The  perioclates  are  remarkable  for  their  sparing  solubility  in  water  :  they  are  easily 
decomposed  by  heat,  like  the  iodates.  It  will  have  been  remarked  in  the  above 
account  of  the  preparation  of  periodic  acid,  that  this  acid  exhibits  a  great  tendency 
to  the  formation  of  basic  salts,  whilst  iodic  acid  is  remarkable  for  its  acid  salts. 

127.  Hydriodic  acid  (HI  =128  parts  by  weight  =  2  volumes). — Iodine 
vapour  combines  with  hydrogen,  under  the  influence  of  heated  platinum, 
to  form  hydriodic  acid  gas.  The  gas  is  best  prepared  by  decomposing 
water  with  iodine  in  the  presence  of  phosphorus  ;  BHgO  +  Ig  +  P,  =  6HI 
+  2H,P03. 

100  grains  of  potassium  iodide  are  dissolved  in  50  grains  of  water  in  a  retort  (fig. 
189),  and  200  grains  of  iodine  are  added  ;  when  this  has  dissolved,  10  grains  of 
amorphous  phosphorus  are  introduced,  and  the 
mixture  heated  very  gradually,  the  gas  being 
collected  by  downward  displacement  in  stop- 
pered bottles,  which  must  be  placed  in  readiness, 
as  the  gas  comes  off  very  rapidly.  These 
quantities  will  fill  four  pint  bottles  with  the  gas. 


Fig.  189. — Preparation  of 
hydriodic  acid. 


Hydriodic  acid  gas  is  very  similar  in 
its  properties  to  hydrochloric  and  hydro- 
bromic  acids,  fuming  strongly  in  moist 
air,  very  readily  absorbed  by  water, 
liquefied  only  under  strong  pressure,  and 
solidified  by  extreme  cold.  It  is  much 
heavier,  its  specific  gravity  being  4*44. 
If  a  bottle  of  hydriodic  acid  gas  be  placed  in  contact  with  a  bottle  con- 
taining chlorine  or  bromine  vapour  diluted  with  air  (fig.  148)  it  will  be 
instantly  decomposed,  with  separation  of  the  beautiful  violet  vapour  of 
iodine. 

The  aqueous  solution  of  hydriodic  acid  is  most  conveniently  prepared 
by  passing  hydrosulphuric  acid  gas  through  water  in  which  iodine  is 
suspended,  HgS  + 12  =  2HI  +  S,  the  separated  sulphur  being  filtered  off, 
and  the  solution  boiled  to  expel  the  excess  of  hydrosulphuric  acid.* 
Solution  of  hydriodic  acid  differs  greatly  from  hydrochloric  and  hydro- 
bromic  acids,  in  being  decomposed  by  exposure  to  air,  its  hydrogen  being 
oxidised  and  iodine  separated,  which  dissolves  in  the  liquid,  and  renders 
it  brown. 

This  tendency  of  the  hydrogen  of  hydriodic  acid  to  combine  with 
oxygen  renders  that  acid  a  powerful  reducing  agent.  It  is  even  capable 
of  converting  sulphuric  acid  into  hydrosulphuric  acid — 

H2SO4   +    SHI   =    H2S   -F    4H2O    +   Ig, 

so  that  when  potassium  iodide  is  heated  with  concentrated  sulphuric  acid, 
hydrosulphuric  acid  is  evolved  in  considerable  quantity. 

The  action  of  hydriodic  acid  upon  the  metals  and  their  oxides  is  gene- 
rally similar  to  that  of  the  other  hydrogen  acids. 

In  organic  chemistry,  hydriodic  acid  is  often  employed  for  removing 
oxygen  and  replacing  it  by  hydrogen. 

When  potassium  is  heated  in  a  measured  volume  of  hydriodic  acid, 


*  Strong  solution  of  hydriodic  acid  is  able  to  converi;  sulphur  into  hydrosulphuric  acid. 


180  POTASSIUM  IODIDE. 

the  iodine  is  removed,  and  the  hydrogen  occupies  half  the  original  volume. 
Hence  1  volume  of  hydrogen  is  combined  with  1  volume  of  iodine  vapour 
in  2  volumes  of  hydriodic  acid. 

Like  chlorine  and  bromine,  iodine  is  capable  of  displacing  hydrogen 
from  many  organic  compounds,  and  of  taking  its  place ;  but  its  action  in 
this  respect  is  much  feebler.  The  circumstance  that  the  organic  com- 
pounds containing  iodine  are  generally  much  less  volatile,  and  therefore 
more  manageable,  than  those  of  chlorine  and  bromine,  leads  to  the  ex- 
tensive employment  of  this  element  in  researches  upon  organic  substances. 

With  olefiant  gas,  iodine  forms  a  crystalline  solid  compound  (C2H4I2) 
corresponding  to  Dutch  liquid  (p.  96). 

Carbon  tetra-iodide,  d^,  is  obtained  by  decomposing  carbon  tetrachloride 
with  aluminium  iodide,  in  presence  of  carbon  disulphide.  It  forms  octa- 
hedral crystals  which  are  very  unstable. 

128.  Iodide  of  nitrogen.- — The  action  of  chlorine,  bromine,  and  iodine 
upon  ammonia  exemplifies  the  difference  in  their  attraction  for  hydrogen; 
for  whilst  chlorine  and  bromine,  acting  upon  ammonia,  cause  the  libera- 
tion of  a  certain  amount  of  nitrogen,  iodine  simply  removes  two-thirds  of 
the  hydrogen,  and  itself  fills  up  the  vacancies  thus  occasioned,  no  nitrogen 
being  liberated,  NH3+ I4  =  ]S'HI2-I- 2HI,  the  hydriodic  acid  thus  formed 
combining  with  more  ammonia  to  form  ammonium  iodide. 

To  j)repare  the  iodide  of  nitrogen,  20  grains  of  iodine  are  rubbed  to  powder  in  a 
mortar  and  mixed  with  half  an  ounce  (measured)  of  strong  ammonia  :  the  mortar 
is  covered  with  a  glass  plate,  and  after  about  half  an  hour  the  iodide  of  nitrogen  is 
(;ollected  in  separate  portions  upon  four  filters,  which  are  allowed  to  drain  and 
spread  out  to  dry.  The  brown  solution  contains  iodine  dissolved  in  ammonium 
iodide. 

Another  method  consists  in  dissolving  iodine  in  a  mixture  of  hj'drochloric  with 
ft  little  nitric  acid,  with  the  aid  of  heat,  and  adding  ammonia,  which  decomposes 
the  ICl  in  solution,  and  gives  a  black  precipitate  of  the  iodide  of  nitrogen. 

The  iodide  is  a  black  powder,  which  explodes  with  a  loud  report  even 
when  touched  with  a  feather,  emitting  fumes  of  hydriodic  acid  and 
j)urple  vapour  of  iodine  :  its  explosion  is  probably  represented  by  the 
equation — 

NHI2   =   I^   +   HI   +   I, 
its  violence  being  accounted  for  by  the  sudden  evolution  of  a  large  volume 
of  gas  and  vapour  from  a  small  volume  of  solid.     Even  when  allowed  to 
fall  from  the  height  of  a  few  feet  upon  the  surface  of  water,  it  explodes 
if  perfectly  dry.     In  the  moist  state  it  slowly  undergoes  decomposition. 

When  dry  NH3  gas  is  passed  over  iodine  cooled  by  ice,  iodammonium 
iodide  (NH3I)  I  is  produced. 

129.  Iodine  forms  two  compounds  with  chlorine,  monoMoride  (ICl) 
and  trichloride  (ICI3).  The  former  is  obtained  by  distilling  1  part  of 
iodine  with  4  parts  of  potassium  chlorate.  It  fuses  at  76°  F.,  and  boils 
at  214°  F. 

The  trichloride  forms  fine  red  needle-like  crystals,  and  is  produced 
when  iodine  is  acted  upon  with  an  excess  of  chlorine.  Bromides  of  iodine 
have  also  been  obtained,  but  their  composition  is  not  well  known. 

130.  Potasduvi  iodide  (KT  =  166  parts  by  weight). — This  salt  is  the 
most  useful  compound  of  iodine,  being  largely  employed  in  medicine  and 
in  photography.  It  is  generally  prepared  by  decomposing  ferrous  iodide 
with  potassium  carbonate. 


IODIDE  OF  POTASSIUM — FLUORINE.  181 

The  iodide  of  iron  or  ferrous  iodide  "(also  a  useful  medicine)  is  made 
by  placing  2  parts  of  iodine  in  contact  with  1  part  of  iron  filings  and  10 
parts  of  water.  The  iodine  combines  with  part  of  the  iron,  evolving  con- 
siderable heat,  and  producing  FeTc, . 

The  liquid  is  decanted  from  the  excess  of  iron,  and  one-third  of  the 
weight  of  iodine  previously  employed  is  dissolved  in  it.  In  this  way  two- 
thirds  of  the  ferrous  iodide  are  converted  into  f&rHc  iodide  (Fe^Ig),  so 
that  the  solution  contains  a  mixture  of  one  molecule  of  Felg  and  one  of 
Fe.jig.  It  is  now  boiled,  and  potassium  carbonate  is  gradually  added  as 
long  as  it  causes  a  dark  green  precipitate  of  magnetic  oxide  of  iron,  Feig 
+  Fe.,Ig-F4K2C03  =  8KI-i-FeO.Fe203  +  4C02,  the  carbonic  acid  gas  is 
evolved  with  effervescence,  and  if  the  solution  be  filtered  and  evaporated, 
it  deposits  beautiful  cubical  (or  sometimes  octahedral)  crystals,  which  are 
generally  milk-white  and  opaque,  but  occasionally  quite  transparent. 
Pure  potassium  iodide  remains  dry  in  ordinary  air ;  but  if  an  excess  of 
potassium  carbonate  is  employed  in  its  preparation,  the  crystals  retain 
some  of  that  salt,  and  become  damp  when  exposed  to  air.  The  potassium 
iodide  dissolves  easily  in  water  and  alcohol.  If  the  solution  be  pure,  it 
does  not  become  coloured  when  mixed  with  pure  hydrochloric  acid ;  but 
if  any  potassium  iodate  be  present  in  it,  a  brownish  colour  will  be  pro- 
duced, due  to  iodine  liberated  in  the  action  of  the  iodic  acid  upon  the 
hydriodic  acid;  HI03-1-5HI  =  SH^O -F- Ig.  The  iodate  is  liable  to  be 
present  in  those  specimens  which  are  prepared  by  dissolving  iodine  in 
potash,  to  obtain  a  mixture  of  iodide  and  iodate  of  potassium,  the  latter 
salt  being  afterwards  decomposed  by  heat. 

By  saturating  solution  of  potassium  iodide  with  iodine,  G.  S.  Johnson 
obtained  fine  crystals  of  potassium  tri-iodide  (KI3).  Aramonium  tri- 
iodide,  NH^Ig,  was  obtained  in  a  similar  way. 

fluori:n^e. 

F  =  19  parts  by  weight. 

131.  The  most  ornamental  mineral  substance  occurring  in  any  abund- 
ance in  this  country  is  known  as  Jiuor  spar  or  Derbyshire  spar  (fluoride 
of  calcium),  and  is  found  with  several  beautiful  shades  of  colour — blue, 
purple,  violet,  or  green,  and  sometimes  perfectly  colourless,  either  in  large 
masses  or  in  crystals,  which  have  the  form  of  a  cube  or  of  some  solid 
derived  from  it.  The  use  of  this  mineral  as  a  flux  in  smelting  ores  dates 
from  a  very  remote  period,  and  from  this  use  the  name  fluor  appears  to 
have  been  originally  derived ;  but  we  have  no  record  of  its  chemical  ex- 
amination till  about  a  century  since,  when  !Margraf  found  his  glass  retort 
powerfully  corroded  in  distilling  this  mineral  with  sulphuric  acid,  and 
Scheele  soon  after  announced  that  it  contained  lime  and  fluoric  acid. 
But  though  this  chemist  had  fallen  into  the  error  to  which  analysts  are 
continually  liable,  of  mistaking  products  for  educts,  his  experiments,  as 
they  were  afterwards  perfected  by  Gay-Lussac  and  Thenard,  deserve  par- 
ticular consideration. 

132.  Hydrofluonc  acid  (HF  =  20  parts  by  weight  =  2  volumes).* — If 
powdered  fluor  spar  be  mixed  with  twice  its  weight  o?  oil  of  vitriol,  and 

*  From  some  determinations  of  the  specific  gravity  of  the  vapour  at  low  temperatures, 
Mallet  considers  the  molecule  to  be  H2F2=40,  and  to  undergo  dissociation  into  2HF  at 
temperatures  approaching  100°  C. 


182  HYDKOFLUORIC  ACID. 

heated  in  a  leaden  retort  (fig.  190),  the  neck  of  which  fits  tightly  into  a 
leaden  condensing-tube,  cooled  in  a  mixture  of  ice  and  salt,  a  colourless 
liquid  distils  over,  and  the  residue  in  the  retort  is  found  to  consist  of 
calcium  sulphate* — 

CaF2   +   H2SO4   =   CaSO^    +    2HF. 

The  colourless  liquid  (hydrofluoric  acid)  possesses  most  remarkable  pro- 
perties :  it  is  powerfully  acid,  fumes  strongly  in  the  air,  and  has  a  most 

pungent  irritating  odour.  If  the  air  is  at 
all  warm,  the  liquid  begins  to  boil  when 
taken  out  of  the  freezing  mixture.  Should 
the  operator  have  the  misfortune  to  allow 
a  drop  to  fall  upon  his  hand,  it  will 
produce  a  very  painful  sore,  even  its 
vapour  producing  pain  under  the  finger 
nails.  Its  attraction  for  water  is  so  great, 
that  the  acid  hisses  like  red  hot  iron  when 
brought  in  contact  with  it.  But  its  most 
surprising  property  is  that  of  rapidly 
corroding  glass,  which  has  already  been 
alluded  to  as  noticed  by  Margraf.  Experiment  soon  proved  that  great 
analogy  existed  between  the  properties  of  this  new  acid  and  those  of 
hydrochloric  acid ;  and  Ampere  was  led  to  institute  a  comparison  bet\?een 
them,  which  caused  him  to  adopt  the  opinion  that  the  acid  was  a 
hydrogen-acid,  containing  a  new  salt  radical,  which  he  named  fluorine : 
the  name  of  the  acid  was  then  changed  from  fluoric  to  hydrofluoric  acid. 

This  liquid  has  since  been  proved  to  be  a  solution  of  hydrofluoric  acid 
in  water ;  for  if  it  be  distilled  with  phosphoric  anhydride,  which  retains 
the  water,  it  evolves  hydrofluoric  acid  gas,  which  resembles  hydrochloric 
acid  gas  in  fuming  strongly  on  contact  with  moist  air  and  being  eagerly 
absorbed  by  water,  but  has  a  far  more  pungent  odour.  The  perfectly 
dry  gas  has  very  little  action  upon  glass. 

Pure  hydrofluoric  acid  is  prepared  by  heating  dry  potassium  hydro- 
jluate  (KHF2)  to  redness  in  a  platinum  still.  It  is  then  obtained  as  a 
colourless  liquid,  which  boils  at  67°  F.,  and  has  the  specific  gravity 
0-988  at  55°  F.  The  pure  acid  scarcely  aff"ects  metals,  excepting  potas- 
sium and  sodium.  It  corrodes  glass,  however,  rapidly,  though  its  vapour 
has  little  action  on  glass  unless  moisture  is  present.  It  combines  eagerly 
with  sulphuric  and  phosphoric  anhydrides,  with  great  evolution  of  heat, 
a  circumstance  in  which  it  resembles  water,  and  differs  altogether  from 
its  more  obvious  analogue,  hydrochloric  acid.  It  is  also  found  that  it 
combines  energetically  with  the  fluorides  of  potassium  and  sodium,  pre- 
cisely as  water  combines  with  the  oxides  of  those  metals,  whilst  nothing 
of  the  kind  is  noticed  in  the  case  of  hydrochloric  acid. 

It  is  remarkable  that  the  solution  of  hydrofluoric  acid,  in  its  concen- 
trated form,  is  not  so  heavy  as  a  somewhat  weaker  acid.  Thus  the  acid 
of  sp.  gr.  1*06  acquires  the  sp.  gr.  1'15  on  addition  of  a  little  water  ;  but 
on  adding  more  water,  its  sp.  gr.  is  again  reduced.  It  would  hence 
appear  that  the  acid  of  1"15  is  a  definite  hydrate  of  hydi-ofluoric  acid  :  its 

*  The  mineral  kryolite  (fluoride  of  aluminium  and  sodium)  may  be  advantageously  sub- 
stituted for  fluor  spar,  being  more  easily  obtained  in  a  pure  state.  For  preparing  the  acid 
on  a  large  scale,  iron  retorts  are  employed. 


HYDROFLUORIC  ACID.  183 

compositiou  corresponds  to  HF.2H2O.  It"  distils  unchanged  at  248°  F. 
The  sokition  is  generally  kept  in  bottles  made  of  gutta-percha. 

The  action  of  hydrofluoric  acid  upon  metals  and  their  oxides  resembles 
that  of  hydrochloric  acid.  It  dissolves  all  ordinary  metals  except  gold, 
platinum,  silver,  mercury,  and  lead.  Strange  to  say,  it  has  but  little 
action  on  magnesium. 

The  property  which  renders  this  acid  so  useful  to  the  chemist  is  its 
power  of  dissolving  silica  even  in  its  most  refractory  form.  When  sand 
or  flint  reduced  to  powder  is  digested  in  a  leaden  or  platinum  vessel 
with  hydrofluoric  acid,  it  is  gradually  dissolved;  and  if  the  solution 
be  evaporated,  the  whole  of  the  silica  will  be  found  to  have  disappeared 
in  the  form  of  gaseous  silicon  tetrafluoride ;  Si02  +  4HF  =  SiF4  + 2H2O. 
If  the  silica  be  combined  with  a  base,  the  metal  will  be  left  as  a  fluoride, 
decomposable  by  sulphuric  or  hydrochloric  acid.  This  renders  hydro- 
fluoric acid  a  most  valuable  agent  in  the  analysis  of  the  numerous  mineral 
silicates  which  resist  the  action  of  other  acids. 

The  corrosion  of  glass  by  hydrofluoric  acid  is  now  easily  explained. 
Ordinary  glass  consists  of  silicate  of  sodium  or  potassium  combined  with 
silicate  of  calcium  or  lead.  The  hydrofluoric  acid  attacks  and  removes 
the  silica,  and  thus  eats  its  way  into  the  glass. 

In  order  to  demonstrate  the  action  of  this  acid  upon  glass,  a  glass  plate  is  warmed 
sufficiently  to  melt  wax,  a  piece  of  which  is  then  rubbed  over  it,  until  the  glass  is 
covered  with  a  thin  and  pretty  uniform  coating.  Upon  this  a  word  or  drawing  may 
be  engraved  with  a  sharp  point  so  that  the  lines  shall  expose  the  glass.  A  mixture 
of  powdered  fluor  spar  with  concentrated  sulphuric  acid  is  then  poured  over  it,  and 
allowed  to  remain  for  a  quarter  of  an  hour  :  the  acid  mixture  is  washed  off,  aud  the 
plate  gently  warmed  to  melt  the  wax,  which  may  be  wiped  off  with  a  little  tow, 
when  it  will  be  found  that  the  hydrofluoric  acid  evolved  from  the  mixture  has  cor- 
roded those  portions  of  the  glass  from  which  the  graver  had  removed  the  wax.  It 
has  been  attempted  to  apply  this  process  to  the  production  of  engravings,  but  the 
brittleness  of  the  plate  has  formed  a  very  serious  obstacle. 

If  a  leaden  or  platinum  dish  be  at  hand,  it  is  better  to  place  the  glass  to  be  etched 
over  the  dish  containing  the  mixture  of  fluor  spar  and  sulphuric  acid  exposed  to  a 
very  gentle  heat. 

The  solution  of  hydrofluoric  acid  etches  glass  without  deadening  the 
surface,  as  is  the  case  with  the  vapour ;  but  a  solution  of  fluoride  of 
potassium  or  ammonium  mixed  with  sulphuric  acid  does  produce  a  dead 
surface,  and  is  much  used  for  engraving  on  glass.  An  ink  sold  for  writ- 
ing on  glass  with  a  steel  pen  is  composed  of  barium  and  ammonium 
fluorides  and  sulphuric  acid. 

Many  ingenious  experiments  have  been  made  in  order  to  obtain  fluorine 
in  the  separate  state,  but  it  was  found  that  it  invariably  combined  with 
some  portion  of  the  material  of  the  vessel  in  which  the  operation  was 
conducted.  The  most  successful  of  the  early  attempts  to  isolate  fluorine 
appears  to  have  been  made,  at  the  suggestion  of  Davy,  in  a  vessel  of 
fluor  spar  itself,  which  could  not,  of  course,  be  supposed  to  be  in  any 
way  atfected  by  it.  A  greenish  gas  was  obtained,  possessing  chemical 
properties  similar  to  those  of  chlorine,  but  of  much  higher  intensity. 
The  difficulty,  however,  of  obtaining  vessels  of  fluor  spar  adapted  to  these 
experiments  appears  to  have  prevented  any  complete  investigation  of  this 
most  interesting  element.  v» 

The  most  recent  experiments,  in  which  the  tetrafluorides  of  cerium 
and  lead  were  decomposed  by  heat,  have  furnished  a  gas  resembling 
chlorine  in  odour. 


184  FLUORIDE  OF  SILICON. 

Solutions  of  the  fluorides  of  potassium  and  the  other  alkali  metals  cor- 
rode glass  slowly,  like  hydrofluoric  acid.  These  fluorides  are  capable  of 
combining  with  the  acid ;  thus  fluoride  of  potassium  forms  KF.HF, 
which,  when  dry,  is  a  convenient  source  of  hydrofluoric  acid  gas  when 
moderately  heated.  The  only  fluoride  possessed  of  much  practical  in- 
terest beside  the  fluoride  of  calcium,  is  the  mineral  kryoUte  {Kpvo<i,  frost), 
which  is  a  double  fluoride  of  aluminium  and  sodium  (NagAlFg),  found 
abundantly  in  Greenland,  and  valuable  as  a  source  of  aluminium  and 
soda.  The  tojxiz  contains  fluorine,  but  in  what  form  of  combination  is 
not  certain ;  its  other  constituents  are  alumina  aud  silica. 

Magnesium  fluoride  (MgFg)  forms  the  mineral  Sellaite  which  is  found, 
crystallised,  in  Savoy. 

Fluorides  are  also  found,  though  in  very  small  quantity,  in  sea  water, 
and  they  have  been  discovered  in  plants  and  animals.  Human  bone  con- 
tains about  2  per  cent,  of  calcium  fluoride. 

It  will  be  remembered  that  fluorine  is  the  only  element  which  is  not 
known  to  form  any  compound  with  oxygen. 

133.  Silicon  tetrafluoride  (SiF4  =  104  parts  by  weight  =  2  volumes). — 
If  a  mixture  of  powdered  fluor  spar  and  glass  be  heated,  in  a  test-tube 
or  small  flask,  with  concentrated  sulphuric  acid,  a  gas  is  evolved  which 
has  a  very  pungent  odour,  and  produces  thick  Avhite  fumes  in  contact 
with  the  air  :  it  might  at  fii-st  be  mistaken  for  hydrofluoric  acid,  but  if  a 
glass  rod  or  tube  be  moistened  with  water  and  exposed  to  the  gas,  the  wet 
surface  becomes  coated  with  a  white  film,  which  proves,  on  examination, 
to  be  silica.  This  result  originated  the  belief  that  the  gas  consisted  of 
fluoric  (now  hydrofluoric)  acid  and  silica  ;  but  Davy  corrected  this  view 
by  showing  that  it  really  contained  no  oxygen,  and  consisted  solely  of 
silicon  and  fluorine.  The  gas  is  now  called  silicon  tetrafluoride,  and 
represents  silica  in  whicb  the  oxygen  has  been  displaced  by  fluorine  : 
the  change  of  places  between  these  two  elements  in  the  above  experiment 
is  represented  by  the  subjoined  equation — 

2CaF2   +   SiO,   -f-    2H2SO4   =    2CaS04   -f-   SiF^   +   2B..f). 

Fluor  o;ii„.  e„i„i.,.  :„  _-!j  Calcium  Silicon 

«par.  '"^"=''-  Sulphunc  acid.  stt,phate.       tetrafluoride. 

The  formation  of  the  crust  of  silica  upon  the  wetted  surface  of  the 
glass  is  due  to  a  decomposition  which  takes  place  between  the  tetra- 
fluoride and  the  water,  in  which  the  oxygen  and  fluorine  again  change 
places;  SiF^-t- 2H20  =  Si0.2+ 4HF,  Since  this  latter  equation  shows 
that  hydrofluoric  acid  is  again  formed,  it  would  be  expected  that  the 
glass  beneath  the  deposit  of  silica  would  be  found  corroded  by  the  acid; 
this,  however,  is  not  the  case,  and  when  the  experiment  is  repeated  upon 
a  somewhat  larger  scale,  so  that  the  water  which  has  acted  upon  the 
gas  may  be  examined,  it  will  be  found  to  hold  in  solution,  not  hydrofluoric 
acid,  but  an  acid  which  has  little  action  upon  glass,  and  is  composed  of 
hydrofluoric  acid  and  fluoride  of  silicon,  so  that  the  hydrofluoric  acid  pro- 
duced when  water  acts  upon  the  fluoride,  combines  with  a  portion  of  the 
latter  to  produce  the  new  acid  2HF.SiF^,  or  H^SiFg,  hrjdrojluo-silidc  acid. 

For  the  preparation  of  silicon  tetrafluoride,  ]  oz.  of  fluor  spar,  and  1  oz.  of  powdered 
<,'lass  are  mixed  together,  and  heated  in  a  Florence  flask,  with  7  oz.  (measured)  of 
oil  of  vitriol,  the  gas  being  collected  in  dry  bottles  by  downward  displacement  (see 
ticj.  176,  p.  157).  If  a  little  of  the  gas  be  poured  from  one  of  the  bottles  into  a  flask 
lilied  up  to  the  neck  with  water,  the  surface  of  the  latter  will  become  covered  with 


HYDROFLTJO-SILICIC  ACID. 


185 


a  layer  of  silica,  so  that  if  the  flask  be  quickly  inverted,  the  water  will  not  pour  from 
it,  and  will  seem  to  have  been  frozen.  In  a  similar  manner,  a  small  tube  tilled  with 
water  and  lowered  into  a  bottle  of  the  gas,  will  appear  to  have  been  frozen  when 
withdrawn.  A  stalactite  of  silica  some  inches  in  length  may  be  obtained  by  allow- 
ing water  to  drip  gently  from  a  pointed  tube  into  a  bottle  of  the  gas.  Characters 
written  on  glass  with  a  wet  brush  are  rendered  opaque  by  pouring  some  of  the  gas 
upon  them. 

134.  Hydrofluo-silidc  acid  or  silico-fiuoric  acid  (H2SiFg  =  144  parts  by- 
weight). — This  acid  is  obtained  in  solution  by  passing  silicon  tetrafluoride 
into  water — 

3Sir,   +   2H,0   =   2H,SiF,   +   SiO,. 


The  gas  must  not  be  passed  directly  into  the  water,  lest  the  separated 
silica  should  stop  the  orifice  of  the  tube,  to  prevent  which  the  latter 
should  dip  into  a  little  mercury 
at  the  bottom  of  the  water, 
when  each  bubble,  as  it  rises 
through  the  mercury  into  the 
water,  will  become  surrounded 
with  an  envelope  of  gelatinous 
silica,  and  if  the  bubbles  be 
very  regular,  they  may  even 
form  tubes  of  silica  extending 
through  the  whole  height  of 
the  water. 

Crystals  of  H,SiF6,2Aq. 
have  been  obtained  by  passing 
SiF^  into  solution  of  HF. 

For  preparing  hydrofluo-silicic 
acid,  it  will  be  found  convenient  to 
employ  a  gallon  stoneware  bottle 
(tig.  191),  furnished  with  a  wide 
tube  dipping  into  a  cup  of  mercury 
placed  at  the  bottom  of  the  water. 
1  lb.  of  finely  powdered  tluor  spar, 

1  lb.  of  fine  sand,  and  64  measured  ounces  of  oil  of  vitriol  are  introduced  into  the 
bottle,  which  is  gently  heated  upon  a  sand-bath,  the  gas  being  passed  into  about  5 
pints  of  water.  After  six  or  seven  hours  the  water  will  have  become  pasty,  from  the 
separation  of  gelatinous  silica.  It  is  poured  U])on  a  filter,  and  when  the  liquid  has 
drained  through  as  far  as  possible,  the  filter  is  wrung  in  a  cloth,  to  extract  the 
remainder  of  the  acid  solution,  which  will  have  a  sp.  gr.  of  about  1'078. 

A  dilute  solution  of  hydrofluo-silicic  acid  may  be  concentrated  by  evapo- 
ration up  to  a  certain  point,  when  it  begins  to  decompose,  evolving  fumes 
of  silicon  tetrafluoride,  hydrofluoric  acid  remaining  in  solution  and  volatilis- 
ing in  its  turn  if  the  heat  be  continued.  Of  course  the  solution  corrodes 
glass  and  porcelain  when  evaporated  in  them.  If  the  solution  of  hydrofluo- 
silicic  acid  be  neutralised  with  potash,  and  stirred,  a  very  characteristic 
crystalline  precipitate  of  potassium  silico-fluoride  is  formed — 

HgSiFg  -f  2KH0  =  KgSiFg  {Potassium  silico-Jluoride)  +  211^  . 

But  if  an  excess  of  potash  be  employed,  a  precipitate  of  gelatinous  silica 
will  be  separated,  potassium  fluoride  remaining  in  the  soiutioU' — 

HgSiFg   -f-    6KH0    =    6KF    +   4H.p    +    SiO^. 

One  of  the  chief  uses  of  hydrofluo-silicic  acid  is  to  separate  the  potassium 


Fig.  191. — Preparation  of  hydrofluo-silicic 
acid. 


1  86  GENERAL  REVIEW  OF  THE  HALOGENS. 

from  its  combination  with  certain  acids,  in  order  to  obtain  these  in  the 
separate  state. 

135.  Boron  trifiuoride  {BF3)  may  be  prepared  by  a  process  similar  to  that  employed 
for  silicon  fluoride,  but  it  is  also  obtained  by  strongly  heating  a  mixture  of  powdered 
boraeic  anhydride  with  twice  its  weight  of  fluor  spar  in  an  iron  tube  ;  SCaFg  +  BgO , 
=  3CaO  +  2BF3. 

The  boron  fluoride  is  a  gas  wliich  fumes  strongly  in  rtioist  air,  like  the  silicon 
fluoride.  It  is  absorbed  eagerly  by  water,  with  evolution  of  heat.  One  volume  of 
water  is  capable  of  dissolving  700  volumes  of  boron  fluoride,  producing  a  corrosive 
heavy  liquid  (sp.  gr.  1"77),  which  fumes  in  air,  and  chars  organic  substances  on 
accouut  of  its  attraction  for  water.  This  solution  is  known  aa  fiuoboric  or  borofluoric 
acid,  and  its  formation  is  explained  by  the  equation — 

2BF3  +   3H.^0   =   B2O3.6HF  (FZwoftonc  one?). 

When  the  solution  is  heated,  it  evolves  boron  fluoride,  until  its  specific  gravity  is 
reduced  to  1  "58,  when  it  distils  unchanged. 

Hydroflicoboric  acid  is  obtained  in  solution  by  adding  a  large  quantity  of  water  to 
fluoboric  acid  ;  2(B203.6HF)  =  H3BO3  +  SHaO  +  SHBF^  {Hydrofiuoboric  acid). 

This  acid  resembles  the  hydrofluo-silicic  ;  its  hydrogen  may  be  exchanged  for 
metals  to  form  borofliiorides. 

136.  General  review  of  chlorine,  Irromine,  iodine,  and  fluorine. — These 
four  elements  compose  a  natural  group,  the  members  of  whicli  are  con- 
nected by  the  similarity  of  their  chemical  properties  far  more  closely  than 
those  of  any  other  group  of  elements.  They  are  usually  styled  the 
halogens,  from  their  tendency  to  produce  salts  resembling  sea  salt  in  their 
composition  (aAs,  the  sea),  and  such  salts  are  called  haloid  salts.  These 
elements  are  also  called  salt-radicals,  from  their  property  of  forming  salts 
by  direct  union  with  the  metals.  Each  of  these  elements  is  mimatomic, 
and  combines  with  an  equal  volume  of  hydrogen  to  form  an  acid  which 
occupies  the  joint  volumes  of  its  constituents. 

The  halogens  also  supply  the  most  prominent  example  of  the  gradation 
in  properties  sometimes  observed  among  the  members  of  the  same  natui-al 
group  of  elements. 

In  the  order  of  their  chemical  energy,  that  is,  of  the  force  with  which 
they  hold  other  elements  in  chemical  combination  with  them,  fluorine 
s'lould  stand  first,  its  combining  energy  being  so  great  as  to  cause  a  serious 
difficulty  in  isolating  it  all;  chlorine  would  rank  next,  then  bromine,  and 
iodine  last. 

The  atomic  weights  follow  the  inverse  order  of  their  chemical  energies : 
fluorine^  19  ;  chlorine,  35*5;  bromine,  80;  iodine,  127, — numbers  which, 
of  course,  also  represent  their  relative  specific  gravities  in  the  state  of 
vapour. 

A  similar  gradation  is  observed  in  the  physical  state  and  colour  of  those 
three  which  are  well  known,  chlorine  being  a  yellow  gas,  bromine  a  red 
liquid,  boiling  at  145°  F.,  and  iodine  a  black  solid,  boiling  at  347°  F. 

Even  in  the  exceptions  which  occur  to  the  order  of  chemical  energy 
above  alluded  to,  the  same  progression  is  noticed:  thus  fluorine  has  so 
little  attraction  for  oxygen  that  no  oxide  is  known ;  chlorine  has  less 
attraction  for  oxygen  than  bromine  (chloric  acid  being  less  stable  than 
bromic),  whilst  bromine  has  less  than  iodine,  which  is  said  to  be  capable 
even  of  uniting  directly  with  ozonised  oxygen  to  form  iodic  acid. 

The  compounds  of  these  elements  with  hydrogen  are  all  gases  distin- 
guished by  a  powerful  attraction  for  moisture  and  great  similarity  of 
odour. 


OKES  AND  MINERALS  CONTAINING  SULPHUR.  187 

Their  potassium-salts  all  crystallise  in  the  same  (cubical)  form. 

The  silver  fluoride  is  deliquescent  and  soluble  in  water ;  the  chloride 
is  insoluble  in  water,  but  dissolves  very  easily  in  ammonia ;  the  bromide 
dissolves  with  some  difficulty  in  ammonia  ;  and  the  iodide  is  insoluble.    / 

SULPHUR. 

S  =  32  parts  by  weight  =  1  volume  (at  1900°  F.). 

137.  Sulphur  is  remarkable  for  its  abundant  occurrence  in  nature  in 
the  uncombined  state,  in  many  volcanic  districts.  It  is  also  found,  as 
sulphuretted  hydrogen,  in  many  mineral  waters,  and  very  abundantly  in 
combination  with  metals,  forming  the  numerous  ores  known  as  sulphurets 
or  sulphides,  of  which  the  following  are  the  most  abundant: — 

Iron  pyrites,  Iron  disulphide,  FeSg 

Copper  pyrites,  Sulphide  of  iron  .and  copper,  Cu^S-Fe^Sg 

Galena,  Sulphide  of  lead,  PbS 

Blende,  Sulphide  of  zinc,  ZnS 

Crude  antimony.  Sulphide  of  antimony,  SbjSg 

Cinnabar,  Sulphide  of  mercury,  HgS  . 

Sulphur  is  plentifully  distributed  also,  in  combination  with  oxygen 
and  a  metal,  in  the  form  of  sulphates,  of  which  the  most  conspicuous 
are  : — 

Gypsum,  Sulphate  of  calcium,  CaS04.2H20 

Heavy  spar,  Sulphate  of  barium,  BaS04 

Celestine,  Sulphate  of  strontium,  SrS04 

Epsom  salts.  Sulphate  of  magnesium,  MgSO^.ZHjO 

Glauber's  salt.  Sulphate  of  sodium,  Na2S04.  lOHjO. 

In  plants,  sulphur  is  also  found  in  the  fonn  of  sulphates,  and  as  a  con- 
stituent of  the  vegetable  albumen  (of  which  it  forms  about  1*5  per  cent.) 
present  in  the  sap.  It  is  also  contained  in  certain  of  the  essential  oils 
remarkable  for  their  peculiar  pungent  odour,  such  as — 

Esssence  of  garlic,     CgHj^S . 
Essence  of  mustard,  C^H^NS, 

In  animals,  sulphur  occurs  as  sulphates,  as  a  constituent  of  albumen, 
fibrine,  and  caseine  (in  neither  of  which  does  it  exceed  2  per  cent.) ;  and 
in  bile,  one  of  the  products  from  which  (taurine,  CgH^NOgS)  contains  25 
per  cent,  of  sulphur. 

For  our  supplies  of  sulphur  we  are  chiefly  indebted  to  Sicily,  where 
large  quantities  of  it  are  found  in  an  uncombined  state  in  beds  of  blue 
clay.  Magnificent  crystalline  masses  of  strontium  sulphate  are  often 
found  associated  with  it ;  the  sulphur  itself  sometimes  occurs  in  the 
form  of  transparent  yellow  octahedra,  but  more  frequently  in  opaque 
amorphous  masses.  The  districts  in  which  sulphur  are  found  are  usually 
volcanic,  and  those  which  border  the  Mediterranean  are  particularly  rich 
in  it.     Sulphur  has  also  been  found  in  Iceland  and  California. 

The  native  sulphur  being  commonly  distributed  in  veins  through  masses 
of  gypsum  and  celestine  has  to  be  separated  from  these  by  the  action  of 
heat.  When  the  ores  contain  more  than  12  per  cent,  of  siulphur,  the  bulk 
of  it  is  melted  out,  the  ore  being  thrown  into  rough  furnaces  or  cauldrons 
with  a  little  fuel,  and  smothered  up  with  earth,  so  as  to  prevent  the  com- 
bustion of  the  sulphur,  which  runs  down  in  the  liquid  state  to  the  bottom 


188 


EXTRACTION  OF  SULPHUR. 


of  the  cauldron,  and  is  drawn  out  into  wooden  moulds.*  But  when  the 
proportion  of  sulphur  is  small,  the  ore  is  heated  so  as  to  convert  the 
sulphur  into  vapour,  which  is  condensed  in  another  vessel.  The  operation 
is  conducted  in  rows  of  earthen  jars  (A,  fig.  192),  heated  in  a  long  furnace, 
and  provided  with  short  lateral  pipes,  which  convey  the  sulphur  into 
similar  jars  (B)  standing  outside  the  furnace,  in  which  the  vapour  of  sul- 
phur condenses  in  the  liquid  state,  and  flows  out  into  pails  of  water.     The 


Fig.  192. — Distillation  of  sulphur. 

sulphur  obtained  by  this  process  is  imported  as  rough  sulphur,  and  con- 
tains 3  or  4  per  cent,  of  earthy  impurities.  In  order  to  separate  these,  it 
is  redistilled,  in  this  country,  in  an  iron  retort  (A,  fig.  193),  from  which 
the  vapour  is  conducted  into  a  large  brick  chamber  (B),  upon  the  sides  of 
which  it  is  deposited  in  the  form  of  a  pale  yellow  powder  (Jlowei's  of  sul- 
phur, or  sublimed  sulphur).  When  the  operation  has  been  continued  for 
some  time,  the  waUs  of  the  chamber  become  sufficiently  hot  to  melt  the 


Fig.  193. — Sulphur  refinery. 

sulphur,  Avhich  is  allowed  to  collect,  and  afterwards  cast  in  wooden 
moulds,  forming  roll  sulphur  or  brimstone.  Distilled  sulphur  is  obtained 
by  allowing  the  vapour  to  pass  from  the  retort  into  a  small  receiving- 
vessel  (C)  cooled  by  water,  where  it  condenses  in  the  liquid  state :  this 

*  High  pressure  steam  has  been  applied  with  advantage  for  melting  the  sulphur  out  of 
the  ores,  which  are  enclosed  in  an  iron  vessel,  or  the  ores  are  heated  in  a  boiler  with  a  66 
per  cent,  solution  of  calcium  chloride  at  120°  C.  The  sulphur  is  sometimes  extracted  by 
dissolving  it  with  carbon  disulphide. 


SULPHUR  DISTILLED  FROM  PYRITES. 


189 


variety  of  sulphur  is  preferred  for  the  manufacture  of  guripowder,  for 
reasons  which  will  be  stated  hereafter. 

Sulphur  is  readily  distilled  on  a  small  scale  in  a  Florence  flask  (fig.  194),  another 
flask  cut  off  at  the  neck  being  employed  as  a 
receiver.  The  flask  containing  the  sulphur  should 
be  supported  upon  a  thin  iron  wire  triangle,  and 
heated  by  a  gauze-burner,  at  first  gently,  and  after- 
wards to  the  full  heat.  Flowers  of  sulphur  will  at 
first  condense  in  the  receiver,  and  will  be  followed 
by  distilled  sulphur  when  the  temperature  increases. 
A  slight  explosion  of  the  mixture  of  sulphur  vapour 
and  air  may  take  place  at  the  commencement  of  the 
distillation.  An  ounce  of  sulphur  may  be  distilled 
in  a  few  minutes. 


Fig. 


194.— Distillation  of 
sulphur. 


We  are  by  no  means  entirely  dependent 
upon  Sicily  for  sulphur,  for  this  element  can 
be  easily  extracted  from  iron  and  copper  pyrites,  both  of  which  are  found 
abundantly  in  this  country. 

Iron  pyrites  forms  the  yellow  metallic-looking  substance  which  is 
oftsn  met  with  in  masses  of  coal,  sometimes  in  distinct  cubical  crystals,  and 
which  is  to  be  picked  up  in  large  quantities  on  some  sea-beaches,  where  it 
occurs  in  rounded  nodules, 
rusty  outside,  but  having 
a  fine  radiated  metallic 
fracture.  When  this 
mineral  is  strongly  heated^ 
it  gives  up  part  of  its 
sulphur ;  at  a  very  high 
temperature  one-half  of 
the  sulphur  may  be  sepa- 
rated, FeS^  =  FeS  -I-  S,  but 
by  an  ordinary  furnace 
heat  only  about  one-fourth 
can  be  obtained.  The 
distillation  of  iron  pyrites 
is  sometimes  effected  in 
conical  fireclay  vessels  (fig. 
195)  closed  at  the  wider 
end,  and  stopped  towards  the  other  with  a  perforated  plate,  to  allow  the 
passage  of  the  sulphur  vapour.  Each  vessel  contains  100  lbs.  of  pyrites, 
and  yields  14  lbs.  of  sulphur. 

The  sulphur  obtained  in  this  way  has  a  green  colour,  due  to  the  pre- 
sence of  a  little  sulphide  of  iron  carried  over  mechanically  during  the 
distillation  :  in  order  to  purify  it,  it  is  melted  and  allowed  to  cool  slowly, 
when  the  sulphide  of  iron  subsides  :  the  upper  portion  of  the  mass  is  then 
further  purified  by  distillation. 

Sulphur  may  also  be  obtained  from  copper  pyrites  (CuoS.Fe.2S3)  in  the 
process  of  roasting  the  ore,  previously  to  the  extraction  of  the  copper. 
The  ore  is  heaped  up  into  a  pyramid,  the  base  of  which  is  about  30  feet 
square :  a  layer  of  powdered  ore  is  placed  at  the  bottojji,  to  prevent  too 
rapid  access  of  air :  above  this  there  is  a  layer  of  brushwood :  a  wooden 
chimney  is  placed  in  the  centre,  and  is  made  to  communicate  with  air- 
passages  left  between  the  faggots  :  around  this  chimney  the  large  fragments 


Fig.  195. — Furnace  for  distillation  of  sulphur 
from  pyrites. 


190  ACTION  OF  HEAT  UPON  SULPHUR. 

of  the  ore  are  piled  to  a  height  of  about  8  feet,  and  a  layer  of  powdered 
ore,  about  12  inches  deep,  is  strewn  over  the  whole.  The  heap  contains 
about  2000  tons  of  pyrites,  and  will  yield  20  tons  of  sulphur.  The  fire 
being  kindled  by  dropping  lighted  faggots  down  the  chimney,  burns  very 
slowly,  because  of  the  limited  access  of  air,  and  after  a  few  days  sulphur 
is  seen  to  exude  from  the  surface,  and  is  received  in  cavities  made  for 
the  purpose  in  different  parts  of  the  heap.  The  roasting  requires  five  or 
six  months  for  its  completion.  In  this  operation  a  part  of  the  sulphur 
has  been  separated  by  the  mere  action  of  heat,  and  another  part  has  been 
displaced  by  the  oxygen  of  the  air,  which  has  converted  a  portion  of  tlie 
iron  into  an  oxide.  A  part  of  the  separated  sulphur  has  been  burnt,  the 
rest  having  escaped  combustion  on  account  of  the  limited  access  of  air. 

The  sulphur  extracted  from  pyrites  is  generally  found  to  contain  a  little 
arsenic,  which  is  frequently  associated  with  those  minerals.  Immense 
quantities  of  sulphur  are  consumed  in  this  country  for  the  manufacture  of 
sulphuric  acid,  gunpowder,  lucifer  matches,  vulcanised  caoutchouc,  and 
for  making  the  sulphurous  acid  gas  employed  in  bleaching  processes. 

Much  sulphur  has  recently  been  extracted  from  the  tank-waste  of  the 
alkali  works,  by  a  process  which  will  be  described  in  the  manufacture  of 
carbonate  of  soda. 

138.  Properties  of  sulphur. — In  its  ordinary  forms  sulphur  has  a 
characteristic  yellow  colour,  though  milk  of  sulphur,  or  precipitated  sul- 
phur (obtained  by  adding  an  acid  to  the  solution  of  sulphur  in  an  alkali), 
is  white.  It  suffers  electrical  disturbance  with  remarkable  facility,  so 
that  when  powdered  in  a  dry  mortar  it  clings  to  it  with  great  pertinacity. 
One  of  the  most  remarkable  features  of  sulphur  is  its  inflammability, 
due  to  its  tendency  to  combine  with  oxygen  at  a  moderately  elevated 
temperature.  It  melts  at  a  heat  not  much  above  the  boiling-point  of 
water  (239°  F.),  and  inflames  at  about  500°  F.,  burning  with  a  pale  blue 
flame,  and  emitting  the  well-known  suffocating  odour  of  sulphurous  acid 
gas  (SOg).  The  changes  in  the  physical  condition  of  this  element  under 
the  influence  of  heat  are  very  extraordinary.  If 
a  quantity  of  sulphur  be  introduced  into  a  Florence 
flask  and  subjected  to  a  gradually  increasing  heat 
(fig.  196),  it  is  soon  converted  into  a  pale  yellow 
limpid  liquid  (250°  F.),  the  colour  of  which 
becomes  gradually  brown  as  the  temperature  rises, 
until,  at  about  350°  F.,  it  is  nearly  black  and 
opaque,  and  is  so  viscid  that  the  flask  may  be 
inverted  without  spilling  it :  at  this  point  the 
temperature  of  the  sulphur  remains  stationary  for 
a  time,  notwithstanding  that  it  is  still  over  the 
flame,  showing  that  heat  is  becoming  latent  in 
Fie  196  converting  the  sulphur  into  the  new  modification. 

On  continuing  the  heat  the  sulphur  once  more 
becomes  liquid  (500°),  though  not  so  mobile  as  at  first,  and  at  a  much 
higher  temperature  (836°  F.)  it  boils,  and  is  converted  into  a  brownish 
red,  very  heavy  vapour  :  at  this  point  of  the  experiment  an  explosion  of 
the  mixture  of  sulphur  vapour  with  air  often  takes  place.  The  flask 
may  now  be  removed  from  the  flame,  and  a  little  of  the  sulphur  poured 
into  a  vessel  of  water,  through  which  it  will  descend  in  a  continuous 
stream,  forming  a  soft  elastic  string  like  india-rubber  :  the  portion  remain- 


ELECTRO- POSITIVE  AND  ELECTRO-NEGATIVE  SULPHUR,  191 

ing  in  the  flask  will  be  observed,  as  it  cools,  to  pass  again  through  the 
same  states,  becoming  viscid  at  350°,  and  very  liquid  at  250° ;  another 
portion  may  now  be  poured  into  water,  thij-ough  which  it  will  fall  in 
isolated  drops,  solidifying  into  yellow  brittle  crystalline  buttons  of  ordinary 
sulphur.  As  the  portion  of  sulphur  left  in  the  flask  cools,  it  will  be 
found  to  deposit  small  tufts  of  crystals,  and  ultimately  to  solidify  altogether 
to  a  yellow  crystalline  mass. 

The  brown  ductile  sulphur,  when  kept  for  a  few  hours,  will  become  yel- 
low and  brittle,  passing,  in  great  measure,  spontaneously  into  the  crystalline 
sulphur.  The  change  is  accelerated  by  a  gentle  heat,  and  is  attended  with 
evolution  of  the  heat  which  the  sulphur  was  found  to  absorb  at  350°  F. 
Both  these  varieties  of  sulphur  are  of  course  insoluble  in  water,  and  they 
are  not  dissolved  to  any  great  extent  by  alcohol  and  ether.  If  the  crystal- 
line variety  be  shaken  with  a  little  carbon  disulphide,  it  rapidly  dissolves, 
and  on  allowing  the  solution  to  evaporate  spontaneously,  it  deposits 
beautiful  octahedral  crystals,  resembling  those  of  native  sulphur  (Sg.  197). 
Ductile  sulphur,  however,  is  insoluble  in  carbon  disulphide. 

When  flowers  of  sulphur  are  shaken  with  carbon  disulphide,  a  con- 
siderable quantity  passes  into  solution,  the  remainder  consisting  of  the 
amorphous,  or  insoluble  sulphur.  Roll  sulphur  dissolves  to  a  greater 
extent,  and  sometimes  entirely,  in  the  disulphide,  and  distilled  sulphur 
is  always  easily  soluble. 

The  soluble  and  insoluble  forms  of  sulphur  appear  to  represent  distinct 
chemical  varieties  of  the  element.  When  a  solution  of  hydric  sulphide 
(H.^S)  is  decomposed  by  the  galvanic  battery,  the  hydrogen,  as  would  be 
expected,  is  separated  at  the  negative  pole,  and  the  sulphur  at  the  positive 
pole  (p.  8).  The  sulphur,  therefore,  was  the  electro-negative  element  of 
the  compound.  This  sulphur  is  soluble  in  carbon  disulphide.  When 
an  acid  is  added  to  a  solution  of  an  alkaline  sulphide  containing 
more  than  one  atom  of  sulphur,  the  excess  of  the  latter  is  precipi- 
tated, and  is  then  also  found  to  be  soluble  in  carbon  disulphide  ;  for  it 
played  an  electro-negative  part  towards  the  metal  with  which  it  was  in 
combination. 

When  sulphurous  acid  is  decomposed  by  the  battery,  the  sulphur  is 
separated  at  the  negative  pole,  showing  that  it  played  an  electro-positive 
part  in  the  sulphurous  acid.  This  electro-positive  sulphur  is  insoluble  in 
carbon  disulphide.  The  sulphur  in  the  chloride  of  sulphur  (S^Clg)  also 
plays  an  electro-positive  part,  and  accordingly  when  this  compound  is 
decomposed  by  water,  the  sulphur  which  separates  is  insoluble  in  carbon 
disulphide.  The  existence  of  these  two  forms  of  sulphur  affords  some 
support  to  the  theory  of  the  dual  constitution  of  the  elements  noticed  at 
p.  53.  When  a  beam  of  solar  light  is  thrown  by  a  lens  through  a  solu- 
tion of  sulphur  in  carbon  disulphide,  a  precipitation  of  insoluble  sulphur 
takes  place  in  the  track  of  the  beam. 

The  electro-positive  sulphur  would  be  expected  to  manifest  a  greater 
attraction  for  oxygen  than  the  electro-negative  variety,  and  accordingly  it 
is  found  to  be  far  more  easily  oxidised  by  nitric  acid.  Electro-positive  or 
insoluble  sulphur  is  converted  into  electro-negative  or  soluble  sulphur  by 
the  action  of  a  moderate  heat,  itself  evolving  heat  durieg  the  process  of 
conversion  :  when  melted  in  contact  with  sulphurous  acid  gas,  the 
soluble  sulphur  is  converted  externally  into  the  insoluble  form. 

Crystalline  or  soluble  sulphur  is  capable  of  existing  in  two  distinct 


192 


ALLOTROPIC  FORMS  OF  SULPHUR. 


Fig.  197. 


Fig.  198. 


forms.     The  natural  form  of  crystallised  sulphur  is  the  octahedron  with 
a  rhombic   base  (fig.   197),  and  this  is  the  usual  form   which  sulphur 

assumes  when  crystallised  from  its  solutions. 
But  if  sulphur  be  melted  in  a  covered 
crucible,  allowed  to  cool  until  the  surface 
has  congealed,  and  the  remaining  liquid 
portion  poured  out  after  piercing  the  crust 
(with  two  holes,  one  for  admission  of  air), 
the  crucible  will  be  lined  with  beautiful 
needles,  which  are  oblique  prisms  (fig.  198). 
These  crystals  are  brownish  -  yellow  and 
transparent,  when  freshly  made,  but  they 
soon  become  opaque  yellow;  and  although 
Ihey  retain  their  prismatic  appearance,  they  have  now  changed  into  minute 
rhombic  octahedra,  the  change  being  attended  with  evolution  of  heat.* 
On  the  other  hand,  if  a  crystal  of  octahedral  sulphur  be  exposed  for  a 
short  time  to  a  temperature  of  about  230°  F.  (in  a  boiling  saturated 
solution  of  common  salt,  for  example),  it  becomes  opaque,  in  consequence 
of  the  formation  of  a  number  of  minute  prismatic  crystals  in  the  mass. 

The  difference  between  these  two  forms  of  crystalline  sulphur  extends 
to  their  fusing-points  and  specific  gravities,  the  prismatic  sulphur  fusing  at 
248°  F.,  and  the  octahedral  sulphur  at  239°  F.,  the  specific  gravity  of 
the  prisms  being  1"98,  and  that  the  octahedra  2*05. 

Eoll  sulphur  when  freshly  made,  consists  of  a  mass  of  oblique  prismatic 
crystals,  but  after  being  kept  for  some  time,  it  consists  of  octahedra,  although 
the  mass  generally  retains  the  specific  gravity  proper  to  the  prismatic  form. 
This  change  in  the  structure  of  the  mass,  taking  place  when  its  solid 
condition  prevented  the  free  moA'^ement  of  the  particles,  gives  rise  to  a 
state  of  tension  which  may  account  for  the  extreme  brittleness  of  roll  sul- 
]ihur.  If  a  stick  of  sulphur  be  held  in  the  warm  hand,  it  often  splits, 
from  unequal  expansion.  These  peculiarities  of  sulphur  deserve  careful 
study,  as  helping  to  elucidate  the  spontaneous  alterations  in  the  structure 
of  glass,  iron,  &c.,  under  certain  conditions. 

Flowers  of  sulphur  do  not  present  a  crystalline  structure,  but  consist  of 
spherical  granules  composed  of  insoluble  sulphur  enclosing  soluble  sulphur. 
Hot  oil  of  turpentine  dissolves  sulphur  freely,  and  when  the  solution  is 
allowed  to  stand,  the  crystals  which  are  deposited  whilst  the  solution  is 
hot  have  the  prismatic  form,  but  as  it  cools,  octahedra  are  separated. 
The  following  table  exhibits  the  chief  allotropic  forms  of  sulphur  : — 


Sp.  jfr. 

Fusing  point     In  Carbon  DlsuIpUde 

Octahedral      .     . 
Electro-negative . 

:  i 

2-05 

239°  F.              Soluble. 

Prismatic  . 

1-98 

248°                   Soluble. 

Ductile      .     .     . 

:  ) 

Amorphous     . 

. 

1-96 

Becomes  octahedral.    Insoluble. 

Electro-positive  . 

. 

The  octahedral  is  by  far  the  most  stable  of  the  three,  and  is  the  ultimate 
condition  which  the  others  assume. 

Other  varieties  of  sulphur,  such  as  a  black  and  a  red  modification,  have 
been  described,  but  they  are  of  minor  importance. 

*  Spring  lias  sliown  that  a  pressure  of  6000  atmospheres  converts  prismatic  sulphur  and 
plastic  sulphur  into  the  octahedral  variety. 


SPECIFIC  GEAVITY  OF  SULPHUR  VAPOUE.  19'3 

Sulphur  is  capable  of  entering  into  direct  combination  with  several  other 
elements.  It  unites  with  chlorine  und  Avith  some  of  the  metals,  if  hnely 
divided,  even  at  the  ordinary  temperature,  and  it  is  capable  of  combining 
at  a  high  temperature  with  all  the  non-metals  except  nitrogen,  and  with 
nearly  all  the  metals. 

If  a  mixture  of  2  parts  of  copper  filings  and  1  part  of  sulphur,  or  of  equal  weights 
of  iron  tilings  and  sulphur,  be  heated  in  a  Florence  flask  or  a  test-tube,  the  combina- 
tion will  be  attended  with  vivid  combustion. 

The  so-called  Lemery's  volcano  was  made  by  mixing  iron 
filings  with  two-thirds  of  their  weight  of  powdered  sulphur, 
and  burying  several  pounds  of  the  moist  mixture  in  the 
earth,  when  the  heat  evolved  by  the  rusting  of  part  of  the 
iron  provoked  the  energetic  combination  of  the  remainder 
with  the  sulphur,  and  the  consequent  development  of  much 
steam.*  Firework  compositions  containing  iron  filings 
and  sulphur  may  cause  ignition  if  damp. 

Several  metals  may  be  made  to  burn  in  sulphur  vapour, 
as  in  oxygen,  by  heating  the  sulphur  in  a  Florence  flask, 
with  a  gauze  burner,  so  as  to  keep  the  flask  constantly  filled 
with  the  brown  vapour.  Potassium  and  sodium,  introduced 
in  deflagrating  spoons,  take  fire  spontaneously  in  the 
vapour  (tig.  199). 

A  coil  of  copper  wire  glows  vividly  in  sulphur  vapour,  .  """ 

and  becomes  converted  into  a  brittle  mass  of  sulphide  of  *''§•  199. 

copper.     When  sulphur  is  exposed  to  sunshine  in  an  at- 
mosphere of  hydride  of  antimony  or  arsenic,  it  becomes  converted  into  hydrosulphuric 
acid  gas  and  sul[)hide  of  antimony  or  arsenic. 

Sulphur  dissolves,  though  slowly,  in  boiling  concentrated  nitric  and 
sulphuric  acids,  being  oxidised  by  the  former  into  sulphuric  acid,  and  by 
the  latter  into  sulphur  dioxide.  It  is  far  more  rapidly  converted  into 
sulphuric  acid  by  a  mixture  of  nitric  acid  and  potassium  chlorate.  The 
alkalies  dissolve  sulphur  when  heated,  yielding  yellow  or  red  solutions 
which  contain  hyposulphites  and  sulphides  of  the  alkali  metals. 

There  is  a  very  general  resemblance  in  composition  between  the  com- 
pounds of  sulphur  and  those  of  oxygen  vv'ith  the  same  elements. 

139.  Influence  of  temperature  upon  the  specific  gravity  of  gases  and 
vapours. — The  specific  gravity  of  a  gas  or  vapour  being  defined  as  its 
weight  compared  with  that  of  an  equal  volume  of  dry  and  pure  air  at  the 
same  temperature  and  pressure,  it  might  be  supposed  that  so  long  as  the 
temperatures  were  equal,  their  actual  thermometric  value  would  not  in- 
fluence the  specific  gravity.  Indeed,  with  those  gases  and  vapours  which 
are  condensible  with  difficulty,  this  is  actually  the  case.  Thus,  if  equal 
volumes  ^f  oxygen  and  air  be  weighed,  either  at  a  low  or  a  high  tempera- 
ture, provided  their  temperatures  are  the  same,  their  weights  will  always 
stand  to  each  other  nearly  in  the  ratio  of  1-1057  :  1. 

But  with  many  vapours  it  is  found  that  if  they  be  weighed  at  tempera- 
tures too  nearly  approaching  to  their  condensing  points,  their  specific 
gravities  are  much  higher  than  they  are  found  to  he  at  higher  tempera- 
tures. Sulphur  aifords  a  very  well-marked  instance  of  this.  It  boils  at 
836°  F.,  and  if  its  vapour  be  weighed  at  a  temperature  of  900°F.,  it  is 
found  to  weigh  6*617  times  as  much  as  an  equal  volume  of  air  at  900°  F., 
so  that  it  is  96  times  as  heavy  as  hydrogen,  or  1  atom  (j;f  sulphur  would 

*Rust-joint  cement  is  a  mixture  of  80  parts  iron  fib'ngs,  1  of  sal  ammoniac,  and  2  of  sul- 
phur, made  into  a  paste  with  water  ;  it  is  vfery  useful  for  making  the  joints  of  iron  tubes 
air-tight,  for  it  sets  into  a  hard  cement,  the  iron  combining  with  the  sulphur. 

£1 


194 


SOURCES  OF  SULPHURETTED  HYDROGEN. 


occupy  J  volume.  But  if  the  vapour  of  sulphur  be  weighed  at  1900°  R,  it 
is  found,  to  weigh  only  2 "23  times  as  much  as  an  equal  volume  of  air  at 
the  same  temperature  and  pressure,  so  that  it  is  only  32  times  as  heavy 
as  hydrogen,  and  1  atom  of  sulphur  occupies  1  volume. 

According  to  Troost,  the  sulphur  vapour  at  900°  F.  is  really  a  con- 
densed molecule,  like  ozone,  since  its  specific  gravity  remains  unaltered 
under  diminished  pressure. 


Hydrosulphuric  Acid. 

HoS  =  34  parts  by  weight  =  2  volumes. 

140.  Sulphuretted  hydrogen  or  hydric  sulphide,  or  hydrosulphuric  acid, 
has  been  already  mentioned  as  occurring  in  some  mineral  waters,  as  at 
Harrowgate.  It  is  also  found  in  the  gases  emanating  from  volcanoes, 
sometimes  amounting  to  one-fourth  of  their  volume.  It  is  a  product  of 
the  putrefaction  of  organic  substances  containing  sulphur,  and  is  one  of 
the  causes  of  the  sickening  smell  of  drains,  &c.  Eggs,  which  contain  a 
considerable  proportion  of  sulphur,  evolve  sulphuretted  hydrogen  as  soon 
as  they  begin  to  change,  and  hence  the  association  between  this  gas  and 
the  "  smell  of  rotten  eggs."  The  same  smell  is  observed  when  a  kettle 
boils  over  upon  a  coke  or  coal  fire,  the  hydrogen  liberated  from  the  water 
combining  with  the  sulphur  present  in  the  fuel. 

Hydrosulphuric  acid  is  also  found  among  the  products  of  destructive 
distillation  of  organic  substances  containing  sulphur ;  it  was  mentioned 
among  the  products  from  coal,  in  which  it  is  for  the  most  part  combined 
Avith  the  ammonia  formed  at  the  same  time,  producing  ammonium 
sulphide. 

It  may  be  produced,  though  not  in  large  quantity,  by  the  direct  union 
of  hydrogen  with  sulphur  vapour  at  a  high  temperature,  or  by  passing  a 
mixture  of  sulphur  vapour  and  steam  through  a  tube  filled  with  red  hot 
pumice  stone  (the  latter  encouraging  the  action  by  its  porosity).  Hydro- 
sulphuric acid  is  more  readily  formed  by  heating  a  damp  mixture  of 

sulphur  and  wood  charcoal, 
and  may  be  obtained  in  large 
quantity  by  heating  a  mix- 
ture of  equal  weights  of 
sulphur  and  tallow,  the  latter 
furnishing  the  hydrogen. 

Preparation  of  hydrosul- 
phuric acid. — For  use  in  the 
laboratory,  where  it  is  very 
largely  employed  in  testing 
for  and  separating  metals, 
hydrosulphuric  acid  is  gener- 
ally prepared  by  decomposing 
ferrous  sulphide  with  diluted 
sulphuric  acid ;  FeS  +  H^Sp^ 
=  HgS  -f  FeSO^  {/eivous  sul- 
phate). 


Fig.  200. 


To  obtain  ferrous  sulphide,  a  mixture  of  3  parts  of  iron  filings  with  2  parts  of 
flowers  of  sulphur  is  thrown,  by  small  portions  at  a  time,  into  an  earthen  crucible 
( A,  fig.   200)  heated  to  redness  in  a  charcoal  fire,  the  crucible  being  covered  after 


PREPARATION  OF  SULPHURETTED  HYDROGEN.  195 

each  portion  has  been  added.     The  iron  and  sulphur  combine,  with  combustion,  and 

wlien  the  whole  of  the  mixture  has  been  introduced,  th^  crucible  is  allowed  to  cool, 

the  mass  of  ferrous  sulphide  broken  out,  and  a  few  fragments  of  it  are  introduced 

into  a  bottle  (tig.  201)  provided  with  a  funnel  tube  for  the  addition  of  the  acid,  and 

a  bent  tube  for  conducting  the  gas  through  a  small 

quantity  of  water,  to  remove  any  splashes  of  ferrous 

sulphate.     From  the  second  bottle  the  gas  is  conducted 

by  a  glass  tube  with  a  caoutchouc  joint,  either  down 

into  a  gas-bottle,  or  into  water,   or  any  other  liquid 

upon  which  the  gas  is  intended  to  act.     The  fragments 

of  ferrous  sulphide  should  be  covered  with  enough 

water  to  till  the  gas-bottle  to  about  one-third,  and 

strong  sulphuric  acid  added  by  degrees  through  the 

funnel,  the  bottle  being  shaken  until  effervescence  is 

observed.     An  excess  of  strong  sulphuric  acid  stops 

the  evolution  of  gas  by  precipitating  a  quantity  of       ^^S-  201. — Preparation  of 

white  anhydrous  ferrous  sulphate,  which  coats  the  hydro.sulphuric  acid. 

suipliide  and  defends  it  from  the  action  of  the  acid. 

When  no  more  gas  is  required,  the  acid  liquid  should  be  at  once  poured  away,  leaving 

the  fragments  of  ferrous  sulphide  at  the  bottom  of  the  bottle  for  a  fresh  operation. 

The  liquid,  if  set  aside,  will  deposit  beautiful  green  crystals  of  copperas  or  ferrous 

sulphate  (FeSO^,  THjO). 

Since  the  feirous  sulphide  prepared  as  above  generally  contains  a  little  metallic 
iron,  the  sulphuretted  hydrogen  is  mixed  with  free  hydrogen,  which  does  not  gene- 
rally interfere  with  its  uses.  The  pure  gas  may  be  prepared  by  heating  antimony  sul- 
phide (crude  antimony)  in  a  flask  with  hydrochloric  acid — 

Sb^Sj  -I-   6HC1  =  3H,S   +  2SbCl3. 

If  hydrochloric  acid  be  diluted  with  more  than  6  molecules  of  water,  it  is  not 
capable  of  decomposing  the  antimony  sulphide ;  hence,  w-hen  the  sulphide  is  heated 
with  an  acid  somewhat  stronger  than  this,  the  subsequent  addition  of  water  repre- 
cipitates  the  antimony  sulphide  with  the  orange  colour  which  it  always  presents 
when  precipitated. 

Properties  of  kydrosulphuric  acid. — This  gas  is  at  once  distinguished 
f  .'oni  all  others  by  its  disgusting  odour.  It  is  one-fifth  heavier  than  air 
(sp.  gr.  1'1912).  Its  gaseous  state  is  not  permanent,  but  a  pressure  of 
17  atmospheres  is  required  to  reduce  it  to  a  colourless  liquid,  which 
congeals  to  a  transparent  solid  at  -  122°  F.  Water  absorbs  about  three 
times  its  volume  of  sulphuretted  hydrogen  at  the  ordinary  temperature  ; 
both  the  gas  and  its  solution  are  feebly  acid  to  blue  litmus  paper.  The 
gas  is  very  combustible,  burning  with  a  blue  flame  like  that  of  sulphur, 
and  yielding,  as  the  chief  products,  water  and  sulphurous  acid  gas  HgS 
4- O3  =  H^O  +  SO2  ;  a  little  sulphuric  acid  (H.2SO4)  is  also  formed,  and 
unless  the  supply  of  air  is  very  good ,  some  of  the  sulphur  wUl  be  separated ; 
thus,  if  a  taper  be  applied  to  a  bottle  filled  with  sulphuretted  hydrogen, 
a  good  deal  of  sulphur  will  be  deposited  upon  the  sides.  This  combusti- 
bility of  sulphuretted  hydrogen  is  of  the  greatest  importance  in  those 
l)rocesses  of  chemical  manufacture  in  which  this  gas  is  evolved  (as  in  the 
preparation  of  ammoniacal  salts  from  gas  liquors),  enabling  it  to  be  dis- 
posed of  in  the  furnace  instead  of  becoming  a  nuisance  to  the  neighbour- 
hood. The  gas  causes  fainting  when  inhaled  in  large  quantity,  and 
appears  much  to  depress  the  vital  energy  when  breathed  for  any  length 
of  time  even  in  a  diluted  state. 

"When  dissolved  in  water,  hydrosulphuric  acid  is  slowly  acted  upon  by 
the  oxygen  of  the  air,  which  converts  its  hydrogen  into  water,  and  causes 
a  white  deposit  of  (electro-negative  or  soluble)  sulphur. 

This  is  a  great  drawback  to  the  use  of  this  indispensable  chemical  in  the  labor- 
atory, since  the  solution  of  hydrosulphuric  acid  is  so   soon  rendered   useless.     To 


196  PROPERTIES  OF  HYDROSULPHURIC  ACID. 

obviate  it  as  far  as  possible,  the  solution  should  be  made  either  with  boiled  water  (free 
from  dissolved  air),  or  with  water  which  has  already  been  once  charged  with  the  gas 
and  spoilt  by  keeping,  for  all  the  oxygen  dissolved  in  this  water  will  have  been  con- 
sumed by  the  former  portion  of  gas.  The  gas  should  be  passed  through  the  water 
until,  on  closing  the  bottle  with  the  hand  and  shaking  violently,  the  pressure  is 
found  to  act  outwards,  showing  the  water  to  be  saturated  with  the  gas.  By  closing 
the  bottle  with  a  greased  stopper,  and  inverting  it,  the  solution  may  be  preserved 
for  some  weeks,  even  though  occasionally  opened  for  use. 

In  preparing  the  solution  of  hydrosulphuric  acid,  a  certain  quantity  of  the  gas 
always  escapes  absorption.  .  To  prevent  this  from  becoming  a  nuisance,  the  bottln 
containing  the  water  to  be  charged  with  gas  may  be  covered  with  an  air-tight 
caoutchouc  cap  having  two  tubes,  through  one  of  which  passes  the  glass  tube  con- 
veying the  gds  down  into  the  water,  and  through  the  other,  a  tube  conducting  the 
excess  of  gas  either  into  a  gas-burner,  where  it  may  be  consumed,  or  into  a  solution  of 
ammonia  which  will  absorb  it,  forming  the  very  useful  ammonium  sulphide. 

Concentrated  nitric  acid  acts  upon  hydric  sulphide,  oxidising  the 
hydrogen  and  a  part  of  the  sulphur,  ammonium  sulphate  being  found  in 
the  solution,  and  a  pasty  mass  of  sulphur  separated.  Chlorine,  bromine, 
and  iodine  at  once  appropriate  its  hydrogen  and  separate  the  sulphur. 

The  hydrogen  of  the  hydrosulphuric  acid  is  oxidised  immediately  by 
nitrous  anhydride  (^N'gO^),  the  sulphur  being  separated,  and  a  considerable 
quantity  of  ammonia  produced  ;  NgO^  ■+-  6H2S  =  2NH3  -f  SHqO  +  Sg  . 

In  its  action  upon,  the  metals  and  their  oxides,  hydrosulphuric  acid 
resembles  hydrochloric  and  the  other  hydrogen  acids.  Many  of  the  metals 
displace  the  hydrogen  and  form  metallic  sulphides.  This  usually  requires 
the  assistance  of  heat,  but  mercury  and  silver  act  upon  the  gas  at  the 
ordinary  temperature.  Thus,  if  hydric  sulphide  be  collected  over  mercury, 
the  surface  of  the  latter  becomes  coated  with  a  black  film  of  mercurous 
sulphide  ;  H^S  +  Hgg  =  H2  -f  Hg.^S.  In  a  sinular  way  the  surface  01 
silver  is  slowly  tarnished  when  exposed  to  air  containing  sulphuretted 
hydrogen,  its  surface  being  covered  with  a  black  film  of  silver  sulphide. 
It  is  on  this  account  that  silver  plate  is  so  easily  blackened  by  the 
air  of  towns.  An  egg  spoon  is  always  blackened  by  the  sulphur  from  the 
egg.  Silver  coins  kept  in  the  pocket  with  lucifer  matches  are  blackened, 
from  the  formation  of  a  little  silver  sulphide.  The  original  brightness 
of  the  coin  may  be  restored  by  rubbing  it  with  a  solution  of  potassium 
cyanide,  which  dissolves  the  silver  .sulphide.  Friction  with  strong 
ammonia  will  also  remove  the  tarnish,  and  its  application  is  safer  than 
that  of  the  poisonous  cyanide. 

When  heated  in  the  gas,  several  metals  displace  the  hydrogen  from  it. 
Thus,  potassium  acts  upon  it  in  a  corresponding  manner  to  that  in  which 
it  acts  upon  water,  ioTming  potassium  hydrosulpJiide  (KHS). 

Tin  removes  the  whole  of  the  sulphur  from  hydrosulphuric  acid  at  a 
moderate  heat ;  Sn  +  HgS  =  Hg  +  SnS  . 

When  hydrosulphuric  acid  acts  upon  a  metallic  oxide,  it  generally  con- 
verts it  into  a  sulphide  corresponding  to  the  oxide,  whilst  the  hydrogen 
and  oxygen  unite  to  form  water.  Lead  oxide  in  contact  with  the  gas 
yields  black  lead  sulphide  and  water ;  PbO  -I-  HgS  =  PbS  4-  HgO.  Paper 
impregnated  with  a  salt  of  lead  is  used  as  a  test  for  the  presence  of  this 
gas.  Thus,  if  paper  be  spotted  with  a  solution  of  lead  nitrate  (or  acetate) 
it  will  indicate  the  presence  of  even  minute  quantities  of  hydric  sulphide 
(in  impure  coal  gas,  for  example)  by  the  brown  colour  imparted  to  the 
spots — 

Pb(:N'03)2  +  HgS  =  2HXO3  -1-  PbS. 


SULPHIDES  OF  THE  METALS.  197 

It  is  in  tins  manner  that  paints  containing  whij.e  lead  (lead  carbonate) 
are  darkened  by  exposure  to  the  air  of  towns.  Cards  glazed  with  white 
lead,  and  engravings  on  paper  whitened  with  that  substance,  suffer  a 
similar  change.  Paintings,  whether  in  oil  or  water-colours,  in  which 
lead  is  an  ingredient,  are  also  injured  by  air  containing  sulphuretted 
hydrogen.  It  has  been  found  that  such  colours,  damaged  by  the  forma- 
tion of  lead  sulphide  are  restored  by  the  continued  action  of  light  and  air, 
the  black  sulphide  becoming  oxidised  and  converted  into  the  white 
sulphate,  PbS  +  O^  =  PbSO^.  In  the  dark  this  restoration  does  not  takf* 
place,  so  that  it  is  often  a  mistake  to  screen  pictures  from  the  light  by  a 
curtain. 

The  action  of  hydrosulphuric  acid  upon  the  chlorides  and  other  haloid 
salts  of  the  metals  generally  resembles  its  action  upon  the  oxides  of  the 
same  metals. 

Most  of  the  sulphides  of  the  metals,  like  the  corresponding  oxides,  are 
insoluble  in  water,  but  many  of  the  sidphides  are  also  insoluble  in  diluted 
acids  and  in  alkalies,  so  that  when  hydrosulphuric  acid  is  brought  into 
contact  with  the  solutions  of  metals,  it  will  often  precipitate  the  metal  in 
the  form  of  a  sulphide  having  some  characteristic  colour  or  other  property 
by  which  the  metal  may  be  identified. 

Any  solution  of  lead  will  give  a  black  precipitate  with  solution  of  hydrosulphuric 
acid,  the  lead  sulphide  being  insoluble  in  diluted  acids  and  in  alkalies. 

A  solution  of  antimony  (tartar-emetic,  for  example,  the  tartrate  of  antimony  and 
potassium)  mixed  with  an  excess  of  hydrochloric  acid,  gives  an  oran^c-coloured  pre- 
cipitate (SbjSg)  on  adding  hydrosulphuric  acid  ;  but  if  another  portion  be  mixed  with 
an  excess  of  potash  before  adding  the  hydrosulphuric  acid,  there  will  be  no  precipi- 
tate, for  the  antimony  sulphide  is  soluble  in  alkalies. 

Cadmium  chloride  gives  a  brilliant  yellow  precipitate  of  cadmium  sulphide  on 
adding  hj'Jrosulphuric  acid. 

Zinc  sulphate  yields  a  %chifc  precipitate  of  zinc  sulphide  (ZnS),  but  if  a  little  hydro- 
chloric acid  be  previously  added,  no  precijjitate  is  formed,  the  zinc  sulphide  being 
soluble  in  acids.  On  neutralising  the  hydrochloric  acid  with  ammonia,  the  zinc 
sulphide  is  at  once  precipitated. 

It  is  evident  that,  in  a  solution  containing  cadmium  and  zinc,  the  metals  may  be 
separated  by  acidifying  the  liquid  with  hydrochloric  acid,  and  adding  excess  of 
hydrosulphuric  acid,  which  precipitates  the  cadmium  sulphide  only.  On  filtering 
the  solution,  and  adding  ammonia,  the  zinc  sulphide  is  precipitated. 

Sulphur- acids  and  sulphtcr-bases. — Those  sulphides  which  are  soluble 
in  the  alkalies  are  often  designated  sulphur-acids,  whilst  the  sulphides  of 
the  alkali  metals  are  sulphur-bases.  These  two  classes  of  sulphides  com- 
bine to  form  sulphur-salts  analogous  in  composition  to  the  oxygen-salts  of 
the  same  metals.     Thus,  there  have  been  crystallised,  the  salts — 

Sodium  sulphostannate,         .         .         .        ^Na^SnS^ . 
,,       sulphantimoniate,     .         .         .        NaSbSg . 
,,       sulpharseniate,  .         .         .        Na3AsS4 . 

The  action  of  air  iipon  the  sulphides  of  the  metals  is  often  turned  to 
account  in  chemical  manufactures.  At  the  ordinary  temperature,  the 
sulphides  of  those  metals  which  form  alkaline  oxides  (such  as  sodium 
and  calcium),  when  exposed  to  the  air  in  the  presence  of  water,  yield 
first,  mixtures  of  the  hydrate  and  bisulphide,  SNa.^S -f-^O -t- H2O  —  NugSj 
+  2NaH0 ;  and  afterwards  the  hyposulphite,  'NaS^  +  0^  =  l^a.jSJJ^.  This 
change  is  sometimes  turned  to  account  for  the  manufacture  of  sodium 
hyposulphite. 


198  PERSULPHIDE  OF  HYDEOGfEN. 

When  the  metal  forms  a  less  powerful  base  with  oxygen,  the  sulphide 
is  often  converted  into  sulphate  by  exposure  to  moist  air ;  thus,  CuS 
+  O4  =  CuSO^,  which  is  taken  advantage  of  for  the  separation  of  copper 
from  tin  ores. 

Tlie  black  ferrous  sulphide  (FeS),  when  exposed  to  moist  air,  becomes' 
converted  into  red  ferric  oxide,  with  separation  of  sulphur,  2FeS  +  O3 
=  FcgOg  +  Sg,  a  change  which  enables  the  gas  manufacturer  to  revive,  by 
the  action  of  air,  the  ferric  oxide  employed  for  removing  the  sulphuretted 
hydrogen  from  coal  gas. 

When  roasted  in  air  at  a  high  temperature,  the  sulphides  correspond- 
ing to  the  more  powerful  bases  are  converted  into  sulphates ;  thus, 
ZnS  +  04  =  ZnS04,  which  explains  the  production  of  zinc  sulphate  by 
roasting  blende.  But  in  most  cases  part  of  the  sulphur  is  converted  into 
sulphurous  acid  gas  at  the  same  time.  Cuprous  sulphide,  for  instance,  is 
partly  converted  into  cupric  oxide  by  roasting,  CugS  +  O4  =  2CuO  +  SOg, 
a  change  of  great  importance  in  the  extraction  of  copper  from  its  ores. 

141.  Hydric  persulpMde. — The  composition  of  this  substance  is  not  yet  satisfactorily 
ascertained.  The  similarity  of  its  chemical  properties  to  those  of  hydric  peroxide 
prompts  the  wish  that  its  formula  may  be  H2S2.  Some  analyses,  however,  seem  to 
lead  to  the  formula  HgSj,  but  since  the  persulphide  is  a  liquid  capable  of  dissolving 
free  sulphur,  which  is  not  easily  separated  from  it,  there  is  much  difficulty  in  deter- 
mining the  exact  proportion  of  this  element  with  which  the  hydrogen  is  combined. 

When  equal  weights  of  slaked  lime  and  sulphur  are  boiled  with  water,  an  orange- 
coloured  liquid  is  formed,  which  contains  calcium  hyposulphite,  calcium  disulphide, 
and  calcium  pentasulphide  (CaSj)  ;  3CaO  +  S8  =  CaSjj03  +  2CaS.2. 

When  hydrochloric  acid  is  added  to  the  filtered  solution,  an  abundant  precipitation 
of  sulphur  occurs,  and  much  hydrosulphuric  acid  is  evolved — 

CaSj   +   2HCI  =  CaCla   +   HjjS   +   S. 

But  if  the  solution  be  poured  by  degrees  into  a  slightly  warm  mixture  of  hydro- 
chloric acid  with  twice  its  bulk  of  water,  and  constantly  stirred,  a  yellow  heavy  oily 
liquid  collects  at  the  bottom,  which  is  the  hydric  persulphide — 

CaS.^   +   2HC1  =   H2S2  (?)   +   CaCljj. 

The  acid  having  been  kept  in  excess,  the  persulphide  has  been  preserved  from  the 
decomposition  which  it  suffered  in  the  presence  of  the  alkaline  solution  in  the 
former  experiment.  For  the  hydric  persulphide  very  closely  resembles  the  peroxide 
in  the  facility  with  which  it  may  be  decomposed  into  hydrosulphuric  acid  and  sulphur  ; 
It  undergoes  spontaneous  decomposition  even  in  sealed  tubes,  and  the  hydrosulphuric 
acid  then  becomes  liquefied  by  its  own  pressure.  Most  of  the  substances,  the  contact 
of  which  promotes  the  decomposition  of  the  hydric  peroxide,  have  the  same  effect 
upon  the  persulphide.  This  compound  has  a  peculiar  odour,  which  afieets  the  eyes ; 
of  course,  its  vapour  is  mixed  with  that  of  hydrosulphuric  acid  resulting  from  its 
decomposition. 

Oxides  of  Sulphur. 

1 42.  Only  two  compounds  of  sulphur  with  oxygen  have  been  obtained 
ill  the  separate  state,  viz.,  sidphuroiis  anhydride  (SOg)  aud  sulphuric 
anhydride  (SOg). 

Sulphur  Dioxidk  or  Sulphurous  Anhydride. 
SO2  =  64  parts  by  weight  =  2  volumes. 

143.  In  nature,  sidphurous  acid  gas  is  but  rarely  met  with;  it  exists 
in  the  gases  issuing  from  volcanoes.  Although  constantly  discharged 
into  the  air  of  towns  by  the  combustion  of  coal  (containing  sulphur),  it  is 
so  easily  oxidised  and  converted  into  sulphuric  acid  that  no  considerable 


PREPARATION  OF  SULPHUR  DIOXIDE.  199 

quantity  is  ever  foimd  in  the  atmosphere.  Sulphurous  acid  gas  has  been 
already  mentioned  as  the  sole  product  of  the  combustion  of  sulphur  in  dry 
air  and  oxygen,*  but  it  is  generally  prepared  for  chemical  purposes  by 
removing  part  of  the  oxygen  from  sulphuric  acid,  which  is  easily  effected 
by  heating  it  with  metallic  copper — 

2H,S04   +    Cu   =   CUSO4   +    2H2O   +   SO,. 

Sulphuric  acid.  Copper  sulphate. 

300  grains  of  copper  clippings  are  heated  in  a  Florence  flask  with  4  oz.  (measured) 
of  strong  sulphuric  acid,  the  gas  being  conducted  by  a  bent  tube  down  to  the  bottom 
of  a  dry  bottle  closed  with  a  perforated  card  (see  tig.  176,  p.  157).  Some  time  will 
elapse  before  the  gas  is  evolved,  for  sulphuric  acid  acts  upon  copper  only  at  a  high 
temperature  ;  but  when  the  evolution  of  gas  fairly  commences,  it  will  proceed  very 
rapidly,  so  that  it  is  necessary  to  remove  the  flame  from  rmder  the  flask.  The  gas 
will  contain  a  little  suspended  vapour  of  sulphuric  acid,  which  renders  it  turbid. 

When  the  operation  is  finished,  and  the  flask  has  been  allowed  to  cool,  it  will  be 
found  to  contain  a  grey  crystalline  powder  at  the  bottom  of  a  brown  liquid.  The 
latter  is  the  excess  of  sulphuric  acid  employed,  and  retains  very  little  copper,  since 
cupric  sulphate  is  insoluble  in  strong  sulphuric  acid.  If  the  liquid  be  poured  oft", 
and  the  flask  filled  up  with  water,  and  set  aside  for  some  time,  the  crystalline  powder 
will  dissolve,  forming  a  blue  solution  of  sulphate  of  copper,  yielding  that  salt  in  fine 
prismatic  crystals  by  evaporation  and  cooling.  The  dark  powder  remaining  undis- 
solved after  extracting  the  whole  of  the  sulphate,  consists  chiefly  of  cuprous  suphide, 
the  production  of  which  is  interesting,  as  showing  how  far  the  deoxidising  effect  of 
the  copper  may  be  carried  in  this  experiment. 

Sulphur  dioxide  is  a  very  heavy  (sp.  gr.  2*25)  colourless  gas,  character- 
ised by  its  odour  of  burning  brimstone.  It  condenses  to  a  clear  liquid  at 
0°  F.  (the  temperature  of  a  mixture  of  ice  and  salt)  even  at  the  ordinary 
pressure  of  the  air,  and  has  been  frozen  to  a  colourless  crystalline  solid 
at  -  105°  F. 

The  liquefaction  of  the  gas  is  easily  exhibited  by  passing  it  down  to  the  bottom  of 
a  tube  (A,  fig.  202)  closed  at  one  end,  and  suiTOunded  with  a  mixture  of  pounded 
ice  with  half  its  weight  of  salt.  The  tube  should  have 
been  previously  drawn  out  to  a  narrow  neck  at  B, 
which  may  afterwards  be  sealed  by  the  blowpipe,  the 
lower  part  of  the  tube  being  still  surrounded  by  the 
freezing  mixture,  since  the  liquid  sulphur  dioxide 
boils  at  14°  F.  The  tube  need  not  be  very  strong,  for 
at  the  ordinary  temperature  the  vapour  exerts  a  pressure 
of  only  2 '5  atmospheres.  Liquid  sulphur  dioxide  is  a 
convenient  agent  for  producing  (by  its  rapid  evapora- 
tion) the  low  temperature  (  -  39°  F.)  required  to  ettect 
the  solidification  of  mercury.  A  small  globule  of  this 
metal  may  readily  be  frozen  by  dropping  some  liquid 
sulphur  dioxide  upon  it  in  a  watch-glass  placed  in  a 
strong  draught  of  air.  The  tube  containing  the  sulphur 
dioxide  should  be  held  in  a  woollen  cloth  or  glove. 
The  attractive  experiment  of  freezing  water  in  a  red 
hot  crucible  may  also  be  made  with  the  liquid.     A  Fig.  202. 

platinum  crucible  being  heated  to  redness,  and  some 

liquid  sulphur  dioxide  j^ured  into  it,  from  a  tube  which  has  been  cooled  for  half  an 
hour  in  ice  and  salt,  the  liquid  becomes  surrounded  with  an  atmosphere  of  sulphurous 
acid  gas,  which  prevents  its  contact  with  the  metal  (as.sumes  the  spheroidal  state), 
and  its  temperature  is  reduced  by  its  own  evaporation  to  so  low  a  degree  that  a  little 
water  allowed  to  flow  into  it  will  at  once  become  converted  into  opaque  ice.  Liquid 
SO2  is  employed  in  freezing  machines.  The  lowest  temperature  yet  reached  -  220°  F. 
(  -  140°  C.)  is  obtained  by  the  evaporation  of  a  solution  of  solid  CO2  in  liquid  SOo. 
This  mixture  was  employed  in  liquefying  oxygen,  hydrogen,  and^itrogen  uuder  very 
high  pressure. 

*  According  to  Berthelot,  a  notable  quantity  of  SO3  is  produced  at  the  same  time. 


200  BLEACHING  BY  SULPHUKOUS  ACID. 

Sulphurous  acid  gas  is  very  easily  absorded  by  water,  as  may  be  sbown 
by  pouring  a  little  water  into  a  bottle  of  the  gas,  closing  the  bottle  with 
the  palm  of  the  hand,  and  shaking  it  violently  (see  fig.  164,  p.  149), 
when  the  diminished  pressure  due  to  the  absorption  of  the  gas  will  cause 
the  bottle  to  be  sustained  against  the  hand  by  the  pressure  of  the 
atmosphere.  Water  absorbs  43"5  times  its  bulk  of  the  gas  at  the  ordi- 
nary temperature.  The  solution  is  believed  to  contain  sulphurous  acid, 
H.SOg,  formed  by  the  reaction  HgO  +  SOg  =  H2SO3,  but  this  body  has 
not  been  obtained  in  the  separate  state.  If  the  solution  be  exposed  to  a 
low  temperature,  a  crystallised  hydrate  is  obtained,  the  composition  of 
which  does  not  appear  to  be  accurately  settled.  When  the  solution  of 
sulphurous  acid  is  kept  for  some  time  in  a  bottle  containing  air,  its  smell 
gradually  disappears,  the  acid  absorbing  oxygen  and  becoming  converted 
into  sulphuric  acid. 

Sulphur  dioxide,  like  carbon  dioxide,  possesses  in  a  high  degree  the 
power  of  extinguishing  flame.  A  taper  is  at  once  extinguished  in  a 
liottle  of  the  gas,  even  when  containing  a  considerable  proportion  of  air. 
One  of  the  best  methods  of  extinguishing  burning  soot  in  a  chimney  con- 
sists in  passing  up  sulphurous  acid  gas  by  burning  a  few  ounces  of  sulphur 
in  a  pan  placed  over  the  fire. 

The  principal  uses  of  sulphurous  acid  gas  depend  upon  its  property  of 
bleaching  many  animal  and  vegetable  colouring  matters.  Although  a  far 
less  powerful  bleaching  agent  than  chlorine,  it  is  preferred  for  bleaciiing 
silk,  straw,  wool,  sponge,  isinglass,  baskets,  &c.,  which  would  be  injured 
by  the  great  chemical  energy  of  chlorine.  The  articles  to  be  bleached 
are  moistened  with  water  and  supended  in  a  chamber  in  which  sulphurous 
acid  gas  is  produced  by  the  combustion  of  sulphur.  The  colouring 
matters  do  not  appear  in  general  to  be  decomposed  by  the  acid,  but 
rather  to  form  colourless  combinations  with  it,  for  in  course  of  time  the 
original  colour  often  reappears,  as  is  seen  in  straw,  flannel,  &q,.,  which 
become  yellow  from  age,  the  sulphurous  acid  probably  being  oxidised  into 
sulphuric  acid.  Stains  of  fruit  and  port  wine  on  linen  are  conveniently 
removed  by  solution  of  sulphurous  acid. 

The  red  solution  obtained  by  boiling  a  few  chips  of  logwood  with  river  water 
(distilled  water  does  not  give  so  fine  a  colour),  serves  to  illustrate  the  bleaching  pro- 
perties of  sulphurous  acid.  A  few  drops  of  the  solution  of 
the  acid  will  at  once  change  the  red  colour  of  the  solution 
to  a  light  yellow  ;  but  that  the  colouring  power  is  suspended 
and  not  destroyed,  may  be  shown  by  dividing  the  yellow 
liquid  into  two  parts,  and  adding  to  them,  respectively, 
potash  and  diluted  sulphuric  acid,  which  will  restore  the 
colour  in  a  modified  form.  To  contrast  this  with  the  com- 
plete decomposition  of  the  colouring  matter,  a  little  sul- 
phurous acid  may  be  added  to  a  weak  solution  of  the 
potassium  permanganate,  when  the  splendid  red  solution 
at  once  becomes  perfectly  colourless,  and  neither  acid  nor 
alkali  can  effect  its  restoration. 

If  a  bunch  of  damp  coloured  flowers  be  suspended  in  a 

bell-jar  over  a  crucible  containing  a  little  burning  sulphur 

Fig.  203.  (fig.  203),  many  of  the  flowers  will  be  completely  bleached 

by  the  sulphurous  acid,  and  by  plunging  them  afterwards 

into  diluted  sulphuric  acid  and  ammonia,  their  colours  may  be  partly  restored  with 

some  very  curious  modifications. 

Another  very  useful  property  of  sulphurous  acid  is  that  of  arresting 
fermentation  (or   putrefaction),    apparently   by  killing   the  vegetable  or 


SULPHITES. 


201 


Fk 


animal  growth  which  is  the  cause  of  the  fermentation.  This  is  commonly 
designated  the  antiseptic  or  antizymutic  property  of  sulphurous  acid,  and 
is  turned  to  account  Avhen  casks  for  wine  or  beer  are  sulphured  in  order  to 
prevent  the  action  of  any  substance  con- 
tained in  the  pores  of  the  wood,  and 
capable  of  exciting  fermentation,  upon  the 
fresh  liquor  to  be  introduced.  If  a  little 
solution  of  sugar  be  fermented  with  yeast 
in  a  flask  provided  with  a  funnel  tube 
(fig.  204),  a  solution  of  sulphurous  acid 
poured  in  through  the  latter  will  at  once 
arrest  the  fermentation.  The  salts  of  sul- 
phurous acid  (sulphites)  are  also  occa- 
sionally used  to  arrest  fermentation,  in 
the  manufacture  of  sugar,  for  instance. 
Clothes    are    sometimes    fumigated    with 

sulphurous  acid  gas  to  destroy  vermin,  and  the  air  of  rooms  is  disinfected 
by  burning  sulphur  in  it. 

The  disposition  of  sulphurous  acid  to  absorb  oxygen  and  pass  into  sul- 
phuric acid,  renders  it  a  powerful  deoxidising  or  reducing  agent.  Solu- 
tions of  silver  and  gold  are  reduced  to  the  metallic  state  by  sulphurous  acid 
and  sulphites. 

If  a  solution  of  sulphurous  acid  be  lieated  for  some  time  in  a  sealed  tube  to  340°  F. 
one  portion  of  the  acid  deoxidises  another,  sulphur  is  se[)arated,  and  sulphuric  acid 
formed  ;  3H3S03  =  2H.^SOi+H20  +  S . 

Sulphurous  acid  gas  combines  with  ammonia  gas  to  form  two  solid  compounds 
(XHjV^SOa,  andNH3.S0,. 

Chlorine  combines  with  an  equal  volume  of  sulphur  dioxide,  under  the  influence 
of  bright  sunshine,  or  in  presence  of  charcoal,  to  produce  a  colourless  liquid,  the 
vapour  of  which  is  verj'  acrid  and  irritating  to  the  eyes.  Its  composition  is  rej)re- 
sented  by  SO2CI.2,  and  it  is  sometime?  called  chlorosul2)huric  acid,  though  it  does  not 
combine  with  bases,  and  is  decomposed  by  water,  yielding  hydrochloric  and 
sulphuric  acids.  It  is  also  known  as  chloride  of  stilphtiryle.  The  chloride  of  thionyle* 
SOClj,  is  a  colourless  volatile  liijuid  obtained  by  the  action  of  sulphurous  acid  gas  on 
phosphorus  pentuchloride.  It  is  decomposed  by  water,  yielding  hydrochloric  and 
sulphurous  acids. 

Potassium  and  sodium,  when  heated  in  sulphurous  acid  gas,  burn  vividly,  pro- 
ducing the  oxides  and  sulphides  of  the  metals. 

IroH,  lead,  tin,  and  zinc  are  also  converted  into  oxides  and  sulphides  when  heated 
in  sulplmrous  acid  gas  ;  SOjj  +  Zn3  =  ZnS  +  2ZnO  . 

Sulphites. — The  acid  character  of  sulphurous  acid  is  rather  feeble, 
although  stronger  than  that  of  carbonic  acid.  There  is  much  general  re- 
semblance between  the  sulphites  and  carbonates,  in  point  of  solubility, 
the  sulphites  of  the  alkali  metals  being  the  only  salts  of  sulphurous  acid 
which  are  freely  soluble  in  water.  Sulphurous  acid,  H.^SOg  being  dibasic 
like  carbonic,  forms  two  classes  of  salts,  the  normal  sulphites  (for  example, 
sodium  sulphite,  XagSO^),  and  acid  sulphites  (as  hydropotassic  sulphite, 
KHSO3). 

Sodium  sulphite  is  extensively  manufactured  for  the  use  of  the  paper- 
maker,  who  employs  it  as  an  anticldore  for  killinr/  the  bleach,  that  is, 
neutralising  the  excess  of  chlorine  after  bleaching  the  rags  with  chloride 
of  lime  and  sulphuric  acid  (see  p.  156) —  ^_ 

:NX,S03   +   H,0   +   CI2   =   Xa^SO,   +    2HC1. 

*  Qelov,  sulphur. 


202  SULPHURIC  ACID. 

It  is  prepared  "by  passing  sulphurous  acid  gas  over  damp  crystals  of 
sodium  carbonate,  when  carbonic  acid  gas  is  expelled,  and  sodium  sulphite 
formed,  which  is  dissolved  in  water  and  crystallised.  It  forms  oblique 
prisms,  having  the  composition  NagSOg'TAq.,  which  effloresce  in  the  air, 
becoming  opaque,  and  slowly  absorbing  oxygen,  passing  into  sodium  sul- 
phate (Xa2S04).     Its  solution  is  slightly  alkaline  to  test-papers. 

For  the  manufacture  of  sodium  sulphite  the  sulphurous  acid  gas  is 
obtained  either  by  the  combustion  of  sulphur  or  by  heating  sulphuric 
acid  with  charcoal ;  2H2SO4  +  0  =  2Il.p  +  CO,  -I-  2SO2  . 

The  carbon  dioxide  of  course  will  not  interfere  with  this  application  of 
the  sulphur  dioxide. 

Sulphuric  Acid. 
H2SO4  =  98  parts  by  weight. 

144.  More  than  four  centuries  ago,  the  alchemist  Basil  Valentine  sub- 
jected (jreen  citriol,  as  it  was  then  called  (sulphate  of  irou)^  to  distillation, 
and  obtained  an  acid  liquid  which  he  named  oil  of  vitriol.  The  process 
discovered  by  this  laborious  monk  is  even  now  in  use  at  Xordhausen  in 
Saxony,  and  the  Nordhausen  oil  of  vitriol  is  an  important  article  of  com- 
merce. The  crystals  of  ferrous  sulphate  (FeSO^THgO)  are  exposed  to  the 
air  so  that  they  may  obsorb  oxygen,  and  become  converted  into  the  basic 
ferric  sul2)hate  ;  GFeSO^  -f  O3  =  2Fe2(S04)3.Fe203. 

This  salt  is  partially  dried,  and  distilled  in  earthenware  retorts,  when 
a  mixture  of  sulphuric  acid  and  sulphuric  anhydride  distils  over,  and  is 
sent  into  commerce  as  Nordhausen  or  fuming  sulphuric  add  Feg(S04)3 
+  2H2O  =  FeoOg  +  2H2SO4  +  SO3.  The  ferric  oxide  (Eeff^)  which  is  left 
in  the  retorts,  is  the  red  powder  known  as  colcothar,  which  is  used  for 
polishing  plate  glass  and  metals. 

The  green  vitriol  employed  for  preparing  the  Nordhausen  acid  is  obtained  from 
iron  pyrites  (FeSj).  A  particular  variety  of  this  mineral,  white  pyrites  (or  efflores- 
cent pyrites),  when  exposed  to  moist  air,  undergoes  oxidation,  yielding  ferrous 
sulphate  and  sulphuric  acid  ;  FeSij  +  H20  +  07=FeS04+  Hi,S04. 

Large  masses  of  this  variety  of  pyrites  in  mineralogical  cabinets  may  often  be 
seen  broken  up  into  small  fragments,  and  covered  with  an  acid  efflorescence  of  ferrous 
sul[ihate  from  this  cause.  Ordinary  iron  pyrites  is  not  oxidised  by  exposure  to  the 
air  unless  it  be  first  subjected  to  distillation  in  order  to  separate  a  portion  of  the 
sulphur  which  it  contains. 

Fuming  sulpliuric  acid  is  now  made  in  England  by  dissolving  sulphuric  anhydride 
in  about  twice  its  weight  of  oil  of  vitriol.  In  order  to  procure  the  sulphuric 
anhydride,  oil  of  vitriol  (H.2SO4)  is  decomposed  by  a  high  temperature  into  steam, 
sulphurous  acid  gas,  and  oxygen ;  the  vapour  of  water  is  removed  by  passing  the 
gases  through  oil  of  vitriol,  and  the  SOj  and  O  are  caused  to  combine  by  passing  them 
over  hot  platinised  asbestos.  The  fuming  acid  is  kept  in  vessels  of  tinned  iron 
upon  which  it  has  no  action. 

The  Xordhausen  acid  is  readily  distinguished  from  English  sulphuric 
acid  by  its  fuming  in  the  air  when  the  bottle  is  opened.  This  is  due  to 
the  escape  of  a  little  vapour  of  sulphuric  anhydride.  It  is  heavier  than 
the  English  acid,  its  specific  gravity  being  1-9.  It  is  chiefly  used  for 
dissolving  indigo  in  preparing  the  Saxony  blue  dye,  also  in  making 
alizarine,  and  is  a  convenient  source  of  the  anhydride ;  for  if  it  be  gently 
heated  in  a  retort,  the  anhydride  is  disengaged,  and  may  be  condensed 
in  silky  crystals  in  a  receiver  kept  cool  by  ice,  whilst  ordinary  sulphuric 
acid  (H2SO4)  is  left  in  the  retort. 


MANUFACTURE  OF  OIL  OF  VITEIOL.  203 

An  acid  containing  40  or  50  per  cent,  of  dissolved  sulphuric  anhydride 
is  solid  at  ordinary  temperatures,  whilst  that  containiiig  60  or  70  percent, 
is  liquid  even  helow  0°  C. 

The  process  adopted  at  Nordhausen,  though  simple  in  theory,  is  expen- 
sive, on  account  of  the  consumption  of  fuel  and  the  breaking  of  the  retorts, 
so  that  the  price  of  the  acid,  compared  with  that  of  English  manufacture, 
is  very  high. 

The  first  step  towards  the  discovery  of  our  present  process  was  also 
made  by  Valentine,  when  he  prepared  his  oleum  sulphuris  per  cavipanum, 
by  burning  sulphur  under  a  bell-glass  over  water,  and  evaporating  the 
acid  liquid  thus  obtained.  The  same  experimenter  also  made  a  very  im- 
portant advance  when  he  burnt  a  mixture  of  sulphur,  antimony  sulphide, 
and  nitre  under  a  bell-glass  placed  over  water ;  but  it  was  not  until 
the  middle  of  the  18th  century  that  it  was  suggested  by  some  French 
chemists  to  burn  the  sulphur  and  nitre  alone  over  water ;  a  process  by 
which  the  acid  appears  actually  to  have  been  manufactured  upon  a  pretty 
large  scale.  The  substitution  of  large  chambers  of  lead  for  glass  vessels 
by  Dr.  Roebuck  was  a  great  improvement  in  the  process,  and  about  the 
year  1770  the  preparation  of  the  acid  formed  an  important  branch  of 
manufacture  ;  since  then  the  process  has  been  steadily  improving  until, 
at  the  present  time,  upwards  of  100,000  tons  are  annually  consumed  in 
Great  Britain,  and  a  very  large  quantity  is  exported.  The  diminution  in 
the  price  of  oil  of  vitriol  well  exhibits  the  progress  of  improvement  in  its 
production,  for  the  original  oil  of  sulpliiir  appears  to  have  been  sold  for 
about  half-a-crown  an  ounce,  and  that  prepared  by  burning  sulphur  with 
nitre  in  glass  vessels  at  the  same  price  per  pound ;  but  when  leaden 
chambers  were  introduced,  the  price  fell  to  a  shilling  per  pound,  and  at 
present  oil  of  vitriol  can  be  purchased  at  the  rate  of  five  farthings  per 
pound. 

The  description  of  the  present  process  of  manufacture  will  be  best 
understood  after  a  consideration  of  the  chemical  changes  upon  which  it 
depends. 

It  has  been  seen  that  when  sulphur  is  burnt  in  air,  sulphur  dioxide  is 
the  chief  product.  When  this  acts  upon  nitric  acid,  in  the  presence  of 
water,  sulphuric  acid  and  nitric  oxide  are  formed — 

3SO2    +    2HNO3   +    2H2O    =    3H2SO4   +    2N0. 

Xitric  oxide,  in  contact  with  air,  combines  with  its  oxygen  to  form 
nitric  peroxide  (J^Og). 

If  nitric  peroxide  is  brought  into  contact  with  sulphurous  acid  gas  and 
water,  it  is  again  converted  into  nitric  oxide,  with  formation  of  sulphuric 
acid;  NOg  +  SO,  +  H^O  =  :^f 0 -f  H^SO^ . 

It  appears,  therefore,  that  nitric  oxide  may  be  employed  to  absorb 
oxygen  from  the  air,  and  to  convey  it  to  the  sulphur  dioxide,  so  that 
theoretically,  an  unlimited  quantity  of  sulphur  might  be  converted  into 
sulphuric  acid  by  a  given  quantity  of  nitric  oxide,  with  a  sufficient  supply 
of  air  and  water. 

To  illustrate  these  important  chemical  principles  of  the  manufacture  of  sulphuric 
acid,  the  following  experiments  may  be  performed  : —  * 

1.  A  quart  bottle  of  nitric  oxide  (p.  141),  is  placed  mouth  to  mouth  with  a  pint 
bottle  of  oxygen,  when  both  bottles  will  be  filled  with  the  red  nitric  peroxide. 

2.  The  quart  bottle  of  this  red  gas  is  placed  mouth  to  mouth  with  a  quart  bottle 


20  i 


THEORY  OF  PRODUCTION  OF  OIL  OF  VITRIOL. 


Fig.  205. 


of  sulphurous  acid  gas  (fig.  205),  when  the  red  colour  will  soon  disappear,  and  the 
sides  of  the  bottles  will  be  covered  with  a  crystalline  substance  formed  by  the  reaction 

between  the  nitric  peroxide,  the  sulphur  dioxide,  and 
the  small  quantity  of  water  present  in  the  gases — 

2SO4  +  3NO2  +  H2O  =  2(NOHS04)  +  NO . 

3.  A  little  water  is  shaken  round  in  the  bottles, 
when  the  crystals  will  be  dissolved  with  effervescence, 
evolving  nitric  oxide  and  peroxide,  and  producing 
sulphuric  acid — 

2(NOHS04)  +  H2O  =  NO  +  NO2  +  2H2SO4. 

In  the  presence  of  abundance  of  water  this  crystal- 
line compound  is  not  produced,  as  may  be  shown  by 
the  following  modification  of  the  experiment. 

A  large  glass  flask  or  globe  *  (A,  fig.  206)  is  fitted 
with  a  cork,  through  which  are  passed — 
(a)  A  tube  connected  with  a  flask  (D)  containing  copper  and  strong  sulphuric  acid, 
for  evolving  sulphurous  acid  gas  ; 

{b)  A  tube  connected  with  a  flask  (B)  containing  copper  and  diluted  nitric  acid 
(sp.  gr.  1  "2)  for  supplying  nitric  oxide  ; 

(c)  A  tube  proceeding  from  a  small  flask  (E)  containing  water. 
On  applying  a  gentle  heat  to  the  flask  containing  nitric  acid  and  copper,  the  nitric 
oxide  passes  into  the  globe  and  combines  with  the  oxygen  of  the  air,  filling  the 

globe  with  red  nitric  peroxide. 
The  nitric  oxide  flask  may  then 
be  removed.  Sulphurous  acid  gas 
is  then  generated  by  heating  the 
flask  containing  sulphuric  acid 
and  copper  ;  the  sulphurous  acid 
gas  will  soon  decolorise  the  red 
nitric  jieroxide,  the  contents  of  the 
globe  becoming  colourless,  and 
the  crystalline  compound  form- 
ing abundantly  on  the  sides  ;  the 
sulphur  dioxide  flask  may  then 
be  removed.  Steam  is  sent  into 
the  globe  from  the  flask  contain- 
ing water,  when  the  crystalline 
compound  will  be  dissolved,  and 
sulphuric  acid  will  collect  at  the 
bottom  of  the  globe.  If  air  be 
now  blown  into  the  globe,  the 
nitric  oxide  will  again  acquire  the 
red  colour  of  nitric  ]»eroxide. 
If  the  experiment  be  repeated,  the  steam  being  introduced  simultaneously  with 
the  sulphurous  acid  gas,  no  crystalline  compound  whatever  will  be  formed,  the 
sulphur  dioxide  being  at  once  converted  into  sulphuric  acid. 

Since  the  cork  is  somewhat  corroded  in  this  experiment,  it  is  preferable  to  have 
the  mouth  of  the  flask  ground  and  closed  by  a  ground  glass  plate,  perforated  with 
holes  for  the  passage  of  the  tubes.  The  perforations  are  easily  made  by  ])lacing  the 
glass  ydate  flat  against  the  wall  and  piercing  it  with  the  point  of  a  revolving  rat's- 
tail  file  dipped  in  turpentine  ;  tlie  file  is  then  gradually  worked  through  the  hole 
until  the  latter  is  of  the  required  size. 

The  process  employed  for  the  manufacture  of  English  oil  of  vitriol  will 
now  be  easily  understood. 

A  series  of  chambers  is  constructed  of  leaden  plates,  the  edges  of 
^vhich  are  united  by  autogenous  soldering  (that  is,  by  fusing  their  edges, 
without  solder,  which  would  be  rapidly  corroded  by  the  acid  vapours) ; 
the  leaden  chambers  are  supported  and  strengthened  by  a  framework  of 
timber  (hg.  207). 

*  The  operation  is,  of  course,  more  striking  if  oxygen  is  employed  instead  of  air,  the  globe 
in  fig.  206  being  filled  with  oxygen  by  displacement  at  the  commencement. 


Fig.  206. — Preparation  of  sulphuric  acid. 


EEACTIONS  IN  THE  VITRIOL  CHAMBERS. 


205 


The  sulplmrous  acid  gas  is  generated  by  burning  sulphur  or  iron  pyrites 
in  a  suitable  furnace  (A)  adjoining  the  chambers,  an'd  so  arranged  that 
fche  gas  produced  may  be  mixed  with  about  the  proper  quantity  of  air  to 
furnish  the  oxygen  required  for  its  conversion  into  sulphuric  acid. 

Nitnc  acid  vapour  is  evolved  from  a  mixture  of  sodium  nitrate  and  oil 
of  vitriol  (see  p.  136)  contained  in  an  iron  pan  which  is  heated  by  the 
combustion  of  the  sulphur,  so  that  the  nitric  acid  is  carried  into  the  cham- 
bers with  the  current  of  sulphurous  acid  gas  and  air. 


//  /////' w////////v/M/WMm'/y^////yy''^^' 


Fig.  207.  — Sulphuric  acid  chambers. 

Water  covers  the  floor  of  the  chambers  to  the  depth  of  about  2  inches, 
and  jets  of  steam  are  introduced  at  different  jarts  from  an  adjacent 
boiler  (B). 

The  sulphurous  acid  gas  acts  upon  the  nitric  acid  vapour,  in  the  presence 
of  the  water,  forming  nitric  oxide  and  sulphuric  acid,  which  rains  down 
into  the  water  on  the  floor  of  the  chambers — 

3S0.,  +  2HX0,  +  2H,0  =  2X0  +  aH.SO,. 

If  this  nitric  oxide  were  permitted  to  escape  from  the  chambers,  and  a 
fresh  quantity  of  nitric  acid  vapour  introduced  to  oxidise  another  portion 
of  sulphur  dioxide,  it  is  evident  that  2  molecules  (170  parts  by  weight)  of 


206  REACTIONS  IN  THE  VITRIOL  CHAMBERS. 

sodium  nitrate  would  be  required  to  furnish  the  nitric  acid  for  the  con- 
version of  3  atoms  (96  parts  by  weight)  of  sulphur,  whereas,  in  practice, 
6  parts  by  weight  only  of  nitrate  are  employed  for  96  parts  of  sulphur. 

For  the  nitric  oxide  (NO)  at  once  acquires  oxygen  from  the  air  ad- 
mitted together  with  the  sulphurous  acid  gas,  and  becomes  nitric  peroxide 
(XOg),  which  oxidises  more  sulphurous  acid  gas  in  the  presence  of  water, 
converting  it  into  sulphuric  acid  — 

SO2  +  NO2  +  H2O  -  H2SO4  +  NO. 

A  great  reduction  in  the  volume  of  the  gas  in  the  chamber  thus  takes 
place  (2  volumes  SOg  and  2  volumes  NO2  yielding  2  volumes  NO),  so  that 
there  is  room  for  the  introduction  of  a  fresh  quantity  of  the  mixture  of 
sulphurous  acid  gas  and  air  from  the  furnace,  upon  which  the  nitric  oxide 
acts  as  before,  taking  up  the  oxygen  from  the  air  and  handing  it  over  to 
the  sulphur  dioxide,  in  the  presence  of  water,  to  produce  a  fresh  supply  of 
sulphuric  acid. 

But  the  nitrogen  of  the  air  takes  no  part  in  these  changes ;  and  since 
the  oxygen  consumed  in  converting  the  sulphur  into  sulphuric  acid  is 
accompanied  by  four  times  its  volume  of  nitrogen,  a  very  large  accumula- 
tion of  this  gas  takes  place  in  the  chambers,  and  provision  must  be  made 
for  its  removal  in  order  to  allow  space  for  those  gases  which  take  part  in 
the  change.  The  obvious  plan  would  appear  to  be  the  erection  of  a  simple 
chimney  for  the  escape  of  the  nitrogen  at  the  opposite  end  of  the  chamber 
to  that  at  which  the  sulphurous  acid  gas  and  air  enter  it :  and  this  plan 
was  formerly  adopted,  but  the  nitrogen  carries  off  with  it  a  portion  of  the 
nitric  oxide  which  is  so  valuable  in  the  chamber,  and  to  save  this  the 
escaping  nitrogen  is  now  generally  passed  through  a  leaden  chamber  (Gay- 
Lussac's  tower)  (C)  filled  with  coke,  over  which  oil  of  vitriol  is  allowed  to 
trickle  :  the  oil  of  vitriol  absorbs  the  nitric  oxide,*  and  flows  into  a  cistern 
(D),  from  which  it  is  forced  up,  by  the  pressure  of  steam,  to  the  top  of 
another  chamber  (Glover's  tower)  (E)  arranged  with  shelves  in  cascade 
or  packed  with  flints,  through  which  the  hot  sulphurous  acid  gas  and  air 
are  made  to  pass  as  they  enter,  when  they  take  up  the  nitrous  anhydride 
from  the  oil  of  vitriol,  and  carry  it  with  them  into  the  chamber. 

Before  the  introduction  of  this  plan  it  required  a  quantity  of  sodium 
nitrate  amounting  to  ^th  or  yV*'^  ^^  ^^^  weight  of  the  sulphur  to  convert 
it  into  sulphuric  acid,  whereas  about  ^V^h,  or  even  less,  is  now  often 
made  to  suffice. 

In  the  vitriol  chambers  represented  in  fig.  207,  the  mixture  of  gases  passing  from 
the  first  square  chamber  into  the  second  contains  a  large  excess  of  sulphurous  acid  gas, 
wliieh  is  oxidised  and  converted  into  sulphuric  acid  by  the  nitric  acid  flowing  down 
tlie  cascade  represented  at  the  entrance  to  the  second  chamber.  The  mixture  of 
sulphuric  acid  with  excess  of  nitric  acid  and  other  oxides  of  nitrogen  which  is  thus 
formed,  is  made  to  psvss  back  into  the  first  chamber,  in  order  to  be  deoxidised  by  the 
excess  of  sulphurous  acid  gas.  It  is  thence  conducted  by  a  pipe,  not  shown  in  the 
figure,  into  the  middle  chamber  of  much  larger  size,  where  the  principal  reaction 
between  the  sulphurous  acid  gas,  the  nitric  oxide  gas,  and  the  oxygen  of  the  air, 
takes  place.  The  reaction  is  completed  during  the  passage  through  the  two  last 
small  chambers,  and  the  gases  are  finally  cooled  by  passing  through  a  chamber  sur- 
ruunded  with  cold  water  before  being  discharged  into  the  Gay-Lussac's  tower  C. 

The  sulphuric  acid  is  allowed  to  collect  on  the  floor  of  the  chamber 
until  it  has  a  specific  gravity  of  about  1  '6,  and  contains  70  per  cent,  of  oil 

*  Strictly  speaking,  it  is  nitrous  anhydride,  N^Oj,  which  is  absorbed  by  the  H2SO4, 
theie  being  still  enough  0  to  convert  2N6  into  N2O3 . 


COMMERCIAL  VARIETIES  OF  SULPHURIC  ACID.  207 

of  vitriol  (H^SO^).  If  it  were  allowed  to  become  more  concentrated  than 
this,  it  would  absorb  some  of  the  oxides  of  nitrogen  in  the  chamber,  so  that 
it  is  now  drawn  off. 

This  acid  is  quite  strong  enough  for  some  of  the  applications  of  sul- 
phuric acid,  particularly  for  that  which  consumes  the  largest  quantity  in 
this  country,  viz.,  tlie  conversion  of  common  salt  into  sodium  sulphate  as 
a  preliminary  step  in  the  manufacture  of  carbonate  of  soda.  To  save  the 
expense  of  transporting  the  acid  for  this  purpose,  the  vitriol  chambers 
form  part  of  the  plant  of  the  alkali  works. 

To  convert  this  weak  acid  into  the  ordinary  oil  of  vitriol  of  commerce, 
it  is  run  off  into  shallow  leaden  pans  set  in  brickwork,  and  supported  on 
iron  bars  over  the  flue  of  a  furnace,  where  it  is  heated  until  so  much 
water  has  evaporated  that  the  specific  gravity  of  the  acid  has  increased  to 
1  '72.  The  concentration  cannot  be  carried  further  in  leaden  pans,  because 
the  strong  acid  acts  upon  the  lead,  and  converts  it  into  sulphate — 
2H2SO4  +  Pb  =  PbSO^  +  2H2O  +  SOg. 

The  concentration  of  the  acid  is  now  often  effected  by  high  pressure 
steam  passing  through  leaden  worms  immersed  in  the  acid  which  is  con- 
tained in  wooden  vats  lined  with  lead. 

The  acid  of  1*72  sp.  gr.  contains  about  80  per  cent,  of  true  oil  of  vitriol, 
and  is  largely  employed  for  making  superphosphate  of  lime,  and  in  other 
rough  chemical  manufactures.  It  is  technically  called  hrown  acid,  having 
acquired  a  brown  colour  from  organic  matter  accidentally  present  in  it. 

To  convert  this  brown  acid  into  commercial  oil  of  vitriol,  it  is  boiled 
down,  either  in  glass  retorts  or  platinum  stills,  when  water  distils  over, 
accompanied  by  a  little  sulphuric  acid,  and  the  acid  in  the  retort  becomes 
colourless,  the  brown  carbonaceous  matter  being  oxidised  by  the  strong 
sulphuric  acid,  with  formation  of  carbonic  and  sulphurous  acid  gases. 
When  dense  white  fumes  of  oil  of  vitriol  begin  to  pass  over,  showing 
that  all  the  superfluous  water  has  been  expelled,  the  acid  is  drawn  off  by 
a  siphon. 

The  very  diluted  acid  which  distils  off  is  employed  instead  of  water  on 
the  floor  of  the  leaden  chamber. 

The  cost  of  the  acid  is  very  much  increased  by  this  concentration.  It  cannot  be 
conducted  in  open  vessels,  partly  on  account  of  the  loss  of  sulphuric  acid,  partly  be- 
cause concentrated  sulphuric  acid  absorbs  moisture  from  the  open  air  even  at  the 
boiling-point.  The  loss  by  breakage  of  the  glass  retorts  is  very  considerable,  althougli 
it  is  reduced  as  far  as  ])ossible  by  heating  them  in  sand,  and  keeping  them  always  at 
about  the  same  temperature  by  supplying  them  with  hot  acid.  But  the  boiling- 
point  of  the  concentrated  acid  is  very  high  (640°  F. ),  and  the  retorts  consequently 
become  so  hot  that  a  current  of  cold  air  or  an  accidental  splash  of  acid  will  frequently 
crack  them  at  once.  Moreover  the  acid  boils  with  succiission  or  violent  bumping, 
caused  by  sudden  bursts  of  vapour,  which  endanger  the  safety  of  the  retort. 

V/ith  platinum  stills  the  risk  of  fracture  is  avoided,  and  the  distillation  may  be 
conducted  more  rapidly,  the  brown  acid  (sp.  gr.  1  "72),  being  admitted  at  the  top, 
and  the  oil  of  vitriol  (sp.  gr.  1'84)  drawn  off  by  a  platinum  siphon  from  the  bottom 
of  the  still,  which  is  protected  from  the  open  fire  by  an  iron  jacket.  But  since  a 
platinum  still  costs  £2000  or  £3000,  the  interest  upon  its  value  increases  the  cost  of 
production  of  the  acid. 

When  the  perfectly  pure  acid  is  required,  it  is  actually  distilled  over  so  as  to  leave 
the  solid  impurities  (sulphate  of  lead,  &c. )  behind  in  the  retort.  Some  fragments 
of  rock  crystal  should  be  introduced  into  the  retort  to  moderate  the  bursts  of  vapour, 
and  heat  applied  by  a  ring  gas-burner  with  somewhat  divergent  ^ets. 

Divested  of  working  details,  this  most  important  chemical  manufacture 
may  be  thus  described  : — 


208  PROPERTIES  OF  SULPHURIC  ACID. 

A  mixture  of  sulphurous  acid  gas,  air,  steam,  and  a  little  vapour  of 
nitric  acid,  is  introduced  into  a  leaden  chamber  containing  a  layer  of 
water.  The  nitric  acid  is  reduced  by  the  sulphurous  acid  gas  to  the  state 
of  nitric  oxide  (NO),  which  takes  up  oxygen  from  the  air  (forming  NO2), 
and  gives  it  to  the  sulphurous  acid  gas,  which  it  converts  into  sulphuric 
acid.  This  is  absorbed  by  the  water,  forming  diluted  sulphuric  acid, 
which  is  concentrated  by  evaporation  lirst  in  leaden  pans,  and  afterwards 
in  glass  retorts  or  platinum  stills.  The  nitric  oxide  becomes  the  vehicle 
by  which  the  oxygen  of  the  air  is  transferred  to  the  sulphur  dioxide. 

Properties  of  oil  of  vitriol. — The  properties  of  concentrated  sulphuric 
acid  are  very  characteristic.  Its  great  weight  (sp.  gr.  1"842),  freedom 
from  odour,  and  oily  appearance,  distinguish  it  from  any  other  liqui<l 
commonly  met  with,  which  is  fortunate,  because  it  is  difficult  to  preserve 
a  label  upon  the  bottles  of  this  powerfully  corrosive  acid.  Although,  if 
absolutely  pure,  it  is  perfectly  colourless,  the  ordinary  acid  used  in  the 
laboratory  has  a  peculiar  grey  colour,  due  to  traces  of  organic  matter. 
Its  high  boiling-point  (640°  F.)  has  been  already  noticed ;  and  although 
its  vapour  is  perfectly  transparent  in  the  vessel  in  which  the  acid  is  boiled, 
as  soon  as  it  issues  into  the  air  it  condenses  into  voluminous  dense  clouds 
of  a  most  irritating  description.  Even  a  drop  of  the  acid  evaporated  in 
an  open  dish  will  fill  a  large  space  with  these  clouds.  Oil  of  vitriol 
solidifies  when  cooled  to  about  -  30°  F.,  but  the  acid  once  solidified 
requires  a  much  higher  temperature  to  liquefy  it  again.  Oil  of  vitriol 
rapidly  corrodes  the  skin  and  other  organic  textures  upon  which  it  falls, 
usually  charring  or  blackening  them  at  the  same  time.  Poured  upon  a 
piece  of  wood,  the  latter  speedily  assumes  a  dark  brown  colour ;  and  if  a 
few  lumps  of  sugar  be  dissolved  in  a  very  little  water,  and  stirred  with 
oil  of  vitriol,  a  violent  action  takes  place,  and  a  semi-solid  black  mass  is 
produced.  This  property  of  sulphuric  acid  is  turned  to  account  in  the 
manufacture  of  blacking,  in  which  treacle  and  oil  of  vitriol  are  employed. 
These  effects  are  to  be  ascribed  to  the  powerful  attraction  of  oil  of  vitriol 
for  water.  Woody  fibre  (CgH^QOg)  (which  composes  the  bulk  of  wood, 
paper,  and  linen),  and  sugar  {(^\'^22^i\),  i^iay  be  regarded,  for  the  pur- 
pose of  this  explanation,  as  composed  of  carbon  associated  with  5  and  1 1 
molecules  of  water,  and  any  cause  tending  to  remove  the  water  would 
tend  to  eliminate  the  carbon. 

The  great  attraction  of  this  acid  for  water  is  shown  by  the  high  tem- 
perature (often  exceeding  the  boiling-point  of  water)  produced  on  mixing 
oil  of  vitriol  with  water,  which  renders  it  necessary  to  be  careful  in  dilut- 
ing the  acid. 

The  water  should  be  placed  in  a  jug,  and  the  oil  of  vitriol  poured  into  it  in  a  thin 
stream,  a  glass  rod  being  used  to  mix  the  acid  with  the  water  as  it  flows  in.  Ordi- 
nary oil  of  vitriol  becomes  turbid  when  mixed  with  water,  from  the  separation  of 
sulphate  of  lead  (formed  from  the  evaporating  pans),  which  is  soluble  in  the  concen- 
trated, but  not  in  the  diluted  acid,  so  that  if  the  latter  be  allowed  to  stand  for  a  few 
hours,  the  sulphate  of  lead  settles  to  the  bottom,  and  the  clear  acid  may  be  poured 
oft'  free  from  lead.  Diluted  sulphuric  acid  has  a  smaller  bulk  than  is  occupied  by  the 
acid  and  water  before  mixing. 

The  heat  evolved  on  combining  one  molecular  weight  of  H.^SO^  with  one  of  water 
amounts  to  69  7  centigrade  units.  Decreasing  quantities  of  heat  are  evolved  for 
successive  additions  of  water,  until  120  molecules  of  water  have  been  added. 

Even  when  largely  diluted,  sulphuric  acid  corrodes  textile  fabrics  very 
rapidly,  and  though  the  acid  be  too  dilute  to  appear  to  injure  them  at 


PROPERTIES  OF  SULPHURIC  ACID.  209 

first,  it  will  be  found  that  the  water  evaporates  by  degrees,  leaving  the 
acid  in  a  more  concentrated  state,  and  the  fibre  is  then  perfectly  rotten. 
The  same  result  ensues  at  once  on  the  application  of  heat ;  thus,  if  charac- 
ters be  written  on  paper  with  the  diluted  acid,  they  will  remain  invisible 
until  the  paper  is  held  to  the  fire,  when  the  acid  will  char  the  paper,  and 
the  writing  will  appear  intensely  black. 

If  oil  of  vitriol  be  left  exposed  to  the  air  in  an  open  vessel,  it  very  soon 
increases  largely  in  bulk  from  the  absorption  of  water,  and  a  flat  dish  of 
oil  of  vitriol  under  a  glass  shade  (fig. 
208)  is  frequently  employed  in  the 
laboratory  for  drying  substances  with- 
out the  assistance  of  heat.  The  drying 
is  of  course  much  accelerated  by 
placing  the  dish  on  the  plate  of  an 
air-pump,  and  exhausting  the  air  from 
the  shade,  so  as  to  effect  the  drying 
in   vacuo.     It    will    be    remembered  <   -v _ " ;  \  ''': '  -z-\::^-^^^Sss£^fi^ 

also  that  oil  of  vitriol  is  in  constant       ^ig.  208.-Drying  over  oil  of  vitriol, 
use  for  drying  gases. 

At  a  red  heat,  the  vapour  of  oil  of  vitriol  is  decomposed  into  water, 
sulphurous  acid  gas,  and  oxygen  ;  HgSO^  =  HgO  +  SOg  +  0  . 

When  sulphur  is  boiled  with  oil  of  vitriol,  the  latter  gradually  dissolves 
the  melted  sulphur,  converting  it  into  sulphurous  acid  gas — - 

S  +  2H2SO4  =  3SO2  +  2H2O. 

All  ordinary  metals  are  acted  upon  by  concentrated  sulphuric  acid  when 
heated,  except  gold  and  platinum  (the  latter  does  not  quite  escape  when 
long  boiled  with  the  acid),  the  metal  being  oxidised  by  one  portion  of 
the  acid,  which  is  thus  converted  into  sulphur  dioxide,  the  oxide  reacting 
with  another  part  of  the  sulphuric  acid  to  form  a  sulphate.  Thus,  when 
silver  is  boiled  with  strong  sulphuric  acid,  it  is  converted  into  sulphate  of 
silver,  which  is  soluble  in  hot  water — 

Ag2  +  2H2SO4  =  Ag.SO^  +  2H2O  +  SO2. 
Should  the  silver  contain  any  gold,  it  is  left  behind  in  the  fonn  of  a  dark 
powder.  Sulphuric  acid  is  extensively  employed  for  the  separation  or 
parting  of  silver  and  gold.  This  acid  is  also  employed  for  extracting  gold 
from  copper  ;  and  when  sulphate  of  copper  is  manufactured  by  dissolving 
that  metal  in  sulphuric  acid  (see  p.  199),  large  quantities  of  gold  arc 
sometimes  extracted  from  the  accumulated  residue  left  undissolved  by  the 
acid.  If  the  sulphuric  acid  contains  nitric  acid,  it  dissolves  a  considerable 
quantity  of  gold,  which  separates  again  in  the  form  of  a  purple  powder 
when  the  acid  is  diluted  with  water,  the  sulphate  of  gold  formed  being 
reduced  by  the  nitrous  acid  when  the  solution  is  diluted. 

Some  of  the  uses  of  sulphuric  acid  depend  upon  its  specific  action  on 
certain  organic  substances,  the  nature  of  which  has  not  yet  been  clearly 
explained.  Of  this  kind  is  the  conversion  of  paper  into  vegetable  parch- 
ment by  immersion  in  a  cool  mixture  of  two  measures  of  oil  of  vitriol  and 
one  measure  of  water,  and  subsequent  washing.  The  conversion  is  not 
attended  by  any  change  in  the  weight  of  the  paper.         ^ 

Sulphuric  acid  forms  definite  combinations  with  water.  By  evaporating 
diluted  sulphuric  acid  in  vacuo  at  212°  F.,  an  acid  is  left  which  has  the 
composition  H2S0^.2H20  (sp.  gr.   1-63).     If  this  acid  be  evaporated  in 

0 


210 


SULPHURIC  ANHYDRIDE. 


Fig.  209. 


air  at  400°  F.,  as  long  as  steam  escapes,  the  remaining  acid  has  the  com- 
position H2SO4.H2O  (sp.  gr.  1-78),  This  acid  is  caMed  glacial  mlphuric 
acid,  hecause  it  solidifies  to  a  mass  of  ice-like  crystals  at  47°  F.  It  is 
sometimes  sold  instead  of  HgSO^,  and  may  be  known  by  its  freezing 
in  winter. 

145.  Anhydrous  sulphuric  acid  or  sulphuric  anhydride  (803=  80). — 
Sulphurous  acid  and  oxygen  gases  combine  to  form  sulphuric  anhydride 
(SO3)  when  passed  through  a  tube  containing  heated  platinum  or  certain 
metallic  oxides,  such  as  those  of  copper  and  chromium,  the  action  of 
which  in  promoting  the  combination  is  not  thoroughly  understood. 

The  combination  may  be  shown  by  passing  oxygen  from  the  tube  A  (fig.  209) 
connected  with  a  gas-holder,  through  a  strong  solution  of  sulphurous  acid  (B),  so 

that  it  may  take  up  a  quantity  of  that  gas, 
afterwards  through  a  tube  (C)  containing 
pumice-stone  soaked  w^itli  oil  of  vitriol,  to 
remove  the  water,  and  then  through  a  bulb 
(D)  containing  platinised  asbestos  (see  p. 
143).  The  mixture  of  the  gases  issuing 
into  the  air  is  quite  invisible,  but  when  the 
bulb  is  gently  heated,  combination  takes 
place,  and  dense  white  clouds  are  formed 
in  the  air,  from  the  combination  of  the 
sulphuric  anhydride  (SO3)  produced,  with 
the  atmospheric  moisture. 

Sulphuric  anhydride  forms  a  white 
mass  of  crystals  resembling  asbestos  ; 
it  fumes  when  exposed  to  air,  since  it  emits  vapour  which  condenses  the 
moisture  of  the  air,  and  it  soon  deliquesces  from  absorption  of  water, 
becoming  sulphuric  acid  ;  SO3  4-  HgO  =  HgSO^.  When  thrown  into 
water  it  hisses  like  red  hot  iron,  from  the  sudden  formation  of  steam.  It 
fuses  at  65°  F.,  and  boils  at  110°  F.  The  vapour  is  decomposed,  as  men- 
tioned above,  into  sulphurous  acid  gas  and  oxygen,  when  passed  through 
a  red  hot  tube.  Phosphorus  burns  in  its  vapour,  combining  with  the 
oxygen  and  liberating  sulphur.  Baryta  glows  when  heated  in  the  vapour 
of  sulphuric  anhydride,  and  combines  with  it  to  form  barium  sulphate. 

Sulphuric  anhydride  is  capable  of  combining  with  olefiant  gas  (CgH^) 
and  similar  hydrocarbons,  and  absorbs  these  from  mixtures  of  gases.  In 
the  analysis  of  coal  gas,  a  fragment  of  coke  wetted  with  ^Nordhausen 
sulphuric  acid  is  passed  up  into  a  measured  volume  of  the  gas  standing 
over  mercury  to  absorb  these  illuminating  hydrocarbons. 

An  interesting  method  of  obtaining  the  sulphuric  anhydride  consists 
in  pouring  2  parts  by  weight  of  oil  of  vitriol  over  3  parts  of  phosphoric 
anhydride,  contained  in  a  retort  cooled  in  ice  and  salt,  and  afterwards 
distilling  at  a  gentle  heat,  when  the  phosphoric  anhydride  retains  water, 
and  the  SO3  may  be  condensed  in  a  cooled  receiver. 

When  oil  of  vitriol  is  converted  into  vapour,  its  molecular  weight  (98 
parts)  is  found  to  yield  4  volumes  of  vapour  instead  of  2,  which  is 
explained  by  a  dissociation  or  temporary  decomposition  of  the  molecule 
of  H0SO4  into  HgO  (2  volumes),  and  SO3  (2  volumes).  On  cooling  these 
recombine  to  form  HgSO^ . 

146.  Sulphates — Action  of  sidphuric  acid  upon  metallic  oxides. — At 
common  temperatures  sulphuric  acid  is  capable  of  displacing  all  other 
acids  from  their  salts  ;  many  cases  will  be  remembered  in  which  this 
power  of  sulphuric  acid  is  turned  to  account. 


SULPHATES. 


211 


So  great  is  the  acid  energy  of  sulphuric  acid,  that  when  it  is  allowed 
to  act  upon  an  indifferent  or  acid  metallic  oxide,  it  causts  the  separation 
of  a  part  of  the  oxygen,  and  reacts  with  the  basic  oxide  so  produced. 
Advantage  is  sometimes  taken  of  this  circumstance  for  the  preparation  of 
oxygen;  for  instance,  when  manganese  dioxide  is  heated  with  sulphuric 
acid,  sulphate  of  manganese  is  produced,  and  oxygen  disengaged — 

MnOg  +  HgSO^  =  MnSO^  +  0  +  HgO. 

Again,  if  chromic  anhydride  be  treated  in  the  same  way,  chromic  sulphate 
will  be  produced,  with  liberation  of  oxygen — 

2Cr03  +  SH^SO,  =  Cr2.3SO^  +  O3  +  3H2O. 

A  mixture  of  potassium  dichromate  (K20.2Cr03)  and  sulphuric  acid  is 
sometimes  used  as  a  source  of  oxygen. 

Sulphuric  acid  is  a  dibasic  acid,  that  is,  it  contains  two  atoms  of 
hydrogen  which  may  be  replaced  by  a  metal.  In  normal  sulphates,  both 
atoms  of  H  are  so  replaced,  as  in  K2SO4,  the  normal  potassium  sulphate. 
When  only  a  part  of  the  H  is  replaced,  acid  sulphates  are  produced;  thus 
KHSO4  is  acid  potassium  sulphate,  which  is  very  useful  in  blowpipe  and 
metallurgic  chemistry,  because,  when  heated,  it  yields  normal  potassium 
sulphate  and  sulphuric  acid;  2KHS04  =  K2S04  + H^SO^.  When  the 
two  atoms  of  H  in  H.^SO^  are  replaced  by  different  metals,  double  sid- 
phates  are  formed ;  potassium-alum,  KA1(S04)2,  is  an  example  of  this 
class,  in  which  one-fourth  of  the  H  in  2H2SO4  is  replaced  by  potassium, 
and  the  other  three  atoms  by  triatomic  aluminium. 

The  following  table  exhibits  the  composition  of  the  sulphates  most 
frequently  met  with  : — 


Chemical  Name. 

Common  Name. 

Formula. 

Potassium  sulphate 

Sal  polychre.st 

K,S04 

Sodium  sulphate 

Glauber's  Salt 

Na.,SO4.10H2O 

Hydropotassic  sulphate 

KHSO4 

Ammonium  sulphate 

(NH4),S04 

Barium  sulphate 

Heavy  spar 

BaS04 

Calcium  sulphate 

Gypsum 

CaS04.2H20 

Magnesium  sulphate 

Epsom  salts 

MgS04.7H20 

Potassium-aluminium  sulphate 

Potasli-alnm 

KAl(S04)2.r2H.,0 

Alumiuium-animoninm  sulphate 

Ammonia-alum 

NH4Al(5O,).,.12H.,0 

Potassium-chromium  sulphate 

Chrome-alum 

KCr(S04)2.12H,0 

Ferrous  sulphate 

Green  vitriol          ) 
Copperas                \ 

FeS04.7H20 

Manganous  sulphate 

AInS04.5HaO 

Zinc  sulphate 

White  vitriol 

ZuSO4.7H.3O 

Lead  sulphate 

PbS04 

Cupric  sulphate 

Blue  vitriol           ) 
Blue  stone             \ 

CuSO^.SHaO 

In  consequence  of  the  tendency  of  sulphuric  acid  to  break  up  into  sul- 
phur dioxide  and  oxygen  at  a  high  temperature,  most  of  the  sulphates  are 
decomposed  by  heat ;  cupric  sulphate,  for  example,  when  very  strongly 
heated,  leaves  cupric  oxide,  whilst  sulphur  dioxide  an^  oxygen  escape ; 
CUSO4  =  CuO  +  SO2  -f-  0.  Ferrous  sulphate  is  more  easily  decomposed  ; 
2FeS0,  =  1X03  +  SO2 -H  SO3  . 

The  normal  sulphates  of  potassium,  sodium,  barium,  strontium,  calcium, 


212  HYPOSULPHITE  OF  SODA.. 

and  lead  are  not  decomposed  by  heat,  and  sulphate  of  magnesium  is  only 
partly  decomposed  at  a  very  high  temperature. 

When  a  sulphate  of  an  alkali  or  alkaline  earth  metal  is  heated  with  char- 
coal, the  carbon  removes  the  whole  of  the  oxygen,  and  a  sulphide  of  the 
metal  remains,  thus — 

KoSO.  (Potassium  sulphate)    +    C^    =    K.iS  (Potassiurn  sulphide)    +    4C0  . 

Hydrogen,  at  a  high  temperature,  effects  a  similar  decomposition. 

Even  at  the  ordinary  temperature,  calcium  sulphate  in  solution  is 
sometimes  deoxidised  by  organic  matter ;  this  may  occasionally  bo  noticed 
in  well  and  river  waters  when  kept  in  closed  vessels  ;  they  acquire  a  strong 
smell  of  hydrosulphuric  acid,  in  consequence  of  the  conversion  of  a  part 
of  the  calcium  sulphate  into  sulphide  by  the  organic  constituents  of  the 
water,  and  the  subsequent  decomposition  of  the  calcium  sulphide  by  the 
carbonic  acid  present  in  the  water. 

Adds  containing  Hydrogen,  Sulphur,  and  Oxygen. 
Hyposnlphurous  (formerly  hydrosulphurous),  .  .     HjSO.^ 


\ 


Sulphurous, 

Sulpliuric,  .... 

Thiosulphuric  (formerly  hyposulphurous), 

Dithionic, 

Trithionic,  .... 

Tetrathionic,  .... 

Pentathionic,  .... 


H^SO, 
H2SO4 
HjSgOj 
HjSjOg 
HjSjOg 

H,S,0« 


147.  Hi/posulphurous  or  thiosalphunc  acid*  (HgSgOg). — This  acid  has 
not  been  obtained  in  the  separate  state  ;  but  many  salts  are  known  which 
are  evidently  derived  from  it,  and  such  salts  are  called  hyposulphites  or 
thiosulphates. 

The  sodium  hyposulphite  is  by  far  the  most  important  of  these  salts, 
being  very  largely  employed  in  photography,  and  as  a  substitute  for 
sodium  sulphite  as  an  antichlore.  The  simplest  method  of  preparing  it 
consists  in  digesting  powdered  roll  sulphur  with  solution  of  sodium 
sulphite  (Na2S03),  when  the  latter  dissolves  an  atom  of  sulphur  and 
becomes  hyposulphite  (NagSgOg),  which  crystallises  from  the  solution, 
when  sufficiently  evaporated,  in  fine  prismatic  crystals,  having  the 
formula  Na^SgOySHgO. 

On  a  large  scale,  sodium  hyposulphite  is  more  economically  prepared 
from  the  calcium  hyposulphice  obtained  by  exposing  the  refuse  (tank-waste 
or  soda-waste)  of  the  alkali  works  to  the  air  for  some  days.  This  refuse 
contains  a  large  proportion  of  calcium  sulphide,  which  becomes  converted 
into  hyposulphite  by  oxidation  ;  2CaS  +  04  =  CaSgOg  +  CaO . 

The  hyposulphite  is  dissolved  out  by  water,  and  the  solution  mixed 
with  sodium  carbonate,  when  calcium  carbonate  is  precipitated  and 
sodium    hyposulphite    remains    in    solution ;  CaSgOj  +  NagCOg  =  CaCOj 

+  XaA03- 

The  most  remarkable  and  useful  property  of  the  sodium  hyposulphite 
is  that  of  dissolving  the  chloride  and  iodide  of  silver,  which  are  insoluble 
in  water  and  most  other  liquids. 

On  mixing  a  solution  of  silver  nitrate  with  one  of  sodium  chloride,  a  white 
precipitate  of  silver  chloride  is  obtained,  the  separation  of  which  is  promoted  by 
stirring    the    liquid;    AgN03  +  NaCl  =  AgCl  +  NaN03 .     The    precipitate    may    be 

*  '  V-TTo,  under,  containing  less  oxygen  than  sulphurous  acid.  The  name  hyposulphurous 
acid  is  now  often  bestowed  upon  the  acid  H2SO2  (p.  214). 


HYPOSULPHITE  OF  SODA.  213 

allowed  to  settle  and  washed  twice  or  thrice  by  decantation.  One  portion  of  the 
silver  chloride  is  trausfeiTed  to  another  glass,  mixed  with  water,  and  solution  of 
sodium  hyposulphite  added  by  degrees.  The  silver  chloride  is  very  easily  dissolved, 
yielding  an  intensely  sweet  solution,  which  contains  the  hyposulphite  of  sodium  and 
silver,  produced  by  double  decomposition  between  the  silver  chloride  and  sodium 
hyposulphite  ;  AgCl  +  Na^SoOs  =  NaCl  +  NaAgSaOg . 

The  sodium  silver  hyposulphite  may  be  obtained  in  crystals  from  the  solution. 

When  the  silver  chloride  is  acted  on  by  a  smaller  proportion  of  the  hyposulphite, 
another  hyposulphite  of  sodium  and  silver  is  formed,  which  is  veiy  insoluble  in 
water — 

2AgCl  +   3Na.A03  =  Ag2]Sra4(S203)3   +   2NaCl. 

Hence  the  necessity  for  using  a  strong  solution  of  the  hyposulphite  in  fixing  photo- 
graphic prints. 

If  the  other  portion  of  the  silver  chloride  be  exposed  to  the  action  of  light,  and 
especially  of  direct  sunlight,  it  assumes  by  degrees  a  dark  slate  colour,  from  the  for- 
mation of  silver  subchloride,  4AgCl  +  H-fi  ■■=  2 AggCl  +  HCl  +  HCIO  .  By  treating  this 
darkened  silver  chloride  with  sodium  hyposulphite,  as  before,  the  unaltered  silver 
chloride  will  be  entirely  dissolved,  but  the  subchloride  will  be  decomposed  into 
monochloride,  which  dissolves  in  the  hyposulphite,  and  metallic  silver,  which  is  left 
in  a  very  Hnely-divided  state  as  a  black  powder  ;  AgoCl  =  AgCl  +  Ag.  The  application 
of  these  facts  in  photography  is  well  illustrated  by  the  following  experiments : — A 
sheet  of  paper  is  soaked  for  a  minute  or  two  in  a  solution  of  10  grains  of  common  salt 
in  an  ounce  of  water  contained  in  a  flat  dish.  It  is  then  dried,  and  soaked  for  three 
minutes  in  a  solution  of  50  grains  of  silver  nitrate  in  an  ounce  of  water.  The  paper 
thus  becomes  impregnated  with  silver  chloride  formed  by  the  decomposition  between 
the  sodium  chloride  and  the  silver  nitrate.  It  is  now  hung  up  in  a  dark  place  to  dry. 
If  a  piece  of  lace,  or  a  fern  leaf,  or  an  engraving  on  thin  paper,  with  well-marked 
contrast  of  light  and  shade,  be  laid  upon  a  sheet  of  the  prepared  paper,  pressed  down 
upon  it  by  a  plate  of  glass  and  exposed  for  a  short  time  to  sunlight,  a  perfect  repre- 
sentation of  the  object  will  be  obtained,  those  parts  of  the  sensitive  paper  to  which 
the  light  had  access  having  been  darkened  by  the  fonnation  of  silver  subchloride, 
whilst  those  parts  which  were  protected  from  the  light  remain  unchanged. 

But  if  this  photographic  print  were  again  exposed  to  the  action  of  light,  it  would 
soon  be  obliterated,  the  unaltered  silver  chloride  in  the  white  parts  being  acted  on 
by  light  in  its  turn.  The  print  is  therefore  ^-ec^  by  soaking  it  for  a  short  time  in  a 
saturated  solution  of  sodium  hyposulphite,  which  dissolves  the  white  unaltered  silver 
chloride  entirely,  and  decomposes  the  subchloride  formed  by  the  action  of  light, 
leaving  the  black  finely-divided  metallic  silver  in  the  paper.  The  print  should  now 
be  washed  for  two  or  three  hours  in  a  gentle  stream  of  water,  to  remove  all  the  silver 
hyposulphite,  when  it  wUI  be  quite  permanent. 

The  power  of  sodium  hyposulphite  to  dissolve  silver  chloride  has  also 
been  turned  to  account  for  extracting  silver  from  its  ores  in  which  it  is 
occasionally  present  in  the  form  of  chloride. 

The  behaviour  of  solution  of  sodium  hyposulphite  with  powerful 
acids  explains  the  circumstance  that  the  hyposulphurous  acid  has  not  been 
isolated,  for  if  the  solution  be  mixed  with  a  little  diluted  sulphuric  or 
hydrochloric  acid,  it  remains  clear  for  a  few  seconds,  and  then  becomes 
suddenly  turbid  from  the  separation  of  sulphur,  at  the  same  time  evolving 
a  powerful  odour  of  sulphur  dioxide,  1128203  =  HgO  +  S +  SO2.  This 
disposition  of  the  hyposulphurous  acid  to  break  up  into  sulphur  dioxide 
and  sulphur  also  explains  the  precipitation  of  metallic  sulphides,  which 
often  takes  place  when  sodium  hyposulphite  is  added  to  the  acid  solutions 
of  the  metals.  Thus,  if  an  acid  solution  of  antimonious  chloride  (obtained 
by  boiling  crude  antimony  ore  (Sb.,S3)  with  hydrochloric  acid)  be  added 
to  a  boiling  solution  of  sodium  hyposulphite,  the  sulphur,  separated  from 
the  hyposulphurous  acid,  combines  with  the  antimony  toJorm  a  fine  orange- 
red  precipitate  of  antimonious  sulphide  (Sb2S3),  which  is  used  in  painting 
under  the  name  of  antimony  vermilion.  On  the  large  scale,  the  solution 
of  calcium  hyposulphite  obtained  from  the  alkali  waste  is  employed  in 


214  DITHIONIC  ACID. 

the  preparation  of  antimony  vermilion,  as  being  less  expensive  than  the 
sodimn-salt.  Lead  hyposulphite  dissolved  in  sodium  hyposulphite  is 
used  as  a  hair-dye,  depositing  the  black  lead  sulphide. 

Wlien  crystals  of  sodium  hyposulphite  are  heated  in  the  air,  they 
lirst  fuse  in  their  water  of  crystallisation,  then  dry  up  to  a  Avhite  mass, 
Avhich  burns  with  a  blue  flame,  leaving  a  residue  of  sodium  sulphate. 
If  heated  out  of  contact  with  air,  sodium  pentasulphide  wiU  be  left 
with  the  sodium  sulphate  4(Na2S2035Il20)  =  2OH2O +  3^82804  +  ^8285. 

Some  of  the  reactions  of  sodium  hyposulphite  become  more  intelligible 
when  the  salt  is  represented  as  sodium  sulphate  (^82804)  in  which  an 
atom  of  sulphur  has  displaced  an  atom  of  oxygen  (Na2S03S). 

Ilydrosulphurous  acid*  (HgSOj). — When  an  aqueous  solution  of  sulphurous  acid  is 
])laced  in  contact  with  zinc,  the  metal  is  dissolved,  forming  a  yellow  solution  of  zinc 
hydrosulphite  ;  2H.,S03  +  Zn2=Zn(HS02)2  +  Zn(OH)2. 

The  solution  bleaches  organic  colours,  and  reduces  the  salts  of  silver,  mercury,  and 
copper  to  the  metallic  state.     It  is   very  unstable,  soon  becoming  colourless  zinc 
kjl.osulphite  ;  Zn(HS02)o  =  ZnS203+H20. 
'^The  sodium  hydrosulphite,  NaHS02,  is  obtained  by  digesting  zinc  in  solution  of 
acid  sulphite  of  sodium  ;  NaHS03  +  Zn  =  ZnO  +  NaHS02. 

It  forms  needle-like  crystals  ver}'  soluble  in  water,  insoluble  in  strong  alcohol,  and 
becoming  acid  sulphite  of  sodium,  NaHSOg,  by  absorption  of  oxygen  from  the  air. 
By  decomposing  the  sodium  hydrosulphite  with  oxalic  acid,  hydrosulphurous  acid  is 
obtained  as  an  orange-yellow  unstable  liquid. 

148.  Hyposulphuric  acid  or  dithionic  acid  (HaS-^Og  or  HSO3)  has  not  at  present 
acquired  any  practical  importance.  To  prepare  a  solution  of  the  acid,  manganese 
dioxide  in  a  state  of  fine  division  is  suspended  in  water  and  exposed  to  a  current 
of  sulphurous  acid  gas,  the  water  being  kept  very  cold  whilst  the  gas  is  passing.  A 
solution  of  manganous  hyposulphate  is  thus  obtained  ;  2SO2  +  MnOg  =  MnS.20g.  Some 
manganous  sulphate  is  always  formed  at  the  same  time  ;  SOj  +  Mn02  =  MnS04,  and 
if  the  temperature  be  allowed  to  rise,  this  will  be  produced  in  large  quantity. 

The  solution  containing  the  sulphate  and  hyposulphate  is  decomposed  by  solution 
of  baryta  (baryta-water),  when  manganous  oxide  is  precipitated,  together  with  barium 
sulphate,  and  barium  hyposulphate  is  left  in  solution.  To  the  filtered  solution 
diluted  sulphuric  acid  is  carefully  added  until  all  the  barium  is  precipitated  as 
sulphate,  when  the  solution  of  hyposulphuric  acid  is  filtered  off  and  evaporated  in 
vacuo  over  oil  of  vitriol.  It  forms  a  colourless  inodorous  liquid,  which  is  decomposed 
when  heated,  into  sulphuric  acid  and  sulphur  dioxide ;  H.2S20g  =  H.2SO4  +  SOj. 
Oxidising  agents  (nitric  acid,  chlorine.  &c.)  convert  it  into  sulphuric  acid. 

The  hyposidphates  are  not  of  any  practical  importance  ;  they  are  all  soluble,  and  are 
decomposed  by  heat,  leaving  sulphates,  and  evolving  sulphur  dioxide. 

149.  Trithionic  acid  (H2S30fi)  or  s^iJphuretted  hyposulphuric  acid,  is  also  a  prac- 
tically unimportant  acid.  It  is  prepared  from  the  potassium  trithionate  which  is 
formed  by  boiling  a  strong  solution  of  acid  sulphite  of  potassium  with  sulphur  until 
the  solution  becomes  colourless,  and  filtering  the  hot  solution  from  any  undissolved 
sulphur;  6KHSO3  + 8  =  2X28305  + KgSOj  +  SHaO.  The  solution  deposits  potassium 
trithionate  in  prismatic  crystals.  By  dissolving  these  in  water,  and  decomposing 
the  solution  with  perchloric  acid,  the  potassium  is  precipitated  as  perchlorate,  and  a 
solution  of  trithionic  acid  is  produced,  from  which  the  acid  has  been  obtained  in 
crystals.  It  is,  however,  very  unstable,  being  easily  resolved  into  sulphur  dioxide, 
sulphuric  acid,  and  free  sulphur — 

HaSaOg  =   H2SO4   +   SO.   +   8. 

150.  Tetrathionic  add  (H284O5)  is  rather  more  stable  than  the  preceding  acid, 
though  equally  devoid  of  practical  importance.  It  is  formed  when  barium  hypo- 
sulphite, suspended  in  a  little  water,  is  treated  with  iodine,  when  the  tetrathionate 
is  obtained  in  crystals  ;  2(BaS203)  +  l2=Bal2  +  BaS406. 

V>\-  exactly  precipitating  the  barium  from  a  solution  of  the  tetrathionate  by  adilition 
of  diluted  sulphuric  acid,  the  solution  of  tetrathionic  acid  may  be  obtained.     "When 

*  Often  called  hyposulphurons  acid.  Bemthsen  gives  the  formula  of  the  acid  as 
H:;^2^4'  ^"d  that  of  the  sodium  salt  as  Na2S.204 . 


BISULPHIDE  OF  CARBON. 


215 


the  solution  is  boiled,  it  is  decomposed  into  sulphuric  acid,  sulphur  dioxide,  and 
free  sulphur  ;  HjS^Og  =  H2SO4  +  SO2  +  So . 

When  solution  of  ferric  chloride  is  added  to  sodium  hyposulphite,  a  fine  purple 
colour  is  at  first  produced,  which  speedily  vanishes,  leaving  a  colourless  solution. 
The  purple  colour  appears  to  be  due  to  the  formation  of  the  ferric  hyposulphite,  which 
speedily  decomposes,  the  ultimate  result  being  expressed  by  the  equation  Fe^Cls 
+  2(1^0^8^03)  =  Na2S406  +  2FeCl2  +  2NaCl . 

151.  Pentathionic  add  (HgSgOg)  possesses  some  interest  as  resulting  from  the  action 
of  sulphuretted  hydrogen  upon  sulphur  dioxide,  when  much  sulphur  is  deposited, 
and  pentathionic  acid  remains  in  solution;  3H2S  +  4S02  =  H2Sg06  +  2H20  +  S2.  To 
obtain  a  concentrated  solution  of  the  acid,  sulphuretted  hydrogen  and  sulphur  dioxide 
are  passed  alternately  through  the  same  portion  of  water  until  a  large  deposition  of 
sulphur  has  taken  place.  This  is  allowed  some  hours  to  settle ;  the  clear  liquid 
poured  off  and  the  solution  concentrated  by  evaporation,  first  over  a  water-bath,  and 
finally,  in  vacuo,  over  oil  of  vitriol ;  for  a  concentrated  solution  of  pentathionic  acid 
is  decomposed  by  heat  into  sulphuric  acid  and  sulphur  dioxide,  with  separation  of 
sulphur  ;  HoSgOs  =  H2SO4  +  SO2  +  S3  . 

Persulphuric  acid  is  the  name  given  by  Berthelot  to  a  crystalline  compound,  S2O7 
formed  from  SOj  and  0  under  the  influence  of  electricity  of  high  tension. 


/ 


Bisulphide  of  Cakbox  or  Carbon  Bisulphide. 

€82  =  76  parts  by  weight. 

152.  This  very  important  compound  (also  called  bisulphuret  of  carbon) 
is  found  in  small  quantity  among  the  products  of  destructive  distillation 
of  coal,  and  is  very  largely  manufactured  for  use  as  a  solvent  for  sulphur, 
phosphorus,  caoutchouc,  fatty  matters,  &c.  It  is  one  of  the  few  compounds 
of  carbon  which  can  be  obtained  by  the  direct  union  of  their  elements, 
and  is  prepared  by  passing  vapour  of  sulphur  over  charcoal  heated  to 
redness.     It  is  remarkable  that  no  heat  is  evolved  in  this  act  of  combination. 

In  small  quantity  carbon  sulphide  is  easily  prepared  in  a  tube  of  German  glass 
(combustion-tube)  about  two  feet  long  and  half  an  inch  in  diameter  (fig.  210). 


Fig.  210. 

This  tube  is  closed  at  one  end,  and  a  few  fragments  of  sulphur  dropped  into  it,  so 
as  to  occupy  two  or  three  inches.  The  rest  of  the  tube  is  filled  up  with  small  frag- 
ments of  recently  calcined  wood  charcoal.  The  tube  is  placed  in  a  combustion- 
furnace,  and  its  open  end  connected  by  a  perforated  cork  with  a  glass  tube,  which 
dips  just  below  the  surface  of  water  contained  in  a  bottle  placed  in  a  vessel  of  very 
cold  water.  That  part  of  the  tube  which  contains  the  charcoal  is  first  surrounded 
with  red  hot  charcoal,  and  when  it  is  heated  to  redness  a  little  red  hot  charcoal  is 
placed  near  the  end  containing  the  sulphur  (hitherto  protected  by  a  sheet-iron  screen), 
so  that  the  vapour  of  sulphur  may  be  slowly  passed  over  the  red  hot  charcoal.  The 
disulphide  being  insoluble  in  water,  and  much  heavier  (sp.  gr.  ^  '27),  is  deposited  be- 
neath the  water  in  the  receiver.  To  purify  the  carbon  disulphide  from  the  water  and  the 
excess  of  sulphur  which  is  deposited  with  it,  the  water  is  carefully  drawn  ort'  with  a 
small  siphon,  the  disulphide  transferred  to  a  flask,  and  a  few  fragments  of  calcium 
chloride  dropped  into  it  to  absorb  the  water.     A  bent  tube  connected  with  a  Liebig's 


216 


PREPAKATION  OF  BISULPHIDE  OF  CAKBON. 


condenser,  or  with  a  worm,  is  attached  to  the  flask  (fig.  211)  by  a  perforated  cork, 
and  the  flask  is  gently  heated  in  a  water- bath,  when  the  carbon  disulphide  is 
distilled  over  as  a  2)erfectly  colourless  liquid.  The  inflammability  of  the  disulphide 
renders  great  care  necessary. 

On  a  large  scale,  a  fire-clay  or  cast-iron 
retort  is  filled  with  fragments  of  charcoal 
and  heated  to  redness,  pieces  of  sulphur 
being  occasionally  dropped  in  through  an 
earthenware  tube  passing  to  the  bottom  of 
the  retort.  "When  very  large  quantities 
are  made,  coke  is  employed,  and  the 
vapour  of  sulphur  is  obtained  from  iron 
pyrites.  The  carbon  disulphide  is  pos- 
sessed of  some  very  remarkable  properties : 
it  is  a  very  brilliant  liquid,  the  light 
passing  through  which  at  certain  angles 
is  partly  decomposed  into  its  component 
coloured  rays  before  it  reaches  the  eye. 
These  properties  are  dependent  upon  its  high  refractive  and  dispersive 
powers,  which,  are  turned  to  great  advantage  in  optical  experiments, 
especially  in  spectru7n  analysis,  where  the  rays  emanating  from  a 
coloured  flame  are  analysed  by  passing  them  through  a  prismatic  bottle 
filled  with  carbon  disulphide.  It  is  also  highly  diathennanous,  that  is, 
it  allows  rays  of  heat  to  pass  through  it  with  comparatively  little  loss,  so 
that  if  it  be  rendered  opaque  to  light  by  dissolving  iodine  in  it,  the  rays 
of  light  emanating  from  a  luminous  object  may  be  arrested,  whilst  the 
calorific  rays  are  allowed  to  pass.  Carbon  disulphide  is  a  very  volatile 
liquid,  readily  assuming  the  form  of  vapour  at  the  ordinary  temperature, 
and  boiling  at  11 8° '5  F.  Its  vapour,  when  diluted  with  air,  has  a  very 
disgusting  and  exaggerated  odour  of  sulphuretted  hydrogen,  but  the  smell 
at  the  mouth  of  the  bottle  is  ethereal  and  not  unpleasant  if  the  disul- 
phide has  been  carefully  purified. 

The  rapid  evaporation  of  carbon  disulphide  is,  of  course,  productive  of  great  cold. 
If  a  few  drops  be  placed  in  a  watch-glass  and  blown  upon,  they  soon  pass  off  in 
vapour,  and  the  temperature  of  the  glass  is  so  reduced  that  some  of  the  disulphide  is 
frozen  ;  this  melts  when  the  glass  is  placed  in  the  palm  of  the  hand.  If  a  glass  plate 
be  covered  with  water,  a  watch-glass  containing  carbon  disulj)hide  placed  on  it,  and 
evaporation  promoted  by  blowing  through  a  tube,  the  watch-glass  will  be  frozen  on 
to  the  plate,  so  that  the  latter  may  be  lifted  up  by  it. 

The  carbon  disulphide  is  exceedingly  inflammable  ;  it  takes  fire  at 
a  temperature  far  below  that  required  to  inflame  ordinary  combustible 
bodies,  and  burns  with  a  bright  blue  flame,  producing  carbonic  and 
sulphurous  acid  gases  (CS2-l-06  =  C02-f- 2SO2),  ^^^  having  a  great  ten- 
dency to  deposit  sidphur  unless  the  supply  of  air  is  very  good. 

The  heat  of  combustion  of  CS^  exceeds  by  222  centigrade  units  the  sum  of  the  heat 
evolved  by  the  combustion  of  its  constituents  in  the  separate  form. 

If  a  little  carbon  disulphide  be  dropped  into  a  small  beaker,  it  may  be  inflamed 
by  holding  in  its  vapour  a  test-tube  containing  oil  heated  to  about  300°  F.,  which 
will  be  found  incapable  of  firing  gimpowder  or  of  inflaming  any  ordinary  combustible 
substance. 

The  abundance  of  sulphur  separated  in  the  flame  of  carbon  disulphide  enables  it 
to  burn  iron  by  converting  it  into  sulphide.  If  some  carbon  disulphide  be  boiled 
in  a  test-tube  provided  with  a  piece  of  glass  tube  from  which  the  vapour  may  be 
burnt,  and  a  piece  of  thin  iron  wire  be  held  in  the  flame  (fig.  212),  it  will  burn  with 
vivid  scintillation,  the  fusible  ferrous  sulphide  dropping  off. 


PROPERTIES  OF  BISULPHIDE  OF  CARBON. 


217 


The  vapour  of  carbon  disulphide  acts  very  injuriously  if  breathed  for 
any  length  of  time,  producing  symptoms  somewhat  resembling  those 
caused  by  sulphuretted  hydrogen.  Its  poisonous  properties  have  been 
turned  to  account  for  killing  insects  in  grain  without  injuring  it. 

The  chief  applications  of  carbon  disulphide  depend  upou  its  power  of 
dissolving  the  oils  and  fats.  After  as 
much  oil  as  possible  has  been  extracted 
from  seeds  and  fruits  by  pressure,  a  fresh 
quantity  is  obtained  by  treating  the 
pressed  cake  with  carbon  disulphide, 
which  is  afterwards  recovered  by  distil- 
lation from  the  oil.  In  Algiers  it  is 
employed  for  extracting  the  essential  oils 
in  which  reside  the  perfumes  of  roses, 
jasmine,  lavender,  &c. 

Carbon  disulphide  has  often  been 
made  a  starting-point  in  the  attempts  to 
produce  organic  compounds  by  synthesis. 
It  may  be  employed  in  the  formation  of 
the  hydrocarbons  which  are  usually  de- 
rived from  organic  sources  ;  for  if  it  be 
mixed  with  hydric  sulphide  (by  passing 
that  gas  through  a  bottle  containing 
the  disulphide  gently  warmed),  and  passed  over  copper-turnings  heated 
to  redness  in  a  porcelain  tube,  olehant  gas  will  be  produced ;  2CS2 
+  2HoS-fCug  =  6CuS-l-C2H,. 

The  action  of  carbon  disulphide  upon  ammonia  is  practically  import- 
ant for  the  easy  production  of  ammonmra  sulphocyanide,  which  is  formed 
when  the  disulphide  is  dissolved  in  alcohol,  and  acted  on  by  ammonia 
with  the  aid  of  heat — 


Fig.  212. 


CSfl 


Carbon  bisulphide. 


-I-     2NH3    = 


H^S 


+ 


NH4CNS. 


Animoniuin  sulphocyanide. 


Carbon  disulphide  is  often  called  sulphocarbonic  acid;  it  combines 
with  some  of  the  sulphur-bases  to  form  sul/phocarhonates  or  thiocarhonates, 
which  correspond  to  the  carbonates,  containing  sulphur  in  place  of  oxygen. 
Thus,  when  a  solution  of  potassium  sulphide  is  mixed  with  an  excess  of 
carbon  disulphide,  potassium  sulphocarbonate  is  obtained  in  orange-yellow 
crystals.  Even  the  hydrogen  compound  corresponding  in  composition  to 
the  unknown  H.2CO3  may  be  obtained  as  a  yellow  oily  liquid  by  decom- 
posintj  potassium  sulphocarbonate  with  hydrochloric  acid  ;  KgCSg  +  2HC1 
^H^CSg-f  2KC1. 

Potassium  thiocarbonate  is  applied  for  the  destruction  of  the  phylloxera 
insect  which  infests  vines. 

As  Avould  be  expected,  the  sulphocarbonates,  when  boiled  with  water, 
exchange  their  sulphur  for  oxygen,  becoming  carbonatesj  K2CS3  -i-  SHgO 
=  K,C03  +  3H,S. 

The  carbon  disulphide  vapour  in  coal  gas  is  one  of  the  most  injurious 
of  the  impurities,  and  one  of  the  most  difficult  to  remove  with  economy. 

It  is  especially  injurious,  because,  when  burning  in  the  presence  of 
aqueous  vapour,  a  part  of  its  sulphur  is  converted  into  sulphuric  acid,  the 
corrosive  effects  of  which  are  so  damaging.     Several  processes  have  been 


218  CARBONIC  OXYSULPHIDE. 

devised  for  its  removal.  The  gas  has  been  washed  with  the  ammoniacal 
liquor  (containing  ammoniutn  sulphide)  which  absorbs  the  disulphide. 
Steam,  at  a  high  temperature,  has  been  employed  to  convert  it  into 
hydrosulphuric  acid  and  carbon  dioxide,  which  are  both  easily  removed 
from  the  gas;  CS2  +  2H20  =  C02  +  2H2S.  Lime  at  a  red  heat  decom- 
poses it  in  a  similar  way;  CSg  +  3CaO  =  CaCOg  +  2CaS.  Oxide  of  lead 
dissolved  in  caustic  soda  has  been  used  to  convert  it  into  sulphide  of  lead  ; 
CSo  +  2PbO  +  2XaH0  =  2PbS  +  Na2C03  +  H2O.  Its  removal  as  sulpho- 
carbonate  by  an  alcoholic  solution  of  potash  or  soda  has  also  been  pro- 
possd.  At  present,  however,  it  retains  its  character  as  one  of  the  most 
troublesome  impurities  with  which  the  gas  manufacturer  has  to  deal. 

Carbonic  oxysulphide,  COS  =  60  parts  by  weight  =  2  volumes.  This  compound, 
which  may  be  regarded  as  hydrosulphuric  acid  in  which  CO  has  replaced  H2,  is 
formed  when  a  mixture  of  carbonic  oxide  with  sulphur  vapour  is  acted  on  by  electric 
sparks,  or  passed  through  a  red  hot  porcelain  tube. 

It  is  easily  prepared  by  gently  heating  the  potassium  sulphocyanide  with  oil  of 
vitriol  diluted  with  four-tifths  of  its  volume  of  water,  and  collecting  the  gas  over 
mercury. 

The  action  of  the  sulphuric  acid  upon  the  sulphocyanide  produces  hydrosulpho- 
cyauicacid;  KCNS  (potassium  sulphocyanide)  +HjS04  =  HCNS  +  KHS04;  which  is 
then  decomposed  by  the  water,  in  the  presence  of  the  excess  of  sulphuric  acid,  into 
the  carbonic  oxysulphide  gas  and  ammonia,  which  combines  with  the  sulphuric  acid, 
HCNS  +  Hj0  =  NH3  +  C0S.  The  gas  has  a  peculiar  disagreeable  odour,  recalling 
that  of  carbon  disulphide  ;  it  is  more  than  twice  as  heavy  as  air  (sp.  gr.  2*11),  and  is 
very  inflammable,  burniug  with  a  blue  flame,  and  yielding  carbonic  and  sulphurous 
acid  gases.  Potash  absorbs  and  decomposes  it,  yielding  carbonate  and  sulphide  of 
potassium  ;  COS  +  4KHO  =  K2S  +  KjC03  +  2HjO . 

153.  Silicon  disulphide  (SiSj),  corresponding  in  composition  to  carbon  disulphide, 
is  obtained  by  burning  silicon  in  sulphur  vapour,  or  by  passing  vapour  of  carbon 
disulphide  over  a  mixture  of  silica  and  charcoal.  Unlike  the  carbon  compound,  it  is 
a  white  amorphous  solid,  absorbing  moisture  when  exposed  to  air,  and  soluble  in 
water,  which  gradually  decomposes  it  into  silica  and  hydrosulphuric  acid.  When 
heated  in  air  it  burns  slowly,  yielding  silica  and  sulphurous  acid  gas. 

154.  Nitrogen  sulphide  (NS)  is  a  yellow  crystalline  explosive  substance,  produced 
when  chloride  of  sulphur,  dissolved  in  carbon  disulphide,  is  acted  on  by  gaseous 
ammonia,  8NH3  +  38X1,  =  6NH4CI  +  2NS  +  S4,  when  ammonium  chloride  is  deposited, 
and  the  filtered  liquid,  allowed  to  evaporate,  deposits  sulphide  of  nitrogen  mixed  with 
sulphur,  which  may  be  dissolved  out  by  carbon  disulphide,  in  which  the  nitrogen 
compound  is  nearly  insoluble  :  this  substance  is  remarkable  for  its  sparing  solubility, 
its  irritating  odour,  and  its  explosibility  when  struck  ormoderately  heated,  its  elements 
being  held  together  by  a  very  feeble  attraction. 

155.  Chlorides  OP  SULPHUR. — The  subchloride,  ox  chloride  of  sulphur, 
or  sulphur  monochloride  (S2CI2  =135  parts  by  weight),  is  the  most 
important  of  these,  since  it  is  employed  in  the  process  of  vulcanising 
caoutchouc.  It  is  very  easily  prepared  by  passing  dry  chlorine  over 
sulphur  very  gently  heated  in  a  retort  (fig.  213) ;  the  sulphur  quickly 
melts,  and  the  sulphur  monochloride  distils  over  into  the  receiver  as  a 
yellow  volatile  liquid  (boiling-point,  280°  F.),  which  has  a  most  peculiar 
odour.  It  fumes  strongly  in  air,  the  moisture  decomposing  it,  forming 
hydrochloric  and  sulphurous  acids,  and  causing  a  deposit  of  sulphur  upon 
the  neck  of  the  bottle — 

2S2CI2  +  3H2O  =  4HC1  +  H2SO3  +  S3. 

When  poured  into  water,  it  sinks  (sp.  gr.  1  '68)  and  slowly  undergoes 
decomposition ;  the  separated  sulphur,  of  course,  belongs  to  the  electro- 
positive variety  (see  p.  192),  and  the  solution  contains,  beside  hydro- 
chloric and  sulphurous  acids,  some  of  the  acids  containing  a  larger  pro- 


SELENIUM. 


219 


portion  of  sulphur.  If  phosphorus  dissolved  in  carbon  disulphide  be 
mixed  with  sulphur  monochloride,  the  liquid  will  take  firft  on  addition  of 
ammonia.  The  specific  gravity  of  the  vapour  of  S2CI2  is  4*7,  showing 
that  it  is  68  times  as  heavy  as  hydrogen,  giving  for  its  molecular  weight 
136,  which  agrees  very  nearly  with  that  calculated  (135).  / 


-J- -=^^-^ —  ~-^-E—    ■  T ' 

Fig.  213. — Preparation  of  sulphur  monochloride. 

Sulphur  dichloride  (SClg)  is  a  far  less  stable  compound  than  the  preceding  chloride, 
from  which  it  is  obtained  by  the  action  of  an  excess  of  chlorine.  It  is  a  dgj'k  red 
fuming  liquid,  easily  resolved,  even  by  sunlight,  into  free  chlorine  and  sulphur 
monochloride 

Sulphur  di-iodide  (SIg)  is  a  crystalline  unstable  substance,  produced  by  the  direct 
union  of  its  elements,  and  occasionally  employed  in  medicine. 

Sulphur  moniodide  (S.2I.2)  is  obtained  in  large  tabular  crystals,  resembling  iodine, 
by  decompnsing  the  sulphur  monochloride  with  ethyle  iodide ;  SjCla  +  2C2H5I 
=  SJ„  +  2C,H5C1. 

Selenium, 

Se  =  79'5  parts  by  weight. 

156.  Selenium  (SeA^cr;,  tJie  moon]  is  a  rare  element,  very  closely  allied  to  sulphur 
in  its  natural  history,  physical  characters,  and  chemical  relations  to  other  bodies.  It 
is  found  sparingly  in  the  free  state  associated  with  some  varieties  of  native  sulphur, 
but  more  commonlj'  in  combination  with  metals,  forming  selenides,  which  are  found 
together  with  the  sulphides.  The  iron  pyrites  of  Fahlun,  in  Sweden,  is  especially 
remarkable  for  the  presence  of  selenium,  and  was  the  source  whence  this  element  was 
first  obtained.  The  Fahlun  pyrites  is  employed  for  the  manufacture  of  oil  of  vitriol, 
and  in  the  leaden  chambers  a  reddish-brown  deposit  is  found,  which  was  analysed  by 
Berzelius  in  1817,  and  found  to  contain  the  new  element. 

In  order  to  extract  selenium  from  the  seleniferous  deposit  of  the  vitriol  works,  it 
may  be  boiled  with  sulphuric  acid  diluted  with  an  equal  volume  of  water,  and 
nitric  acid  added  in  small  portions  until  the  oxidation  is  completed,  when  no  more  red 
fumes  will  escape.  The  solution,  containing  selenious  and  selenic  acids,  is  largely 
diluted  with  water,  filtered  from  the  undissolved  matters,  mixed  with  about  one- 
fourth  of  its  bulk  of  hydrochloric  acid,  and  somewhat  concentrated  bj'  evaporation, 
when  the  hydrochloric  acid  reduces  the  selenic  to  selenious  acid — 
H^SeO^  +  2HC1  =  H^SeOs  +  H„0  +  C\ . 

A  current  of  sulphurous  acid  gas  is  now  passed  through  the  solution,  when  the 
selenium  is  precipitated  in  fine  red  flakes,  which  collect  into  a  dense  black  mass 
when  the  liquid  is  gently  heated  ;  H.^SeOs  +  H.^O  +  2S0.2=  2H.SO4  +  Se . 

The  proportion  of  selenium  in  the  deposit  from  the  leaden  chambers  is  variable.  The 
author  has  obtained  3  per  cent,  by  this  process. 

Selenium,  like  sulphur,  is  capable  of  existing  in  three  allotropic  states  :  the  red 
amorphous  variety  precipitated  from  its  solutions,  or  sublimed  like  flowers  of  sul- 
phur J  the  black  vitreous  form  ;  and  the  crystalline  form,  deposited  from  its  solution 


220  TELLURIUM. 

in  carbon  disulphide,  in  which  it  is  far  less  easily  dissolved  than  sulphur.  Vitreous 
selenium,  when  heated,  fuses  at  a  little  above  100°  C,  boils  below  a  red  heat,  and 
is  converted  into  a  deep  yellow  vapour,  which  expands  when  heated  in  the  same 
anomalous  manner  as  vapour  of  sulphur.  The  crystalline  selenium  has  a  much 
higher  fusing  point. 

Seleniujn  is  less  combustible  than  sulphur  ;  when  heated  in  air  it  burns  with  a  blue 
flame,  and  emits  a  peculiar  odour  like  that  of  putrid  horse-radish,  which  appears  to 
be  due  to  the  formation  of  a  little  selenietted  hydrogen  from  the  moisture  of  the  air. 
When  heated  with  oil  of  vitriol,  selenium  forms  a  green  solution  which  deposits  the 
selenium  again  when  poured  into  water. 

Vitreous  selenium  is  a  very  bad  conductor  of  electricity,  but  crystalline  selenium 
is  a  fair  conductor,  and  conducts  better  in  light  than  in  darkness,  which  is  taken 
advantage  of  in  the  photophone. 

Selenium  dioxide  (SeO.2),  corresponding  to  sulphur  dioxide,  is  the  product  of  com- 
bustion of  selenium  in  oxygen.  It  is  best  obtained  by  dissolving  selenium  in  boiling 
nitric  acid  (which  would  convert  sulphur  into  sulphuric  acid),  and  evaporating  to 
dryness,  when  the  selenium  dioxide  remains  as  a  white  solid  which  sublimes  in  needle- 
like crystals  when  heated.  When  dissolved  in  boiling  water,  it  yields  crystalline 
selenious  acid,  H^SeOg. 

Selenic  acid  (H2Se04). — Potassium  seleniate  is  formed  when  selenium  iso  xidised  by 
fused  nitre  ;  2KN03  +  Se  =  K2Se04  4-2NO.  By  dissolving  the  potassium  seleniate  in 
water,  and  adding  lead  nitrate,  a  precipitate  of  lead  seleniate  (PbSe04)  is  obtained, 
and  if  this  be  suspended  in  water  and  decomposed  by  passing  hydrosulphuric  acid 
gas,  lead  will  be  removed  as  insoluble  sulphide,  and  a  solution  of  selenic  acid  will  be 
obtained  ;  PbSe04  +  HjS  =  H2Se04  +  PbS.  This  solution  may  be  evaporated  till  it  has 
a  sp.  gr.  of  2 '6,  when  it  very  closely  resembles  oil  of  vitriol.  It  is  decomposed,  how- 
ever, at  about  550°  F.,  evolving  oxygen,  and  becoming  selenious  acid.  It  oxidises 
the  metals  like  oil  of  vitriol,  and  even  dissolves  gold.  The  seleniates  closely  re-semblo 
the  sulphates,  but  they  are  decomposed  when  heated  with  hydrochloric  acid,  chlorine 
being  evolved  and  selenious  acid  produced. 

Hydroselenie  acid,  or  selenietted  hydrogen  (HjSe),  is  the  exact  parallel  of  sulphuretted 
hydrogen,  and  is  produced  by  a  similar  process.  It  is  even  more  offensive  and 
poisonous  than  that  gas,  and  acts  in  a  similar  way  upon  metallic  solutions,  precipi- 
tating the  selenides. 

There  are  two  chlorides  of  selenium :  the  monochloride,  SsjClj,  a  brown  volatile 
lit^uid  corresponding  to  sulphur  monochloride ;  and  the  tetrachloride,  SeCl4,  a  white 
crystalline  solid,  without  any  well-established  analogue  in  the  sulphur  series. 

Notwithstanding  the  resemblance  between  the  two  elements,  there  are  two  sul- 
phides  of  seleiiium,  a  disulphide  (SeSj)  and  a  trisulphide  (SeSg).  The  former  is 
obtained  as  a  yellow  precipitate  when  hydrosulphuric  acid  is  passed  into  solution  of 
selenious  acid. 

Tellurium. 
Te  =  129  parts  by  weight. 

157.  Tellurium  (from  tellu^,  the  earth)  is  connected  with  selenium  by  analogies 
stronger  than  those  which  connect  that  element  with  sulphur.  It  is  even  less  fre- 
quently met  with  than  selenium,  being  found  chiefly  in  certain  Transylvanian  gold 
ores.  It  occasionally  occurs  in  an  uncombined  form,  but  more  frequently  in  com- 
bination with  metals.  Foliated  or  graphic  tellurium  is  a  black  material  containing 
the  tellurides  of  lead,  silver,  and  gold.  Bismuth  telluride  is  also  found  in  nature. 
Arsenical  pyrites  sometimes  contains  tellurium,  apparently  as  TeSg . 

Tellurium  is  extracted  from  the  foliated  ore  by  a  process  similar  to  that  for  ob- 
taining selenium.  From  bismuth  telluride  it  is  procured  by  strongly  heating  the 
ore  with  a  mixture  of  potassium  carbonate  and  charcoal,  when  potassium  telluride 
is  formed,  which  dissolves  in  water  to  a  purple-red  solution,  from  which  tellurium  is 
dej)osited  on  exposure  to  air. 

Tellurium  much  more  nearly  resembles  the  metals  than  the  non-metals  in  its 
physical  i>roperties,  and  is  on  that  account  often  classed  among  the  former,  but  it  is 
not  capable  of  forming  a  true  basic  oxide.  In  appearance  it  is  very  similar  to  bismuth 
(with  which  it  is  so  frequently  found),  having  a  pinkish  metallic  lustre,  and  being, 
like  that  metal,  crystalline  and  brittle.  It  fuses  below  a  red  heat,  and  is  converted 
into  a  yellow  vapour  at  a  high  temperature.  When  heated  in  air  it  burns  with  a  bhie 
flame  edged  with  green,  and  emits  fumes  of  tellurium  dioxide  (TeOg)  and  a  peculiar 
odour. 


TELLURIUM.  221 

Like  selenium,  tellurium  is  dissolved  by  strong  sulphuric  acid,  yielding  a  purple- 
red  solution,  from  which  water  precipitates  it  unchanged.  ^ 

The  oxides  of  tellurium  correspond  in  composition  to  those  of  selenium.  Tellurous 
acid  (H2're03)  is  precipitated  when  a  solution  of  tellurium  in  diluted  nitric  acid  is 
])oured  into  water.  If  the  nitric  solution  is  boiled,  a  crystalline  precipitate  of 
tellurous  anhydride  is  obtained.  Unlike  selenious  acid,  tellurous  acid  is  sparingly 
soluble  in  water.  The  anhydride  is  easily  fusible,  forming  a  yellow  glass,  which 
becomes  white  on  cooling,  and  may  be  sublimed  unchanged.  Tellurous  acid  is  rather 
a  weak  acid,  and  with  some  of  the  stronger  acids  the  anhj-^dride  forms  soluble  com- 
pounds in  which  it  takes  the  part  of  a  very  feeble  base. 

Telluric  acid  (H2Te04)  is  also  a  weak  acid  obtained  by  oxidi.sing  tellurium  with 
nitre,  precipitating  the  potassium  tellurate  with  barium  chloride,  and  decomposing 
the  barium  tellurate  with  sulphuric  acid.  On  evaporating  the  solution,  crystals  of 
telluric  acid  (HgTe042H20)  are  obtained,  which  become  H2Te04  at  a  moderate  heat, 
and  when  heated  nearly  to  redness  are  converted  into  an  orange-yellow  powder,  which 
is  the  anhydride.  In  this  state  it  is  insoluble  in  acids  and  alkalies.  When  strongly 
heated,  it  evolves  oxygen,  and  becomes  tellurous  anhydride.  The  tellurates  are 
unstable  salts  which  are  converted  into  tellurites  when  heated. 

Tellurettcd  hydrogen  or  hydrotelluric  add  (HaTe)  exhibits  in  the  strongest  manner 
the  chemical  analogy  of  tellurium  with  selenium  and  sulphur.  It  is  a  gas  very 
similar  to  sulphuretted  hydrogen  in  smell,  and  in  most  of  its  other  properties. 
When  its  aqueous  solution  is  exposed  to  the  air,  it  yields  a  brown  deposit  of  tellurium. 
When  passed  into  metallic  solutions  it  precipitates  the  tellurides.  The  gas  is  pre- 
pared by  decomposing  telluride  of  zinc  with  hydrochloric  acid. 

The  most  characteristic  property  of  tellurium  compounds  is  that  of  furnishing  the 
purple  solution  of  potassium  telluride,  when  fused  with  potassium  carbonate  and 
charcoal,  and  treated  with  water.  Two  solid  chlorides  of  tellurium  have  been  obtained; 
TeClg  is  a  black  solid  with  a  violet-coloured  vapour,  and  is  decomposed  by  water  into 
tellurium  and  TeCl4.  The  latter  may  be  obtained  as  a  white  crystalline  volatile  solid, 
decomposed  by  much  water,  into  hydrochloric  and  tellurous  acids.  There  are  also 
two  sulphides  of  tellurium  corresponding  to  the  oxides,  from  which  they  may  be  ob- 
tained as  dark  brown  precipitates  by  the  action  of  hydrosulphuric  acid.  They  are  both 
soluble  in  alkaline  sulphides. 

158.  Review  of  the  sulphur  group  of  elements. — The  three  elements — 
sulphur,  selenium,  and  tellurium — exhibit  a  relation  of  a  similar  character 
to  that  observed  between  the  members  of  the  chlorine  group,  both  in 
their  physical  and  chemical  properties. 

Sulphur  is  a  pale  yellow  solid,  easily  fusible  and  volatile,  without  any 
trace  of  metallic  lustre,  and  of  specific  gravity  2*05  (sp.  gr.  of  vapour, 
2 "23).  Selenium  is  either  a  red  powder  or  a  lustrous  mass  appearing 
black,  but  transmitting  red  light  through  thin  layers  ;  much  less  fusible 
and  volatile  than  sulphur,  and  of  specific  gravity  4  "8  (sp.  gr.  of  vapour, 
5  "68).  Tellurium  has  a  brilliant  metallic  lustre,  is  much  less  fusible  and 
volatile  than  selenium,  and  of  specific  gravity  6 '65  (sp.  gr.  of  vapour,  9'0). 

Sulphur  (atomic  weight  32)  has  the  most  powerful  attraction  for  oxy- 
gen, hydrogen,  and  the  metals.  Selenium  (atomic  weight  79*5)  ranks 
next  in  the  order  of  chemical  energy.  Tellurium  (atomic  weight  129) 
has  a  less  powerful  attraction  for  oxygen,  hydrogen,  and  the  metals,  than 
either  sulphur  or  selenium.  This  element  appears  to  stand  on  neutral 
ground  between  the  non-metallic  bodies  and  the  less  electro-positive 
metals. 

PHOSPHORUS. 

P=31  parts  by  weight.* 

159.  This  is  the  only  element  for  the  ordinary  preparation  of  which 

animal  substances  are  employed.     It  is  never  known  to  fccur  uncombined 

*  The  vapour  of  phosphorus  is  62  times  as  heavy  as  hydrogen,  so  that  its  atom  only 
occupies  half  a  volume,  if  the  atom  of  hydrogen  be  taken  to  occupy  one  volume  ;  and  the 
molecule  of  phosphorus  (P4)  occupying  two  volumes  would  consist  of  four  atoms  instead  of 
two. 


222  PHOSPHOBUS. 

in  nature,  but  it  is  found  abundantly  in  the  form  oi  phosphate  of  lime  or 
tricalcic  diphosphate,  SCaO.PaOg  or  Ca3(P04)2,  which  is  contained  in  the 
minerals  coprolite,  phosphorite,  and  apatite,  and  occurs  diffused,  thougli 
generally  in  small  proportion,  through  all  soils  upon  which  plants  will 
grow,  for  this  substance  is  an  essential  constituent  of  the  food  of  most 
plants,  and  especially  of  the  cereal  plants  which  form  so  large  a  propor- 
tion of  the  food  of  animals.  The  seeds  of  such  plants  are  especially  rich 
in  the  phosphates  of  calcium  and  magnesium. 

Animals  feeding  upon  these  plants  still  further  accumulate  the  phos- 
phorus, for  it  enters,  chiefly  in  the  form  of  calcium  phosphate,  into  the 
composition  of  almost  every  solid  and  liquid  in  the  animal  body,  and  is 
especially  abundant  in  the  bones,  which  contain  about  three-fifths  of 
their  weight  of  calcium  phosphate.  It  is  from  this  source  that  our 
supply  of  phosphorus  is  chiefly  derived. 


Composition  of  the  Bones  of  Oxen. 

Animal  matter,    . 
Calcium  phosphate, 

, ,       fluoride, 

, ,        cai'bonate, 
Magnesium  phosphate 


30-58 

57-67 

2-69 

6-99 

2-07 

100-00 


What  is  here  termed  animal  matter  is  a  cartilaginous  substance,  con- 
verted into  gelatin  when  the  bones  are  heated  with  water  under  pressure, 
and  containing  carbon,  hydrogen,  nitrogen,  and  oxygen.  It  was  formerly 
the  custom  to  get  rid  of  this  by  burning  the  bones  in  an  open  fire,  but 
the  increased  demand  for  chemical  products,  and  the  diminished  supply 
of  bones,  have  taught  economy,  so  that  the  cartilaginous  matter  is  no^^r 
dissolved  out  by  heating  the  bones  with  water  at  a  high  pressure  for  the 
manufacture  of  glue ;  or  the  bones  are  subjected  to  destructive  distilla- 
tion, so  as  to  save  the  ammonia  which  they  evolve,  and  the  bone  charcoal 
thus  produced  is  used  by  the  sugar-refiner  until  its  decolorising  powers 
are  exhausted,  when  it  is  heated  in  contact  with  air  to  burn  away  the 
charcoal,  and  leave  the  honeash,  consisting  chiefly  of  calcium  phosphate, 
Ca3(P04)q .  In  order  to  extract  the  phosphorus,  the  bone-ash  is  heated 
for  some  time  with  diluted  sulphuric  acid,  which  removes  the  greater  part 
of  the  calcium  in  the  form  of  the  sparingly  soluble  sulphate,  leaving  the 
phosphoric  acid  in  the  solution,  which  is  strained  from  the  deposit,  eva- 
porated to  a  syrup,  mixed  with  charcoal,  thoroughly  dried  in  an  iron  pot, 
and  distilled  in  an  earthen  retort  (fig.  214),  when  the  carbon  removes  the 
oxygen,  and  phosphorus  distils  over,  being  condensed  in  a  receiver  contain- 
ing water  to  protect  it  from  the  action  of  the  air. 

In  this  process,  the  sulphuric  acid  does  not  remove  the  whole  of  the  calcium  from 
the  phosphate,  a  portion  remaining  in  the  solution  containing  the  phosphoric  acid, 
so  that  this  solution  is  generally  said  to  contain  superphosphate  of  lime,  and  the 
action  of  the  sulphuric  acid  is  thus  represented — 

Bone  phosphate,  CaaCPO^)^  +  2H<jS04  =  CaH4(P04)2  superphosphate  +  2CaS04  . 

AVhen  the  superphosphate  is  dried,  it  becomes  converted  into  calcium,  metaphosphate 
Ca(  P03)o,  and  on  distilling  this  with  charcoal — 

3Ca(P0,),  +  C,„  =  Ca3(P04)j  +  lOCO  -h  P4. 

On  the  small  scale,  for  the  sake  of  illustration,  phosphorus  may  be  prepared  by  a 
process  which  has  also  been  successfully  employed  for  its  manufacture  in  quantity, 


EXTRACTION  OF  PHOSPHORUS  FROM  BONES, 


223 


and  consists  in  heating  a  mixture  of  hone-ash  and  charcoal  in  a  stream  of  hydrochloric 
acid  gas  ;  CajlPOJa  +  6HC1  +  Cg  =  SCaCl^  +  SCO  +  Hg  +  P^  .  ^ 


Fig.  214. — Extraction  of  phosphorus. 

A  mixture  of  equal  weights  of  well-dried  charcoal  and  hone-ash,  both  in  fine 
powder,  is  introduced  into  a  porcelain  tube,  and  placed  in  a  charcoal  furnace  (fig.  215). 
One  end  of  the  tube  is  connected  with  a  flask  (A),  containing  fused  salt  and  sulphuric 
acid  for  evolving  hydrochloric  acid,  and  the  other  is  cemented  with  putty  into  a 
bent  retort  neck  (B),  for  conveying  the  phosphorus  into  a  vessel  of  water  (C).  On 
heating  the  porcelain  tube  to  bright  redness,  phosphorus  distils  over  in  abundance. 
The  hydrogen  and  carbonic  oxide  inflame  as  they  escape  into  the  air,  from  their  con- 
taining phosphorus  vapour. 

When  first  prepared,  the  phosphorus  is  red  and  opaque,  from  the  pre- 
sence of  some  suboxide  of  phosphorus  and  mechanical  impurities ;  the 
latter  are  removed  by  melt- 
ing the  phosphorus  under 
warm  water,  and  squeezing 
it  through  wash-leather. 
The  phosphorus  is  then 
fused  under  ammonia  to 
remove  any  acid  impurity, 
and  afterwards  under  potas- 
sium dichromate  acidified 
with  sulphuric  acid,  Avheu 
the  chromic  acid  oxidises 
thesuboxideof  phosphorus, 
and  converts  it  into  phos- 
phoric acid  which  dissolves. 
The  phosphorus  is  then 
thoroughly  washed,  melted 
under  water,  and  drawn  up 
into  glass  tubes,  where  it 
solidifies  into  the  sticks  in 
which  it  is  sold.  These 
are  always  preserved  under 
water  from  the  action  of 
oxygen  and  in  tin  cases 
from  that  of  light. 

Pure  ordinary  phospho- 
rus is  almost  colourless  and  transparent,  but  when  exposed  to  light,  and 
especially  to  direct  sun  light,  it  gradually  acquires  an  opaque  red  colour, 


Fig.  215. 


224  INFLAMMABILITY  OF  PHOSPHORUS. 

from  its  partial  conversion  into  the  allotropic  variety  known  as  red  or 
amorphous  phosphorus.  By  tying  bands  of  black  cloth  round  a  stick  of 
phosphorus  and  exposing  it,  under  water,  to  the  action  of  sunlight, 
alternate  zones  of  red  may  be  produced. 

Even  though  the  phosphorus  be  screened  from  light,  it  will  not  remain 
unchanged  unless  the  water  be  kept  quite  free  from  air,  which  irregularly 
corrodes  the  surface  of  the  phosphorus,  rendering  it  white  and  opaque. 
This  action  is  accelerated  by  exposure  to  light. 

The  most  remarkable  character  of  ordinary  phosphorus  is  its  easy  in- 
flammability. It  inevitably  takes  fire  in  air  when  heated  a  little  above 
its  melting-point  (111°"5  F.),  burning  with  a  brilliant  white  flame,  which 
becomes  insupportable  when  the  combustion  takes  place  in  oxygen  (p.  25), 
and  evolving  dense  white  clouds  of  phosphoric  anhydride.  When  a 
piece  of  dry  phosphorus  is  exposed  to  the  air,  it  combines  slowly  with 
oxygen,"^  and  its  temperature  often  becomes  so  much  elevated  during  this 
slow  combustion,  that  it  melts  and  takes  fire,  especially  if  the  combustion 
be  encouraged  by  the  warmth  of  the  hand  or  by  friction.  Hence,  ordinary 
phosphorus  must  never  be  handled  or  cut  in  the  dry  state,  but  always 
under  water,  for  it  causes  most  painful  burns. 

The  slow  oxidation  of  phosphorus  is  attended  with  that  peculiar  lumi- 
nous appearance  which  is  termed pJiosphorescence  (^ws,  light,  <f>ep(i),  to  bear), 
but  this  glow  is  not  seen  in  pure  oxygen  or  in  air  containing  a  minute 
proportion  of  olefiant  gas  or  oil  of  turpentine.  It  will  be  remembered  that 
the  slow  oxidation  of  phosphorus  is  attended  with  the  formation  of  ozone. 

The  characteristic  behavioiir  of  phosphorus  in  air  is  best  observed  when  the  phos- 
phorus is  in  a  finely-divided  state.     When  a  fragment  of  phosphorus  is  shaken  with 

a  little  carbon  disulphide,  it  is  quickly 
dissolved,  and  if  the  solution  be  poured 
"^■■MSr^ — ^^       C^.  upon  a  piece  of  filtering  paper  (fig.  216), 

and  allowed  to  evaporate  in  a  darkened 
room,  the  very  thin  film  of  phosphorus 
which  is  left  will  exhibit  a  glow  increasing 
in  brilliancy  till  the  phosphorus  bursts  out 
into  spontaneous  combustion. 

If  phosphorus  be  dissolved  in  olive  oil, 
at  a  gentle  heat,  the  solution  is  strongly 
])hosphorescent  when  shaken  in  a  bottle 
lig.  216.  containing  air,  or  when  rubbed  upon  the 

hands. 
Characters  may  be  written  on  paper  with  a  stick  of  phosphorus  held  in  a  thickly- 
folded  piece  of  damp  paper  (having  a  vessel  of  water  at  hand  into  which  to  plunge 
the  phosphorus  if  it  should  take  fire).  When  the  paper  is  held  with  its  back  to  the 
fire,  or  to  a  hot  iron,  in  a  darkened  room,  a  twinkling  combustion  of  the  finely-divided 
phosphorus  will  ensue,  and  the  letters  will  be  burnt  into  the  paper.  Phosphorus 
which  has  been  partly  oxidised  is  even  more  easily  inflamed  than  pure  phosphorus. 
If  a  few  small  pieces  of  phosphorus  be  placed  in  a  dry  stoppered  bottle,  gently  warmed 
till  they  melt,  and  then  shaken  round  the  sides  of  the  bottle  so  as  to  become  partly 
converted  into  red  oxide  of  phosphorus,  it  will  be  found,  long  after  the  bottle  is  cold, 
to  be  spontaneously  inflammable,  so  that  if  a  wooden  match  tipped  with  sulphur  be 
rubbed  against  it,  "the  phosphorus  which  it  takes  up  will  ignite  when  the  match  is 
brought  into  the  air,  kindling  the  sulphur,  which  will  inflame  the  wood.  This  was 
one  t)f  the  earliest  forms  in  which  phosphorus  was  employed  for  the  purpose  of  pro- 
curing an  instantaneous  light.  If  the  stopper  be  greased,  the  phosphorus  may  be 
preserved  unchanged  for  a  long  time. 

In   the  last  experiment,  if  the  wood  had  not  been   tipped  with   sulphur,  the 

*  The  white  fumes  evolved  by  phosphorus  in  moist  air  are  said  to  consist  partly  of 
amiiiouium  nitrate,  formed  by  the  action  of  the  ozonised  oxygen  upon  the  air  and  aqueous 
vapour. 


PREPARATION  OF  AMORPHOUS  PHOSPHORUS. 


225 


phosphorus  would  not  have  kindled  it,  the  flame  of  phosphorus  generally  being  unable 
to  ignite  solid  combustibles,  because  it  deposits  upon  them  a  coatjng  of  phosphoric 
anliydride,  which  protects  them  from  the  action  of  air.  Hence,  in  the  manufacture 
of  lucifer  matches,  the  wood  is  first  tipped  with  sulphur,  or  wax,  or  paraffin,  which 
easily  give  off  combustible  vapours  to  be  kindled  by  the  flame  of  the  phosphorus 
composition,  and  thus  to  inflame  the  wood. 

If  a  small  stick  of  phosphorus  be  carefully  dried  with  filtering  paper,  and  dropped 
into  a  cylinder  of  oxj-gen,  which  is  afterwards  covered  with  a  glass  plate,  no  lumino- 
sity will  be  observed  in  a  darkened  room  until  the  cylinder  is  placed  under  the  air 
pump  receiver,  and  the  air  slowly  exhausted.  When 
the  oxygen  has  thus  been  rarefied  to  about  one-fifth 
of  its  former  density,  the  phosphorescence  will  be 
seen.  A  similar  eftect  may  be  produced  by  covering 
the  cylinder  of  oxygen  containing  the  phosphorus 
(having  removed  the  glass  plate)  with  another 
cylinder,  about  four  times  its  size  (fig.  217),  filled 
with  carbonic  acid  gas,  which  will  gradually  dilute 
the  oxygen  and  produce  phosphorescence.  By  sus- 
pending— in  a  bottle  of  air  containing  a  strongly 
luminous  piece  of  phosphorus— a  piece  of  paper  with 
a  drop  of  oil  of  turpentine  upon  it,  the  glow  may  be 
almost  instantaneously  destroyed.  A  small  tube  of 
olefiant  gas  or  coal  gas  dropped  into  the  bottle  will 
also  extinguish  the  luminosity.* 

Ordinary  phosphorus  is  slowly  converted  into  vapour  at  common 
temperatures,  and  emits,  in  the  air,  white  fumes  with  a  peculiar  alliaceous 
smell,  which  appear  phosphorescent  in  the  dark.  When  heated  out  of 
contact  with  air,  it  boils  at  550°  F.,  and  is  converted  into  a  colourless 
vapour. 

The  luminosity  of  phosphorus  vapour  is  seen  to  advantage  when  a  piece  of  phos- 
phorus is  boiled  with  water  in  a  narrow-necked  flask,  or  a  test-tube  with  a  cork  and 
narrow  tube.  The  steam  charged  with  vapour  of  phosphorus  has  all  the  appearance 
of  a  blue  flame,  in  a  darkened  room,  but  of  course  combustibles  are  not  inflamed  by 
it,  since  its  temperature  is  not  higher  than  212°  F.  Phosphorus  may  be  distilled, 
with  perfect  safety,  in  an  atmosphere  of  carbonic  acid  gas,  the  neck  of  the  retort 
being  allowed  to  dip  under  water  in  the  receiver. 

Although  ordinary  phosphorus  is  of  a  decidedly  glassy  or  vitreous 
structure,  and  not  at  all  crystalHne,  it  may  be  obtained  in  dodecahedral 
crystals,  by  allowing  its  solution  in  carbon  bisulphide  to  evaporate  in 
an  atmosphere  of  carbonic  acid  gas. 

The  conversion  of  ordinary  phosphorus  into  the  red  or  amorphous  phos- 
pl/onis  is  one  of  the  most  striking  instances  of  allotropic  modification. 
When  phosphorus  is  heated  for  a  considerable  length  of  time  to  about 
450°  F.  in  vacuo,  or  in  an  atmosphere  in  which  it  cannot  burn,  it  becomes 
converted  into  a  red  infusible  mass  of  amorphous  phosphorus.  This  form 
of  phosphorus  differs  as  widely  from  the  vitreous  form  as  graphite  differs 
from  diamond.  It  is  almost  unchangeable  in  the  air,  evolves  no  vapour, 
is  not  luminous,  cannot  be  inflamed  by  friction,  or  even  by  any  heat  short 
of  500°  F.,  when  it  actually  becomes  reconverted  into  ordinary  phos- 
phorus, t  Amorphous  phosphorus  is  insoluble  in  the  solvents  for  ordinary 
phosphorus.  The  two  varieties  also  differ  greatl}'-  in  specific  gravity,  that 
of  the  ordinary  phosphorus  being  1'83,  and  of  the  amorphous  variety  2*14. 

*  Chappuis  finds  that  when  phosphorus  is  suspended  in  oxjgen,  the  space  glows  for  a 
short  time  on  adding  a  little  ozone. 

+  According  to  Hittorf,  the  reconversion  does  not  take  place  till  800°  F.,  the  red  phos- 
phorus being  convertible  into  vapour  below  that  temperature,  without  fusion. 

P 


226 


PROPERTIES  OF  PHOSPHORUS. 


The  conversion  of  vitreous  into  amprplious  phosphorus  may  be  effected  by  heating 
it  in  a  flask  (A,  fi^.  218)  placed  in'an  oil-bath  (B),  maintained  at  a  temperature 
ranging  from  450°  to  460°  F.,  the  flask  being  furnished  with  a  bent  tube  (C)  dipping 
into  mercury,  and  with  another  tube  (D)  for  supplying  carbonic  acid  gas,  dried  by 
passing  over  calcium  chloride.     The  flask  should  be  thoroughly  filled  with  carbonic 

acid  gas  before  applying  heat,  and  the 
tube  delivering  it  may  then  be  closed 
with  a  small  clamp(E).  Afterexposure 
to  heat  for  about  forty  hours,  but  little 
ordinary  phosphorus  will  remain,  and 
this  may  be  removed  by  allowing  the 
mass  to  remain  in  contact  with  carbon 
disulphide  for  some  hours,  and  subse- 
quently washing  it  with  fresh  disul- 
phide till  the  latter  leaves  no  phos- 
phorus when  evaporated. 

On  the  large  scale,  the  red  phos- 
phorus is  prepared  by  heating  about 
200  lbs.  of  vitreous  phosphorus  to  450° 
~  F.  in  an  iron  boiler.  After  three  or 
four  weeks  the  phosphorus  is  found 
to  be  converted  into  a  hard  red  brittle 
J?ig.  218.  mass,  which  is  ground  by  millstones 

under  water,  and  separated  from  the  ordinary  phosphorus  either  by  carbon  disul- 
phide or  caustic  soda,  in  which  the  latter  is  soluble.  The  temperature  requires 
careful  regulation,  for  if  it  be  allowed  to  rise  to  500°,  the  red  phosphorus  quickly 
resumes  the  vitreous  condition,  evolving  the  heat  which  it  had  absorbed  during  its 
conversion,  and  thus  converting  much  of  the  phosphorus  into  vapour.  This  recon- 
version may  be  shown  by  heating  a  little  red  phosphorus  in  a  narrow  test-tube, 
when  drops  of  vitreous  phosphorus  condense  on  the  cool  part  of  the  tube.  The 
colour  of  diff"erent  specimens  of  amorphous  phosphorus  varies  considerably  ;  that 
I)repared  on  the  large  scale  is  usually  of  a  dark  purplish  colour,  but  it  may  be  obtained 
of  a  briglit  scarlet  colour.  Ehombohedral  crystals  of  phosphorus,  resembling  crystals 
of  arsenic  in  form  and  metallic  appearance,  have  been  obtained  by  fusing  phosphorus 
with  lead,  and  dissolving  out  the  latter  with  diluted  nitric  acid  (sp.  gr.  1*1). 

Ordinary  phosphorus  is  very  poisonous,  whilst  amorphous  phosphorus 
appears  to  be  harmless.  The  former  is  employed,  mixed  with  fatty  sub- 
stances, for  poisoning  rats  and  beetles.  Cases  are,  unhappily,  not  very 
rare  of  children  being  poisoned  by  sucking  the  phosphorus  composition 
on  lucifer  matches.  The  vapour  of  phosphorus  also  produces  a  very 
injurious  effect  upon  the  persons  engaged  in  the  manufacture  of  lucifer 
matches,  resulting  in  the  decay  of  the  lower  jaw-bone.  The  evil  is  much 
mitigated  by  good  ventilation,  or  by  diffusing  turpentine  vapour  through 
the  air  of  the  workroom,  and  attempts  have  been  made  to  obviate  it 
entirely  by  substituting  amorphous  phosphorus  for  the  ordinary  variety, 
V»ut,  as  might  be  expected,  the  matches  thus  made  are  not  so  sensitive  to 
friction  as  those  in  which  the  vitreous  phosphorus  is  used. 

The  difference  between  the  two  varieties  of  phosphorus,  in  respect  to 
chemical  energy,  is  seen  when  they  are  placed  in  contact  with  a  little 
iodine  on  a  plate,  when  the  ordinary  phosphorus  undergoes  combustion 
and  the  red  phosphorus  remains  unaltered. 

Ordinary  phosphorus  is  capable  of  direct  union  with  oxygen,  chlorine, 
bromine,  iodine,  sulphur,  and  most  of  the  metals,  with  which  it  forms 
2)hosphides  or  pJiosphurets.  Even  gold  and  platinum  unite  with  this 
element  when  heated,  so  that  crucibles  of  these  metals  are  liable  to  cor- 
rosion when  heated  in  contact  with  a  phosphate  in  the  presence  of  a 
reducing  agent,  such  as  carbon.  Thus  the  inside  of  a  platinum  dish  or 
crucible  is  roughened  when  vegetable  or  animal  substances  containing 


MANUFACTURE  OF  LUCIFER  MATCHES.  227 

phosphates  are  incinerated  in  it.  The  presence  of  small  quantities  of 
phosphorus  in  metallic  iron  or  copper  produces  considerable  effect  upon 
their  physical  qualities. 

Phosphorus  has  the  property,  a  very  remarkable  one  in  a  non-metal,  of 
precipitating  some  metals  from  their  solutions  in  the  metallic  state.  If  a 
stick  of  phosphorus  be  placed  in  a  solution  of  sulphate  of  copper,  it 
becomes  coated  with  metallic  copper,  the  phosphorus  appropriating  the 
oxygen.  This  has  been  turned  to  advantage  in  copying  very  delicate 
objects  by  the  electrotype  process,  for  by  exposing  them  to  the  action  of  a 
solution  of  phosphorus  in  ether  or  carbon  disulphide,  and  afterwards  to 
that  of  a  solution  of  copper,  they  acquire  the  requisite  conducting  metallic 
film,  even  on  their  finest  filaments.  Solutions  of  silver  and  gold  are 
reduced  in  a  similar  manner  by  phosphorus. 

By  floating  very  minute  scales  of  ordinary  phosphorus  upon  a  dilute  solution  of 
chloride  of  gold,  the  metal  will  be  reduced  in  the  form  of  an  extremely  thin  film, 
which  may  be  raised  upon  a  glass  plate,  and  will  be  found  to  have  various  shades 
of  green  and  violet  by  transmitted  light,  dependent  upon  its  thickness,  whilst  its 
thickest  part  exhibits  the  ordinary  colour  of  the  metal  to  reflected  light.  By  heat- 
ing the  films  on  the  plate,  various  shades  of  amethyst  and  ruby  are  developed.  If  a 
very  dilute  solution  of  chloride  of  gold  in  distilled  water  be  placed  in  a  perfectly 
clean  bottle,  and  a  few  drops  of  ether,  in  which  phosphoras  has  been  dissolved, 
poured  into  it,  a  beautiful  ruby-coloured  liquid  is  obtained,  the  colour  of  which  is 
due  to  metallic  gold  in  an  extremely  finely-divided  state,  and  on  allowing  it  to  stand 
for  some  months,  the  metal  subsides  as  a  purple  powder,  leaving  the  liquid  colourless. 
If  any  saline  impurity  be  present  in  the  gold  solution,  the  colour  of  the  reduced  gold 
will  be  amethyst  or  blue.  These  experiments  (Faraday)  illustrate  very  strikingly  the 
use  of  gold  for  imparting  ruby  and  purple  tints  to  glass  and  the  glaze  of  porcelain. 

160.  Lucifer  matches  are  made  by  tipping  the  wood  with  sulphur,  or 
wax,  or  paraffin,  to  convey  the  flame,  and  afterwards  with  the  match 
composition,  which  is  generally  composed  of  saltpetre  or  potassium  chlorate, 
phosphorus,  red  lead,  and  glue,  and  depends  for  its  action  on  the  easy 
inflammation,  by  friction,  of  phosphorus  when  mixed  with  oxidising  agents 
like  saltpetre  (KNO3),  potassium  chlorate  (KCIO3),  or  red  lead  (Pb304), 
the  glue  only  serving  to  bind  the  composition  together  and  attach  it  to 
the  wood.  The  composition  used  by  different  makers  varies  much  in 
the  nature  and  proportions  of  the  ingredients.  In  this  country,  potassium 
chlorate  is  most  commonly  employed  as  the  oxidising  agent,  such  matches 
usually  kindling  with  a  slight  detonation ;  but  the  German  manufacturers 
prefer  either  potassium  nitrate  or  lead  nitrate,  together  with  lead  dioxide 
or  red  lead,  which  produce  silent  matches. 

Sulphide  of  antimony  (which  is  inflamed  by  friction  with  potassium 
chlorate,  see  p.  165)  is  also  used  in  those  compositions  in  which  a  part  of 
the  phosphorus  is  employed  in  the  amorphous  form,  and  fine  sand  or 
powdered  glass  is  very  commonly  added  to  increase  the  susceptibility  of 
the  mixture  to  inflammation  by  friction. 

The  match  composition  is  coloured  either  with  ultramarine  blue,  Prus- 
sian blue,  or  vermilion.  In  preparing  the  composition,  the  glue  and  the 
nitre  or  chlorate  are  dissolved  in  hot  water,  the  phosphorus  then  added 
and  carefully  stirred  in  until  intimately  mixed,  the  whole  being  kept  at  a 
temperature  of  about  100°  F.  The  fiue  sand  and  colouring  matter  are 
then  added,  and  when  the  mixture  is  complete,  it  is  spread  out  upon  a 
stone  slab  heated  by  steam,  and  the  sulphured  ends  of  the  matches  are 
dipped  into  it. 

The  safety  matches,  which   refuse  to  ignite  unless   rubbed  upon  the 


228  COMPOUNDS  OF  PHOSPHORUS  AND  OXYGEN. 

bottom  of  the  box,  are  tipped  with  a  mixture  of  antimony  sulphide,  potas- 
sium chlorate,  and  powdered  glass,  which  is  not  sufficiently  sensitive  to  be 
ignited  by  any  ordinary  friction,  but  inflames  at  once  when  rubbed  upon  the 
amorphous  phosphorus  mixed  with  glass,  which  coats  the  rubber  beneath  the 
box.  On  this  principle  some  French  matches  have  been  made  which  can 
be  ignited  only  by  breaking  the  match  and  rubbing  the  two  ends  together. 
It  would  be  very  desirable  to  dispense  entirely  with  the  use  of  phos- 
jihorus  in  lucifer  matches,  not  only  because  of  the  danger  from  accident 
and  disease  in  the  manufacture,  but  because  a  very  large  quantity  of 
phosphate  of  lime  which  ought  to  be  employed  for  agricultural  purposes, 
is  now  devoted  to  the  preparation  of  phosphorus,  of  which  six  tons  are 
said  to  be  consumed  annually  in  this  country  for  the  manufacture  of 
matches.  The  most  successful  attempt  in  this  direction  appears  to  be  the 
employment  of  a  mixture  of  potassium  chlorate  and  lead  hyposulphite, 
in  place  of  the  ordinary  phosphorus  composition. 

For  illustration,  very  excellent  matches  may  be  made  upon  the  small  scale  in  the 
following  manner.  The  slips  of  wood  are  dipped  in  melted  sulphur  so  as  to  acquire 
a  slight  coating.  Thirty  grains  of  gelatine  or  isinglass  are  dissolved  in  2  drachms  of 
water  in  a  porcelain  dish  placed  upon  a  steam-bath  ;  20  grains  of  ordinary  phosphorus 
are  then  added,  and  well  mixed  in  with  a  piece  of  stick  ;  to  this  mixture  are  added, 
in  succession,  15  grains  of  red  lead  and  50  grains  of  powdered  potassium  chlorate. 
The  suljjhured  matches  are  dipped  into  this  paste,  and  left  to  dry  in  the  air. 

To  make  the  safety  matches  ;  10  grains  of  powdered  potassium  chlorate  and  10 
grains  of  antimonj'  sulphide  are  made  into  a  paste  with  a  few  drops  of  a  warm 
solution  of  20  grains  of  gelatine  in  2  drachms  of  water,  the  sul})hured  matches  being 
tippea  with  this  composition.  The  rubber  is  prepared  with  20  grains  of  amorphous 
phosphorus,  and  10  grains  of  finely-powdered  glass,  mixed  with  the  solution  of 
gelatine,  and  painted  on  paper  or  cardboard  with  a  brush. 

161.  Phosphorus-fuze  composition. — To  ignite  the  Armstrong  percussion 
shells,  a  very  sensitive  detonating  composition  was  employed,  which  is  com- 
posed of  amorphous  phosphorus,  potassium  chlorate,  shellac,  and  powdered 
glass,  made  into  a  paste  with  spirit  of  wine.  This  was  placed  in  the  little 
cap  designed  for  it,  and  when  dry,  waterproofed  with  a  little  shellac  dis- 
solved in  spirit.     The  fuzes  were  found  too  sensitive  to  bear  transport. 

Such  a  composition  may  be  prepared  with  care  in  the  following  manner  : — Four 
grains  of  powdered  potassium  chlorate  are  moistened  on  a  plate  with  6  drops  of  spirit 
of  wine,  4  grains  of  powdered  amorphous  phosphorus  are  added,  and  the  whole  mixed, 
at  arm's  length,  with  a  bone-knife,  avoiding  great  pressure.  The  mixture,  which 
should  still  be  quite  moist,  is  spread  in  small  portions  upon  ten  or  twelve  pieces  of 
filtering  paper,  and  left  in  a  safe  place  to  dry.  If  one  of  these  be  gently  pressed  with 
a  stick,  it  explodes  with  great  violence.  It  is  dangerous  to  press  it  with  the  blade  of 
a  knife,  as  the  latter  is  commonly  broken,  and  the  pieces  projected  with  considerable 
force.  A  stick  dipped  in  oil  of  vitriol  of  course  explodes  it  immediately.  If  a  bullet 
be  placed  very  lightly  upon  one  of  the  pellets,  and  the  paper  tenderly  wrapped  round 
it,  a  percussion  shell  may  be  extemporised,  which  explodes  with  a  loud  report  when 
dropped  upon  the  floor. 

The  detonating  toys  known  as  amorces  fulminantes  are  made  by  enclosing  this 
composition  between  two  pieces  of  thin  paper.  1000  of  them  contain  half  an  ounce 
of  the  composition. 

162.  Oxides  of  Phosphorus. 


Name. 

Foinmla. 

By  Weight. 

Pbosi>horus. 

Oxygen. 

Suboxide  of  phosphorus,    .         .         .1             P4O 
Pliosphorous  anhydride,     .         .         .   |             PgOj 
Phosphoric  anhydride,        .         .         .   \            PjOg 

124 
62 
62 

16 
48 
80 

PREPARATION  OF  PHOSPHORIC  ACID.  229 

Phosphoric  Acids  and  Phosphates. 

163.  The  phosphates  are  by  far  the  most  important  of  the  compounda 
of  phosphorus.  They  have  been  already  noticed  as  almost  the  only  forms 
of  combination  in  which  that  element  is  met  with  in  nature,  and  as  indis- 
pensable ingredients  in  the  food  of  plants  and  animals.  No  other  mineral 
substance  can  bear  comparison  with  calcium  phosphate  as  a  measure  of 
the  capability  of  a  country  to  support  animal  life.  Phosphoric  acid  itself 
is  very  useful  in  calico-printing  and  in  some  other  arts. 

The  mineral  sources  of  this  acid  appear  to  be  phosphorite,  coprolite,  and 
apatite,  all  consisting  essentially  of  calcium  phosphate  Ca3(P04)2,  but 
associated  in  each  case  with  calcium  fluoride,  which  is  also  contained, 
with  calcium  phosphate,  in  bones,  and  would  appear  to  indicate  an  organic 
origin  for  these  minerals.  Phosphorite  is  an  earthy-looking  substance, 
forming  large  deposits  in  Estremadura.  Apatite  (from  ciTraTato,  to  cheat,  in 
allusion  to  mistakes  in  its  early  analysis)  occurs  in  prismatic  crystals,  and 
is  met  with  in  the  Cornish  tin-veins.  Both  these  minerals  are  largely 
imported  from  Spain,  Norway,  and  America,  for  use  in  this  country  as  a 
manure. 

Coprolites  (/coTrpos,  dung,  \l6o^,  a  stone,  from  the  idea  that  they  were 
petrified  dung)  are  rounded  nodules  of  calcium  phosphate,  which  are  found 
abundantly  in  this  country. 

Large  quantities  of  phosphates  of  calcium  and  magnesium  are  imported 
in  the  form  of  guano,  the  partially  decomposed  excrement  of  sea-fowl. 

Bones,  however,  must  be  regarded  as  the  chief  immediate  source  whence 
the  calcium  phosphate  for  agricultural  purposes  is  derived. 

Phosphoric  acid  is  obtained  from  bone-ash  by  decomposing  it  with 
sulphuric  acid,  so  as  to  remove  as  much  of  the  lime  as  possible  in  the 
form  of  sulphate,  which  is  strained  off,  and  the  acid  liquid  neutralised 
with  ammonium  carbonate,  which  precipitates  any  unchanged  calcium 
phosphate,  and  converts  the  phosphoric  acid  into  ammonium  phosphate. 
On  evaporating  the  solution,  and  heating  the  ammonium  phosphate, 
ammonia  and  water  are  expelled,  and  metaphosphoric  acid  (HPO3)  is  left 
in  a  fused  state,  solidifying  to  a  glass  on  cooling.  Thus  prepared,  however, 
it  always  retains  some  ammonia,  and  is  contaminated  with  soda  derived 
from  the  bones. 

The  pure  acid  is  prepared  by  oxidising  phosphorus  with  diluted  nitric 
acid  (sp.  gr.  1*2),  and  evaporating  the  solution  until  the  phosphoric  acid 
begins  to  volatilise  in  white  fumes  ;  5HNO3  +  P3  =  SHPOg  +  HgO  4-  5X0. 
Some  phosphorous  acid  is  formed  at  an  intermediate  stage.  A  transparent 
glass  {glacial  phosphoric  acid)  is  thus  obtained,  which  eagerly  absorbs 
moisture  from  the  air,  and  becomes  liquid.  That  which  is  sold  in  sticks 
contains  much  sodium  metaphosphate. 

The  addition  of  a  little  bromine  greatly  facilitates  the  action  of  nitric  acid  upon 
phosphorus,  apparently  by  forming  the  phosphorus  pentabromide,  which  is  then 
decomposed  by  water  ;  PBr5  +  4H.20  =  H3P04-H5HBr.  The  hydrobromic  acid  being 
then  acted  on  by  nitric  acid,  bromine  is  set  free  to  act  upon  a  fresh  quantity  of 
phosphorus;  3H Br +  HN03  =  Br3 +  211.^0  +  ^0.  "When  iodine  is  also  added,  the 
action  is  still  better. 

1  oz.  of  phosphorus  is  placed  in  6  oz.  of  water  and  5  grs.  of  iodine  are  added  ;  then, 
drop  by  drop,  30  grs.  of  bromine.  When  the  action  is  over,  6  oz.  of  nitric  acid  (sp. 
gr.  1  •42)  are  added,  and  the  vessel  is  placed  in  cold  water.  When  the  phosphorus 
has  dissolved,  the  solution  is  evaporated  till  its  temperature  rises  to  about  400°  F.  in 
order  to  expel  the  excess  of  nitric  acid,  the  bromine,  and  the  iodine. 


230 


PHOSPHORIC  ANHYDRIDE. 


Phosplwric  anhydnde  ov  phosphorus  pentoxide  (P2^5)  ^^  prepared  by 
burning  pbosphorus  in  dry  air. 

When  required  in  considerable  quantity,  the  anhydride  is  prepared  by  burning  the 
phosphorus  in  a  small  porcelain  dish  (A,  fig.  219)  attached  to  a  wide  glass  tube  (B) 
tor  introducing  the  phosphorus,  and  suspended  in  a  glass  flask  with  two  lateral  necks, 
one  of  wliich  is  connected  with  a  tube  containing  pumice-stone  and  oil  of  vitriol  for 
drying  the  air  as  it  enters,  whilst  the  other  neck  is  provided  with  a  wide  tube  con- 


Fig.  219. 

veying  the  anhydride  into  a  bottle,  connected,  at  C,  with  an  aspirator,  or  cistern  of 
water,  for  drawing  air  through  the  apparatus.  The  first  piece  of  phosphorus  is  kindled 
by  passing  a  hot  wire  down  the  wide  tube,  but  afterwards  the  heat  of  the  dish  will 
always  ignite  the  fresh  piece  as  it  is  dropped  in.  The  wide  tube  must  be  closed  with 
a  cork  whilst  the  phosphorus  is  burning. 

A  small  quantity  of  phosphoric  anhydride  is  more  conveniently  prepared  by  burning 
phosphorus  under  a  large  bell-jar  of  air,  under  which  a  shallow  dish  of  oil  of  vitriol 

has  been  standing  for  an  hour  or  two  to 
dry  the  air.     This  dish  is  carefully  removed 
without  disturbing  the  air  within  the  jar, 
/^  ^^^\  ■<  and  the  well-dried  phosphorus  is  introduced 

in  a  small  porcelain  crucible  standing  upon 
a  large  glass  plate.  The  phosphorus  having 
been  kindled  with  a  hot  wire,  the  flakes  of 
phosphoric  anhydride  will  be  seen  falling 
like  snow  on  to  the  glass  plate,  where  they 
accumulate  in  a  layer  of  considerable  thick- 
ness. To  preserve  it,  the  solid  must  be 
immediatly  scraped  up  with  a  bone  or  plati- 
num knife,  and  thrown  into  a  thoroughly 
Fig.  220.  dry  stoppered  bottle. 

Phosphoric  anhydride  may  be  fused  at  a  very  high  temperature,  and 
even  sublimed  Its  great  feature  is  its  attraction  for  water ;  left  exposed 
to  the  air  for  a  very  short  time,  it  deliquesces  entirely,  becoming  converted 
into  phosphoric  acid.  It  is  often  used  by  chemists  as  a  dehydrating 
agent,  and  will  even  remove  the  water  from  oil  of  vitriol.  When  thrown 
into  water,  it  hisses  like  a  red  hot  iron,  but  does  not  entirely  dissolve  at 
once,  a  few  flakes  of  metaphosphoric  acid  remaining  suspended  in  the 
li(|uid  for  some  time. 


^1=^ 


PYROPHOSPHORIC  AND  ORTHO-PHOSPHORIC  ACIDS.  231 

The  solution  obtained  by  dissolving  phosphoric  anhydride  in  water, 
contains  monohydrated  phosphoric  acid  or  metaphosphoric  acid  (K.fi.V^O^ 
or  HPO3).  If  a  little  silver  nitrate  be  added  to  a  portion  of  it,  a  trans- 
parent gelatinous  precipitate  is  formed,  which  is  the  silver  metaphos- 
phate  (AgNOg  +  HPO3  =  HNO3  +  AgPOg). 

If  the  solution  of  metaphosphoric  acid  be  heated  in  a  flask  for  a  short 
time,  it  will  lose  the  property  of  yielding  a  precipitate  with  silver  nitrate, 
unless  one  or  two  drops  of  ammonia  be  added  to  neutralise  it,  when  an 
opaque  white  precipitate  of  silver  pyrophosphate  (2Ag20.P205  or  Ag^PgO,.) 
is  obtained,  for  the  phosphoric  acid  has  now  been  converted  into  the 
dihydrated  ox pyropihosphonc  acid  (2H2O.P2O5  or  H^PgO-).  The  formation 
of  the  precipitate  is  thus  expressed — 

H,P207  +  4AgN03  +  4NH3  =  H^'fij  +  4NH4NO3. 

When  the  solution  of  pyrophosphoric  acid  is  mixed  with  more  water 
and  boiled  for  a  long  time,  it  gives,  when  tested  with  silver  nitrate  and  a 
little  ammonia,  a  yellow  precipitate  of  silver  orthophosphate  (SAgjO.PgOs 
or  Ag3P0^) ;  the  phosphoric  acid  having  become  converted  into  tHhydrated 
phosphoric  acid  or  orthophosphoHc  acid  (SHgO.PgOj  or  H3PO4),  and  acting 
upon  the  silver  nitrate  in  the  presence  of  ammonia,  thus — 

H3PO,  +  3  AgNOg  +  3NH3  =  AggPO^  +  3NH4NO3. 

The  pyrophosphoric  acid  (H^PgO-)  cannot  be  obtained  by  the  above 
process  without  an  admixture  of  one  of  the  other  acids,  but  it  has  been 
obtained  in  crystals  by  decomposing  the  lead  pyrophosphate  (Pb2P207) 
with  hydrosulphuric  acid,  and  evaporating  the  filtered  solution  in  vacuo 
over  oil  of  vitriol. 

Trihydrated  phosphoric  acid  may  also  be  obtained  in  prismatic  crystals, 
by  evaporating  its  solution  in  a  similar  way.  This  acid  is  also  called 
orthophosphoric  acid  {6p6o<s,  true),  and  common  phosphoric  acid,  in 
allusion  to  the  circumstance  that  the  phosphates  commonly  met  with  and 
employed  in  the  arts  are  the  salts  of  this  acid. 

It  will  be  perceived,  from  their  formulae,  that  metaphosphoric,  HPO3,  orthophos- 
plioric,  H3PO4,  and  pyrophosphoric  acid,  H4P2O7,  are  respectively  monobasic, 
tribasic,  and  tetrabasic  acids.  The  normal  sodium  salts  of  these  acids  are,  respec- 
tively, metaphosphate,  NaPOg,  orthophosphate,  Na-jPOj,  and  pyrophosphate, 
lS'a4P.207.  The  hydrogen  in  orthophosphoric  and  pyrophos- 
phoric acids  may  be  only  partly  replaced  by  a  metal ;  thus 
there  are  two  other  orthophospliates  of  sodium,  viz.,  hydro- 
disodic  phosphate  HXa2P04,  and  dihydrosodic  phosphate 
H2NaP04. 

The  phosphates  commonly  met  with  are  all  derived  from 
orthophosphoric  acid;  for  example,  bone-ash,  or  tricalcic 
orthophosphate,  Ca3(P04)2 ;  superphosphate,  or  monocalcic 
ortho{)hosphate,  CaH4(P04)o ;  common  phosphate  of  soda, 
or  hydrodisodic  orthophosphate,  HXa2P04 ;  microcosuiic  salt, 
or  hydro-ammonio-sodic  orthophosphate  HXH4Xa(P04). 

Pyrophosphates  and  metaphosphates  may  be  obtained  by 
the  action  of  heat  oa  the  hydro-orthophosphates. 

Thus,  if  a  crystal  of  the  common  rhombic  sodium  phosphate 
(HXa^P04.12Aq.)  be  heated  gently  in  a  crucible  (fig.  221), 
it  melts  in  its  water  of  crystallisation,  and  gradually  dries  Fig.  221. 

up  to  a  white  mass,  the  composition  of  which,  if  not  heated 

beyond  300"  F.,  will  be  Xa2HP04.  If  a  little  of  this  white  mass  be  dissolved  in 
water,  the  solution  will  be  alkaline  to  red  litmus  paper  ;  and  if  silver  nitrate  (itself 
neutral  to  test-papers)  be  added  to  it,  a  yellow  precipitate  of  silver  ortho2)hosphate 
will  be  obtained,  and  the  solution  will  become  stronglv  acid — 

Xa2HP04  +  SAgXOa  =  Ag3P04  +  2XaX03  +  HXO3. 


232  HYPOPHOSPHOROUS  ACID. 

If  the  dried  sodium  phosphate  be  now  strongly  heated  oyer  a  lamp,  it  will  lose 
water,  and  become  pyrophosphate  {irvp,  fire)  2Na2HP04  =  H2()  +  Na4P207.  On  dis- 
solving this  in  water,  the  solution  will  be  alkaline,  and  will  give  with  silver  nitrate  a 
white  precipitate  and  a  neutral  solution;  Na4P207  +  4AgN03  =  Ag4P207-t-4NaN03. 

Microcosmic  salt  (NaNH4HP04.4Aq.),  when  dissolved  in  water,  yields  an  alkaline 
solution  which  gives  a  yellow  precipitate  with  silver  nitrate,  the  liquid  becoming 
acid — 

NaNH4HP04  +  SAgNOg  =  Ag3P04  +  NaNOg  +  NH4NO3  +  HNO3  . 

But  if  the  salt  be  heated  in  a  crucible,  it  fuses,  evolving  water  and  ammonia, 
and  leaving  a  transparent  glass  of  sodium  metaphosphate  XaNH4HP04  =  H20 
+  XH3-1-  XaP03,  which  may  be  dissolved  by  soaking  in  water,  yielding  a  slightly  acid 
solution,  which  gives  a  white  gelatinous  precipitate  with  nitrate  of  silver,  the  liquid 
being  neutral ;  NaP03  +  AgNOg  =  AgP03  +  NaN03 . 

All  the  phosphates  may  be  converted  into  orthophosphates,  by  fusing  them  with 
alkaline  hydrate  or  carbonate.* 

164.  Phosphormis  anhydride  (P2O3)  is  the  product  of  the  slow  combustion  of  pho.s- 
phorus.  If  a  piece  of  phosphorus  be  heated  in  a  long  glass  tube,  into  which  a  very 
slow  current  of  dry  air  is  drawn  through  a  very  narrow  tube,  it  bums  with  a  pale  blue 
flame,  and  white  flakes  of  phosphorous  anhydride  are  deposited.  It  is  more  easily 
converted  into  vapour  than  phosphoric  acid.  It  eagerly  absorbs  moisture  from  the 
air,  and  is  decomposed  when  strongly  heated  in  a  sealed  tube,  yielding  free  phosphorus 
and  phosphoric  anhydride  ;  5P203=3P205  +  P4. 

Phosphoroiis  acid,  H3PO3,  is  obtained  in  solution,  mixed  with  phosphoric  and 
hypophosphoric  acids,  when  sticks  of  phosphorus  arranged  in  separate  tubes  open  at 
both  ends,  and,  placed  in  a  funnel  over  a  bottle,  are  exposed  under  a  bell-jar,  open  at 
the  top,  to  air  saturated  with  aqueous  vapour.  To  obtain  the  pure  acid,  chlorine  is 
very  slowly  passed  through  phosphorus  fused  under  water,  when  the  phosi)horous 
chloride  first  formed  is  decomposed  by  the  water  into  phosphorous  and  hydrochloric 
acids;  PCl3-j-3H20  =  H3P03-l-3HCl.  The  hydrochloric  acid  is  expelled  by  a 
moderate  heat,  when  the  phosphorous  acid  is  deposited  in  prismatic  crystals.  When 
heated,  it  is  decomposed  into  phosphoric  acid  and  gaseous  phosphuretted  hydrogen ; 

4H3P03=3H3P04  +  PH3. 

Solution  of  phosphorous  acid  gradually  absorbs  oxygen  from  the  air,  becoming 
phosphoric  acid.  This  tendency  to  absorb  oxygen  causes  it  to  act  as  a  reducing  agent 
upon  many  solutions  ;  thus  it  precipitates  finely-divided  metallic  silver  from  a  solution 
of  the  nitrate,  by  which  its  presence  may  be  recognised  in  the  water  in  which  ordinary 
phosphorus  has  been  kept.  The  solution  of  phosphorous  acid  even  reduces  sulphurous 
acid,  producing  sulphuretted  hydrogen  and  sulphur,  the  latter  being  formed  by  the 
action  of  the  sulphuretted  hydrogen  upon  the  sulphurous  acid;  H2SO3 -I- 3H3PO3 
=  3H3P04-fH2S. 

If  solution  of  phosphorous  acid  be  poured  into  a  hydrogen  apparatus,  some  hydric 
phosphide  is  formed  which  imparts  a  fine  green  tint  to  the  hydrogen  flame. 

Hypophosphoric  acid,  H4P20g,  is  precipitated  as  a  sparingly  soluble  sodium  hypo- 
phosphate,  Na4P.,Og.lOAq.,  on  adding  sodium  carbonate  to  the  syrupy  liquid  produced 
by  the  oxidation  of  moist  phosphorus  in  the  air.  From  the  sodium  salt,  a  lead-salt 
may  be  obtained  by  decomposition  with  lead  acetate,  and  by  treating  this  with  hydro- 
sulphuric  acid,  an  aqueous  solution  of  H4P20g  is  obtained.  It  is  intermediate  in  pro- 
perties between  phosphorous  and  phosphoric  acids,  and  gives  with  silver  nitrate  a 
white  precipitate  which  is  not  blackened  on  boiling. 

165.  Hypophosphorous  acid  (H3PO2). — When  phosphorus  is  boiled  with  barium 
hydrate  and  water,  the  latter  is  decomposed,  its  hydrogen  combining  with  part  of 
the  phosphorus  to  form  hydric  phosphide  (spontaneously  inflammable),  which 
escapes,  whilst  the  oxygen  of  the  water  unites  with  another  part  of  the  phosphorus, 
forming  hypophosphorous  acid,  which  acts  on  the  barj'ta  to  foiTU  barium  hypo- 
phosphite  ;  this  may  be  obtained  by  evaporating  the  solution,  in  crystals  having  the 
composition  BaH4(P0,),.  The  action  ot  phosphorus  upon  barium  hydrate  may  be 
represented  by  the  equation  3Ba(OH)2  -1-  6H2O  +  Pg  =  3BaH4(P02)2  -I-  2PH3. 

•Barium  hydrate.  Barium  hypophosphite. 

Some  barium  orthophosphate  is  also  formed  at  the  same  time,  as  the  result  of  a 
secondary  action. 

*  It  has  been  remarked  that  the  pliancy  of  the  acid  character  of  phosphoric  acid  par- 
ticularly fits  it  to  take  part  in  the  vital  phenomena.  It  maybe  regarded  as  three  acids 
in  one. 


GASEOUS  PHOSPHUEETTED  HYDROGEN. 


233 


By  dissolving  the  barium  hypophosphite  in  water,  and  decomposing  it  with  the 
requisite  quantity  of  sulphuric  acid,  so  as  to  precipitate  the  barium ^as  sulphate,  a 
solution  is  obtained  which  may  be  concentrated  by  careful  evaporation.  If  this 
hypophosphorous  acid  be  heated,  it  evolves  hydric  phosphide,  and  becomes  converted 
into  phosphoric  acid;  2H.jP02  =  H3P04  +  PH3.  When  exposed  to  the  air  it  absorbs 
oxygen,  and  becomes  converted  into  phosphorous  and  phosphoric  acids.  It  is  a 
more  powerful  reducing  agent  than  phosfihorous  acid.  The  latter  acid  does  not 
reduce  a  solution  of  sulphate  of  copper,  but  hypophosphorous  acid,  when  gently  wanned 
with  it,  gives  a  black  precipitate  oi  hydride  of  copper  (CuH),  which  is  decomposed  by 
boiling,  evolving  hydrogen  and  leaving  metallic  copper. 

When  heated,  the  hypophosphites  evolve  hydric  phosphide,  and  are  converted 
into  phosphates.  The  sodium  hypophosphite  (NaHjPO^)  is  sometimes  used  in 
medicine  ;  its  solution  has  been  known  to  explode  with  great  violence  during  evapora- 
tion, probably  from  a  sudden  disengagement  of  hydric  phosphide. 

The  following  is  a  summary  of  the  acids  formed  hy  phosphorus  with  oxygen  and 
hydrogen — 


Hypophosphorous  acid, 
Hypophosphoric       ,,    . 
Phosphorous             ,,    . 
Metaphosphoric       ,,    . 
Orthophosphoric      ,,    . 

H,P02 

.    .    .    .     h;p.a 
.     .     .     .     H3P03 
.     .     .     .     HP03 

.      .       ;       H3PO4 

Pyrophosphoric        ,,    . 

.         .         .         .         H,P.,0, 

166.  Suboxide  of  phosphorus  is  supposed  to  constitute  the  yellow  or  red  residue 
which  is  left  in  the  dish  when  phosphorus 
burns  in  air,  but  it  is  always  mixed  with  much 
phosphoric  anhydride.  If  phosphorus  be  melted 
under  water  in  a  flask  (fig.  222),  and  oxygen 
gas  be  allowed  to  bubble  through  it  (a  brass 
tube  being  employed  to  convey  the  oxygen), 
each  bubble  of  the  gas  produces  a  brilliant 
flash,  and  the  phosphorus  is  converted  into 
red  flakes,  which  were  believed  to  be  suboxide 
of  ])hosphorus,  but  are  really  amorphous  phos- 
phorus. The  true  suboxide  of  phosphorus  (P4O) 
appears  to  be  formed  when  small  pieces  of  phos- 
phorus are  covered  with  phosphorous  chloride 
exposed  to  the  air,  and  afterwards  heated  with 
water,  when  the  suboxide  is  deposited  as  a  yellow  powder  becoming  red  at  high 
temperatures,  and  inflaming  when  heated  in  air. 


Fig.  222. 


Phosphides  of  Hydrogen. 

167.  Although  phosphorus  and  hydrogen  do  not  combine  directly, 
there  are  three  compounds  of  these  elements  producible  by  processes  of 
substitution,  the  composition  of  which  is  shown  in  the  following  table  : — 


Name. 

Formula. 

By  Weight. 

Phosphorus.      Hydrogen. 

Gaseous  hydric  phosphide, 
Lic^uid  hydric  phosphide, 
Solid  hydric  phosphide,   . 

PH, 
PH2 
PjH  ? 

31 
31 
62 

3 
2 
1 

Gaseous  hydric  phosjjhide  or  pliosphuretted  hydrogen  gas,  or  phosphine 
(PH3  =  34  parts  by  weight  =  2  volumes  =  ^  volume  P-f  3  vohimes  H),  is 
by  far  the  most  important  of  these.  It  has  been  mentioned  above  as 
resulting  from  the  action  of  heat  upon  phosphorous  acid,  and  when 
prepared  by  this  process,  it  is  obtained  as  a  colourless  gas,  with  a  most 
powerful  odour  of  putrid  fish,  inflaming  on  the  approach  of  a  light,  and 
burning  with  a  brilliant  white  flame,  producing  thick  clouds  of  phosphoric 


234 


GASEOUS  PHOSPHUKETTED  HYDROGEN. 


acid.     It  is  slightly  heavier  than  air  (sp.  gr.  1'19),  and  has  been  liquefied 
under  high  pressure. 

The  ordinary  method  of  preparing  this  gas  for  experimental  purposes  consists  in 
boiling  phosphorus  with  a  strong  solution  of  potash,  when  water  is  decomposed,  its 
hydrogen  combining  with  one  part  of  the  phosphorus,  and  its  oxygen  with  another 
part  forming  hypophosphorous  acid,  which  unites  with  the  potash — 

P4  +  3KH0  +  SHjjO  =  PH3  +  SKHoPOj. 

A  few  fragments  of  phosphorus  are  introduced  into  a  small  retort  (fig.  223),  which 
is  then  nearly  filled  with  a  strong  solution  of  potash  (sp.  gr.  I'S),*  and  heated.  The 
extremity  of  the  neck  of  the  retort  should  not  be  plunged  under  water  until  the 

spontaneously  inflammable  gas  is  seen 
burning  at  the  orifice,  and  the  retort  must 
not  be  placed  close  to  the  face  of  the 
operator,  since  explosions  sometimes  take 
place  in  preparing  the  gas,  and  the  boiling 
potash  produces  dangerous  effects.  The 
gas  may  be  collected  in  small  jars  filled 
with  water,  taking  care  that  no  bubble  of 
air  is  left  in  them.  It  contains  hydric 
phosphide  mixed  with  free  hydrogen,  the 
latter  being  formed  from  the  deoxidatiou 
of  water  by  the  potassium  hypophosphite. 
As  each  bubble  of  this  gas  escapes  into 
the  air  through  the  water  of  the  pneumatic 
trough,  it  burns  with  a  vivid  white  flame, 
producing  beautiful  wreaths  of  smoke 
(phosphoric  anhydride),  resembling  the 
gunner's  rings  sometimes  seen  in  firing 
cannon.  Small  bubbles  sometimes  escape 
without  spontaneously  inflaming.  If  a 
bubble  be  sent  up  into  a  jar  of  oxj'gen, 
the  flash  of  light  is  extremely  vivid,  and 
the  jar  must  be  a  strong  one  to  resist  the 


=*s^»sNr=""* 


Fig.  223. — Preparation  of  phosphuretted 
hydrogen. 


concussion.  It  is  advisable  to  add  a  trace  of  chlorine  to  the  oxygen,  to  insure  the 
inflammation  of  each  bubble,  for  an  accumulation  of  the  gas  would  shatter  the  jar. 

If  this  gas  be  passed  through  a  tube  cooled  in  a  freezing  mixture  of  ice  and  salt, 
the  gas  escaping  from  the  tube  is  found  to  have  lost  its  spontaneous  inflammability, 
although  it  takes  fire  on  contact  with  flame.  The  cold  tube  contains  the  liquid 
hydric  phosphide  (PHj),  which  was  present  in  the  gas  in  the  state  of  vapour,  and 
caused  its  spontaneous  inflammability,  for  as  soon  as  the  liquid  comes  in  contact 
with  air  it  takes  fire.  When  exposed  to  light,  the  liquid  phosphide  is  decomposed 
into  the  gaseous  phosphide,  antl  a  yellow  solid  phosphide  (P^H),  which  is  not 
spontaneously  inflammable;  5PH2  =  P2H  +  3PH3.  It  is  for  this  reason  that  the 
spontaneously  inflammable  gas  loses  that  property  when  kept  (unless  in  the  dark), 
depositing  the  solid  phosphide  upon  the  sides  of  the  jar. 

By  passing  a  few  drops  of  oil  of  turpentine  up  through  the  water  into  a  jar  of  the 
spontaneously  inflammable  gas,  this  property  will  be  entirely  destroyed,  whereas 
the  addition  of  a  trace  of  nitrous  acid  imparts  spontaneous  inflammability. 

Hydric  phosphide,  when  passed  through  solutions  of  some  of  the  metals,  pre- 
cipitates their  phosphides.  For  example,  with  sulphate  of  copper  it  gives  a  black 
precipitate  of  phosphide  of  copper,  3CuS04  +  2PH3==3H2S04  +  P2Cu3. 

When  this  black  precipitate  is  heated  with  solution  of  potassium  cyanide,  it  evolves 
self-lighting  hydric  phosphide,  f  In  fact,  this  is  one  of  the  easiest  and  safest  methods 
of  preparing  this  gas ;  for  the  phosphide  of  copper  is  readily  obtained  by  simply 
boiling  phosphorus  in  a  solution  of  sulphate  of  cojiper. 

Phosphine  has  great  pretensions  to  rank  as  the  chemical  analogue  of  ammonia,  for 
although  it  has  no  alkaline  properties,  it  is  capable  of  combining  with  hydrobromic 
and  hydriodic  acids  to  form  crystalline  compounds  analogous  to  ammonium  bromide 
and  iodide  ;  these  compounds,  however,   are  decomposed  by  water.     It  will  be  seen 

*  4.50  grains  of  common  stick  potash  dissolved  in  1000  grains  of  water. 
■f-  Cupric  cyanide  and  potassium  phosphide  being  formed,  and  the  latter  decomposed 
by  water,  giving  hydric  pho.sphide  and  potassium  hypophosphite. 


CHLORIDES  OF  PHOSPHORUS.  235 

hereafter,  that  when  the  hydrogen  of  phosphine  is  displaced  by  certain  compound 
radicals,  such  as  ethyls,  powerful  organic  bases  are  produced. 

The  spontaneously  inflammable  hydric  phosphide  may  also  be  obtained  by  throwing 
fragments  of  calcium  phosphide  into  water  ;  this  substance  is  prepared  by  passing 
vapour  of  phosphorus  over  red  hot  quicklime,  or  simply  by  heating  small  lumps  of 
quicklime  to  bright  redness  in  a  crucible  and  throwing  in  fragments  of  phosphorus, 
closing  the  crucible  immediately.  The  dark  brown  mass  thus  obtained  is  a  mixture 
of  pyrophosphate  and  phosphide  of  calcium,  of  somewhat  variable  composition. 

The  calcium  phosphide  has  beeu  used  in  life-buoys  for  indicating  by  the  flare  their 
position  on  the  water. 

When  phosphine  is  decomposed  by  a  succession  of  electric  sparks,  2  volumes  of 
the  gas  yield  3  volumes  of  hydrogen,  the  phosphorus  being  deposited  in  the  red  or 
amorphous  form. 

168.  Two  chlorides  of  phosphorus  arehnown.  The  trichloride  or  phosphorous  chloride 
(PCI3)  is  prepared  by  acting  upon  phosphorus  with  perfectly  dry  chlorine  in  the  appa- 
ratus employed  (p.  219)  for  preparing  the  chloride  of  sulphur.  Phospliorous  chloride 
distils  over  very  easily  (boiling-point,  173°'4  F. ),  as  a  colourless,  pungent  liquid 
(sp.  gr.  1'62),  which  fumes  strongly  in  air,  its  vapour  decomposing  the  moisture  of 
the  air  and  producing  hydrochloric  acid  fumes.  In  contact  with  water  the  liquid  is 
immediately  decomposed,  yielding  hydrochloric  and  phosphorous  acids,  as  described 
for  the  preparation  of  the  latter  acid  (p.  232).  Its  analogy  to  phosphorotis  anhydride 
is  shown  by  its  absorbing  oxygen  wheu  boiled  in  the  presence  of  that  gas,  and  forming 
the  phoqyhorus  oxychloridc  (PCI3O).  It  also  absorbs  chlorine  with  avidity,  becoming 
converted  into  pentachloride  of  phosphorus  or  phosphoric  chloride  (PClg).  This 
compound,  however,  is  more  conveniently  prepared  by  passing  chlorine  through  a 
solution  of  phosphorus  in  carbon  disulphiile,  carefully  cooled.  On  evaporation,  the 
pentachloride  of  phosphorus  is  deposited  in  white  prismatic  crystals,  which  volatilise 
below  212°  F.,  and  fume  when  exposed  to  air,  from  the  production  of  hydrochloric 
acid.  When  thrown  into  water  it  is  decomposed  into  phosphoric  and  hydrochloric 
acids;  PClg -f  4H2O  =  H3PO4 -f  5HC1.  But  if  it  be  allowed  to  deliquesce  in  air,  only 
a  partial  decomposition  takes  place,  and  the  phosphorus  oxychloiide  is  formed, 
PCI5  +  H^O  =  PCI3O  +  2HC1 . 

This  oxychloride  may  also  be  produced  by  heating  phosphoiic  chloride  with  phos- 
phoric anhydride;  PgOg -f  3PClg  =  5PCI3O.  A  more  instructive  method  of  preparing 
it  consists  in  distilling  the  phosphoric  chloride  with  crystallised  boracic  acid,  SPClj 
+  3H„O.B,,03  =  3PCl30  +  6HC1  +  Bfi^. 

Some  of  the  organic  acids  (succinic,  for  example)  may  be  obtained  in  the  anhy- 
drous state,  as  the  boracic  acid  is  in  this  case,  by  distilling  the  hydrate  with 
phosphoric  chloride.  The  phosphorus  oxychloride  distils  over  (boiling-point,  230° 
F. )  as  a  heavy  (sp.  gr.  1 7)  colourless  fuming  liquid  of  pungent  odour.  Of  course,  it 
is  decomposed  by  water,  yielding  hydrochloric  and  phosphoric  acids.  It  will  be 
found  of  the  greatest  use  in  efl'ecting  certain  transformations  in  organic  substances. 

The  analogy  between  water  and  hydrosulphuric  acid  would  lead  to  the  expectation 
that  a  sulphochloride  of  phosphorus  (PCI3S),  corresponding  to  the  oxychloride,  would 
be  formed  by  the  action  of  hydrosulphuric  acid  upon  phosphoric  chloride  ;  PClg-f  H.2S 
=  PCI3S  -f  2HC1.  It  is  a  colourless  fuming  liquid,  which  is  slowly  decomposed  by 
water,  giving  phosphoric,  hydrochloric,  and  hydrosulphuric  acids  ;  PCI3S  +  dHgO 
---=H3P04  +  3HCl  +  HoS.  When  acted  on  by  solution  of  soda,  the  sulphochloride  of 
phosphorus  loses  its  chlorine  to  the  sodium,  and  acquires  an  equivalent  quantity  of 
oxygen,  a  sodium  sulphoxy-jihosphate  (Na3P03S.12H20)  being  deposited  in  crys- 
tals. This  salt  evidently  corresponds  in  composition  to  the  sodium  orthophospliate 
(Na3PO4.i2H.2O),  and  its  production  is  expressed  by  the  equation,  FClgS  +  CXaHO 
=  3XaCl  -t-  NagPOgS  +  3H2O.  Salts  of  similar  composition  may  be  obtained  with  other 
metallic  oxides. 

The  bromides  and  oxyhromide  of  phosphorus  correspond  to  the  chlorine  compounds. 

Iodine  in  the  solid  state  combines  very  energetically  with  phosphorus,  but  if  the 
two  elements  be  brought  together  in  a  state  of  solution  in  carbon  disulphide,  a  more 
moderate  action  ensues,  and  two  iodides  of  phosphortis  may  be  obtained  in  crystals  ; 
a  tri-iodide  (PI3)  corresponding  to  the  trichloride,  and  a  biniodide  (PL),  which  has 
no  analogue  either  among  the  oxj'gen,  chlorine,  or  bromine  compounds  of  phosphorus. 
PI5  has  also  been  obtained. 

The  addition  of  a  very  small  quantity  of  iodine  to  ordinary  phosphorus,  fused  in  a 
flask  tilled  with  carbonic  acid  gas,  materially  accelerates  its  conversion  into  the  red 
modilication,  and  allows  the  change  to  be  eflected  at  a  much  lower  temperature  than 


286  .  THOSPHAMIDES. 

that  required  when  the  phosphorus  is  heated  alone,  probably  because  successive 
portions  of  vitreous  phosphorus  combine  with  the  iodine  to  form  an  unstable  iodide 
from  wliich  the  heat  separates  the  phosphorus  in  the  amorphous  form. 

169.  The  sulphides  of  phosphorus  may  be  formed  by  the  direct  combination  of 
their  elements.  If  ordinary  phosphorus  be  used,  the  experiment  is  not  unattended 
with  danger,  and  should  be  performed  under  water.  It  is  safer  to  combine  the 
amorphous  phosphorus  with  sulphur,  at  a  moderate  heat,  in  an  atmosphere  of  car- 
bonic acid  gas. 

There  appear  to  be  at  least  three  sulphides  of  phosphorus,  viz.,  the  subsulphide 
(PaS),  the  sesquisulphide  (P2S3),  representing  phosphorous  anhydride  (PjOg),  and  the 
pentasulphide  (P.2S5)),  analogous  to  phosphoric  anhydride  (PjOj). 

PgS  is  a  yellow  oily  liquid  which  may  be  distilled  out  of  contact  with  air. 

PgSg  is  a  yellow  solid,  easily  fusible,  and  capable  of  subliming  in  a  crystalline 
form  if  air  be  excluded.  It  may  be  produced  by  the  action  of  hydric  sulphide  upon 
phosphoric  chloride  ;  2PCI3  +  3H2S  =  P^S,^  +  6HC1 . 

PgSg  crystallises  more  readily  in  a  fused  state  than  P^Sj.  Both  these  sulphides, 
unlike  the  PgS,  are  easily  decomposed  by  water. 

170.  Phosphamides  or  amides  of  plwsphmic  acid. — When  phosphorus  oxychloride 
is  acted  on  by  ammonia,  ammonium  chloride  and  phosphotriamidc  are  produced ; 
the  former  is  dissolved  by  water,  which  leaves  the  phosphotriamidc  as  a  white  in- 
soluble body,  not  easily  attacked  by  acids  and  alkalies;  PCl30  +  6NH3  =  3NH4CI 
+  NyHgPO  (Phosphotriamide). 

If  the  sulphochloride,  PCI3S,  be  substituted  for  the  oxychloride,  the  corresponding 
sulphosphotriamide,  N3HSPS,  is  obtained. 

The  action  of  ammonia  on  phosphoric?  chloride  yields  chlorophosphamide,  N.H.PCL ; 
PCI5  +  2NH3 = 2HC1  +  N2H4PCI3 . 

When  this  is  boiled  with  water,  a  very  stable  insoluble  substance  is  obtained, 
which  is  phosphodiarnide  ;  N2H4PCI3  +  HgO  =  3HC1  +  N2H3PO  (phosphodiamide). 

When  heated,  it  evolves  ammonia  and  hecomts  phosphmiumamide  ;  N2H,P0  =  NHa 
+  NPO. 

The  phosphamides  may  be  regarded  as  being  derived  from  the  ammonium  ortho- 
phosphates  by  the  abstraction  of  3H2O  ;  thus — 

(NH4)3P04  minus  SHgO  =  NgHfiPO  Phosphotriamide. 
(NH4)2HP04  ,,  „  =  N2H3PO  Phosphodiamide. 
NH4H2PO4         „         ,,      =  NPO         Phosphomonamide. 

When  boiled  with  potassium  hydrate,  the  phosphamides  acquire  the  elements  of 
water,  and  are  converted  into  ammonia  and  potassium  orthophosphate. 

ARSENIC. 

As  =  75  parts  by  weight.  * 

171.  This  element  is  often  classed  among  the  metals,  because  it  has  a 
metallic  lustre  and  conducts  electricity,  but  it  is  not  capable  of  forming 
a  base  with  oxygen,  and  the  chemical  character  and  composition  of  its 
compounds  connect  it  in  the  closest  manner  with  phosphorus. 

In  its  mode  of  occurrence  in  nature  it  more  nearly  resembles  the 
sulphur  group  of  elements,  for  it  is  occasionally  found  in  the  uncombined 
state  (native  arsenic),  but  far  more  abundantly  in  combination  with 
various  metals,  forming  arsenides,  which  frequently  accompany  the  sul- 
phides of  the  same  metals.  The  following  are  some  of  the  chief  arsenides 
and  arsenio-sulpMdes  found  in  the  mineral  kingdom — 


Kupfernickel, 

NiAs 

Arsenical  nickel, 

NiAs, 

Tin -white  cobalt. 

CoAs^ 

Mispickel  or  arsenical  pyrites. 

FeS2.FeAs2 

Cobalt-glance, 

CoS.,.CoAs2 

Nickel-glance, 

NiS;.NiAs2 

*  The  specific  gravity  of  the  vapour  of  arsenic,  like  that  of  phosphorus,  indicates  that 
7.T  parts  by  weight  only  occupy  half  a  volume.  Hence  the  molecule  of  arsenic  must  be 
represented  by  As4=2  volumes. 


ARSENIC. 


237 


But  arsenic  also  occurs,  like  the  metals,  in  combination  with  sulphur, 
thus  we  have — 


Red  orpiment  or  realgar, 
Yellow  orpiment, 


As,S2 
AS2S3 


It  is  from  these  minerals  that  arsenic  derives  its  name  (apcrevLKov, 
orpiment)  ;  the  sulphides  of  arsenic  are  also  found  in  combination  with 
other  sulphides  ;  thus  red  silver  ore  is  a  cc»mpound  of  the  sulphides  of 
silver  aud  arsenic  (SAg^S.As^Sg)  ;  Termantite  contains  sulphide  of  arsenic 
combined  with  the  sulphides  of  iron  and  copper ;  and  grey  copper  ore 
is  composed  of  sulphide  of  arsenic  with  the  sulphides  of  copper,  silver, 
zinc,  iron,  and  antimony.  In  an  oxidised  form  arsenic  is  found  in  con- 
(Jjirrite,  which  contains  arsenious  anhydride  (A82O ,)  and  cuprous  oxide. 
Cobalt-bloom  consists  of  cobalt  arseniate  or  Co3( As04)2 . 

Arsenical  pyrites  is  one  of  the  principal  sources  of  arsenic  and  its  com- 
pounds, though  a  considerable  quantity  is  also  obtained  in  the  form  of 
arsenious  anhydride  as  a  secondary  product  in  the  working  of  certain  ores, 
especially  those  of  copper,  tin,  cobalt,  and  nickel. 

The  substance  used  in  the  arts  under  the  name  of  arsenic  is  really  the 
oxide  of  arsenic  or  arsenious  anhydride  (AsgOg)  ;  pure  arsenic  itself  has 
very  few  useful  applications,  so  that  it  is  not  the  subject  of  an  extensive 
manufacture.  It  can  be  extracted  from 
arsenical  pyrites  (FeSg-FeAs^)  by  heating 
it  in  earthen  cylinders  fitted  with  iron 
receivers,  in  which  the  arsenic  condenses 
as  a  metallic-looking  crust,  the  heat  ex- 
pelling it  from  the  pyrites  in  the  form  of 
vapour. 

On  a  small  scale  it  may  be  obtained  by  heating 
a  mixture  of  white  arsenic  with  half  its  weight 
of  recently  calcined  charcoal  in  a  crucible  (Hg. 
224),  the  mixture  being  covered  with  two  or  three 
inches  of  charcoal  in  very  small  fragments,  and 
the  crucible  so  placed  that  this  charcoal  may  be 
heated  to  redness  first,  in  order  to  ensure  the 
reduction  of  any  oxide  which  might  escape  from  Fxtraction  of  arsenic 

below.     In  order  to  collect  the  arsenic,  another     *^g-  ^^4-— Extraction  ot  arsenic, 
crucible,  having  a  small  hole  drilled  through  the  bottom  for  the  escape  of  gas,  is 
cemented  on  to  the  first,  in  an  inverted  position,  with  fire-clay,  aud  protected  from 
the  tire  by  an  iron  plate  with 
a  hole  in  it  for  the  crucible. 
The    reduction    of    arsenious 
anhydride  by  charcoal  is  thus 
represented — 

Asp.,  +  C3  =  As2  +  SCO . 

For  the  sake  of  illustration, 
a  small  quantity  of  arsenic 
may  be  prepared  from  white 
arsenic  by  a  method  commonly 
employed  in  testing  for  that 
substance.  A  small  tube  of 
German  glass  is  drawn  out  to 
a  narrow  point  (A,  fig.  225), 
and  sealed  with  the  aid  of  the  blowpipe 


Fie 


225. — Reduction  of  arsenious  oxide. 
A  very  minute  quantity  of  white  ar.senic  is 
introduced  into  the  point  of  the  tube,  and  a  few  fragments  of  charcoal  are  placed  in 
the  tube  itself  at  B.     The  charcoal  is  heated  to  redness  with  a  blowpipe  flame,  and 
the  point  is  then  heated  so  as  to  drive  the  white  arsenic  in  vapour  over  the  red  hot 


238 


PROPERTIES  OF  ARSENIC. 


charcoal,  when  a  shining  black  ring  of  arsenic  (C)  will  be  deposited  upon  the  cooler 
portion  of  the  tube. 

The  arsenic  thus  obtained  is  a  brittle  mass  of  a  dark  steel-grey  colour 
and  brilliant  metallic  lustre  (sp.  gr.  5-7).  It  does  not  fuse  when  heated, 
unless  in  a  sealed  tube,  since  it  is  converted  into  vapour  at  356°  F.  It  is 
not  changed  by  exposure  to  air,  unless  powdered  and  moistened,  when 
it  is  slowly  converted  into  AsgOg.  "When  heated  in  air,  it  oxidises 
rapidly  at  about  160°  F.,  giving  off  white  fumes  of  arsenious  anhydride 
and  a  characteristic  garlic  odour  (recalling  that  of  phosphorus),  which  is 
also  produced  when  arsenical  pyrites  is  struck  with  a  hammer  or  pick. 
At  a  red  heat  it  burns  in  air  with  a  bluish  white  flame,  and  in  oxygen 
with  great  brilliancy.  It  is  not  dissolved  by  water  or  any  simple  solvent 
(herein  resembling  the  metals),  but  is  oxidised  and  dissolved  by  nitric 
acid. 

In  its  chemical  relations  to  other  elements,  arsenic  much  resembles 
phosphorus,  undergoing  spontaneous  combustion  in  chlorine,  and  easily 
combining  with  sulphur.  Like  phosphorus  also,  it  combines  with  many 
metals,  even  with  platinum,  to  form  arsenides,  and  its  presence  often 
affects  materially  the  properties  of  the  useful  metals.  There  are,  some 
reasons  for  believing  in  the  existence  of  two  allotropic  forms  of  arsenic, 
differing  in  chemical  activity  like  those  of  phosphorus. 

Pure  arsenic  does  not  produce  symptoms  of  poisoning  till  a  consider- 
able period  after  its  administration,  being  probably  first  oxidised  in  the 
stomach  and  intestines,  and  converted  into  arsenious  acid. 


Oxides  op  Arsenic. 

172.  Arsenic   forms  two   compounds  with   oxygen,  corresponding   to 
phosphorous  and  phosphoric  anhydrides. 


Formula. 

By  Weight. 

Arsenic. 

Oxygen. 

Arsenious  anhydride, . 
Arsenic  anhydride,     . 

ASoOg 

AS2O5 

150 
150 

48 
80 

Arsenious  anhydride  (AsgOg  =198  parts  by  weight  =  1  volume 
=  1  volume  As  +  3  volumes  0).* — Unlike  phosphorus,  arsenic,  when 
burning  in  air,  only  combines  with  three  atoms  of  oxygen.  Arsenious 
anhydride,  or  ichite  arsenic,  is  a  very  useful  substance  in  many  branches 
of  industry.  It  is  employed  in  the  manufacture  of  glass,  of  several 
colouring-matters,  and  of  shot.  A  large  quantity  is  also  consumed  for 
the  preparation  of  arsenic  acid  and  arseniate  of  soda ;  it  is,  indeed,  the 
source  from  which  nearly  all  the  compounds  of  arsenic  are  procured. 
Small  quantities  of  crystalline  arsenious  anhydride  are  occasionally  found 
associated  with  the  ores  of  nickel  and  cobalt. 

White  arsenic  is  manufactured  by  roasting  the  arsenical  pyrites,  chiefly 
obtained  from  the  mines  of  Silesia,  in  m-uffles  or  ovens,  through  which 
air  is  allowed  to  pass,  when  the  arsenic  is  converted  into  AsgO^,  and  the 
sulphur  into  SOg,  which  are  conducted  into  large  chambers  in  which  the 
As.,03  is  deposited  as  a  very  fine  powder.     The  iron  of  the  pyrites  is 

*  The  specitic  gravity  of  the  vapour  of  arsenious  anhydride  is  198  times  that  of  hydrogen, 
instead  of  99  times  according  to  the  usual  law. 


ARSENIOUS  ANHYDEIDE.  239 

left  partly  as  oxide,  and  partly  as  sulphate  of  iron.  The  removal  of  the 
AS2O3  from  the  condensing  chambers  is  a  very  unwholesome  operation, 
owing  to  its  dusty  and  very  poisonous  character.  The  workmen  are 
cased  in  leather,  and  protect  their  mouths  and  noses  with  damp  cloths,  so 
as  to  avoid  inhaling  the  fine  powder. 

This  rough  white  arsenic  is  subjected  to  a  second  sublimation  on  a 
smaller  scale  in  iron  vessels,  when  it  is  obtained  in  the  form  of  a  semi- 
transparent  glassy  mass  known  as  vitreous  arsenimts  acid,  which  gradually 
becomes  opaque  when  kept,  and  ultimately  resembles  porcelain.  The 
white  arsenic  sold  in  the  shops  is  a  fine  powder,  dangerously  resembling 
flour  in  appearance,  but  so  much  heavier  (sp.  gr.  3 '7)  that  it  ought  not 
to  be  mistaken  for  it.  When  examined  under  the  microscope,  it  appears 
in  the  form  of  irregular  glassy  fragments,  mixed  with  octahedral  crystals. 
White  arsenic  softens  when  gently  heated,  but  does  not  fuse  (unless  in  a 
sealed  tube),  being  converted  into  vapour  at  380°  F.,  and  depositing  in 
brilliant  octahedral  crystals  upon  a  cool  surface.  The  experiment  may  be 
made  in  a  small  tube  sealed  at  one  end,  the  upper  part  of  which  should 
be  slightly  warmed  before  heating  the  arsenious  anhydride,  so  as  to 
prevent  too  rapid  condensation,  which  is  unfavourable  to  the  formation 
of  distinct  crystals.*  The  octahedra  are  best  examined  with  a  binocular 
microscope.  This  common  poison  may  fortunately  be  still  more  easily 
recognised  by  sprinkling  it  upon  a  red  hot  coal,  when  a  strong  odour 
of  garlic  is  perceptible,  due  to  the  reduction  of  the  AS2O3  by  the  heated 
carbon ;  the  vapour  of  white  arsenic  itself  is  inodorous.  The  sparing 
solubility  of  white  arsenic  in  water  is  very  unfavourable  to  its  action  as 
a  poison,  for,  when  thrown  into  ordinary  liquids,  it  is  dissolved  in  very 
small  quantity,  the  greater  part  of  it  collecting  at  the  bottom.  Even 
when  taken  into  the  stomach  in  a  solid  state,  its  want  of  solubility 
delays  its  operation  sufficiently  to  give  a  better  chance  of  antidotal 
treatment  than  in  the  case  of  most  other  common  poisons.  Its  compara- 
tive insolubility  is  shown  by  its  being  almost  tasteless. 

When  thrown  into  water,  arsenious  anhydride  exhibits  great  repulsion 
for  the  particles  of  that  liquid,  and  collects  in  a  characteristic  manner 
round  little  bubbles  of  air.  forming  small  white  globes  which  are  not 
wetted  by  the  water.  Even  if  stirred  with  the  water,  and  allowed  to 
remain  in  contact  with  it  for  some  hours,  a  pint  of  water  (20  oz.)  would 
not  take  up  more  than  20  grs.  The  smallest  dose  which  has  been 
known  to  prove  fatal  is  2'5  grs.  If  boiling  water  be  poured  upon  pow- 
dered white  arsenic,  and  allowed  to  remain  in  contact  with  it  till  cold,  it 
will  dissolve  about  ^J-g-  of  its  weight  (22  grs.  in  a  pint). 

When  powdered  white  arsenic  is  boiled  with  water  for  two  or  three 
hours,  100  parts  by  weight  of  water  may  be  made  to  dissolve  11  "5  parts 
of  the  anhydride,  and  when  the  solution  is  alloAved  to  cool,  about  9  parts 
will  be  deposited  in  octahedral  crystals,  leaving  2  "5  parts  dissolved  in  100 
of  water  (219  grs.  in  a  pint). 

This  great  increase  in  the  solubility  of  the  arsenious  anhydride  by  long 
boiling  with  Avater  is  usually  attributed  to  the  conversion  of  the  opaque 
or  crystalline  variety,  which  always  composes  the  powder,  into  the 
vitreous  modification,  -which  is  the  more  soluble  in  water.     Water,  heated 

*  When  arsenious  anhydride  is  fused  in  a  long  tube,  sealed  at  both  ends,  and  buried  in 
hot  sand,  the  mass,  after  cooling,  is  found  to  contain  some  prismatic  crystals,  which  are 
also  sublimed  on  those  parts  of  the  tube  which  have  been  heated  above  390°  F. 


240  ARSENITES. 

with  arsenious  anhydride  in  a  sealed  tube,  may  be  made  to  dissolve  its 
own  weight  of  it ;  as  the  solution  cools,  it  first  deposits  prismatic  crystals, 
and  afterwards  the  ordinary  octahedral  form.  The  solution  is  very  teebly 
acid  to  blue  litmus  paper. 

White  arsenic  dissolves  abundantly  in  hot  hydrochloric  acid  (a  part  of 
it  being  converted  into  arsenious  chloride),  and  as  the  solution  cools, 
part  of  the  anhydride  is  deposited  in  large  octahedral  crystals.  It  is  said, 
that  if  the  vitreous  form  be  dissolved  in  hydrochloric  acid,  the  formation 
of  these  crystals  will  be  attended  by  flashes  of  light,  visible  in  a  darkened 
room ;  but  the  opaque  variety  does  not  exhibit  this  phenomenon. 

The  vitreous  arsenious  anhydride  has  a  slightly  higher  specific  gravity 
than  the  opaque  form,  and  fuses  rather  more  easily.  The  opaque  variety 
appears  to  be  identical  in  its  properties  with  crystallised  arsenious  anhydride. 

Solutions  of  the  alkalies  readily  dissolve  arsenious  anhydride,  forming 
alkaline  arsenites,  the  solutions  of  which  are  capable  of  dissolving  arsenious 
anhydride  more  easily  than  water,  and  deposit  it  in  crystals  on  cooling. 
Arsenious  anhydride  is  sometimes  deposited  in  prismatic  crystals  from 
its  solution  in  potash,  and  the  same  form  has  been  found  native.  On 
adding  a  small  quantity  of  hydrochloric  acid  to  the  solution  of  the  alka- 
line arsenite,  a  white  precipitate  of  arsenious  anhydride  is  formed. 

White  arsenic  has  the  property  of  preventing  the  putrefaction  of  skin 
and  similar  substances,  and  is  occasionally  employed  for  the  preservation 
of  objects  of  natural  history,  &c. 

Arse7utes. — Arsenious  acid,  properly  so  called,  has  not  yet  been  obtained 
in  the  separate  state.  The  aqueous  solution  of  white  arsenic,  when  neu- 
tralised exactly  with  ammonia,  yields,  with  silver  nitrate,  a  yellow  preci- 
pitate having  the  composition  Ag'gAsOg  ;  with  cupric  sulphate,  a  green 
])recipitate  having  the  composition  Cu"HAs03 ;  with  zinc  sulphate,  a 
white  precipitate  containing  Zn"3(As03)2,  and  with  magnesium  sulphate, 
a  white  precipitate  of  Mg"HAs03.  ^^  would  appear,  therefore,  that  the 
arsenious  acid  from  which  these  salts  are  derived  is  a  tribasic  acid  having 
the  formula  HgAsOg,  corresponding  to  boracic  acid  H3BO3 .  Arsenious 
acid  does  not  destroy  the  alkaline  reaction  of  the  alkalies,  and  it  does 
not  decompose  the  alkaline  carbonates  unless  heat  is  applied,  proving  it 
to  be  a  feeble  acid.  The  ammonium  arsenite  is  very  unstable,  evolving 
ammonia  freely  when  exposed  to  the  air.  When  arsenious  anhydride 
is  dissolved  in  a  hot  solution  of  ammonia,  octahedral  crystals  of  it  are  de- 
posited on  cooling,  notwithstanding  the  presence  of  ammonia  in  large  excess. 

When  the  carbonates  of  potassium  and  sodium  are  fused  with  an  excess 
of  arsenious  anhydride,  brilliant  transparent  glasses  are  obtained  which 
are  similar  in  composition  to  glass  of  borax  (KgAs^O^  and  NagAs^O^). 

If  an  alkaline  arsenite  be  fused  in  contact  with  platinum,  the  latter  is 
easily  melted,  combining  with  a  small  proportion  of  arsenic  to  form  a 
fusible  platinum  arsenide,  a  portion  of  the  arsenite  being  converted  into 
arseniate.  The  alkaline  arseniates  are  so  much  more  stable  than  the 
arsenites,  that  the  latter  exhibit  a  great  tendency  to  pass  into  the  former, 
with  separation  of  arsenic. 

The  arsenites  of  potassium  and  sodium  in  solution  are  sometimes 
employed  as  sheep-dipping  compositions ;  and  an  arsenical  soap,  com- 
posed of  potassium  arsenite,  soap,  and  camphor,  is  used  by  naturalists 
to  preserve  the  skins  of  animals.  Sodium  arsenite  is  also  occasionally 
employed  for  preventing  incrustations  in  steam-boilers,  being  prepared 


AliSENIC  ACID.  241 

for  that  purpose  by  dissolving  2  molecules  of  white  arsenic  and  1  mole- 
cule of  sodium  carbonate. 

Scheele's  green  is  an  arsenite  of  copper  prepared  by  dissolving  white 
arsenic  in  a  solution  of  potassium  carbonate,  and  decomposing  the  arsenite 
of  potassium  thus  produced  by  adding  sulphate  of  copper,  when  the 
arsenite  of  copper  is  precipitated.  This  poisonous  colour  is  used  to 
impart  a  bright  green  tint  to  paper  hangings,  and  is  sometimes  injurious 
to  the  health  of  the  occupants  of  rooms  thus  decorated,  since  the  arsenite 
of  copper  is  often  easily  rubbed  off  the  paper,  and  diffused  through  the 
air  in  the  form  of  a  fine  dust,  a  small  portion  of  which  is  inhaled  with 
every  breath. 

The  presence  of  the  arsenite  of  copper  in  a  sample  of  such  paper  is  readily  proved 
by  soaking  it  in  a  little  ammonia,  which  will  dissolve  the  arseniie  of  copper  to  a  blue 
liquid,  the  presence  of  arsenic  in  which 
may  be  shown  by  acidifying  it  with  a 
little  pure  hydrochloric  acid,  and  boiling 
with  one  or  two  strips  of  pure  copper, 
which  will  become  covered  with  a  steel- 
grey  coating  of  arsenide  of  copper.  On 
washing  the  copper,  drying  it  on  filter- 
paper,  and  heating  it  in  a  small  tube 
(fig.  226),  the  arsenic  will  be  converted 
into  arsenious  anhydride,  which  will 
deposit  in  brilliant  octahedral  crystals 
on  the  cool  part  of  the  tube.  It  is 
obvious  that,  to  avoid  mistakes,  the 
ammonia,  hydrochloric  acid,  and  copper  Fig,  226. 

should  be  examined  in  precisely  the  same 

way,  without  the  suspected  paper,  so  as  to  render  it  certain  that  the  arsenic  is  not 
derived  from  them. 

The  effective  green  colour  of  the  arsenite  of  copper  also  leads  to  its 
employment  as  a  colour  for  feathers,  muslin,  &c.,  where  it  is  very  inju- 
rious to  the  health  of  the  work-people.  It  has  even  been  ignorantly  or 
recklessly  used  for  colouring  twelfth-cake  ornaments,  &c. 

Emerald-green  is  a  combination  of  arsenite  and  acetate  of  copper 
obtained  by  mixing  hot  solutions  of  equal  weights  of  white  arsenic  and 
acetate  of  copper. 

In  quantities  short  of  poisonous  doses,  white  arsenic  appears  to  have  a 
remarkable  effect  upon  the  animal  body.  Grooms  occasionally  employ  it 
to  improve  the  appearance  of  horses,  and  in  Styria  it  seems  to  be  taken 
by  men  and  women  for  the  same  purpose,  apparently  favouring  the  secre- 
tion of  fat.  It  is  said  that  a  continuance  of  the  custom  develops  a 
craving  for  this  drug,  and  enables  large  doses  to  be  taken  without  imme- 
diate danger,  though  the  ultimate  consequences  are  very  serious. 

Solution  of  potassium  arsenite  {Fowler's  solution)  has  long  been  nsed  in 
\  medicine. 

173.  Ai'senic  acid  ('H^AsO^).— This  acid  has  acquired  great  importance 
in  the  chemical  arts  during  the  List  few  years,  having  been  employed  to 
replace  the  expensive  tartaric  acid  used  in  calico-printing,  and  to  furnish, 
by  its  action  upon  aniline,  the  magnificent  dye  known  as  Magenta. 

Arsenic  acid  is  prepared  by  oxidising  white  arsenic  with  three-fourths 
of  its  weight  of  nitric  acid  of  sp.  gr.  1  -35,  when  it  dissolves  with  evolution 
of  much  heat  and  abundant  red  fumes  of  nitrous  anhydride — 
As.,03  +  2HXO3  -I-  2H2O  =  NoOg  4-  2H3ASO4. 

Q 


242  ARSENIETTED  HYDROGEN. 

After  cooling,  the  solution  deposits  very  deliquescent  prismatic  crystals 
containing  2H.jAsO4.Aq.  When  these  are  heated  to  212°  F.  they  melt,  and 
the  liquiii  gradually  deposits  needle-like  crystals  of  arsenic  acid,  HgAsO^, 
corresponding  to  orthophosphoric  acid.  At  300°  F.  (149°  C),  2H3ASO4 
lose  HgO,  and  at  500°  F.  (260°  C),  they  lose  SHgO,  becoming  AsgOj, 
arsenic  anhydride,  which  is  decomposed  at  a  red  heat  into  As.^Og  and  O3 . 

Arsenic  anhydride  has  very  much  less  attraction  for  water  than  the 
phosphoric  anhydride  to  which  it  corresponds ;  it  deliquesces  slowly  in 
air,  and  dissolves  rather  reluctantly  in  water.  Neither  does  it  appear 
that  its  combinations  with  water  differ  from  each  other,  like  the  phosphoric 
acids,  in  the  salts  to  which  they  give  rise,  arsenic  acid  forming  tribasic 
salts  only,  like  common  phosphoric  acid.  The  arseniates  correspond  very 
closely  to  the  orthophosphates,  with  which  they  are  isomorphous  {i.e., 
identical  in  crystalline  form).  Thus  the  three  arseniates  of  sodium  are 
similar  in  composition  to  the  three  orthophosphates,  their  formulae  being 
Na3As04.12Aq.  ;  NagH ASO4. 1 2 Aq.  ;  and  2(NaH2As04)Aq. 

The  common  arseniaie  of  soda  (Xa2HAs047Aq.)  is  largely  used  by 
calico-printers  as  a  substitute  for  the  dung-baths  formerly  employed,  since, 
like  the  common  phosphate  of  soda,  it  possesses  the  feebly  alkaline  pro- 
perties required  in  that  particular  part  of  the  process.  It  is  manufactured 
by  combining  arsenious  acid  with  soda,  and  heating  the  resulting  arsenite 
with  sodium  nitrate,  from  which  it  acquires  oxygen,  becoming  converted 
into  sodium  arseniate. 

Calcic  arseniate,  2CaHAs04.7H20,  has  been  found  in  crystalline  crusts 
at  Joachimsthal. 

Arsenic  acid  is  a  much  more  powerful  acid  than  arsenious  acid,  being 
comparable,  in  this  respect,  with  phosphoric  acid-  It  appears  to  be  less 
poisonous  than  arsenious  acid. 

174.  Arsenietted  hydrogen  or  hydric  arsenide  (AsHg  =  78  parts  by  weight 
=  2  vols.  =  I  vol.  As  -f-  3  vols.  H). — The  only  compound  of  arsenic  and 
hydrogen,  the  existence  of  which  has  been  satisfactorily  established,  is  that 
which  corresponds  to  ammonia  and  phosphine.  It  is  prepared  by  the  action 
of  sulphuric  acid  diluted  with  three  parts  of  water  upon  the  zinc  arsenide, 
obtained  by  heating  equal  weights  of  zinc  and  arsenic  in  an  earthen 
retort ;  ZngAs^-f  3H2S02  =  2AsH3-i-3ZnS04.  The  gas  is  so  poisonous  in 
its  character  that  its  preparation  in  the  pure  state  is  attended  with  danger. 
It  has  a  sickly  alliaceous  odour,  and  may  be  liquefied  at  -  40°  F.  It  is 
inflammable,  burning  with  a  peculiar  livid  flame,  producing  water  and 
fumes  of  arsenious  anhydride  ;  2ASH3  +  Og  =  AsgOg  +  3H2O.  The  chief 
interest  attaching  to  this  gas  depends  upon  the  circum- 
stance that  its  production  allows  of  the  detection  of 
very  minute  quantities  of  arsenic  in  cases  in  poisoning. 

The  application  of  this  test,  known  as  Marsh's  test,  is  the 
safest  method  of  preparing  arsenietted  hydrogen  in  order  to 
study  its  properties,  for  it  is  obtained  so  largely  diluted  with 
free  hydrogen  that  it  ceases  to  be  so  very  dangerous.  Some 
fragments  of  granulated  zinc  are  introduced  into  a  half  pint 
bottle  (fig.  227),  provided  with  a  funnel-tube  (A),  and  a  narrow 
tube  (B)  bent  at  right  nngles  and  drawn  out  to  a  jet  at  the 
Fig.  227.  extremity  ;  this  tube  should  be  made  of  German  glass,  so  that 

it  may  not  fuse  easily.  The  bottle  having  been  about  one- 
third  filled  with  water,  a  little  diluted  sulphuric  acid  is  poured  down  the  funnel-tube 
so  as  to  cause  a  moderate  evolution  of  hydrogen,  and  after  about  five  minutes  (to  allow 


TERCHLORIDE  OF  ARSENIC.  243 

the  escape  of  the  air)  the  hydrogen  is  kindled  at  the  jet.  If  a  few  drops  of  a  sohition 
obtained  by  boiling  white  arsenic  with  water  be  now  poured  down  the  funnel, 
arsenietted  hydrogen  will  be  evolved  together  with  tlie  hydrogen  — 

As^Oj  +  Zng  +  6H2SO4  =  2ASH3  +  6ZnS04  +  3H^0. 

The  hydrogen  flame  will  now  ac()uire  the  livid  hue  above  referred  to,  and  a  white 
smoke  of  As^Oa  will  rise  from  it.     If  a  piece  of  glass  or  porcelain 
be  depressed  upon  the  flame  (fig.  228),  it  will  acquire  a  metallic-      ^_i.— »_    ^^ 
looking  coating  of  arsenic,  just  as  carbon  would  be  deposited 
from  an  ordinary  gas-flame.     Arsenietted  hydrogi'u  is  easily  Yi".  228. 

decomposed  by  heat,  so  that  if  the  glass  tube  through  which  it 

passes  be  heated  with  a  spirit-lamp  (fig.  229)  a  dark  mirror  of  arsenic  will  be 
deposited  a  little  in  front  of  the  heated  part,  and  the  flame  of  the  gas  will  lose  its 
livid  hue.     These  deposits  of  arsenic  are  extremely  ^ 

thin,  so  that  a  very  minute  quantity  of  arsenic 
is  requii'ed  to  form  them,  thus  rendering  the 
test  one  of  extraordinary  delicacy.  It  must  be 
remembered,  however,  that  both  sulphuric,  acid 
and  zinc  are  liable  to  contain  arsenic,  so  that 
erroneous  results  may  be  very  easily  arrived  at  by 
this  test  in  the  hands  of  any  but  those  specially 
devoted  to  such  investigations. 

Arsenietted  hydrogen,  like  sulphuretted  hydro- 
gen, causes  daik  precipitates  in  many  metallic 
solutions. 

Hydric  phosphide,  hydric  arsenide,  and 
ammonia  constitute  a  group  of  hydrogen 
compounds  having    certain    properties    in  *^S-  2-9. 

common,  which  distinguish  them  from  the  compounds  of  hydrogen  with 
other  elements. 

Two  volumes  of  each  of  these  gases  contain  three  volumes  of  hydrogen. 

They  are  all  possessed  of  peculiar  odours,  that  of  ammonia  being  the 
most  powerful  and  that  of  hydric  arsenide  the  least. 

Ammonia  is  powerfully  alkaline,  phosphine  exhibits  some  tendency  to 
play  an  alkaline  part,  whilst  hydric  arsenide  seems  devoid  of  alkaline 
disposition. 

All  these  are  inflammable,  ammonia  being  the  least  so  of  the  group  ; 
and  all  are  decomposed  by  heat,  ammonia  least  easily,  and  hydric  arsenide 
most  easily. 

They  are  all  producible  from  their  corresponding  oxygen  compounds, 
viz.,  ^2^3'  ^i^Zf  ^^^  ^s^Og,  by  the  action  of  nascent  hydrogen  {e.g.,  by 
contact  with  zinc  and  diluted  sulphuric  acid). 

All  three  are  the  prototypes  of  various  organic  bases  which  contain 
some  compound  radical  in  place  of  the  hydrogen,  thus — 

NHg  is  the  prototype  of  triethylamine,  !N"(C2H5)3 

PH3  ,,  triethyl  phosphine,      P(C2H5)3 

AsHg  ,,  triethylarsine,  As(C2H5)3. 

175.  Arsenic  trichloride  or  arsenioiis  chloride. — Only  one  compound  of  chlorine 
with  arsenic  (AsClg)  is  well  known.*  The  trichloride  may  be  formed  by  the  direct 
union  of  its  elements,  but  the  simplest  laboratory  process  for  procuring  it  consists 
in  heating  white  arsenic  in  dry  chlorine  gas,  in  a  tubulated  retort  (A,  fig.  229), 
extemporised  from  a  Florence  flask  (see  p.  106).  The  arsenious  anhydride  soon 
melts,  and  the  trichloride  distils  over,  leaving  a  melted  mass  in  the  flask,  which 
forms  a  brilliantly  transparent  glass  on  cooling,  the  composition  of  which  varies  some- 

*  Nickles  appears  to  have  succeeded  in  forming  the  pentachloride  by  the  action  of 
hydrocliloric  acid  gas  on  As.,05  in  presence  of  ether  ;  he  describes  it  as  very  unstable,  and 
easily  converted  into  the  trichloride. 


244 


REALGAR — OEPIMENT. 


Fig.  230. 


what  with  the  temperature  employed,  but  appears  to  be  essentially  2AS.2O3.A82O5. 
The  same  vitreous  compound  may  be  obtained  by  fusing  arsenious  and  arsenic  anhy- 
drides together. 

The  reaction   may    be    represented  by   the   equation,    llAsjOj  -f  Cljj  =  4ASCI3 

+  3(2Aa,03.AsA)- 
Ai-senic  trichloride  bears  a  great  general  resemblance  to  phosphorus  trichloride  ; 

it  is  a  heavy  (sp.  gr.  2  2),  pungent, 
fuming  liquid,  decomposed  by  the  mois- 
ture of  the  air,  its  vapours  depositing 
a  white  coating  upon  the  objects  in 
its  immediate  neighbourhood.  When 
poured  into  water  it  deposits  arsenious 
anhydride;  2ASCI3  +  SU.^O  =  AsgOj-l- 
6HC1 ;  but  when  dissolved  in  the 
smallest  possible  quantity  of  water 
it  deposits  crystals  of  the  formula 
AsOCLHaO. 

When  white  arsenic  is  dissolved  in 
hydrochloric  acid,  arsenious  chloride  is 
formed,  As^j  +  6HC1  =  2 AsClj  +  3H.,0, 
and  remains  undecomposed  by  the 
water  in  the  presence  of  strong  hydro- 
•chloric  acid,  but  if  water  be  added, 
arsenious  anhydride  is  precipitated. 
When  the  solution  in  hydrochloric  acid  is  distilled,  the  arsenious  chloride  distils  over, 
and  this  is  sometimes  a  convenient  method  of  separating  arsenic  from  articles  of  food, 
&c.,  in  testing  for  that  poison.  When  heated  in  dry  hydrochloric  acid  gas,  whiti- 
arsenic  yields  a  glassv  compound,  which  contains  As.>03.AsC10  ;  SAs-^Oj  +  2HC1 
=  2(As203.AsC10)  +  H20. 

In  composition  by  volume,  the  arsenious  chloride  resembles  phosphorous  chloride 
containing  ^  volume  of  arsenic  vapour,  and  3  volumes  of  chlorine  condensed  into 

2  volumes,  tlie  specific  gravity  of  its  vapour  being  6 '3. 

Arsenioiis  bromide  much  resembles  the  chloride  in  its  chemical  characters,  but  is 
a  solid  crystalline  substance,  easily  fusible. 

176.  Arsenic  tri-iodide  or  arsenious  iodide  (Aslg)  is  remarkable  for  not  being 
decomposed  by  water,  like  the  corresponding  phosphorus  compound.  When  obtained 
by  heating  arsenic  and  iodine  together,  it  sublimes  in  brick-red  flakes,  which,  if 
prepared  on  a  large  scale,  hang  in  long  laminae,  like  sea-weed.  It  may  be  dissolved 
in  boiling  water,  and  crystallises  out  unchanged.     It  may  even  be  prepared  by  heating 

3  parts  of  arsenic  with  10  of  iodine  and  100  of  water,  when  the  solution  deposits  red 
crystals  of  the  hydrated  tri-iodide,  from  which  the  water  may  be  expelled  by  a 
gentle  heat. 

Aslj  is  precipitated  as  a  golden  crystalline  powder  on  mixing  a  hot  solution  of 
AsoO;,  in  HCl  with  a  strong  solution  of  KI. 

Arsenic  di-iotiide,  Asl,,,  is  obtained  by  heating  1  ])art  of  arsenic  and  2  parts  of 
iodine  in  a  sealed  tube  to  230°  C,  and  crystallising  from  CSjin  an  atmosphere  of  CO^ 
It  forms  red  prismatic  crystals  which  become  black  when  treated  with  water,  accord- 
ing to  the  equation  3Asl2=2Asl3-t-As  , 

The  arsenic  tri-fl\ioride  (AsFg)  resembles  the  trichloride,  but  is  much  more  volatile. 
It  may  be  obtained  by  distilling  4  parts  of  arsenious  anhydride  with  5  of  fluor-spar 
and  10  of  strong  sulphuric  acid,  in  a  leaden  retort  (see  p.  182).  It  does  not  attack 
glass  unless  water  be  present,  which  decomposes  it  into  arsenious  and  hydrofluoric 
acids. 

177.  Sulphides  of  arsenic. — There  are  three  well-known  sulphides  of 
arsenic,  having  the  composition  AsgSg^  AsgSg,  and  AS2S5,  the  two  former 
being  found  in  nature. 

Realgar  (AsgSo)  is  a  beautiful  mineral,  crystallised  in  orange-red 
prisms ;  but  the  red  orpiment  used  in  the  arts  is  generally  prepared  by 
iieating  a  mixture  of  white  arsenic  and  sulphur,  when  sulphurous  acid 
gas  escapes,  and  an  orange-coloured  mass  of  realgar  is  left,  2AS2O3  -1-  S7 
=  2As,S2-f-3S02. 


SULPHIDES  OF  AKSENIC.  245 

Another  process  for  preparing  it  consists  in  distilling  arsenical  pyrites 
with,  sulphur  or  with  iron  pyrites- — ■ 

FeSg-FeAs^    +    2FeS2   =    ^FeS    +    As.Sg 

Ai  senical  pyrites.        Iron  pyrites.       gninhi'dp  Realgar. 

The  realgar  distils  over,  and  condenses  to  a  red  transparent  solid. 
Realgar  burns  in  air  with  a  blue  flame,  yielding  arsenious  and  sulphurous 
anhydrides.  If  it  be  thrown  into  melted  saltpetre,  it  burns  with  a  bril- 
liant white  flame,  being  converted  into  arseniate  and  sulphate  of  potassium. 
This  brilliant  flame  renders  realgar  an  important  ingredient  in  Indian  fire 
and  similar  compositions  for  fire-works  and  signal  lights.  A  mixture  of 
one  part  of  red  orpiment  with  3*5  parts  of  sublimed  sulphur  and  14  parts 
of  nitre  is  used  for  signal-light  composition. 

Realgar  is  not  easily  attacked  by  acids  ;  nitric  acid,  however,  dissolves  it,  witli  the 
aid  of  heat,  forming  arsenic  acid  and  sulphuric  acid,  with  separation  of  part  of  the 
sulphur  in  the  free  state.  Alkalies  (potash,  for  example)  partly  dissolve  it,  leaving  a 
dark  brown  substance,  which  appears  to  contain  free  arsenic,  3As.2S.2  =  2As2S3  +  As2. 

Yelloio  orpiment,  or  arsenious  sulphide  (AS2S3),  is  found  native  in 
yellow  i^rismatic  crystals.  The  paint  known  as  King's  yellowis  a  mixture 
of  arsenious  sulphide  and  arsenious  anhydride,  prepared  by  subliming 
a  mixture  of  sulphur  with  white  arsenic,  S9-I- 2As203  =  2AS2S3  +  SSOg. 
It  is,  of  course,  very  poisonous. 

This  substance,  like  realgar,  is  not  much  affected  by  acids,  excepting  nitric  acid  ; 
but  it  dissolves  entirely  in  potash,  forming  potassium  arsenite  and  sulpharsenite ; 
6KH0  +  AsgS-j  =  K3 ASS3  +  K3  AsOg  -h  3H.jO.  Ammonia  also  dissolves  it  easily,  forming 
a  colourless  solution  which  is  employed  for  dyeing  yellow,  since  if  a  piece  of  stuff  be 
dipped  into  it  and  exposed  to  air,  the  ammonia  will  volatilise,  leaving  the  yellow 
orpiment  behind. 

The  formation  of  the  characteristic  yellow  sulphide  is  turned  to  account  in  testing 
for  arsenic  ;  if  a  solution  prepared  by  boiling  white  arsenic  Avith  distilled  water  be 
mixed  with  a  solution  of  hydrosulphuric  acid,  a  bright  yellow  liquid  is  produced,  which 
looks  opaque  by  reflected,  but  transparent  by  transmitted  light,  and  may  be  passed 
through  a  filter  without  leaving  any  solid  matter  behind.  This  solution  probably 
contains  a  soluble  compound  of  arsenious  sulphide  with  hydrosulphuric  acid  (SHjS. 
As.^Sg)  ;  it  is,  however,  very  unstable,  being  decomposed  by  evaporation,  with  preci- 
pitation of  the  sulphide.  The  addition  of  a  little  hydrochloric  acid,  or  of  sal- 
ammoniac,  and  many  other  neutral  salts,  will  also  cause  a  separation  of  the  sulphide 
from  this  solution  ;  even  the  addition  of  a  hard  water  will  have  that  effect.  If  the 
solution  of  arsenious  acid  be  acidified  with  hydrochloric  acid  before  adding  the 
hydrosulphuric  acid,  the  bright  yellow  sulphide  is  precipitated  at  once,  and  may  be 
distinguished  from  any  other  similar  precipitate  by  its  ready  solubility  in  solution  of 
ammonium  carbonate. 

Arsenic  sulphide  (As.^Sg)  possesses  far  less  practical  importance  than  the  preceding 
sulphides ;  it  may  be  obtained  by  fusing  AsgSj  with  sulphur,  when  it  forms  an  orange- 
coloured  glass,  easily  fusible,  and  capable  of  being  sublimed  without  change.  AVheu 
hydrosulphuric  acid  gas  is  j^assed  through  solution  of  arsenic  acid,  a  white  precipitate 
of  sulphur  is  first  obtained,  the  hj'drogen  reducing  the  arsenic  acid  to  arsenious 
acid ;  H^AsO^  +  HgS  =  H3ASO3  +  H^O  +  S  ;  and  if  the  passage  of  the  gas  be  continued, 
the  arsenious  acid  is  decomposed,  and  arsenious  sulphide  is  precipitated  ;  these 
changes  are  much  accelerated  by  heat.  But  if  a  solution  of  sodium  arseniate  be 
saturated  with  hydro8ul])huric  acid,  it  is  converted  into  sodium  sulpharseniate.  On 
adding  hydrochloric  acid  to  this  solution,  a  bright  yellow  precipitate  of  arsenic 
sulphide  is  obtained. 

Cuprous  sulpharseniate  or  Claritc  (CU3ASS4),  is  found  in  the  Black  Forest. 


246  REVIEW  OF  THE  NOX-METALLIC  ELEMENTS. 


GENERAL  EEVIEW  OF  THE  NON-MEffALLIC  ELEMENTS. 


178.  At  the  conclusion  of  the  history  of  the  non-metals,  it  may  be 
•well  to  call  attention  to  the  points  of  resemblance  which  classify  them 
into  separate  groups  or  families,  most  of  which  are  connected,  by  some 
analogies,  with  one  or  more  members  of  the  class  of  metals. 

Hi/drorjen  stands  alone  among  the  non-metals,  its  chemical  properties 
and  functions  being  widely  difl'erent  from  those  of  any  other  non-metal, 
but  connecting  it  very  closely  with  the  most  highly  electro-positive  (or 
hasyhms)  metals,  such  as  potassium  and  sodium. 

Oxygen,  Sulphur,  Selenium,  and  Tellurium  compose  a  group,  the  mem- 
bers of  which  (in  the  state  of  vapour)  combine  with  twice  their  volume 
of  hydrogen  to  form  compounds  which  (in  the  state  of  vapour)  occupy 
the  same  volume  as  the  hydrogen  occupied  before  combination.  All  these 
hydrogen  compounds  are  capable  of  playing  a  feebly  acid  part,  and  their 
hydrogen  may  be  displaced  by  an  equivalent  weight  of  a  metal  to  produce 
compounds  exhibiting  a  general  agreement  in  chemical  properties.  This 
group  is  connected  with  the  metals  through  tellurium,  not  only  by  its 
physical  properties,  but  by  its  forming  an  oxide  (TeOg),  which  occasion- 
ally acts  as  a  weak  base. 

Nitrogen,  Phosphortis,  and  Arsenic  are  connected  together  by  the  gene- 
ral analogy  of  their  hydrogen  and  oxygen  compounds,  the  two  last  mem- 
ber of  the  group  being  far  more  closely  connected  with  each  other  than 
with  nitrogen.  With  the  metals  they  are  connected  through  arsenic,  the 
hydrogen  compound  of  which  is  very  similar  in  properties,  and  probably 
in  composition,  to  antimonietted  hydrogen ;  arsenious  anhydride  (AsgOg) 
is  also  capable  of  occupying  the  place  of  antimonious  oxide  (SbgOg)  in 
certain  salts  of  that  oxide  ;  and  the  sulphides  of  antimony  correspond  in 
composition,  and  in  some  of  their  properties,  to  those  of  arsenic.  One 
form  of  arsenious  anhydride  (the  prismatic)  is  isomorphous  with  native 
oxide  of  antimony,  and  this  oxide  may  be  obtained  in  octahedra,  the 
ordinary  form  of  arsenious  anhydride,  so  that  these  oxides  are  isodi- 
■morphous. 

Tliese  elements  are  also  connected  with  the  oxygen  group  through 
sulphur,  selenium,  and  tellurium,  the  relations  of  which  to  hydrogen  and 
the  metals  are  somewhat  similar  to  those  of  phosphorus  and  arsenic. 

Carbon,  Boron,  and  Silicon  resemble  each  other  in  their  allotropic 
forms,  their  resistance  to  fusion  and  volatilisation,  and  their  forming 
feeble  acids.  To  the  metals  they  are  allied  through  silicon,  which  re- 
sembles tin  in  the  composition  and  character  of  its  oxide  and  chloride.    . 

This  group  is  connected  with  the  nitrogen  group  through  boron,  for 
boracic  acid  resembles  arsenious  acid  in  its  relations  to  bases,  and  in 
forming  vitreous  compounds  with  the  alkalies.  In  certain  compounds 
boracic  and  arsenious  anhydrides  are  interchangeable. 

Chlorine,  Bromine,  Iodine,  and  Fluorine  are  intimately  connected  by 
numerous  analogies,  which  have  been  already  pointed  out  (p.  186).  Some 
of  the  properties  of  iodine,  as  its  relations  to  oxygen,  and  the  solubility 
of  its  trichloride  in  water,  connect  it  slightly  with  the  metals,  whilst 
some  of  the  properties  of  the  fluorides  connect  this  group  with  the 
oxygen  group  of  non- metallic  elements. 


ATOMIC  TYPES.  247 

Atomicity — Quantivalence. 

On  examining  the  composition  by  volume  of  hydrochloric  acid,  water, 
ammonia,  and  marsh  gas,  it  is  seen  that  equal  volumes  of  these  com- 
pounds, measured  in  the  gaseous  state  at  the  same  temperature  and  pres- 
sure, contain  respectively  1,  2,  3,  and  4  volumes  of  hydrogen. 

Thus  2  volumes  of  hydrochloric  acid  gas  contain  1  volume  of  chlorine  and 
1  volume  of  hydrogen. 
2  volumes  of  water  vapour  contain  1  volume  of  oxygen  and  2 

volumes  of  hydrogen. 
2  volumes  of  ammonia  contain  I  volume  of  nitrogen  and  3  volumes 

of  hydrogen. 
2  volumes  of  marsh  gas  contain  1  volume  (?)  of  imaginary  carbon 
vapour  and  4  volumes  of  hydrogen. 
In  the  case  of  the  marsh  gas,  it  has  been  already  explained  that  the 
volume  occupied  by  a  given  weight  of  carbon  vapour  cannot  be  ascer- 
tained by  experiment,  but  there  are  reasons  to  justify  the  assumption  that 
1 2  parts  by  weight  of  carbon  vapour  would  occupy  the  same  volume  as  1 
part  by  weight  of  hydrogen.     In  the  other  cases,  the  above  statements 
exhibit  the  direct  results  of  experiments  previously  described. 

If  it  be  allowed  that  one  atom  of  each  element  occupies  one  volume, 
then  hydrochloric  acid,  Avater,  ammonia,  and  marsh  gas  will  contain  for 
one  atom  of  chlorine,  oxygen,  nitrogen,  and  carbon,  respectively,  1,  2,  3, 
and  4  atoms  of  hydrogen,  or,  taking  the  symbol  for  each  element  to  re- 
present one  atom — 

Hydrochloric  acid    =    CIH  = 

Water  =    OHH 

Ammonia  =    NHHH      = 

Marsh  gas  =    CHHHH  = 

Since,  on  the  atomic  theory,  hydrogen  is  accepted  as  the  unit  of  atomic 

weight  and  volume,  it  appears  reasonable  to  fix  upon  it  as  representing  the 

unit  of  combining  power,  and  to  classify  the  elements  according  to  the 

tendency  of  their  atoms  to  imitate  the  combining  power  of  one  or  more 

atoms  of  hydrogen. 

By  the  atomicity  or  quantivalence  of  an  element  is  meant  the  number 
expressing  the  hydrogen-atoms  to  which  one  atom  (or  volume)  of  that 
element  is  usually  equivalent. 

Thus,  the  atomicity  of  chlorine  is  =  1,  for  one  volume  (or  atom)  of 
this  element  not  only  combines  with,  and  neutralises  the  properties 
of,  one  atom  (or  volume)  of  hydrogen,  but  is  capable  of  representing, 
or  occupying  the  place  of,  one  atom  of  hydrogen  in  its  compounds  (see 
page  154). 

The  atomicity  of  oxygen  is  =  2,  since  one  volume  (or  atom)  of  oxygen 
combines  with,  and  neutraliseSj  two  atoms  (or  volumes)  of  hydrogen  in 
water,  and  is  generally  capable  of  occupying  the  place  of  two  atoms  of 
hydrogen  in  the  compounds  of  that  element. 

The  atomicity  of  nitrogen  is  =  3,  for  one  volume  (or  atom)  of  nitrogen 
neutralises  the  properties  of  three  atoms  (or  volumes)  of  hydrogen  in 
ammonia,  and  is  often  found  to  occupy  the  place  of  three  atoms  of  hydro- 
gen in  its  compounds. 

The  atomicity  of  carbon  is  =  4,  for  one  volume  (or  atom)  of  imaginary 


Vols. 

Weights. 

H=l 

H=I 

HCl 

=     2 

=   36-5 

HgO 

==    2 

=    18 

H3N 

=    2 

=    17 

H4C 

_    2 

=    16 

248  ATOMIC  TYPES. 

carbon  vapour  is  combined,  in  marsh  gas,  with  four  atoms  (or  volumes)  of 
hydrogen,  and  in  its  compounds  with  other  elements,  one  atom  of  carbon 
is  usually  found  representing  four  atoms  of  hydrogen. 

Since  hydrochloric  acid,  water,  ammonia,  and  marsh  gas  are  the  most 
conspicuous  members  of  large  classes  of  chemical  compounds,  they  are 
often  referred  to  as  types,  and  the  elements,  chlorine,  oxygen,  nitrogen,  and 
carbon  are  taken  as  the  representatives  of  the  various  classes  into  which 
the  elements  are  divided  according  to  their  atomicities. 

Chlorine  is  the  type  of  one-atom  elements  (technically  called  ?now-a^omic 
nni-valent,  monad  elements),  the  atomic  weights  of  which  are  chemically 
equivalent  to  one  part  by  weight  of  hydrogen. 

Oxygen  is  the  type  of  two-atom  elements  {(H-atomic,  hi-valent,  diad 
elements),  of  which  the  atomic  weights  are  chemically  equivalent  to  two 
parts  by  weight  of  hydrogen. 

Nitrogen  is  the  type  of  three-atom  elements  {tri-atomic,  tervalent, 
triad  elements),  of  which  the  atomic  weights  are  chemically  equivalent  to 
three  parts  by  weight  of  hydrogen. 

Carbon  is  the  type  of  four-atom  elements  (tetratomic,  quadrivalent,  tetrad 
elements),  of  which  the  atomic  weights  are  chemically  equivalent  to  four 
parts  by  weight  of  hydrogen.  It  is  remarkable  that  the  four  elements, 
hydrogen,  oxygen,  nitrogen,  and  carbon  which  compose  the  chief  part  of 
living  matter  are,  respectively,  monatomic,  diatomic,  triatomic  and  tetra- 
tomic elements. 

If  the  non-metals  be  classified  according  to  their  quantivalence,  it  will 
be  found  that,  with  only  few  exceptions,  the  classification  will  coincide 
with  that  founded  upon  their  chemical  analogies  in  other  respects.  Thus, 
the  members  of  the  oxygen  group  are  all  diatomic,  or  capable  of  combining 
with  two  atoms  of  hydrogen,  as  shown  by  the  formulae  of  their  hydrogen 
compounds,  HgO,  HgS,  H<,Se,  H2Te.  The  nitrogen  group  is  generally  re- 
presented as  triatomic,  their  hydrogen  compounds  being  NHg,  PHg,  and 
AsHg.  Boron  is  also  a  triatomic  element,  for,  in  BClg,  the  boron  occupies 
the  place  of  three  atoms  of  hydrogen. 

Carbon  and  silicon,  however,  are  tetratomic  elements,  as  shown  in 
marsh  gas,  CH^,  and  in  silicon  tetrachloride,  SiCl^  . 

Chlorine,  bromine,  iodine,  and  fluorine  are  monatomic,  their  hydrogen 
compounds  having  the  formulae,  HCl,  HBr,  HI,  and  HF. 

The  atomicity  or  quantivalence  of  an  element  is  sometimes  expressed 
in  a  formula  by  a  dash,  or  dashes,  placed  above  and  to  the  right  of  the 
element ;  thus  the  symbols,  CI',  O",  N"',  C"",  indicate  the  respective 
atomicities  of  those  elements.  When  the  atomicity  of  an  element  is 
taken  into  account,  it  helps  to  explain  the  constitution  of  compounds 
which  would  otherwise  appear  quite  anomalous.  For  example,  there  is  a 
compound  of  the  molecular  formula,  NgHgP,  obtained  by  the  action  of 
phosphorous  chloride  upon  ammonia ;  recollecting  the  triatomic  character 
of  phosphorus,  we  perceive  this  compound  to  represent  three  molecules 
of  ammonia  (NgHg),  in  which  phosphorus  is  the  substitute  for  three  atoms 
of  hydrogen,  which  is  at  once  expressed  if  the  formula  be  written, 
NgHgP'".  Again,  carbon  oxychloride,  COClo,  appears  an  inexplicable 
association  of  elements,  until  the  tetratomic  character  of  carbon  and 
diatomic  character  of  oxygen  are  taken  into  account,  as  in  the  formula 
C""0"Cr2,  when  it  appears  that  the  diatomic  oxygen  and  the  two  atoms 
of  monatomic  chlorine  are  the  substitutes  for  four  atoms  of  hydrogen  in 


CONSTITUTION  OF  SALTS.  249 

marsh  gas,  CH^,  and  it  might  plausibly  be  given  as  a  reason  why  the 
apparently  indifferent  carbonic  oxide  should  combine  with  chlorine,  that 
the  atomicity  of  the  carbon  is  only  partly  satisfied  in  carbonic  oxide, 
which  contains  only  oxygen  equal  in  value  to  two  atoms  of  hydrogen, 
the  tetratomic  carbon  requiring  the  value  of  two  more  atoms  of  hydrogen 
to  satisfy  it.  In  carbon  dioxide,  C""0"2,  the  two  atoms  of  diatomic  oxygen 
satisfy  the  atomicity  of  the  carbon. 

In  a  similar  manner  the  absorption  of  carbonic  oxide  by  cuprous 
chloride  may  be  explained;  for  the  atomic  formula  of  that  salt  is  Cu'Cl', 
and  hence  it  is  capable  of  supplying  the  two  absent  atoms  in  C""0". 

^lany  more  examples  of  the  same  kind  might  be  gathered  from  the 
preceding  pages,  but  these  will  probably  be  sufl&cient  to  mark  the  im- 
portance of  remembering  the  atomicities  of  the  elements  in  speculative 
chemistry ;  indeed,  without  this  clue  it  is  impossible  to  find  any  meaning 
Avhatever  in  a  very  large  number  of  the  formulae  of  organic  substances, 
whilst  with  it,  not  only  their  constitution,  but  in  many  cases  theu-  mode 
of  formation,  becomes  as  intelligible  as  that  of  the  simplest  mineral  com- 
pounds. 

Structural  Formuloe — Bonds. — In  speculations  relating  to  the  atomic 
structure  of  compounds,  it  is  now  usual  to  represent  graphically  the 
atomicity  of  each  element ;  thus  a  monatomic  element,  like  hydro- 
gen, is  represented  as  affording  one  point  of  attachment,  which  may 
be  indicated  by  writing  the  symbol  H — ;  a  diatomic  element,  like 
oxygen,  affords  two  points  of  attachment,  as  shown  by  writing  its 
atomic  symbol — 0 — ;  accordingly,  to  form  water,  the  diatomic  oxy- 
gen attaches  to  itself  two  atoms  of  hydrogen,  as  represented  by  the 
molecular  formula  H — 0 — H,  whereas  in  hydric  peroxide  (HgOg)  the 
second  atom  of  oxygen  is  linked  by  one  point  of  attachment  to  the  first, 
so  that  the  graphic  expression  for  this  compound  would  be  H — O — 0 — H. 
A  triatomic  element,  sucli  as  nitrogen,  has  three  points  of  attachment, 
y^  and  thus,  in  ammonia,  attaches  to  itself  three  atoms  of  hydrogen 
NzEHg.  The  tetratomic  element,  carbon,  affords  four  points  of  attach- 
ment:=:Ciir,  and  thus  marsh  gas  (CH^)  is  represented  by  H.,.^C=^H2,  and 
carbon  dioxide  by  OzrCz=0.  In  carbon  monoxide,  two  of  the  bonds 
belonging  to  the  carbon  are  represented  as  latent  or  closed,  thus  0=:C:=3, 
so  that  the  carbon  here  plays  the  part  of  a  diatomic  element.* 

constitutio:n"  of  salts. 

179.  The  term  salt,  like  a^id  and  alkali,  was,  of  course,  purely  em- 
pirical in  its  origin,  being  conferred  upon  every  solid  substance  which 
exhibited  any  of  the  prominent  characters  of  sea  salt  (sal,  brine,  adXos,  the 
sea),  such  as  solubility  in  water  and  tendency  to  crystallisation. 

When  the  great  mass  of  chemical  facts  accumulated  by  the  alchemists, 
metallurgists,  and  apothecaries  came  be  to  classified,  and  the  distinction 
between  acids  and  bases  was  recognised,  the  term  salt  was  extended  to  all 
those  substances,  such  as  muriate  of  soda,  nitrate  of  potash,  carbonate  of 
lime,  &c.,  from  which  a  base  and  an  acid  could  be  obtained,  without 
regard  to  their  solubility  or  tendency  to  crystallise.  When  the  analytical 
poAvers  of  the  chemist  were  more  fully  developed,  it  was  found  that 
muriate  of  soda  and  a  large  class  of  similar  salts  did  not  contain  an  acid 

*  For  fuller  information  upon  this  subject,  tlie  student  is  referred  to  Frankland's 
Lecture  Notes  f&r  C/iemical  Students. 


250  NEUTRAL  AND  NORMAL  SALTS.    " 

and  a  base,  but  that  the  acid  and  base  were  produced  and  not  educed  from 
the  salts  by  the  chemical  operations  to  which  they  were  subjected.  Thus 
muriate  of  soda,  from  which  muriatic  acid  had  been  so  aasily  2'jJ'oduced  by  the 
action  of  sulphuric  acid,  was  shown  to  contain  only  sodium  and  chlorine. 

This  led  to  a  classification  of  salts  into  haloid  salts  (aA.9,  the  sea),  or 
those  composed  like  chloride  of  sodium,  of  a  metal  combined  with  a  salt- 
radical  or  halogen,  and  oxy-acid  salts,  or  those  composed  of  a  metallic 
oxide  combined  with  an  oxygen  acid.  (It  will  have  been  remarked  that 
the  tendency  of  modern  chemistry  is  to  represent  this  second  class  of 
salts  by  formulae  which  do  not  admit  the  existence  of  the  metal  as  an 
oxide  in  the  salt.) 

Independently  of  all  differences  of  opinion  with  respect  to  the  actual 
constitution  of  salts,  the  criterion  by  Avhich  the  claims  of  a  substance  to 
this  title  can  be  estimated  is  this :  a  salt  is  a  compound  which  may  he 
formed  by  ike  action  of  an  acid  upon  a  base,  water,  which  is  a  very  general 
result  of  such  action,  being  excepted. 

The  oxy-acid  salts  soon  came  to  be  divided  into  netdral  and  acid  salts, 
according  to  their  effect  upon  vegetable  colours  and  the  organ  of  taste, 
and  a  class  of  basi.c  salts  was  afterwards  added,  when  it  was  found  that  a 
neutral  soluble  salt  sometimes  became  insoluble  by  combining  with  an 
additional  quantity  of  base. 

Further  investigation  has  shown  that  the  neutral  state  of  a  salt,  and  its 
neutrality  to  test-papers,  depend  less  upon  the  proportions  of  the  acid  and 
base  which  are  contained  in  it,  than  upon  the  chemical  energy  of  these 
substances. 

Thus,  potash,  acting  upon  one  molecule  of  sidphuric  add,  forms  a  salt 
which  is  perfectly  neutral  to  taste  and  to  litmus-papers,  whilst  with  one 
molecule  of  carbonic  acid  it  forms  a  strongly  alkaline  salt ;  and  one  mole- 
cule of  sidjihuric  acid  acting  upon  one  molecule  of  oxide  of  zinc  forms  a 
salt  which  is  strongly  acid  to  test-papers. 

A  salt  may,  therefore,  be  neutral  in  chemical  constitution,  and  acid  or 
alkaline  in  reaction  to  test-papers,  and  it  has  been  proposed  to  employ  the 
term  normal  to  designate  those  salts  which  are  neutral  in  chemical  con- 
stitution, and  to  restrict  the  term  neutral  to  those  salts  which  are  neither 
acid  nor  alkaline  to  test-papers.  Thus,  potassium  sulphate  would  be  both 
a  neutral  and  a  normal  salt,  whilst  zinc  sulphate  and  potassium  carbonate 
are  normal,  but  not  neutral  salts. 

The  following  definitions  are  repeated  here,  on  account  of  their  im- 
portance : — 

An  acid  is  a  compound  containing  hydrogen,  the  whole  or  part  of 
which  is  displaceable  by  a  metal. 

A  salt  is  a  compound  derived  from  an  acid  by  the  displacement  of  its 
hydrogen  by  a  metal 

A  monobasic  acid  contains  but  one  atom  of  displaceable  hydrogen,  and 
therefore  can  only  form  one  series  of  salts. 

A  diba-sic  acid  contains  two  atoms  of  displaceable  hydrogen,  and  there- 
fore can  form  two  series  of  salts  (normal  and  acid  salts). 

A  tribasic  acid  contains  three  atoms  of  displaceable  hydrogen,  and 
therefore  can  form  three  series  of  salts  (normal  salts,  and  two  series  of 
acid  salts). 

A  normal  salt  is  one  in  which  the  whole  of  the  displaceable  hydrogen 
has  been  displaced  by  a  metal. 


CONSTITUTION  OF  ACIDS  AND  SALTS. 


251 


An  acid  salt  is  one  in  which  only  part  of  the  displaceable  hydrogen 
has  been  displaced  by  a  metal. 

A  double  salt  is  one  in  which  the  displaceable  hydrogen  has  been 
displaced  by  different  metals. 

A  basic  salt  is  a  combination  of  a  salt  with  a  basic  oxide  or  with  a 
hydrate. 

A  few  examples  may  be  collected  here  to  illustrate  these  definitions  : — 

Monobasic  Acids  and  Salts. 

Xitric  acid,         .....  HNOg 

Potassium  nitrate,  ....  KNO3 

Metaphosphoric  acid,      ....  HPO3 

Sodium  metaphosphate,  .  .  .  KaPOg 

Diltasic  Acids  and  Salts. 


Sulphuric  acid,                 .... 

[N^ormal  potassium  sulphate, 

Acid              „               „                ... 

H2SO4 
KHSO4 

Carbonic  acid  (hypothetical). 

Normal  potassium  carbonate,       .              . 

H2CO3 
K2CO3 

Acid              „                „               .             .             . 

KHCU3 

Tribasic  Acids  and  Salts. 

Orthophosphoric  acid,     .... 

Normal  sodium  orthophosphate, 

Monacid  orthophosphate  (or  common  phosphate), 

Diacid  orthophosphate,  .             . 

Microcosmic  salt,             .... 

Arsenic  acid,      ..... 

H3PO, 

Na3P0, 

Na.,HP04 

NaH^PO^ 

Na(XHJHP04 

H3ASO, 

Normal  sodium  arseniate. 

NagAsO^ 

Monacid  arseniate,           .... 

Na.2HAs04 

Diacid  arseniate,              .... 

NaHgAsO^ 

To  this  view  of  the  constitution  of  acids  and  salts,  it  may  be  objected 
that  it  presupposes  the  existence  of  a  hydrogen  compound  corresponding 
in  composition  to  the  normal  salt.  Thus  the  carbonates  would  be  derived 
from  an  imaginary  carbonic  acid  of  the  formula  H2CO3 ;  the  arseiiites 
from  an  imaginary  arsenious  acid,  HgAsOg,  &c.  Indeed,  out  of  the 
twenty-one  mineral  acids  which  are  of  practical  importance,  there  are 
seven  which  must  be  thus  treated  in  order  to  accommodate  this  theory; 
viz.,  carbonic,  nitrous,  sulphurous,  arsenious,  chromic,  hypochlorous,  and 
chlorous.  It  must,  however,  be  acknowledged  that  no  theory  of  the 
constitution  of  acids  and  salts  has  yet  been  advanced  which  is  thoroughly 
supported  on  all  sides  by  experimental  evidence. 

From  what  has  been  stated  above,  it  will  have  been  seen  that  an 
examination  of  the  acid  itself  is  by  no  means  necessary  in  order  to  ascer- 
tain what  its  hasicitij  is.  If  only  one  series  of  its  salts  can  be  discovered, 
it  is  a  monobasic  acid.  If  a  normal  and  an  acid  salt  (or  a  double  salt) 
can  be  obtained,  the  acid  is  dibasic.  When,  beside  the  normal  salt,  there 
are  two  series  of  acid  salts,  the  acid  is  tribasic. 

Water-type  theory  of  the  constitxdion  of  salts.- — Another  ingenious 
theory  of  the  constitution  of  salts  is  that  known  as  the  water-type  theory, 


252  WATER-TYPE  THEORY  OF  ACIDS  AND  SALTS. 

according  to  which  all  oxygen  acids  are  fashioned  after  the  type  of  water, 
by  the  displacement  of  its  hydrogen  by  a  compound  radical,  such  displace- 
ment being  total  in  the  anhydrides,  and  partial  in  the  acids.  Then,  a 
monobasic  acid  is  formed  upon  the  type  of  one  molecule  of  water,  by  the 
displacement  of  one  atom  of  hydrogen  to  form  the  acid,  and  of  both 
atoms  to  form  the  anhydride.     Thus,  nitric  acid  (HNO3)  would  be  written 

T.^,^    V  0,  and  nitric  anhydride  (NgO^)  would  become  ^^2  I  q  .   and  potas- 

slum  nitrate  (KNO3)  would  be  -^^    \0  ;  a.  glance  at  these  formulae  shows 

why  a  monobasic  acid  like  nitric  acid  does  not  form  either  acid  salts  or 
double  salts,  because  it  contains  only  one  atom  of  hydrogen,  and  therefore 
can  only  form  a  single  salt  with  each  metal  by  displacement  of  that 
hydrogen.  This  view  does  not  ignore  the  existence  of  the  anhydride, 
and  assumes,  as  the  radical  of  the  acid,  the  substance  NOg,  which  has 
the  composition  of  nitric  peroxide.  The  formation  of  nitric  acid  by  the 
action  of  water  upon  nitric  anhydride  would  be  thus  expressed — 
HI  n  ^  NOa  o        H     I  ^       ^'02  In 

H/  ^  +  No^f  ^  =  mj  ^  +  H    l^- 

In  a  similar  manner,  phosphoric  anhydride  (PgOg)  would  be  represented 

by  p.  2  I  0,  metaphosphoric  acid  (HPOg)  by  p^    >  0,  aud  the  sodium 

Na    ) 
metaphosphate  by  p^.    \  ^  •     ^^  ^^^^  csiBQ,  however,  the  radical  POg  is, 

so  far  as  we  know,  imaginary. 

A  dibasic  acid  is  one  which  is  composed  after  the  type  of  a  double 

TT    ) 
molecule  of  water,    tt^  v  Og ,  and  therefore  contains  two  atoms  of  hydro- 
gen which  may  be  displaced  either  entirely  by  a  metal,  yielding  a  normal 
salt,  or  partly  by  a  metal,  yielding  an  acid  salt,  or  by  two  metals,  yield- 
ing  a   double   salt.     For   example,  sulphuric   acid    (HgSO^)   would   be 

SO  "   I  ^2»  O"^  ^w°  molcules  of  water,  in  which  two  atoms  of  hydrogen 

are  displaced  by  the  diatomic  radical  SOg ;  normal  potassium  sulphate 

GO  "  f  ^2'  ^^^^  potassium  sulphate  (bisulphate  of  potash)  ^.^  „    >  Og,  and 

SO  "  1 
sulphuric   anhydride,  q j-.^,  \  Og  . 

Here  the  radical  SOg  has  the  same  composition  as  sulphurous  oxide, 

which  might  well  be  accepted  as  the  radical  of  sulphuric  acid. 

CO"  ) 
Again,  carbonic  anhydride  would  be  p^„   >  0^,  the  imaginary  carbonic 

acid,  p  ?  „  >  O2,  potassium  carbonate,  pA„  >  Og,  acid  potassium  carbonate, 

CO"    (  ^2'  t^arbonate  of  potassium  and  sodium,  p.~.„    >  0^  • 

The  radical  of  carbonic  acid,  therefore  (CO),  "va  ould  have  the  same  com- 
position as  carbonic  oxide,  which  is  seen  to  have  a  diatomic  character  in 
its  compound  with  chlorine  (C0)"Cl2,  where  it  occupies  the  place  of  two 
atoms  of  hydrogen. 

In  applying  this  view  to  pyrophosphoric  acid  (H^PoO-),  some  difficulty 
arises  because  its  formula  cannot  be  written  on  the  type  of  two  molecules 


CONSTITUTION  OF  POLYBASIC  ACIDS.  253 

of  water  (R^O.^)  on  account  of  the  indivisibility  of  the  0-  into  two  whole 
numbers  ;  it  is  therefore  necessary  to  take  four  molecules  of  water  as  the 
type,  when  we  have — 

Type,    TT^  [  0^,  pyrophosphoric  acid,  .p*  q  y,„  V  O4 ,  pyrophosphate  of 

Na  )  •  N^a  H        I 

sodium,     /pt-)  y///    \  O4,  acid  pyrophosphate  of  sodium,  tp  ^  ^„„   j-  0^  . 

Here  the  increased  complexity  of  the  formulae  appears  objectionable. 

A  few  salts  are  known  in  which  two  acids  are  combined  with  the  same  base,  such 
as  the  acetonitrate  of  barium,  composed  of  nitrate  and  acetate  of  barium.  It  is 
obvious  that  the  same  reasoning  which  leads  to  the  conclusion  that  an  acid  capable 
of  forming  a  double  salt  with  two  different  bases  is  dibasic,  or  contains  a  diatomic 
acid  radical,  would  also  support  the  inference  that  a  base  capable  of  forming  a  double 
salt  with  two  different  acids  is  di-acid,  or  contains  a  diatomic  basic  radical.  Hence 
the  existence  of  the  above  acetonitrate  of  barium  countenances  the  belief  that  barium 
is  a  diatomic  metal.     The  formula  of  the  salt  would  then  be  written,  on  the  type  of 

Ba"    ) 
two  molecules  of  water,  thus — (CgHgO)'  /  0^ . 

A  tribasic  acid  is  formed  upon  the  type  of  a  treble  molecule  of  water, 
thus— 

Tj^pe,  TT^  \  0^,  orthophosphoric  acid,  j,?y'i  \  O3 ,  sodium  orthophos- 
phate,  -pry"  \  O3 ,  common  phosphate  of  sodium,  -pryn     \  O3,  microcos- 

mic  salt  (phosphate  of  sodium  and  ammonium),        pry'         r  ^3  • 

But  in  this  case  also  an  unknown  radical,  PO,  is  assumed. 

TT  1 

If  pyrophosphoric  acid  be  represented  by   /poy/pn  v   \  O4,  its  inter- 

TT       ) 

mediate  position  between  metaphosphoric  acid  p^  ,  >  O,    and    orthophos- 

TT       ) 
plioric  acid  -pPy"  \  ^s  is  at  once  ap]3arent. 

Hydroxyle  theory  of  the  constitution  of  acids. — By  a  simple  modification 
of  the  water-type  theory,  the  acids  may  be  represented  as  containing  the 
group  hydroxyle  (HO.  A  monobasic  acid  would  contain  one  hydroxyle 
group ;  thus,  nitric  acid  would  be  HO.NOj ;  a  dibasic  acid  woidd  contain 
(H0)2;  e-g-,  sulphuric  acid  (HO).2.S0.2  ;  and  so  for  other  acids. 

The  three  phosphoric  acids  would  then  become — 

Metaphosphoric,       .  .         OP  \  ^tt 


HPO, 


OP^OH 


Pyrophosphoric,       .  .  <  0 

H4PA  (    opI^^ 

^    '^^  t  OH 
(OH 

Orthophosphoric,     .  .  OP  ^  OH 

H3PO4  t  OH 


CHEMISTRY  OF  THE  METALS. 


180.  The  general  principles  of  chemistry  having  been  explained  and 
illustrated  in  the  hi.story  of  the  non-metallic  elements,  the  chemistry  of 
the  metals  will  be  discussed  with  less  attention  to  details,  which,  however 
interesting  in  a  strictly  chemical  sense,  are  not,  at  present,  of  immediate 
practical  importance. 

The  definition  of  a  metal  has  been  already  given  at  page  29,  as  an 
element  capable  of  forming  a  base  by  union  with  oxygen.  It  will  also  be 
noticed  that  the  metals  are  but  little  disposed  to  form  combinations  with 
hydrogen;  but  that  they  evince  very  powerful  attraction  for  the  chlorine 
group  of  elements,  with  which  they  form,  as  a  rule,  compounds  which 
dissolve,  without  apparent  decomposition,  in  water. 

Classification  of  the  Metals. 

The  metals  may  be  divided  into  ten  classes  or  groups. 

I.  Potasmim  group. — The  metals  of  this  group  are  distinguished  by 
their  property  of  forming  hydrates  which  are  very  soluble  in  water  and 
very  strongly  alkaline.  Each  metal  of  this  group  forms  one  chloride, 
containing  one  atom  of  metal  and  one  atom  of  chlorine. 

Potassium  Group. 


Atomic 
WeiRht. 
Lithium,       .  .  .7 

Sodium,         .  .  .23 

Potassium,    .  .  .     39'1 


Atomic 
Weight. 
Rubidium,       .  .  .       8.5-3 

Caesium,  .  .  .133 


II.  Calcium  group. — The  metals  of  this  group  form  hydrates  which 
are  much  less  soluble  in  water  than  those  of  the  potassium  group,  but 
which  are  also  strongly  alkaline.  Each  metal  of  this  group  forms  a 
chloride,  containing  one  atom  of  the  metal  and  two  atoms  of  chlorine. 

Calcium  Group. 

Atomic  Weight. 
Calcium,  .  .  .  .  .  .40 

Strontium,         .  .  .  .  .  .       87"5 

Barium,  ......     137 

III.  Magnesium  group. — The  metals  of  this  group  also  form  one 
chloride,  containing  one  atom  of  metal  and  two  atoms  of  chlorine ;  but 
they  form  hydrates  which  are  not  soluble  in  water,  and  are  not  strongly 
alkaline. 

Magnesium  Group. 


Atomic 
Weight. 
Glucinum,     .  .  .9-2 

Magnesium,  .  .  .     24'3 


Atomic 
Weight. 
Zinc,  .  .  .  .65 

Cadmium,       .  .  .     112 


CLASSIFICATION  OF  THE  METALS. 


255 


IV.  Aluminium  group. — The  metals  of  this  group  form  one  chloride 
containing  one  atom  of  metal  and  three  atoms  of  chlorine.  Each  metal 
also  forms  one  oxide,  which  is  a  weak  base,  and  contains  two  atoms  of 
the  metal  and  three  atoms  of  oxygen.  The  metals  enclosed  in  paren- 
theses have  been  but  little  studied,  and  it  is  doubtful  whether  their 
chlorides  and  oxides  are  composed  as  above  stated,  though  their  general 
characters  appear  to  give  them  a  place  in  this  group. 


Aluminium, 
(Yttrium, 
Gallium, 
(Zirconium 
( Erbium, 

V.  Iron  gr 


Aluminium 

Group. 

Atomic 

Weight. 

.       27-5 

Indium, 

.        617) 

Lanthanium 

.        69-9) 

Didymium, 

.       89-5) 

(Thorinuni, 

.     112 -6) 

Atomic 

Weight. 

113-4 

139 

144-8 

231-5) 


mup.—ThQ  metals  of  this  group  form  two  compounds  with 
oxygen,  one  of  which  contains  single  atoms  of  the  metal  and  oxygen, 
and  is  a  pretty  strong  base  ;  the  other  contains  two  atoms  of  metal  com- 
bined with  three  atoms  of  oxygen,  and  behaves  to  acids  either  as  a 
weak  base  or  as  an  indifferent  oxide.  (Cerium  will  be  found  to  present  an 
exception  in  the  composition  of  its  oxides.) 


Iron,  . 
Cobalt, 
Nickel, 


Iron  Group. 

Atomic 
Weiglit. 
.      56 
.      59 
.     59 


Uranium, 
(Cerium, 


Atomic 
Weiglit.- 
120 
138) 


VI.  Manganese  group. — The  metals  of  this  group  differ  from  those  of 
the  preceding  groups  by  forming  well-defined  salts  in  which  the  metal 
enters  into  the  composition  of  the  acid  radical  (viz.,  chromates,  man- 
ganates,  vanadiates,  molybdates).  From  the  groups  which  follow,  this 
group  is  distinguished  by  forming  at  least  two  chlorides,  containing 
metal  and  chlorine  in  the  atomic  ratios  of  1  :  2  and  1  :  3  respectively. 


Manganese  Group. 


Vanadium, 
Chromium, 


Atomic 

Weight. 

51-3 

52-5 


Atomic 
Weight. 

55 
,     96 


Manganese, 
Molybdenum,  . 

VII.  Antimony  group. — The  two  members  of  this  group  are  brittle 
metals,  the  chlorides  of  which  are  easily  decomposed  by  water. 


Antimony  Group. 


Atomic  Weight. 
.      120 
.      210 


Antimony,  ..... 

Bismuth,  ...... 

VIII.  Tin  group. — Each  of  the  metals  of  this  group  forms  a  compound 
with  two  atoms  of  oxygen  which  is  insoluble  in  acids  but  dissolves  in 
the  alkalies,  forming  salts. 

Tin  Group. 


Titanium, 
Niobium, 
Tin.    . 


Atomic 
Weight. 
50 
94 
118 


Tantalum, 
Tungsten, 


Atomic 

Weight. 

182 

184 


256 


PERIODIC  LAW  OF  THE  CHEMICAL  ELEMENTS. 


IX.  Silver  group. — The  metals  of  this  group  are  capable  of  forming  an 
insoluble  chloride. 


Copper, 

Silver, 

Mercury, 


Silver  Group. 

Atomic 
Weight. 

63-5 
108 
200 


Thallium, 
Lead, 


Atomic 
Weiffht. 

204 

207 


Atomic 

Weiglit. 

Ehodiuin,    . 

.      104-3 

Platinum 

Kuthenium, 

.     104-2 

Iridium, 

Palladium, 

.     106-5 

Osmium, 

Gold, 

.     196-6 

X.  Platinum  gronjy. — The  metals  of  this  group  form  chlorides  which 
combine  with  the  chlorides  of  the  metals  of  Group  I.   to  form  easily 

crystallised  double  salts. 

Platinum  Group. 

Atomic 
Weight. 
.     197-1 
.     197-1 
.     199 


Periodic  laio  of  the  chemical  elements. — This  law,  as  stated  by 
Mendelejeff,  is  to  the  effect  that  "  the  properties  of  simple  bodies,  the 
constitution  of  their  combinations,  as  well  as  the  properties  of  the  latter, 
are  periodic  functions  of  the  atomic  weights  of  the  elements."  In  other 
words,  if  the  elements  be  arranged  in  the  order  of  their  atomic  weights, 
they  approximate  to  a  series  with  periodically  recurring  changes  in  the 
chemical  and  physical  functions  of  its  members. 

By  observing  the  gaps  which  exist  in  this  series,  Mendelejeff  endeavours 
to  predict  the  properties  of  elements  which  have  yet  to  be  discovered,  and 
(lid  indeed  foretell,  with  considerable  precision,  the  properties  of  gallium, 
in  anticipation  of  its  discovery. 

The  following  table  illustrates  this  periodic  law  :  the  elements  being 
divided  into  7  groups  according  to  the  formulae  of  their  oxides  or  hydrides, 
as  given  at  the  head  of  each  column,  and  into  6  series,  the  members  of 
which  exhibit  similarity  in  physical  and  chemical  functions. 


Group 

1 

2 

3 

4 

5 

6 

7 

Series. 

R^O 

RO 

E2O3 

RO2 

K2O3 

RH2 
RO3 

RH 
R2O7 

1 
2 
3 
4 
5 
6 

Li     7 
Na23 
K    39 

Rb'sS 

G       9 
Mg  24 
Ca    40 
Zn    65 
Sr    87 
Cdll2 

B      11 
Al    27 

Ga"70 

In  113 

C      12 
Si     28 
Ti    48 

Zr"90 
Snll8 

N      14 
P      31 
V      51 
As    75 
Nb   94 
Sb  122 

0      16 

S      32 
Cr    52 
Se     78 
Mo  96 

F      19 
CI     35 
Mn  55 
Br    80 

I     127 

The  blanks  in  such  a  table  indicate  where  new  elements  may  be 
expected.  Thus,  the  4th  and  6th  members  of  group  1  are  as  yet  unknown, 
and  their  properties  must  be  similar  to  those  of  potassium  and  rubidium; 
tlie  third  member  of  group  3,  when  discovered,  will  have  properties  in- 
termediate between  those  of  aluminium  and  gallium. 

This  periodic  classification  of  the  elements  bears  some  resemblance  to 
the  classification  of  organic  compounds  in  homologous  series. 


CARBONATE  OF  POTASH.  257 

POTASSIUM. 

K'  =  39  parts  by  weight. 

The  indispensable  alkali,  potash,  appears  to  have  been  originally 
derived  from  the  granitic  rocks,  where  it  exists,  in  combination  with 
silica  and  alumina,  in  the  well-known  minerals  felspar  and  mica. 
These  rocks  having,  in  course  of  time,  disintegrated  to  form  soils  for  the 
support  of  plants,  the  potash  has  been  converted  into  a  soluble  state,  and 
has  passed  into  the  plants  as  a  necessary  portion  of  their  food. 

In  the  plant  the  potash  is  found  to  have  entered  into  various  forms 
of  combination ;  thus,  most  plants  contain  sulphate  and  chloride  of 
potassium ;  but  the  greater  portion  of  the  potassium  exists  in  the  form  of 
salts  of  certain  vegetable  acids  formed  in  the  plant,  and  when  the  latter 
is  burnt  these  salts  are  decomposed  by  the  heat,  leaving  the  potassium  in 
the  form  of  carbonate. 

Carbonate  of  potash  or  potassium  carbonate,  K.^COg. — When  the  ashes 
of  plants  are  treated  with  water,  the  salts  of  potassium  are  dissolved, 
those  of  calcium  and  magnesium  being  left.  On  separating  the  aqueous 
solution  and  evaporating  it  to  a  certain  point,  a  great  deal  of  the  potassium 
sulphate,  being  much  less  soluble,  is  deposited,  and  the  carbonate  remains 
in  the  solution ;  this  is  evaporated  to  dryness,  when  the  carbonate  is  left, 
mixed  with  much  potassium  chloride,  and  some  sulphate ;  this  mixture 
constitutes  the  substances  imported  from  America  and  other  countries 
where  wood  is  abundant,  under  the  name  of  potashes,  which  are  much  in 
demand  for  the  manufacture  of  soap  and  glass.  When  further  purified, 
these  are  sold  under  the  name  of  pearlash,  but  this  is  still  far  from  being 
pure  potassium  carbonate. 

During  the  fermentation  of  the  grape-juice,  in  the  preparation  of  wine, 
a  hard  crystalline  substance  is  deposited,  which  is  known  in  commerce 
by  the  name  of  argol,  or,  when  purified,  as  cream  of  tartar.  The  chemical 
name  of  this  salt  is  bitartrate  of  potash  or  hydropotassic  tartrate,  for  it  is 
derived  from  potash  and  tartaric  acid,  a  vegetable  acid  having  the  com- 
position Il2C4H^Og.  When  this  salt  (KHC^H^Og)  is  heated,  it  leaves 
potassium  carbonate  mixed  with  carbon;  but  if  the  heat  be  continued, 
and  free  access  of  air  permitted,  the  carbon  will  be  entirely  burnt  away, 
and  potassium  carbonate  will  be  left  {salt  of  tartar). 

In  wine-producing  countries  potassium  carbonate  is  prepared  from 
the  refuse  yeast  which  rises  during  the  fermentation,  and  is  dried  in  the 
sun  in  order  to  be  subsequently  incinerated. 

The  fleeces  of  sheep  contain  a  considerable  proportion  of  salt  of 
potassium  with  an  animal  acid ;  when  the  fleece  is  washed  with  Avater 
this  salt  is  dissolved  out,  and  on  evaporating  the  liquid  and  burning  the 
residue  it  is  converted  into  potassium  carbonate. 

Potassium  carbonate  is  also  made  from  potassium  sulphate  by  a  process 
similar  to  that  by  which  sodium  sulphate  is  converted  into  carbonate 
(182).  Potassium  chloride  is  converted  into  potassium  carbonate  by 
decomposing  it  with  the  carbonate  of  trimethylamine  (see  trimethylamine). 

Hydrate  of  potash  ov  xiotass'mm  hydrate,  KHO. — Carbonate  of  potassium 
was  formerly  called  potash,  and  was  supposed  to  be  an  elementary  sub- 
stance. It  was  known  that  its  alkaline  qualities  were  rendered  far  more 
powerful  by  treating  it  with   lime,  which  caused  it  to  be  termed   mild 

R 


258  CAUSTIC  POTASH. 

alkali,  in  order  to  distinguish  it  from  the  caustic*  alkali  obtained  by 
means  of  lime,  and  possessed  of  very  powerful  corrosive  properties.  Lime, 
it  was  said,  is  derived  from  limestone  by  the  action  of  fire,  and  therefore 
owes  its  peculiar  properties  to  the  acquisition  of  a  certain  amount  of  the 
matter  of  fire,  which,  in  turn,  it  imparts  to  the  mUd  alkali,  and  thus 
confers  upon  it  a  caustic  or  burning  power. 

Black's  researches  in  the  middlle  of  the  eighteenth  century,  which  are 
often  referred  to  as  models  of  inductive  reasoning,  exposed  the  fallacy  of 
this  explanation,  and  proved  that  instead  of  acquiring  anything  from  the 
fire,  the  limestone  actually  lost  carbonic  acid  gas,  and  instead  of  imparting 
anything  to  the  mild  alkali,  the  lime  really  gained  as  much  carbonic  acid 
as  it  previously  lost. 

The  caustic  potash,  so  largely  employed  by  the  soap-maker,  is  obtained 
by  adding  slaked  lime  to  a  boiling  diluted  solution  of  the  potassium 
carbonate,  when  calcium  carbonate  is  deposited  at  the  bottom  of  the 
vessel,  whilst  hydrate  of  potash  remains  in  the  clear  solution — 

K2CO3  +  Ca(H0)2  =  CaCOg  +  2KH0 

Potassium  Calcium  Calcium  Potassium 

carbonate.  hydrate.  carbonate.  hydrate. 

If  the  solution  be  too  strong  the  lime  will  not  decompose  the  carbonate. 

"V\Tien  the  solution  is  evaporated,  the  potassium  hydrate  remains  as  a 
clear  oily  liquid,  which  solidifies  to  a  white  mass  as  it  cools,  an<l  forms 
the  fused  potash  of  commerce,  which  is  often  cast  into  cylindrical  sticks 
for  more  convenient  use.t  The  potassium  hydrate  is  the  most  powerful 
alkaline  substance  in  ordinary  use,  and  is  very  frequently  employed  by 
the  chemist  on  account  of  its  energetic  action  on  the  different  acids.  It 
is  generally  used  in  the  state  of  solution,  the  strength  of  which  is  inferred 
from  its  specific  gravity,  this  being  higher  in  proportion  to  the  amount  of 
potash  contained  in  the  solution. 

Potassium. — Of  the  composition  of  potassium  hydrate  nothing  was 
known  till  the  year  1807,  when  Davy  succeeded  in  decomposing  it  by 
the  galvanic  battery ;  this  experiment,  which  deserves  particular  notice, 
as  being  the  first  of  a  series  resulting  in  the  discovery  of  so  many 
important  metals,  was  made  in  the  following  manner : — A  fragment  of 
potassium  hydrate,  which,  in  its  dry  state,  does  not  conduct  electricity,  was 
allowed  to  become  slightly  moist  by  exposure  to  the  air,  and  placed  upon 
a  plate  of  platinum  attached  to  the  copper  end  of  a  very  powft-ful  galvanic 
battery  ;  when  the  wire  connected  with  the  zinc  end  was  made  to  touch 
the  surface  of  the  hydrate,  some  small  metallic  globules  resembling 
mercury  made  their  appearance  at  the  extremity  of  this  (negative)  wire, 
at  Avhich  the  hydrogen  contained  in  the  hydrate  was  also  eliminated, 
whilst  bubbles  of  oxygen  were  separated  on  the  surface  of  the  platinum 
plate  connected  with  the  positive  "wire  (see  p.  9).  By  allowing  the 
negative  wire  to  dip  into  a  little  mercury  contained  in  a  cavity  upon 
the  surface  of  the  potash,  a  combination  of  potassium  with  mercury 
was  obtained,  and  the  mercury  was  afterwards  separated  by  distillation. 
Tins  process,  however,  furnished  the  metal  in  very  small  quantities,  and, 
th  nigh  it  was  obtained  Avith  greater  facility  a  year  or  two  afterwards  by 
decomposing  potassium  hydrate  with  white  hot  iron,  some  years  elapsed 

*  From  Kaito,  to  bum. 

+  These  have  sometimes  a  greenish  colour,  due  to  the  presence  of  some  potassium 
niaiiKanate. 


POTASSIUM. 


259 


before  any  considerable  quantity  of  potassium  was  prepared  by  tlie  present 
method  of  distilling  in  an  iron  retort  an  iutimate  mixture  of  potassium 
carbonate  and  carbon,  obtained  by  calcining  cream  of  tartar ;  in  this 
process  the  oxygen  of  the 
carbonate  is  removed  by 
the  carbon  in  the  form  of 
carbonic  oxide  (K2C'03  +  C, 
-K2  +  3CO). 

The  annexed  figure  repre- 
sents the  iron  retort  connected 
with  its  copper  receiver,  sur- 
rounded with  cokl  water,  and 
containing  petroleum  to  protect 
tlie  distilled  potassium  from 
oxidation.  The  lateral  tube  of 
the  receiver  permits  the  tube 
of  the  retort  to  be  clearel,  if 
necessary,  during  the  distilla- 
tion, by  the  passage  of  an  iron 
rod. 

Some  of  the  most  strik- 
ing properties  of  this  metal 
have  already  been  referred 
to  (p.  11);  its  softness, 
causing  it  to  be  easily  cut 
like  wax,  the  rapidity  with 
which  its  silvery  surface 
tarnishes  when  exposed  to  the  air,  its  great  lightness  (sp.  gr.  0'865), 
causing  it  to  float  upon  water,  and  its  taking  fire  when  in  contact  with 
that  liquid,  sufficiently  distinguish  it  from  other  metals.  It  fuses  easily 
when  heated,  and  is  converted,  at  a  higher  temperature,  into  a  green 
vapour ;  if  air  be  present,  it  burns  with  a  violet-coloured  flame,  and  is 
converted  into  anhydrous  potash,  or  dipotassium  oxide  (KgO). 

The  property  of  burning  with  this  peculiar  violet-coloured  flame  is 
characteristic  of  potassium,  and  allows  it  to  be  recognised  in  its  com- 
pounds. 


Preparation  of  potassium. 


Fig.  232. —Coloured  flame  test. 

If  a  solution  of  potassium  nitrate  (saltpetre)  in  water  be  mixed  with  enough  spirit 
of  wine  to  allow  of  its  being  inflamed,  the  flame  will  have  a  peculiar  lilac  colour. 
This  colour  may  also  be  developed  by  exposing  a  very  minute  particle  of  saltpetre, 
taken  on  the  end  of  a  heated  platinum  wire,  to  the  reducing  (inner)  blowpipe  flame 
(fig.  232),  when  the  potassium,  being  reduced  to  the  metallic  state  and  passing  into 
the  oxidising  (outer)  flame  in  the  state  of  vapour,  imparts  to  that  flame  a  lilac  tinge. 


260  EXTRACTION  OF  COMMON  SALT. 

The  difficulty  and  expense  attending  the  preparation  of  potassium  have 
jirevented  its  receiving  any  application  except  in  purely  chemical  opera- 
tions, where  its  attraction  for  oxygen,  chlorine,  and  other  electro-negative 
elements,  is  often  tufned  to  account. 

Potassium  chloride  (KCl)  is  an  important  natural  source  of  this  metal, 
being  extracted  from  sea  water,  from  kelp  (the  ash  of  sea-weed),  and 
from  the  refuse  of  the  manufacture  of  sugar  from  beet-root.  It  also  occurs 
ill  combination  with  magnesium  chloride,  forming  the  mineral  known  as 
carnallite  (KCI.MgCl2.6H2O),  an  immense  saline  deposit  overlying  the 
rock-salt  in  the  salt-mines  of  Stassf urth,  in  Saxony.  Carnallite  resembles 
lock-salt  in  appearance,  but  is  very  deliquescent ;  it  promises  to  become 
the  most  important  source  of  potassium  hitherto  discovered.  Considerable 
deposits  containing  chloride  and  sulphate  of  potassium  have  also  been 
found  in  East  Galicia. 

Bicarbonate  of  potash  or  hydropotassic  carbonate  (KHCO3),  which  is 
much  used  in  medicine,  is  obtained  by  passing  carbonic  acid  gas  through 
ii  strong  solution  of  potassium  carbonate,  when  it  is  deposited  in  crystals, 
being  much  less  soluble  in  water  than  the  normal  carbonate. 

Potassium  nitrate  (KISTOg),  or  saltpetre,  will  be  specially  considered 
in  the  section  on  gunpowder. 

SODIUM. 

Na'  =  23  parts  by  weight. 

181.  Sodium  is  often  found,  in  place  of  potassium,  in  the  felspars  and 
other  minerals,  but  we  are  far  more  abundantly  supplied  with  it  in  the 
form  of  common  salt  (sodium  chloride,  NaCl).  occurring  not  only  in  the 
.solid  state,  but  dissolved  in  sea  water,  and  in  smaller  quantity  in  the 
waters  derived  from  most  lakes,  rivers,  and  springs. 

Rock-salt  forms  very  considerable  deposits  in  many  regions;  in  this 
country  the  most  important  is  situated  at  Northwich,  in  Cheshire,  where 
very  large  quantities  are  extracted  by  mining.  Wielitzka,  in  Poland,  is 
celebrated  for  an  extensive  salt-mine,  in  which  there  are  a  chapel  and 
dwelling-rooms,  the  furniture  of  which  is  made  of  this  rock.  Extensive 
beds  of  rock-salt  also  occur  in  France,  Germany,  Hungary,  Spain,  Abyssinia, 
and  Mexico.  Perfectly  pure  specimens  form  beautiful  colourless  cubes, 
and  are  styled  sal  gem ;  but  ordinary  rock-salt  is  only  partially  trans- 
parent, and  exhibits  a  rusty  colour,  due  to  the  presence  of  ii'on.  In  some 
places  the  salt  is  extracted  by  boring  a  hole  into  the  rock  and  filling 
it  with  water,  which  is  pumped  up  when  saturated  Avith  salt,  and  evapo- 
rated in  boilers,  the  minute  crystals  of  salt  being  removed  as  they  are 
deposited. 

At  Droitwich,  in  Worcestershire,  the  salt  is  obtained  by  (Evaporation  from 
the  waters  of  certain  salt  springs.  In  some  parts  of  France  and  Germany 
the  watet'  from  the  salt  springs  contains  so  little  salt  that  it  would  not 
])ay  for  the  fuel  necessary  to  evaporate  the  water,  and  a  very  ingenious 
l)lan  is  adopted  by  which  the  proportion  of  Avater  is  greatly  reduced  with- 
out the  application  of  artificial  heat.  For  this  purpose  a  lofty  scaffolding 
is  erected  and  filled  with  bundles  of  brushwood,  over  ■which  the  salt  water 
is  allowed  to  flow,  having  been  raised  to  the  top  of  the  scaflblding  by 
pumps.  In  trickling  over  the  brushwood  this  water  exposes  a  large  sur- 
face to  the  action  of  the  wind,  and  a  considerable  evaporation  takes  place, 
.so  that  a  much  stronger  brine  is  collected  in  the  reservoir  beneath  the 


EXTRACTION  OF  COMMON  SALT.  261 

scaffolding :  hj  several  repetitions  of  the  operation,  the  proportion  of  water 
is  so  far  diminished  that  the  rest  may  be  economically  evaporated  by  arti- 
ficial heat.  The  brine  is  Pun  into  boilers  and  rapidly  boiled  for  about 
thirty  hours,  fresh  brine  being  allowed  to  flow  in  continually,  so  as  to 
maintain  the  liquid  at  the  same  level  in  the  boiler.  During  this  ebullition 
a  considerable  deposit,  composed  of  the  sulphates  of  calcium  and  sodium, 
is  formed,  and  raked  out  by  the  workmen.  When  a  film  of  crystals  of  salt 
begins  to  form  upon  the  surface,  the  fire  is  lowered,  and  the  temperature  of 
the  brine  allowed  to  fall  to  about  180°  F,,  at  which  temperature  it  is 
maintained  for  several  days  whilst  the  salt  is  crystallising.  The  crystals 
are  afterwards  drained  and  dried  by  exposure  to  air.  The  grain  of  the 
salt  is  regulated  by  the  temperature  at  which  it  crystallises,  the  size  of  the 
crystals  increasing  as  the  temperature  falls.  It  is  not  possible  to  extract 
the  whole  of  the  salt  in  this  way,  since  the  last  portions  which  crystallise 
will  always  be  contaminated  with  other  salts  present  in  the  brine;  but  the 
mother-liquor  is  not  wasted,  for  after  as  much  salt  as  possible  has  been 
obtained,  it  is  made  to  yield  sodium  sulphate  (Glauber's  salt),  magnesium 
sulphate  (Epsom  salts),  bromine,  and  iodine. 

The  process  adopted  for  extracting  the  salt  from  sea  water  depends 
upon  the  climate.  In  Russia,  shallow  pits  are  dug  upon  the  shore  in 
which  the  sea  water  is  allowed  to  freeze,  when  a  great  portion  of  the 
water  separates  in  the  form  of  pure  ice,  leaving  a  solution  of  salt  suffi- 
ciently strong  to  pay  for  evaporation. 

Where  the  climate  is  sufficiently  warm,  the  sea  water  is  allowed  to  run 
very  slowly  through  a  series  of  shallow  pits  upon  the  shore,  where  it  be- 
comes concentrated  by  spontaneous  evaporation,  and  is  afterwards  allowed 
to  remain  for  some  time  in  reservoirs  in  which  the  salt  is  deposited.  The 
coarse  crystals  thus  obtained  are  known  in  commerce  as  bay-salt  Before 
they  are  sent  into  the  market  they  are  allowed  to  drain  for  a  long  time, 
in  a  sheltered  situation,  when  the  magnesium  chloride  with  which  they 
are  contaminated  deliquesces  in  the  moisture  of  the  air  and  drains  off. 
The  hitteiii,  or  liquor  remaining  after  the  salt  has  been  extracted,  is 
employed  to  furnish  magnesia  and  bromine. 

Great  improvements  have  been  made  during  the  last  few  j'ears  in  the  economical 
extraction  of  the  salt  from  sea  water.  It  will  be  remembered  that  1000  parts  of 
sea  water  contain  about 

29  "0  parts  of  sodium  chloride, 
0'5     ,,         potassium  chloride, 
3'0     ,,         magnesium  chloride, 
2"5     ,,         magnesium  sulphate, 
1'5     ,,         calcium  sulphate,  &c. 

In  a  warm  climate,  that  of  Marseilles,  for  example,  the  water  is  allowed  to  evapo- 
rate spontaneously  until  it  has  a  specific  gravity  of  1  '24.  During  this  evaporation 
it  deposits  about  four-fifths  of  its  sodium  chloride.  It  is  then  mixed  with  one-tenth 
of  its  volume  of  water,  and  artificially  cooled  to  0°  F.  (see  p.  127),  when  it  deposits 
a  quantity  of  sodium  sulphate,  resulting  from  the  decomposition  of  part  of  the 
remaining  sodium  chloride  by  the  magnesium  sulphate.  The  mother-liquor  is  evapo- 
rated down  till  its  specific  gravity  is  1  33,  a  fresh  quantity  of  sodium  chloride  being 
deposited  during  the  evaporation.  When  the  liquid  cools  it  deposits  a  double  salt 
composed  of  chlorides  of  potassium  and  magnesium,  from  which  the  latter  chloride 
may  be  extracted  by  washing  with  a  very  little  water,  leaving  the  potassium  chloride 
fit  for  the  market. 

This  process  is  instructive  as  illustrating  the  influence  exerted  upon  the  arrange- 
ment of  the  various  acids  and  bases  in  a  saline  solution  by  the  temperature  to  which 
the  solution  is  exposed,  the  general  rule  being  that  the  .salt  is  formed  which  is  least 
soluble  in  the  liquid  at  the  particular  temperature. 


262 


MANUFACTUKE  OF  ALKALI. 


The  great  tendency  observed  in  ordinary  table  salt  to  become  damp 
when  exposed  to  the  air,  is  due  chiefly  to  the  presence  of  small  quantities 
of  chlorides  of  magnesium  and  calcium,  for  pmre  sodium  chloride  has  very 
much  less  disposition  to  attract  atmospheric  moisture,  although  it  is  very 
easily  dissolved  by  water,  2|  parts  of  this  liquid  being  able  to  dissolve 
one  part  (by  weight)  of  salt. 

In  the  history  of  the  useful  applications  of  common  salt  is  to  be  found 
one  of  the  best  illustrations  of  the  influence  of  chemical  research  upon 
the  development  of  the  resources  of  a  country,  and  a  capital  example  of  a 
manufacturing  process  not  based,  as  such  processes  usually  are,  upon  mere 
experience,  independent  of  any  knowledge  of  chemical  principles,  but 
upon  a  direct  and  intentional  application  of  these  to  the  attainment  of  a 
particular  object. 


Fig.  233.  — Furnace  for  converting  common  salt  into  sulphate  of  soda. 

Until  the  last  quarter  of  the  eighteenth  century,  the  uses  of  common 
salt  were  limited  to  culinary  and  agricultural  purposes,  and  to  the  glazing 
of  the  coarser  kinds  of  earthenware,  whilst  a  substance  far  more  useful  in 
the  arts,  carbonate  of  soda,  was  imported  chiefly  from  Spain  under  the 
name  of  barilla,  which  was  the  ash  obtained  by  burning  a  marine  plant 
known  as  the  salsola  soda.  But  this  ash  only  contained  about  one-fourth 
of  its  weight  of  carbonate  of  soda,  so  that  this  latter  substance  was  thus 
imported  at  a  great  expense,  and  the  manufactures  of  soap  and  glass,  to 
which  it  is  indispensable,  were  proportionally  fettered. 

During  the  wars  of  the  French  Revolution  the  price  of  barilla  had  risen 
so  considerably,  that  it  was  deemed  advisable  by  ISTapoleon  to  offer  a 
premium  for  the  discovery  of  a  process  by  which  the  carbonate  of  soda 
could  be  manufactured  at  home,  and  to  this  circumstance  we  are  indebted 
for  the  discovery,  by  Leblanc,  of  the  process  at  present  in  use  for  the 
manufacture  of  carbonate  of  soda  from  common  salt,  a  discovery  which 
placed  this  substance  at  once  among  the  most  important  raw  materials 
Avith  which  a  country  could  be  furnished. 

182.  Manufachire  of  carbonate  of  soda  from  common  snlt.—  ThB  salt  is 

spread  upon  the  hearth  of  a  reverberatary  furnace  (fig.  233),*  and  mixed 

*  The  hearth  of  this  furnace  is  usually  divided,  as  seen  in  the  figure,  into  two  compart- 
uients,  in  one  of  which  (lined  with  lead),  niore  remote  from  the  grate,  the  decomposition  is 
effected,  the  acid  being  poured  in  through  the  funnel,  while  in  that  nearest  to  the  grate, 
lined  with  firebrick,  the  whole  of  the  hydrochloric  acid  is  expelled,  and  the  sodium  sulphate 
fused. 


MANUFACTURE  OF  ALKALI.  263 

with  an  equal  weight  of  sulphuric  acid,  which  converts  it  into  sodium 
sulphate  (p.  157),  expelling  hydrochloric  acid  in  the  form  of  gas,  which 
would  prove  highly  injurious  to  the  vegetation  in  the  neighbourhood,  and 
is  therefore  usually  condensed  by  being  brought  into  contact  with  water 
(see  p.  158).  The  flame  of  the  fire  is  allowed  to  play  over  the  surface  of 
the  mixture  of  salt  and  sulphuric  acid  until  it  has  become  perfectly  dry  ; 
in  this  state  it  is  technically  known  as  salt  cake,  and  is  next  mixed  with 
about  an  equal  weight  of  limestone  and  rather  more  than  half  its  weight 
of  small  coal ;  this  mixture  is  again  heated  upon  the  hearth  of  a  reverbera- 
tory  furnace,  when  it  evolves  an  abundance  of  carbonic  oxide,  and  yields 
a  mixture  of  sodium  carbonate  with  lime  and  calcium  sulphide  ;  this 
mixture  is  technically  known  as  hlack  ash. 

The  change  which  has  been  efi'ected  in  the  sodium  sulphate  will  be 
easily  understood  ;  for  when  this  salt  is  heated  in  contact  with  carbon 
(from  the  small  coal)  it  loses  its  oxygen,  and  becomes  sodium  sulphide, 
whilst  carbonic  acid  gas  is  evolved;  thus  Isra2S04  +  Cg  =  ]Sra2S  +  2CO2. 
Again,  Avhen  calcium  carbonate  is  heated  in  contact  with  carbon,  carbonic 
oxide  is  given  off,  and  lime  remains;  CaCOg  +  C  =  2C0  4- CaO.  Finally, 
when  sodium  sulphide  and  lime  are  heated  together  in  the  presence  of 
carbonic  acid  gas,  sodium  carbonate  and  calcium  sulphide  are  produced ; 
Is^S  +  CaO  +  CO2  =  Na2C03  +  CaS  . 

When  the  black  ash  is  treated  with  water,  the  sodium  carbonate  is 
dissolved,  leaving  the  calcium  sulphide,  and  by  evaporating  the  solution, 
ordinary  soda  ash  is  obtained.*  But  this  is  by  no  means  pure  sodium 
carbonate,  for  it  contains,  in  addition  to  a  considerable  quantity  of  common 
salt  and  sodium  sulphate,  a  certain  amount  of  caustic  soda,  formed  by 
the  action  of  the  excess  of  lime  upon  the  carbonate.  In  order  to  purify 
it,  the  crude  soda  ash  is  mixed  with  small  coal  or  sawdust  and  again 
heated,  when  the  carbonic  acid  gas  formed  from  the  carbonaceous  matter 
converts  the  caustic  soda  into  carbonate,  and  on  dissolving  the  mass  in 
water  and  evaporating  the  solution,  it  deposits  oblique  rhombic  prisms  of 
common  washing  soda,  having  the  composition  NagCOg.lOAq.  [soda 
crystals). 

A  little  reflection  will  show  the  important  influence  which  this  process 
has  exerted  upon  the  progress  of  the  useful  arts  in  this  country.  The 
three  raw  materials,  salt,  coal,  and  limestone,  we  possess  in  abundance. 
The  sulphuric  acid,  when  the  process  was  first  introduced,  bore  a  high 
price,  but  the  resulting  demand  for  this  acid  gave  rise  to  so  many  im- 
provements in  its  manufacture  that  its  price  has  been  very  greatly 
diminished — a  circumstance  which  has  of  course  produced  a  most  beneficial 
efiect  upon  all  branches  of  manufacture  in  which  the  acid  is  employed. 

The  large  quantity  of  hydrochloric  acid  obtained  as  a  secondary  pro- 
duct has  been  employed  for  the  preparation  of  bleaching  powder,  and 
the  important  arts  of  bleaching  and  calico-printing  have  thence  received 
a  considerable  impulse.  These  arts  have  also  derived  a  more  direct 
benefit  from  the  increased  supply  of  sodium  carbonate,  which  is  so  largely 
used  for  cleansing  all  kinds  of  textile  fabrics.  The  manufactures  of  soap 
and  glass,  which  probably  create  the  greatest  demand  for  sodium 
carbonate,  have  been  increased  and  improved  beyond  all  precedent  by  the 
production  of  this  salt  from  native  sources. 

*  Before  evaporation,  air  is  generally  blown  through  the  liquor  to  oxidise  the  sodiuuj 
sulphide  which  may  remain  unaltered. 


264  EECOVERY  OF  SULPHUR  FEOM  ALKALI  WASTE. 

Hargreave's  process  dispenses  with  the  use  of  sulphuric  acid,  and  converts  the 
sodium  chloride  into  sulphate  by  the  action  of  sulphurous  acid  gas  (obtained  by 
burning  pyrites)  steam,  and  air,  at  a  dull  red  heat — 

2NaCl  +  HgO  +  SO2  +  0  =  ^32804  +  2HC1. 
The  hydrochloric  acid   is  absorbed  by  water,    as  usual,  and  the  sodium  sulphate 
converted  into  carbonate  as  described  above. 

Deacon  passes  chlorine,  sulphurous  acid  gas,  and  steam  over  the  salt,  which  is  made 
to  glide  down  a  series  of  inclined  planes  in  a  tower  strongly  heated:  SO2  +  2H2O 
+  C1.,  =  2HC1  +  H2S04.  The  HCl  is  condensed  and  employed  for  the  production  of 
chlorine,  whilst  the  H2SO4  decomposes  the  NaCl . 

In  the  ammania  soda  process  which  is  now  much  used,  a  strong  solution  of  NaCl  is 
decomposed  by  the  bicarbonate  of  ammonia,  when  bicarbonate  of  soda  is  deposited  as 
a  crystalline  powder,  leaving  ammonium  chloride  in  the  solution  ;  NaCl  +  NH4HC03 
=  NH4C1  +  NaHCOj.  The  bicarbonate  of  soda  is  heated  to  convert  it  into  carbonate  ; 
2NaHC03  =  Na2C03+H20  +  C02.  The  ammonium  chloride  is  heated  with  lime  to 
disengage  the  ammonia  which  is  then  converted  into  bicarbonate  by  the  COg  (in  the 
presence  of  water),  so  that  the  same  ammonia  is  used  over  again. 

The  sodium  carbonate  obtained  by  the  ammonia  process  is  much  prized  by  the 
glass  manufacturer  on  account  of  its  purity. 

Recovery  of  stilphur  from  alkali-waste. — Since  nearly  the  whole  of  the  sulphur 
which  is  employed,  in  the  form  of  sulphuric  acid,  for  decomposing  the  common  salt, 
is  ob';ained  at  the  alkali-works  in  the  form  of  calcium  sulphide  in  the  tank-waste 
left  after  exhausting  the  black  ash  with  water,  several  processes  have  been  devised 
for  recovering  the  sulphur  in  order  to  employ  it  again  for  the  manufacture  of  oil  of 
vitriol.  The  simplest  of  these  consists  in  blowing  air  through  the  moist  tank-waste, 
until  it  is  converted  into  a  mixture  of  calcium  disulphide  and  calcium  hyposulphite, 
the  oxidation  being  stopped  when  one-third  of  the  disulphide  has  been  converted 
into  hyposulphite — 

(1)     2CaS  -F  0  =  CaO  -f-  CaSj.         (2)    CaSj  +  O3  =  CaSjOg. 
When  the  j-^ellow  liquor  thus  obtained  is  decomposed  by  the  muriatic  acid  from  the 
alkali-works  the  sulphur  is  precipitated — 

(2)    CaSjOa  +  2CaS2  +  6HC1  =  S^  +  SCaClg  +  SHjO. 

In  another  process,  the  drainings  from  the  heaps  of  alkali-waste  exposed  to  rain 
are  saturated  with  sulphurous  acid  gas  from  burning  pyrites,  when  calcium  hypo- 
sulphite is  formed,  and,  on  adding  muriatic  acid,  both  the  siilphur  of  the  waste  and 
that  obtained  from  the  pyrites  are  precipitated. 

An  objection  to  these  processes  appears  to  be  the  difficulty  in  procuring  a  sufficient 
quantity  of  muriatic  acid,  for  which  there  is  a  great  demand  on  the  part  of  the  pro- 
ducers of  bleaching  powder  and  bicarbonate  of  soda. 

Another  process  for  recovering  the   sulphur  employs  the  waste  liquor  from  the 
chlorine  stills  (see  p.  148),  which  contains  manganese  dichloride  (MnClg)  and  ferric 
chloride  (Fe^Clg).     On  treating  the  calcium  sulphide  in  the  soda-waste  with  this  still- 
liquor,  calcium  chloride  and  sulphides  of  iron  and  manganese  are  produced — 
MnCl2  +  CaS  =  MnS  +  CaCla ;     Fa^Clg  +  3CaS  =  FegSs  -f  SCaCLj. 

By  exposing  these  sulphides  to  the  air,  in  a  moist  state,  the  sulphur  is  separated, 
and  the  metals  are  converted  into  oxides — 

2MnS  +  O3  =  Mn203  +  83  ;     Fc^Sg  +  03  =  Tcfl.^  +  83. 

By  stirring  these  oxides  with  more  soda- waste,  the  sulphides  are  reproduced  ;  and 
are  afterwards  again  oxidised  by  exposure  to  air  so  as  to  separate  their  sulphur. 
The  sulphur  thus  separated  combines  with  the  calcium  sulphide  in  a  fresh  portion  of 
the  waste,  to  form  disulphide,  one-third  of  which  is  oxidised  by  the  air,  as  in  the 
process  first  described,  and  converted  into  calcium  hyposulphite.  In  order  to  pre- 
cipitate the  sulphur  from  the  liquor  containing  the  calcium  disulphide  and  calcium 
hyposulphite,  the  excess  of  hydrochloric  acid  always  present  in  the  chlorine  still- 
liquor  is  turned  to  account  ;  the  sulphur  liquor  is  run  into  this  until  the  precipitated 
sulphur  begins  to  be  accompanied  by  a  black  precipitate  of  sulphide  of  iron,  showing 
that  all  the  free  acid  has  been  neutralised.  The  still-liquor  thus  neutralised  is  then 
employed  for  decomposing  a  fresh  portion  of  the  soda-waste,  as  at  the  commencement 
of  the  process.  The  precipitated  sulphur  is  pressed  to  free  it  from  the  liquor,  dried, 
and  melted  by  super-heated  steam. 

Although  the  chemistry  of  this  process  is  rather  elaborate,  the  practical  working  is 
said  to  be  very  simple  and  inexpensive. 


SODA  LYE — SODIUM.  265 

The  most  recently  invented  process  for  extracting  sulphur  from  tank- waste  consists 
in  decomposing  the  calcium  sulphide  in  the  waste  with  a  strong  solution  of  magnesium 
chloride  ;  CaS  +  MgCl2  +  HoO  =  CaCl2  +  MgO  +  H2S.  The  H.^S  is  burnt,  and  the  SO.^ 
formed  is  converted  into  H2SO4  in  the  vitriol  chambers  (p.  204). 

In  order  to  recover  the  magnesium  chloride,  the  mixture  of  CaClg  and  MgO  is 
treated,  under  pressure,  with  carbonic  acid  gas  obtained  from  a  lime  kiln  ;  CaClg 
+  MgO  +  C02  =  CaC03  +  MgCl2.  The  magnesium  chloride  may  therefore  be  used  over 
and  over  again. 

The  crystals  of  sodium  carbonate  are  easily  distinguislied  by  their  pro- 
perty of  efflorescing  in  dry  air  (p.  42),  and  by  their  alkaline  taste,  which 
is  much  milder  than  that  of  potassium  carbonate,  this  being,  moreover,  a 
deliquescent  salt.  The  crystals  are  very  soluble  in  water,  requiring  only 
2  parts  of  cold,  and  less  than  their  own  weight  of  boiling  water ;  the 
solution  is  strongly  alkaline  to  test-papers. 

The  substance  commonly  used  in  medicine  under  the  name  of  carbonate 
of  soda,  is  really  the  bicarbonate  (or  hydrosodic  carbonate,  XaHCOg),  and 
is  prepared  by  saturating  the  carbonate  with  carbonic  acid  gas.  It  is 
readily  distinguished  from  the  carbonate,  as  it  is  but  slightly  alkaline,  and 
is  very  much  less  easily  dissolved  by  water. 

Soda  lye,  employed  in  the  manufacture  of  hard  soap,  is  a  solution 
of  sodium  hydrate  (NaHO),  obtained  by  decomposing  the  carbonate 
with  calcium  hydrate  (slaked  lime),  NagCOg  +  Ca(H0)2  =  2NaH0 
-l-CaCOg. 

The  solid  sodium  hydrate  of  commerce  is  generally  obtained  in  the 
process  for  manufacturing  carbonate  of  soda  just  described  :  the  solution 
obtained  by  treating  the  black  ash  with  water  is  concentrated  by  evapora- 
tion, so  that  the  carbonate,  sulphate,  and  chloride  of  sodium  may 
crystallise  out,  leaving  the  hydrate,  which,  is  far  more  soluble,  in  the 
liquid.  The  latter,  which  still  contains  a  compound  of  sulphide  of 
sodium  and  sulphide  of  iron,  which  gives  it  a  red  colour  {red.  liquor)  is 
mixed  with  some  nitrate  of  soda  to  oxidise  the  sulphides,  and  evaporated 
down  until  a  fused  mass  of  sodium  hydrate  is  left,  which  is  poured  out 
into  iron  moulds.* 

Kryolite  (NagAlFg)  is  sometimes  employed  as  a  source  of  the  sodium 
hydrate  which  may  be  obtained  by  decomposing  it  with  slaked  lime. 

183.  Sodium. — Potash  and  soda  exhibit  so  much  similarity  in  their 
properties,  that  we  cannot  be  surprised  at  their  having  been  confounded 
together  by  the  earlier  chemists,  and  it  was  not  till  1736  that  Du  Hamel 
pointed  out  the  difference  betAveen  them.  The  discovery  of  potassium 
naturally  led  Davy  to  that  of  sodium,  which  can  be  obtained  by  processes 
exactly  similar  to  those  adopted  for  procuring  potassium,  to  which  it  will 
be  remembered  sodium  presents  very  great  similarity  in  properties  (p.  12). 
Sodium,  however,  is  readily  distinguished  from  potassium  by  its  burning 
with  a  yellow  liame,  which  serves  even  to  characterise  it  when  in 
combination. 

This  yellow  flame  is  well  seen  by  dissolving  salt  in  water  in  a  plate,  and  adding 
enough  spirit  of  wine  to  render  it  inflammable,  the  mixture  being  well-stirred  while 
burning.     If  a  little  piece  of  sodium  be  burnt  in  an  iron  spoon  held  in  a  flame,  all 

*  Another  plan  of  treating  the  black  ash  liquor  consists  in  allowing  it  to  trickle  through 
a  column  of  coke  against  a  current  of  air,  when  the  sodium  sulphide  is  oxidised,  whilst 
the  sulphide  of  iron  is  deposited.  The  liquor  is  mixed  with  a  little  chloride  of  lime  to 
oxidise  any  remaining  sulphides,  and  concentrated  by  evaporation,  when  carbonate  and 
ferrocyanide  of  sodium  are  deposited  in  crystals.  The  liquor  separated  from  these 
contains  the  sodium  hydrate,  and  is  evaporated  till  it  solidifies  on  cooling. 


266  SODIUM — BORAX. 

the  flames  in  the  room,  even  at  a  remote  distance,  will  be  tinged  yellow  The  blow- 
pipe flame  may  also  be  employed  to  detect  sodium  by  this  colour,  as  in  the  case  of 
])otassium  (p.  259).  In  fireworks,  nitrate  of  soda  is  employed  for  producing  yellow 
flames.  A  very  good  yellow  fire  may  be  made  by  intimately  mixing,  in  a  mortar, 
74  grs.  of  nitrate  of  soda,  20  grs.  of  sulphur,  6  grs.  of  sulphide  of  antimony,  and 
2  grs.  of  charcoal,  all  carefully  dried,  and  very  finely  powdered. 

The  preparation  of  sodium,  by  distilling  a  mixture  of  sodium  carbonate 
and  charcoal,  is  much  easier  than  that  of  potassium,  for  which  reason 
sodium  is  far  less  costly  than  that  metal,  and  has  received  applications, 
on  the  large  scale,  during  the  last  few  years,  for  the  extraction  of  the 
metals  aluminium  and  magnesium.  An  amalgam  of  sodium  (p.  131)  is 
also  employed  with  advantage  in  extracting  gold  and  silver  from  their 
ores.  To  obtain  sodium  in  large  quantity,  a  mixture  of  dried  carbonate 
of  soda,  powdered  coal,  and  chalk  is  distilled  in  iron  cylinders,  when  the 
sodium  passes  over  in  the  form  of  vapour — 

NaoCOg  +  C2  =  Nag  +  3C0. 

The  chalk  is  employed  to  prevent  the  fusion  of  the  mixture. 

184.  Borax,  bihorate  of  soda  (Na20.2B203  or  Na.^B^Oy). — A  very  im- 
portant compound  of  soda  is  used  in  the  arts  under  the  name  of  horax,  in 
which  the  soda  is  combined  with  boracic  anhydride.  It  has  already  been 
stated  that  this  substance  is  deposited  during  the  evaporation  of  the 
Avaters  of  certain  lakes  in  Thibet,  whence  it  is  imported  into  this  country 
in  impure  crystals,  which  are  covered  with  a  peculiar  greasy  coating. 
Borax  has  also  been  found  abundantly  in  Southern  California.  The 
refiner  of  tincal  powders  the  crystals  and  washes  them,  upon  a  strainer, 
with  a  weak  solution  of  soda,  which  converts  the  greasy  matter  into  a 
soap  and  dissolves  it.  The  borax  is  then  dissolved  in  water,  a  quantity 
of  sodium  carbonate  is  added  to  separate  some  lime  which  the  borax 
usually  contains,  and,  after  filtering  off  the  carbonate  of  lime,  the  solution 
is  evaporated  to  the  crystallising  point  and  allowed  to  cool,  in  order  that 
it  may  deposit  the  pure  crystals  of  borax. 

It  appears,  however,  that  the  greater  part  of  the  borax  employed  in  the 
arts  is  manufactured  in  this  country  by  heating  carbonate  of  soda  with 
boracic  acid,  when  the  latter  expels  the  carbonic  acid  and  combines  with 
the  soda.*  The  mass  is  then  dissolved  in  water,  and  the  borax  crystal- 
lised, an  operation  upon  which  much  care  is  bestowed,  since  the  product 
does  not  meet  with  a  ready  sale  unless  in  large  crystals. 

The  solution  of  borax,  having  been  evaporated  to  the  requisite  degree 
of  concentration,  is  allowed  to  crystallise  in  covered  wooden  boxes,  which 
are  lined  with  lead  and  enclosed  in  an  outer  case  of  wood,  the  space 
T)etween  the  sides  of  the  case  and  the  box  being  stuffed  with  some  bad 
conducter  of  heat,  so  that  the  solution  of  borax  may  cool  very  slowly,  and 
large  crystals  may  be  deposited.  In  about  thirty  hours  the  crystallisa- 
tion is  completed,  when  the  liquid  is  drawn  off  as  rapidly  as  possible,  the 
last  portion  being  carefully  soaked  up  with  sponges,  so  that  no  small 
crystals  may  be  afterwards  formed  upon  the  surface  of  the  large  ones ;  the 
case  is  then  again  covered  up,  so  that  the  crystals  may  cool  slowly  with- 
(lut  cracking. 

*  The  ammonia  which  is  evolved  from  the  Tuscan  boracic  acid  employed  in  this  process 
is  luinwn  in  commerce  as  Volainic  aminnnia,  and  is  free  from  the  empyreumatic  odour 
wliicli  gfuerally  accompanies  that  from  coal  and  bones. 


SODIUM  SILICATE.  267 

Borax  is  cliemically  known  as  sodium  anJiydroborate,  and  is  represented, 
in  the  dry  state,  by  the  formula  ^N^agB^O-.  The  ordinary  prismatic  crystals, 
however,  contain  ten  molecules  of  water  of  crystallisation,  and  are 
therefore  represented  by  the  formula  NagB^OY-lOAq.  They  soon  eflfloresce 
and  become  opaque  when  exposed  to  air,  and  may  readily  be  distinguished 
by  their  alkaline  taste  and  action  upon  test-papers,  and  especially  by  their 
behaviour  when  heated,  for  they  fuse  easily  and  intinnesce  most  violently, 
swelling  up  to  a  white  spongy  mass  of  many  times  their  original  bulk; 
this  mass  afterwards  fuses  down  to  a  clear  liquid  which  forms  a  trans- 
parent glassy  mass  on  cooling  {vitrified  borax),  and  since  this  glass  is 
capable  of  dissolving  many  metallic  oxides  with  great  readiness  (borax 
being,  by  constitution,  an  acid  salt,  and  therefore  ready  to  combine  with 
more  base),  it  is  much  used  in  the  metallurgic  arts.  Large  quantities  of 
borax  are  also  employed  in  glazing  stop^",vare. 

185.  Sodium  silicate. — A  combination  of  soda  with  silica  has  long 
been  used,  under  the  name  of  soluble  glass,  for  imparting  a  fire-proof 
character  to  wood  and  other  materials,  and  more  recently,  for  producing 
artificial  stone  for  building  purposes,  and  for  a  peculiar  kind  of  permanent 
fresco-painting  {stereochromy),  the  results  of  which  are  intended  to  with- 
stand exposure  to  the  weather. 

Soluble  glass  is  usually  prepared  by  fusing  15  parts  of  sand  with  8 
parts  of  carbonate  of  soda  and  1  part  of  charcoal.  The  silicic  acid,  com- 
bining with  the  soda,  disengages  the  carbonic  acid  gas,  the  expulsion  of 
which  is  facilitated  by  the  presence  of  charcoal,  which  converts  it  into 
carbonic  oxide.  The  mass  thus  formed  is  scarcely  aff'ected  by  cold  water, 
but  dissolves  when  boiled  wdth  water,  yielding  a  strongly  alkaline  liquid. 

In  using  this  substance  for  rendering  wood  fire-proof,  a  rather  weak 
solution  is  first  applied  to  the  wood,  and  over  this  a  coating  of  lime-wash 
is  laid,  a  second  coating  of  soluble  glass  (in  a  more  concentrated  solu- 
tion) is  then  applied.  The  wood  so  prepared  is,  of  course,  charred,  as 
usual,  by  the  application  of  heat,  but  its  inflammability  is  remarkably 
diminished. 

For  the  manufacture  of  Ransome^s  artificial  stone,  the  soluble  glass  is 
prepared  by  heating  flints,  under  pressure,  with  a  strong  solution  of 
caustic  soda,  to  a  temperature  between  300°  and  400°  F.,  when  the  silica 
constituting  the  flint  enters  into  combination  with  the  soda.  Finely 
divided  sand  is  moistened  with  this  solution,  pressed  into  moulds,  dried,  and 
exposed  to  a  high  temperature,  when  the  silicate  of  soda  fuses  and  cements 
the  grains  of  sand  together  into  a  mass  of  artificial  sandstone,  to  which 
any  required  colour  may  be  imparted  by  mixing  metallic  oxides  with  the 
sand  before  it  is  moulded. 

Silicate  of  soda  is  also  sometimes  used  as  a  dung  substitute  (p.  242)  in 
calico-printing. 

Sodium  sulphate  forms  the  very  common  saline  efflorescence  upon  the 
sui'face  of  brick  walls,  and  has  been  found  covering  the  sandy  soil  of 
the  Desert  of  Atacaraa,  over  a  considerable  area.  The  mineral  known 
as  Thenardite  also  consists  of  sodium  sulphate,  and  Glauberite  is  a 
double  sulphate  of  sodium  and  calcium  (XagSO^.CaSO^)  which  is  nearly 
insoluble  in  water. 

Phosphate  of  soda  or  hydroiiisodic  orthophosphate,  NaoHPOj.  12Aq., 
is  obtained  by  neutralising,  with  sodium  carbonate,  the  impure  phosphoric 


2(58  SALTS  OF  AMMONIUM, 

acid  obtained  by  decomposing  bone-ash  with  sulphuric  acid  (p.  229).  On 
evaporation,  the  phosphate  is  deposited  in  oblique  rhombic  prisms  which 
effloresce  in  air. 

Sodmm  nitrate,  NaNOg,  will  be  more  particularly  noticed  in  the 
section  on  gunpowder.  It  is  imported  from  Peru,  and  used  in  consider- 
able quantity  as  a  manure,  and  for  the  manufacture  of  potassium  nitrate. 

SALTS  OF  AMMONIUM. 

186.  The  great  chemical  resemblance  between  some  of  the  salts  formed 
by  neutralising  acids  with  ammonia,  and  the  salts  of  potassium  and  sodium, 
has  been  already  pointed  out  as  affording  a  reason  for  the  hypothesis  of 
the  existence  of  a  compound  metal,  ammonium  (NH^),  equivalent  in  its 
functions  to  potassium  and  sodium. 

The  compounds  which  are  formed  when  ammonia  (NHJ  combines  with 
the  anhydrides,  such  as  carbonic  (COg)  and  sulphuric  (SO3),  do  not  exhibit 
the  resemblance  to  the  salts  of  potassium  and  sodium  until  water  is  added. 
Thus,  by  the  action  of  dry  ammonia  gas  upon  sulphuric  anhydride,  a 
compound  called  sulphuric  ammonide  is  formed,  having  the  composition 
(N  113)2803.  This  substance  dissolves  in  water  and  crystallises  in  octahedra, 
but  its  solution  is  not  precipitated  by  barium  chloride,  which  always  pre- 
cipitates the  true  sulphates,  nor  by  platinic  chloride  which  precipitates  the 
true  ammonium  salts.  By  long  boiling  with  water,  however,  it  becomes 
converted  into  ammonium  sulphate  (^114)280^,  which  yields  precipitates 
with  both  the  above  tests.  The  phosphoric,  carbonic,  and  sulphurous 
anhydrides  also  combine  with  dry  ammonia  to  form  ammonides,  which 
do  not  respond  to  the  ordinary  tests  for  the  corresponding  salts  of 
ammonium  until  after  water  has  been  assimilated.  The  true  salts  of 
ammonium  are  produced  either  by  the  combination  of  an  acid  with 
ammonia,  or  by  double  decomposition. 

187.  Ammonium  sulphate,  (NH^)2S04,  is  largely  employed  in  the  pre- 
paration of  ammonia-alum,  and  of  artificial  manures,  for  which  purposes 
it  is  generally  obtained  from  the  ammoniacal  liquor  of  the  gas-works  by 
neutralising  with  sulphuric  acid  and  evaporating.  The  rough  crystals  are 
gently  heated  to  expel  tarry  substances,  and  purified  by  recrystallisation. 
The  crystals  have  the  same  shape  as  those  of  potassium  sulphate,  and  are 
easily  soluble  in  water.  "When  heated  to  about  500°  F.  the  ammonium 
sulphate  is  decomposed,  yielding  vapour  of  ammonium  sulphite,  water, 
ammonia,  nitrogen,  and  sulphur  dioxide.  If  muslin  be  dipped  into  a 
solution  of  ammonium  sulphate  in  ten  parts  of  water  and  dried,  it  will  no 
longer  burn  with  flame  when  ignited.  The  mineral  mascagnine  consists 
of  ammonium  sulphate.  This  salt  is  occasionally  found  in  needle-like 
crystals  upon  the  windows  of  rooms  in  which  coal  gas  is  burnt. 

1 88.  Sesquicarhonate  of  ammonia*  (4XH3.  SHgO.  3CO2  or  (K'H,)4H2(C03)3 
is  the  common  carbonate  of  ammonia  of  the  shops,  also  called  smelling 
mlfs  or  Preston  salts,  largely  used  in  medicine,  and  by  bakers  and  con- 
fectioners, for  imparting  lightness  or  porosity  to  cakes,  &c.  It  is  com- 
monly prepared  by  mixing  sal  ammoniac  (ammonium  chloride)  with  twice 
its  weight  of   chalk,  and  distilling  the   mixture  in  an  earthen  or  iron 

*  It   appears  that  the  carbonate  formerly  found  in  commerce  had   the  composition 
4NH3.2H2O.3CO2. 


SAL  AMMONIAC.  269 

retort,  cornmunicating,  through  an  iron  pipe,  with  a  leaden  chamber  or 
receiver,  in  which  the  ammonium  carbonate  collects  as  a  transparent 
fibrous  mass,  which  is  extracted  by  taking  the  receiver  to  pieces,  and 
purified  by  resubliming  it  at  about  130°  F.,  in  iron  vessels  surmounted  by 
leaden  domes.  The  action  of  calcium  carbonate  upon  ammonium  chloride 
would  be  expected  to  furnish  the  normal  carbonate  (NH4)2C03,  but  this 
salt  (even  if  produced)  is  decomposed  by  the  heat  employed  in  the 
process — 

6NH4CI  +  SCaCOg  =  2NH3  +  3CaCl2  +  (NH,)4H2(C03)3 . 

When  a  mass  of  freshly  prepared  sesquicarbonate  of  ammonia  is 
exposed  to  air,  it  evolves  ammonia  and  becomes  gradually  converted  into 
an  opaque  crumbly  mass  of  bicarbonate  of  ammonia  or  hydroammonic 
carbonate — 

(NH4),H2(C03)3  =  l^H,  +  3NH4HCO3. 

Water  effects  this  decomposition  more  rapidly  ;  if  the  powdered  sesqui- 
carbonate of  ammonia  be  washed  with  a  little  water,  bicarbonate  of  am- 
monia is  left,  and  the  solution  contains  the  normal  carbonate  (^114)2003, 
which  may  be  obtained  in  crystals  by  adopting  certain  precautions.  The 
sesquicarbonate  dissolves  in  about  three  times  its  weight  of  cold  water. 
Boiling  water  decomposes  it,  and  the  solution,  on  cooling,  deposits  large 
prismatic  crystals  of  bicarbonate  of  ammonia  (NH^HCOg)  which  is  much 
less  soluble  in  water.  This  salt  has  been  found  in  considerable  quantity, 
forming  crystalline  masses  in  a  bed  of  guano  on  the  western  coast  of 
Patagonia.  Sal  volatile  is  an  alcoholic  solution  of  carbonate  of  ammonia 
obtained  by  distilling  sal  ammoniac  with  carbonate  of  potash  and  rectified 
spirit  of  wine,  or  by  treating  the  sesquicarbonate  of  ammonia  with  hot 
spirit. 

The  commercial  carbonate  of  ammonia  appears  to  contain  a  small  quantity  of 
ammonium  carbamate,  NH4CO2NH2,  which  is  derived  from  the  normal  carbonate  by 
the  loss  of  H2O  ;  (NH4)2C03  =  NH4C02NH2  +  H.p. 

The  ammonium  carbamate  is  deposited  as  a  white  solid  when  ammonia  gas  is  mixed 
with  carbonic  acid  gas.  It  maj'  be  obtained  in  crystals  bj'  passing  COj  and  NHj 
into  the  strongest  solution  of  ammonia. 

Ammonium  carbamate  is  easily  soluble  in  water,  which  soon  converts  it  into  am- 
monium carbonate.  The  aqueous  solution,  when  freshly  prepared,  is  not  precipitated 
by  calcium  chloride,  but  the  calcium  carbonate  is  deposited  on  standing  or  heating. 

When  ammonium  carbamate  is  heated  in  a  sealed  tube  to  130"  C.  it  is  decomposed 
into  ammonium  carbonate  and  urea,  2NH4CO.jNH2  =  (NH4)2C03  +  CON2H4.  Car- 
bamic  acid,  HCO2NH0,  has  not  been  isolated  ;  its  relation  to  carbonic  acid  is  seen  by 
a  comparison  of  their  formulfe — 

CO  \^^  CO  i  ^H 

^^   I   OH  ^"1   NH2 

Hypothetical  carbonic  acid.  Hypothetical  carbamlc  acid. 

Other  carbamates  have  been  obtained  by  passing  COg  through  strongly  ammoniacal 

sohitions  of  different  bases,   and  precipitating  the   carbamates  by  alcohol.     "When 

potassium  cirbamate  is  heated,  it  yields  water  and  potassium  cyanate,    KCO.jKH.^ 

r^KCNO  +  HgO. 

189.  Ammonium  chloride  (NH^Cl),  also  called  munate  of  ammonia  and 
sal  ammoniac. — When  dry  ammonia  gas  is  brought  in  contact  with  an 
equal  volume  of  dry  hydrochloric  acid  gas,  it  has  been  seen  (p.  130)  that 
they  combine  directly  to  produce  this  salt,  the  preparation  of  which  on 
the  large  scale  has  been  noticed  at  p.  124.  It  is  also  sometimes  made  by 
subliming  a  mixture  of  ammonium  sulphate  with  common  salt — 
(NHJ.^SO,  -H  2]SaCl  =  2XH,Cl  +  Xa^SO^. 


270  SULPHIDE  OF  AMMONIUM. 

Its  commercial  form  is  that  of  a  very  tough  translucent  fibrous  mass, 
generally  of  the  dome-like  shape  of  the  receivers,  and  often  striped  with 
brown,  from  the  presence  of  a  little  iron.  It  has  not  the  least  smell  of 
ammonia,  and  is  very  soluble  in  water,  requiring  about  three  parts  of  cold 
water,  and  little  more  than  its  own  weight  of  boiling  water.  As  the  hot 
solution  cools,  it  deposits  beautiful  fern-like  crystallisations  composed  of 
minute  cubes  and  octahedra.  The  liquefaction  of  sal  ammoniac  in  water 
lowers  the  temperature  very  considerably,  which  renders  the  salt  very 
useful  in  freezing  mixtures.  A  mixture  of  equal  weights  of  sal  ammoniac 
and  nitre,  dissolved  in  its  own  weight  of  water,  lowers  the  temperature 
of  the  latter  from  50°  F.  to  10°.  In  this  case  partial  decomposition  takes 
place,  resulting  in  the  production  of  potassium  chloride  and  ammonium 
nitrate,  both  of  which  absorb  much  heat  whilst  being  dissolved  by  water. 
The  solution  of  ammonium  chloride  in  water  is  slightly  acid  to  blue 
litmus  paper.  When  sal  ammoniac  is  heated,  it  passes  off  in  vapour,  at  a 
temperature  below  redness,  without  previously  fusing;  the  vapour  forms 
thick  white  clouds  in  the  air,  and  may  be  recondensed  as  a  white  crust 
upon  a  cold  surface ;  but  it  cannot  be  sublimed  without  some  loss,  a 
portion  being  decomposed  into  hydrochloric  acid,  hydrogen,  and  nitrogen. 
The  specific  gravity  (weight  of  1  volume)  of  the  vapour  of  sal  ammoniac 
is  13 "3  times  that  of  hydrogen,  so  that  53*5  parts,  or  one  molecule,  would 
appear  to  occupy  4  volumes  instead  of  2,  but  this  may  be  explained  by 
supposing  a  temporary  dissociation  of  the  hydrochloric  acid  and  ammonia 
when  the  salt  is  converted  into  vapour,  so  that  the  observed  specific 
gravity  is  really  that  of  a  mixture  of  equal  volumes  of  these  constituent 
gases.  Experimental  evidence  has  been  obtained  in  support  of  this 
view,  for  it  has  been  found  that  free  ammonia  and  hydrochloric  acid  may 
be  separated  by  diffusion  from  the  vapour  obtained  on  heating  ammonium 
chloride. 

This  may  be  shown  by  placing  a  fragment  of  sal  ammoniac  in  a  narrow  test-tube, 
with  a  plug  of  asbestos  at  a  little  distance  above  it  ;  if  a  piece  of  red  litmus  paper  be 
] (laced  in  the  tube,  it  will  be  found,  on  heating  the  sal  ammoniac  and  the  asbestos, 
that  the  NH.,,  being  lighter,  diffuses  most  rapidly  through  the  asbestos,  and  blues 
the  red  litmus,  but  soon  afterwards  the  hydrochloric  acid  difiuses  through,  and  the 
litmus  is  again  reddened. 

Moreover,  the  heat  which  becomes  latent  or  is  absorbed  in  vaporising 
the  sal  ammoniac,  is  almost  exactly  that  which  is  produced  by  the  com- 
bination of  the  hydrochloric  acid  and  ammonia. 

When  ammonium  chloride  is  heated  with  metallic  oxides,  the  hydro- 
chloric acid  often  converts  the  oxide  into  a  chloride  which  is  either  fusible 
or  volatile,  so  that  sal  ammoniac  is  often  employed  for  cleansing  the  sur- 
faces of  metals  previously  to  soldering  them.  Even  those  metallic  oxides 
which  are  destitute  of  basic  properties,  such  as  antimonic  and  stannic 
oxides,  are  convertible  into  chlorides  by  the  action  of  sal  ammoniac  at  a 
high  temperature. 

Ammonium  chloride  is  found  in  volcanic  districts,  and  is  present  in 
very  small  quantity  in  sea  water. 

190.  Hijdrosulpliate  of  ammonia  (2X113.1128),  or  ammonium  sulpJiide 
(NH^)2S,  has  been  obtained  in  colourless  crystals  by  mixing  hydrosulphuric 
acid  gas  with  twice  its  volume  of  ammonia  gas  in  a  vessel  cooled  by  a 
mixture  of  ice  and  salt.  It  is  a  very  unstable  compound,  decomposing  at 
the  ordinary  temperature  qf  the  air  into  free  ammonia  and  ammonium 


SULPHIDES  OF  AMMONIUM.  271 

hydrosuJphide,  NH^HS,  which  may  he  ohtained  in  very  volatile  colourless 
needles  by  passing  equal  volumes  of  NH3  and  HgS  into  a  vessel  cooled  in 
ice.  When  a  solution  of  ammonia  is  saturated  with  hydric  sulphide,  the 
ammonia  is  found  to  have  combined  with  one  molecule,  forming  a  solution 
of  the  ammonium  hydrosulphide  (NH^HS).  The  solution  is  colourless 
when  freshly  prepared,  but  it  soon  becomes  yellow  in  contact  with  the  air, 
from  the  formation  of  ammonium  distdpMde  (SYi.^^^  ammonium  hypo- 
sulphite being  formed  at  the  same  time — 

4NH,HS  +  05  =  (NHJ2S2  +  (NHJaSA  +  2H2O. 

Eventually,  the  solution  deposits  sulphur  and  becomes  colourless,  hypo- 
sulphite, sulphite,  and  sulphate  of  ammonium  being  formed.  When  the 
freshly-prepared  colourless  solution  of  ammonium  hydrosulphide  is  mixed 
with  an  acid,  the  solution  remains  clear,  hydrosulphuric  acid  being  evolved 
with  effervescence;  KH^HS -H HCl  =  NH^Cl -1- H^S  ;  but  if  the  solution 
be  yellow,  a  milky  precipitate  of  sulphur  is  produced,  from  the  decom- 
position of  the  ammonium  disulphide — 

(XH4)2S2  +  2HC1  =  2NH4CI  -t-  H2S  -f-  S. 

The  fresh  solution  gives  a  black  precipitate  of  lead  sulphide  when 
solution  of  lead  acetate  is  added  to  it,  but  after  it  has  been  kept  till  it 
is  of  a  dark  yellow  or  red  colour,  it  gives  a  red  precipitate  of  the  per- 
sulphide  of  lead.  Solution  of  ammonium  sulphide,  prepared  by  mixing 
the  hydrosulphide  with  an  equal  volume  of  solution  of  ammonia,  is  largely 
employed  in  analytical  chemistry  ;  NH^HS  +  ^^^  =  (XH4)2S  .  The 
solution  has  a  very  disagreeable  odour. 

Ammonium  disulphide  is  obtained  in  deliquescent  yellow  crystals,  when  a  mixture 
of  ammonia  gas  with  vapour  of  sulphur  is  passed  through  a  red  hot  porcelain  tube. 
It  is  the  chief  constituent  of  Boyle^s fuming  liquor,  a  fetid  yellow  liquid  obtained  by 
distilling  sal  ammoniac  with  sulphur  and  lime.  The  disulphide  is  sometimes 
deposited  in  yellow  crystals  from  this  liquid.  By  dissolving  sulphur  in  ammonium 
disulphide,  orange-yellow  prismatic  crystals  of  aimnonium  pentMsul2)hide  (NH4)2S5 
may  be  obtained.     Even  a  heptasidphide  {ls'ii),^7  has  been  crystallised. 

It  is  scarcely  possible  to  represent  the  constitution  of  the  higher  sulphides  of 
ammonium  except  on  the  ammonium  hypothesis. 

Ammonium  bromide  (NH4Br),  and  ammonium  iodide  (NH4I),  are  useful  in  pho- 
tography. They  are  both  colourless  crystalline  salts,  but  the  iodide  is  very  liable 
to  become  yellow  or  brown,  from  the  separation  of  iodine,  unless  kept  dry  and  in 
the  dark.     Both  salts  are  extremely  soluble  in  water. 

191.  Lithium  (L  =  7  parts  by  weight)  is  a  comparatively  rare  metal,  obtained  chiefly 
from  the  minerals  lepidolite  {\evis,  a  scale)  or  litkia-mica,  containing  silicate  of 
alumina  with  fluorides  of  potassium  and  lithium  ;  petalite  {■K4ra\ov,  a  leaf),  silicate  of 
soda,  lithia,  and  alumina,  and  triphatie  or  spodumeiu  (inroSJ)?,  ashes),  which  has  a 
similar  composition.  Its  name  (from  \ldos,  a  stone)  was  bestowed  in  the  belief  that 
it  existed  onlj'  in  the  mineral  kingdom,  but  recent  investigation  has  detected  it  in 
minute  proportion  in  the  ashes  of  tobacco  and  other  plants. 

Metallic  lithium  is  obtained  by  decomposing  fused  lithium  chloride  by  a  galvanic 
current.  It  is  remarkable  as  the  lightest  of  the  solid  elements  (sp.  gr.  0"59).  It 
bears  a  general  resemblance  to  potassium  and  sodium,  but  it  is  harder  and  less  easily 
oxidised  than  those  metals.  It  decomposes  water  rapidly  at  the  ordinary  temperature, 
but  does  not  inflame  upon  it. 

Lithium  differs  from  potassium  and  sodium  by  forming  a  sparingly  soluble 
phosphate  (L3PO4)  and  carbonate  (LjCOj).  The  compounds  of  lithium  impart  a  red 
colour  to  the  flame  of  the  blowpipe  (p.  259). 

Lithium  carbonate  is  occasionally  employed  medicinally. 

KuBiDiUM  (Rb'  =  85  parts  by  weight)  and  Cesium  (Cs'  =  133  parts  by  weight) 
were  discovered  so  lately  as  in  1860,  by  Bunsen  and  Kirchhoff,  during  the  analysis 


272 


SPECTRUM  ANALYSIS. 


of  a  certain  spring  water  which  contained  these  metals  in  so  minute  quantity  (2  or  3 
grs.  in  a  ton)  that  they  would  certainly  have  escaped  observation  if  the  analysis  had 
been  conducted  in  the  ordinary  way.  The  discovery  of  these  metals,  as  well  as  of 
three  others  (thallium,  indium,  gallium)  to  be  mentioned  hereafter,  was  the  result  of 
the  application  of  the  method  of  spectrum  analysis,  of  which  a  brief  description  is 
here  given,  although  the  discussion  of  the  optical  principles  upon  which  it  depends 
would  be  misplaced  in  a  chemical  work. 

192.  Spectrum  analysis. — It  has  been  mentioned  above  that  compounds 
of  potassium,  sodium,  and  lithium  impart,  respectively,  lilac,  yellow,  and 
red  colours  to  the  blowpipe  flame  (or  air-gas  flame,  see  p.  107),  or,  in 
other  words,  that  the  highly  heated  vapours  of  the  metals  evolve  luminous 
rays  of  these  particular  colours.  When  the  quantity  of  the  metal  is 
extremely  minute,  and  its  peculiar  luminous  rays  proportionally  scanty, 
their  colour  may  very  easily  escape  notice,  especially  if  two  or  three  metals 
are  j)resent  in  the  flame  at  the  same  time.     But  if  the  light  emanating 

from  the  flame  be  allowed  to 
pass  through  a  narrow  slit 
at  A  (fig.  234),  collected  by 
a  lens,  and  transmitted 
through  a  prism  of  flint 
glass  or  through  a  hollow 
prism  (B)  filled  with  carbon 
disulphide,  all  the  rays  of  one 
colour  will  be  refracted  in  a 
definite  direction,  so  that  the 
spectrum,  or  image  of  the 
slit,  when  thrown  upon  a 
screen,  instead  of  exhibiting 


i  ig.  liDl.     Spectroscope. 


colours  uniformly  distributed  like  the  flame  itself,  will  show  stripes  or 
bands  of  the  various  coloured  rays  existing  in  the  flame.  Thus,  when 
vapour  of  sodium  is  present  in  the  flame,  the  whole  of  the  yellow  light 
emitted  by  it  will  be  collected  in  the  spectrum  into  a  narrow  yellow  stripe 
of  great  intensity,  and  so  extremely  delicate  is  this  test  that  it  is  scarcely 
possible  to  obtain  a  flame  which  does  not  exhibit  this  sodium  line.  The 
heated  vapour  of  lithium  emits  a  mixture  of  red  with  a  few  yellow  rays, 
and  accordingly,  the  spectrum  of  a  flame  containing  lithium  exhibits  a  very 
bright  band  of  red  light,  and  a  comparatively  dull  band  of  yellow  light, 
the  red  band  being  characteristic  of  lithium.  The  potassium  flame  emits 
a  mixture  of  blue  and  red  rays,  so  that  its  spectrum  exhibit;S  a  distinct 
red  band  of  a  darker  colour  than  the  lithium  band,  and  a  feeble  violet 
band.  Instead  of  throwing  the  spectrum  upon  a  screen,  it  is  generally 
passed  through  a  telescope  (C)  to  the  eye  of  the  observer,  and  the  spectro- 
scope so  constructed  has  now  taken  its  place  among  the  apparatus  indis- 
pensable to  the  analytical  chemist.  The  prism  B  may  be  slowly  moved 
round  by  a  handle  attached  to  a  stage  on  which  it  rests,  in  order  that  the 
different  parts  of  the  spectrum  may  be  successively  brought  into  sight. 
By  comparing  the  spectra  of  the  flames  containing  vapours  of  the  metals 
with  a  picture  6r  map  of  the  solar  spectrum  (fig.  235),  the  exact  position 
of  the  various  coloured  bands  may  be  noted,  and  thus,  if  several  metals 
are  present  in  the  same  flame,  they  may  still  be  distinguished  by  the 
colours  and  positions  of  their  bands.  Thus,  if  a  mixture  of  the  chlorides 
of  potassium,  sodium,  and  lithium  be  taken  upon  a  loop  of  platinum  wire 
and  held  in  the  flame,  the  dull  red  line  of  potassium  (K,  fig.  235)  is  seen 


KUBIDIUM — CESIUM. 


273 


close  to  one  end  of  the  spectrum;  at  some  distance  from  it  the  bright  red 
band  (L)  of  lithium;  at  about  the  same  distance  from  this,  the  pale 
yellow  lithium  line ;  and  close  to  this,  the  bright  yellow  band  of 
sodium  (Xa) ;  whilst  near  to  the  other  end  of  the  spectrum  is  the  feeble 
violet  band  of  potassium  (k).  The  chlorides  of  the  metals  are  most 
suitable  for  this  experiment,  on  account  of  their  easy  conversion  into 
vapour. 


Violet.       Indigo.  .Blue 


Green. 


Yellow. 


Oranqe 


Spectrum  furnished  by  solar  light  decomposed  by  a  piism. 


B.edi. 


3    K 


5 


-.3 
to  tj 


Coloured  bands  in  the  spectrum. 
Fig.  235. 

When  examining,  with  the  spectroscope,  the  alkaline  chlorides  extracted  from  the 
spring  water  above  alluded  to,  Bunsen  and  Kirchhoff  observed  two  red  and  two  blue 
bands  in  the  spectrum,  which  they  could  not  ascribe  to  any  known  substance,  and 
which  they  ultimately  traced  to  the  two  new  metals,  rubidium  {rubidus,  dark-red) 
and  ciesium  {csesitts,  sky-blue). 

Kubidium  has  since  been  found  in  small  quantity  in  other  mineral  waters,  in 
lepidolite,  and  in  the  ashes  of  many  plants.  This  metal  is  closely  related  in  pro- 
perties to'  potassium,  but  is  more  easily  fusible  and  convertible  into  vapour,  and 
actually  surpasses  that  metal  in  its  attraction  for  oxygen,  rubidium  taking  tire 
spontaneously  in  air.  It  burns  on  water  with  exactly  the  same  flame  as  potassium. 
Its  hydrate  is  a  powerful  alkali,  like  potash,  and  its  salts  are  isomorphous  with  those 
of  potash.  The  double  chloride  of  platinum  and  potassium,  however,  is  eight  times 
as  soluble  in  boiling  water  as  the  corresponding  salt  of  rubidium,  wliich  is  taken 
advantage  of  in  separating  these  two  allied  metals. 

CcEsium  appears  to  be  even  more  highly  electro-positive  than  rubidium,  forming  a 
strong  alkali,  caesium  hydrate,  and  salts  which  are  isomorphous  with  those  of  potas- 
sium. Csesium  carbonate,  however,  is  soluble  in  alcohol,  which  does  not  dissolve 
tlie  carbonates  of  potassium  and  rubidium.  Moreover,  the  caesium  bitartrate  is  nine 
times  as  soluble  in  water  as  the  rubidium  bitartrate. 

Ciesium  has  been  found  in  lepidolite;  and  the  rare  mineral  pollux  found  in  Elba, 
and  resembling  felspar  in  composition,  is  said  to  contain  a  very  large  quantity  of 
this  metal. 

Metallic  caesium  cannot  be  obtained  by  reduction  with  carbon,  but  it  has  been 
extracted  by  decomposing  its  cyanide  by  the  galvanic  current. 

193.  General  review  of  the  group  of  alkali  metals. — Caesium,  rubidium, 
potassium,  sodium,  and  lithium  constitute  a  group  of  elements  conspicuous 
for  their  highly  electro-positive  character,  the  powerfully  alkaline  nature  of 

S 


274  BARIUM. 

their  hydrates,  and  the  general  solubility  of  their  salts.  Their  chemical 
characters  and  functions  are  directly  opposite  to  those  of  the  electro- 
negative group  containing  fluorine,  chlorine,  bromine,  and  iodine,  and, 
like  those  elements,  they  exhibit  a  gradation  of  properties.  Thus,  csesiiim 
appears  to  be  the  most  highly  electro-positive  member,  rubidium  the  next, 
then  potassium  and  sodium,  whilst  lithium  is  the  least  electro-positive ; 
and  just  as  iodine,  the  least  electro-negative  of  the  halogens,  possesses 
the  highest  atomic  number,  so  caesium,  the  least  electro-negative  (or  most 
electro-positive)  of  the  alkali-metals,  has  a  higher  atomic  weight  than  any 
other  member  of  this  group,  their  atomic  weights  being  represented  by 
the  numbers,  caesium,  133;  rubidium,  85*3;  potassium,  39;  sodium,  23; 
lithium,  7.  As  in  the  case  of  the  halogens  also,  these  are  all  univalent 
elements.  Just  as  chlorine  is  accepted  as  the  representative  of  chlorous 
radicals,  so  potassium  is  commonly  regarded  as  the  type  of  hasi/lous  radicals, 
the  term  radical  being  applied  to  all  substances,  whether  elementary  or 
compound,  which  are  capable  of  being  transferred,  like  chlorine  or 
potassium,  from  one  compound  to  another  without  suffering  decomposition. 

Some  of  the  physical  properties  of  these  elements  exhibit  a  gradation  in 
the  same  order  as  their  atomic  weights  ;  thus  csesium  fuses  at  80°  F.,  rubid- 
ium at  101°,  potassium  at  144°-5,  sodium  at  207°"7,  and  lithium  at  356°,  so 
that,  at  ordinary  temperatures,  rubidium  is  the  softest,  and  lithium  the 
hardest  of  these  metals. 

In  some  of  their  salts  a  similar  gradational  relation  is  observed ;  the 
carbonates,  for  example,  of  caesium,  rubidium,  and  potassium  are  highly 
deliquescent,  absorbing  water  greedily  from  the  air,  whilst  carbonate  of 
sodium  is  not  deliquescent,  and  carbonate  of  lithium  is  sparingly  soluble 
in  water.  The  difficult  solubility  of  the  carbonate  and  phosphate  of  lithium 
constitutes  the  connecting  link  between  this  and  the  succeeding  group  of 
metals,  the  carbonates  and  phosphates  of  which  are  insoluble  in  water. 


BARIUM. 

Ba"  =  137  parts  by  weight. 

194.  Barium,  so  named  from  the  great  weight  of  its  compounds  (ySapvs, 
heavy),  is  found  in  considerable  abundance  in  the  north  of  England,  in 
two  minerals  known  as  Witherite  (barium  carbonate,  BaCOg)  and  heavy 
spar  (barium  sulphate,  BaS04).  Witherite  is  found  in  large  masses  m 
the  lead  mines  at  Alston  Moor,  and  at  Anglesark  in  Lancashire.  It  is 
said  to  be  used  for  poisoning  rats,  and  was  originally  mistaken,  on  account 
of  its  great  weight,  for  an  ore  of  lead. 

The  metal  itself  is  obtained  by  decomposing  fused  barium  chloride  by 
the  galvanic  current.  It  is  a  pale  yellow  malleable  metal  of  sp.  gr.  about 
4,  which  is  easily  oxidised  by  air,  and  rapidly  decomposes  water  at 
common  temperatures. 

Such  compounds  of  barium  as  are  used  in  the  arts  are  chiefly  prepared 
from  heavy  spar  or  barium  sulphate,  which  is  remarkable  for  its  insolu- 
bility in  water  and  acids.  In  order  to  prepare  other  compounds  of  barium 
from  this  refractory  mineral,  it  is  ground  to  powder  and  strongly  heated 
in  contact  with  charcoal  or  some  other  carbonaceous  substance,  which 
removes  the  oxygen  from  the  mineral  in  the  form  of  carbonic  oxide, 
and  converts  it  into   barium  sulphide,    BaSO^ -I- C^  =  4C0 -H  BaS.      This 


BARIUM.  275 

latter  compound,  "being   soluble  in  water,  can  be  readily  converted  into 
otlier  barytic  compounds. 

The  artificial  barium  sulphate,  which  is  used  by  painters,  instead  of 
white  lead,  under  the  name  of  permanent  white,  and  is  employed  for 
glazing  cards,  is  prepared  by  mixing  the  solution  of  barium  sulphide  with 
dilute  sulphuric  acid,  when  the  barium  sulphate  separates  as  a  white 
precipitate,  which  is  collected,  washed,  and  dried — 
BaS  +  H2SO4  =  H2S  +  BaSO,. 

The  artificial  harium  carbonate,  which  is  used  in  the  manufacture  of 
some  kinds  of  glass,  is  prepared  by  passing  carbonic  acid  gas  through  a 
solution  of  barium  sulphide,  when  the  carbonate  is  precipitated;  BaS 
+  ll.p  +  CO2  =  HgS  +  BaCOg. 

In  preparing  compounds  of  barium  fioni  heavy  spar  on  the  small  scale,  it  is  better 
to  convert  the  sulphate  into  barium  carbonate.  50  grs.  of  the  finely-powdered 
sulphate  are  mixed  with  100  grs.  of  dried  carbonate  of  soda,  600  grs.  of  powdereil 
nitre,  and  100  grs.  of  very  finely  powdered  charcoal.  The  mixture  is  placed  on  a 
heap  upon  a  brick  or  iron  plate,  and  kindled  with  a  match,  when  the  heat  evolved 
by  the  combustion  of  the  charcoal  in  the  oxygen  of  the  nitre  fuses  the  barium 
sulphate  with  the  sodium  carbonate,  when  they  are  decomposed  into  barium  carbonate 
and  soiiium  sulfdiate  ;  BaS04  +  N^agCOs  =  Na2S04  +  BaCO,.  The  fused  mass  is  thrown 
into  boiling  water,  which  dissolves  the  sodium  sulphate  and  leaves  the  barium 
carbonate.  The  latter  may  be  allowed  to  settle,  and  washed  several  times,  by 
decantation,  with  distilled  water,  until  the  washings  no  longer  yield  a  precipitate 
with  barium  chloride,  showing  that  the  whole  of  the  sodium  sulphate  has  been 
washed  away  and  pure  barium  carbonate  remains. 

Barium  nitrate,  Ba{N03)2,  is  obtained  by  dissolving  the  carbonate  in 
diluted  nitric  acid,  and  evaporating  the  solution,  when  octahedral  crystals 
of  the  nitrate  are  deposited.  It  is  an  ingredient  in  some  kinds  of  blasting 
powder  used  by  miners.  If  barium  nitrate  be  heated  in  a  porcelain  crucible, 
it  fuses  and  is  decomposed,  leaving  a  grey  porous  mass  of  baryta ;  * 
Ba(N03).3  =  BaO  +  2NO2  +  0 . 

Barium  hydrate  may  be  procured  by  adding  4  oz.  of  the  powdered 
barium  nitrate  to  12  oz.  of  a  boiling  solution  of  sodium  hydrate  of  sp.  gr. 
1*13  (prepared  by  dissolving  3  oz.  of  commercial  sodium  hydrate  in  20 
measured  ounces  of  water)  ;  the  solution  becomes  turbid  from  the  separa- 
tion of  barium  carbonate  produced  from  the  sodium  carbonate  in  the 
hydrate  ;  it  is  boiled  for  some  minutes  and  then  filtered  ;  on  partial  cooling, 
some  crystals  of  undecomposed  barium  nitrate  are  deposited,  and  if  the  clear 
liquid  be  poured  off  into  another  vessel  and  stirred,  it  deposits  abundant 
crystals  of  barium  hydrate  having  the  composition  Ba(HO)28Aq. ;  these 
effloresce  and  become  opaque  when  exposed  to  air,  becoming  Ba(H0)2.Aq.  ; 
when  heated  to  redness,  they  become  pure  barium  hydrate  Ba(IIO)o,  which 
fuses,  but  is  not  decomposed  when  further  heated.  The  hydrate  is 
moderately  soluble  in  water,  the  solution  being  strongly  alkaline  and 
absorbing  carbonic  acid  gas  from  the  air,  depositing  barium  carbonate. 

When  baryta  is  heated  in  a  tube  through  which  oxygen  or  air  is  passed, 
it  absorbs  the  oxygen  and  is  converted  into  barium  dioxide  (BaOg), 
which  is  employed  for  the  preparation  of  hydric  peroxide  (see  p.  53). 

Barium  chloride,  which  is  the  barium  compound  most  commonly 
employed  in  the  laboratory,  may  be  obtained  by  dissolving  the  carbonate 
in  diluted  hydrochloric  acid,  and  evaporating  the  solution ;  on  cooling, 
the  chloride  is  deposited  in  tabular  crystals,  BaCl2.2Aq. 

*  Containing,  according  to  Rammelsberg,  much  barium  peroxide. 


276  STRONTIUM — CALCIUM. 

On  the  large  scale,  it  is  generally  manufactured  by  fusing  heavy  spar 
(barium  sulphate)  with  calcium  chloride  (the  residue  from  the  prepara- 
tion of  ammonia,  see  p.  124)  in  a  i-everberatory  furnace — 

BaS04  +  CaClg  =  CaSO^  +  BaCLj. 

The  mass  is  rapidly  extracted  with  hot  water,  which  leaves  the  calcium 
sulphate  undissolved,  and  the  clear  solution  of  barium  chloride  is  decanted 
and  evaporated.  If  the  calcium  sulphate  and  barium  chloride  were 
allowed  to  remain  long  together  in  contact  with  the  water,  barium  sulphate 
and  calcium  chloride  would  be  reproduced. 

Barium  chlorate,  Ba(C103)2,  is  employed  in  the  manufacture  of  fire- 
works, being  prepared  for  that  purpose  by  dissolving  the  artificial  barium 
carbonate  in  solution  of  chloric  acid ;  it  forms  beautiful  shining  tabular 
crystals.  When  mixed  with  combustible  substances,  such  as  charcoal  and 
sulphur,  it  imparts  a  brilliant  green  colour  to  the  flame,  of  the  burning 
mixture  (see  p.  166). 

All  the  soluble  salts  of  barium  are  very  poisonous. 

STRONTIUM. 
Sr"  =  87  '6  parts  by  weight. 

195.  Strontium  is  less  abundant  than  barium,  and  occurs  in  nature  in 
similar  forms  of  combination.  Strontianite,  the  strontium  carbonate 
(SrCOg),  was  first  discovered  in  the  lead  mines  of  Strontian  in  Argyle- 
shire,  and  has  since  been  found  in  small  quantity  in  some  mineral  waters. 

Gelestine  (so  called  from  the  blue  tint  of  many  specimens)  is  the  stron- 
tium sulphate  (SrS04),  and  is  found  in  beautiful  crystals  associated  with 
the  native  sulphur  in  Sicily.  It  is  also  met  with  in  this  country,  and  is 
the  source  from  which  the  strontium  nitrate  employed  in  firework  com- 
positions is  derived.  The  strontium  sulphate  resembles  barium  sulphate 
with  respect  to  its  insolubility,  and  is  converted  into  the  soluble  strontium 
sulphide  (SrS)  by  calcination  with  carbonaceous  matter.  The  solution  of 
strontium  sulphide  so  obtained  is  decomposed  by  nitric  acid,  and  the 
strontium  nitrate  crystallised  from  the  solution.  This  salt  forms  prismatic 
crystals  which  have  the  formula  Sr(N03)2.4Aq.  It  has  the  property  of 
imparting  a  magnificent  crimson  colour  to  flames,  and  is  hence  largely 
used  for  the  preparation  of  red  theatrical  fire  (see  p.  165).  The  other 
compounds  of  strontium  possess  too  little  practical  importance,  and  too 
nearly  resemble  those  of  barium,  to  require  particular  description  here. 

The  metal  itself  is  prepared  in  a  similar  manner  to  metallic  barium, 
Avhich  it  much  resembles,  but  is  lighter  (sp.  gr.  2  "54).  It  burns,  when 
heated  in  air,  with  a  crimson  flame. 

CALCIUM. 

Ca''= 40  parts  by  weight. 

196.  Jfo  other  metal  is  so  largely  employed  in  a  state  of  combination 
as  calcium,  for  its  oxide,  lime  (CaO),  occupies  among  bases  much  the 
same  position  as  that  which  sulphuric  acid  holds  among  the  acids,  and  is 
used,  directly  or  indirectly,  in  most  of  the  arts  and  manufactures. 

Like  barium  and  strontium,  it  is  found,  though  far  more  abundantly 
than  these,  in  the  mineral  kingdom,  in  the  forms  of  carbonate  and  sul- 
phate, but  it  also  occurs  in  large  quantity  as  calcium  fluoride  (p.  181), 


CARBONATE  OF  LIME.  277 

and  less  frequently  in  the  form  of  phosphate  (p.  222).  Calcium,  more- 
over, is  found  in  all  animals  and  vegetables,  and  its  presence  in  their  food, 
in  one  form  or  other,  is  an  essential  condition  of  their  existence. 

Metallic  calcium  may  be  obtained  by  decomposing  fused  calcium  iodide 
with  metallic  sodium.  It  has  a  light  golden-yellow  colour,  is  harder  than 
lead,  and  very  malleable  ;  it  oxidises  slowly  in  air  at  the  ordinary  tempera- 
ture, but  when  heated  to  redness,  it  fuses  and  bums  with  a  very  brilliant 
white  lightj  being  converted  into  lime  {calx).  It  decomposes  water  at 
the  ordinary  temperature.  It  is  lighter  than  barium  and  strontium,  its 
specific  gravity  being  1  -58. 

Carbonate  of  Limb  or  Calcium  Carbonate  (CaO.COg  or  CaCOg), 
from  which  all  the  manufactured  compounds  of  lime  are  derived,  consti- 
tutes the  different  varieties  of  limestone  which  are  met  with  in  such 
abundance. 

Limestones  and  chalk  are  simply  calcium  carbonate  in  an  amorphous  or 
uncrystallised  state.  The  oolite  limestone,  of  which  the  Bath  and  Port- 
land building-stones  are  composed,  is  so  called  from  its  resemblance  to  the 
roe  of  a  fish  (wor,  an  egg).  Marble,  in  its  different  varieties,  is  an  assem- 
blage of  minute  crystalline  grains  of  calcium  carbonate,  sometimes  varie- 
gated by  the  presence  of  oxides  of  iron  and  manganese,  or  of  bituminous 
matter.  This  last  constituent  gives  the  colour  to  black  marble.  Calcium 
carbonate  is  also  found  in  large  transparent  rhombohedral  crystals,  which 
are  known  to  mineralogists  as  calcareutis  spar,  cole  spar,  or  Iceland  spar. 
When  the  crystals  have  the  form  of  a  six-sided  prism,  the  mineral  is 
termed  Arragonite.  The  attention  of  the  crystallographer  has  long  been 
directed  to  these  two  crystalline  forms  of  calcium  carbonate,  on  account 
of  the  circumstance,  that  if  a  prism  of  arragonite  be  heated,  it  breaks  up 
into  a  number  of  minute  rhombohedra  of  calc  spar.  Satin-spar  is  a 
variety  of  calcium  carbonate. 

Calcium  carbonate  is  a  chief  constituent  of  the  shells  of  fishes  and  of 
egg-shells,  so  that,  except  calcium  phosphate,  no  mineral  compound  has 
so  large  a  share  in  the  composition  of  animal  frames.  Corals  also  con- 
sist chiefly  of  calcium  carbonate  derived  from  the  skeletons  of  innumer- 
able minute  insects.  The  mineral  gaylussite  is  a  double  carbonate  of 
calcium  and  sodium  (CaC03,N'a2C03.5Aq.),  and  is  scarcely  affected  by 
water  unless  previously  heated,  when  water  dissolves  out  the  sodium 
carbonate.  Baryto-calcite  is  a  double  carbonate  of  barium  and  calcium 
(BaC03,CaC03). 

Lime  (CaO). — The  process  by  which  lime  is  obtained  from  the  car- 
bonate has  been  already  alluded  to  under  the  name  of  lime-burning.  In 
order  that  the  carbonic  acid  gas  may  be  completely  expelled  from  the  car- 
bonate of  lime,  it  is  necessary  that  the  products  of  combustion  of  the  fuel 
should  be  allowed  to  pass  over  the  limestone,  since,  although  a  very 
intense  heat  is  insufficient  to  decompose  carbonate  of  lime  when  shut  up 
in  a  crucible,  the  decomposition  is  easily  effected  if  the  carbonate  be 
heated  in  a  current  of  atmospheric  air  or  of  any  other  gas,  especially  if 
aqueous  vapour  be  present,  as  is  the  case  in  the  products  of  combustion 
of  the  fuel. 

Accordingly,  a  kiln  is  commonly  employed  of  the  form  of  an  inverted 
cone  of  brick-work  (fig.  236),  and  into  this  limestone  and  fuel  are 
thrown  in  alternate  layers.  The  former,  losing  its  COg  before  it  reaches 
the  bottom  of  the  furnace,  is  raked  out  in  the  form  of  Imrnt  or  quick 


278 


SULPHATE  OF  LIME. 


lime  (CaO),  whilst  its  place  is  supplied  by  a  fresh  layer  of  limestone 
thrown  in  at  the  top  of  the  kiln.  Fig.  237  represents  another  form  of 
kiln,  in  which  the  limestone  is  supported  upon  an  arch  built  with  large 
lumps  of  the  stone  above  the  fire,  which  is  kept  burning  for  about  three 
days  and  nights,  until  the  whole  of  the  limestone  is  decomposed. 


Fig.  236.  — Lime-kilu. 


Fig.  237.— Lime-kiln. 


The  usual  test  of  the  quality  of  the  lime  thus  obtained  consists  in 
sprinkling  it  with  water,  with  which  it  should  eagerly  combine,  evolving 
much  heat,*  swelling  greatly,  and  crumbling  to  a  light  white  powder  of 
caldum  hydrate  {slaked  lime)  Ca(H0)2.  Lime  which  behaves  in  this 
manner  is  termed /a^  lime;  whereas,  if  it  be  found  to  slake  feebly,it  is 
pronounced  a  poor  lime,  and  is  known  to  contain  considerable  quantities 
of  foreign  substances,  such  as  silica,  alumina,  magnesia,  &c.  Lime  is  said 
to  be  overhurnt  when  it  contains  hard  cinder-like  masses  of  silicate  of  lime, 
formed  by  the  combination  of  the  silica,  which  is  generally  found  in 
limestone,  with  a  portion  of  the  lime,  under  the  influence  of  excessive 
heat  in  the  kiln. 

The  calcium  hydrate  is  about  twice  as  soluble  in  cold  as  it  is  in  hot 
water,  so  that  Ume-icater  should  always  be  made  by  shaking  slaked  lime 
with  cold  distilled  water,  which  dissolves  about  l'700th  of  its  weight ; 
the  solution  is  allowed  to  settle  in  a  closed  bottle,  for  it  absorbs  carbonic 
acid  gas  rapidly  from  the  air.  Crystals  of  calcium  hydrate  have  been 
obtained  by  evaporating  lime-water  in  vacuo. 

Sulphate  of  Lime,  or  Calcium  Sulphate,  in  combination  with  water 
(CaS04.2H20),  is  met  with  in  nature,  both  in  the  form  of  transparent 
prisms  of  selenite,  and  in  opaque  and  semi-opaque  masses  known  as 
alabaster  and  gypsum.  It  is  this  latter  form  which  yields  plaster  of 
Paris,  for  when  heated  to  between  300°  and  400°  F.,  it  loses  about  two- 
thirds  of  its  water,  becoming  3CaS04.2H20,  and  if  the  mass  be  then 
jjowdered,  and  again  mixed  with  water,  the  powder  recombines  with  it 
to  form  a  mass,  the  hardness  of  which  nearly  equals  that  of  the  original 
gypsum. 

In  the  preparation  of  plaster  of  Paris,  a  number  of  large  lumps  of 
gypsum  are  built  up  into  a  series  of  arches,  upon  which  the  rest  of  the 

*  Tlie  sudden  slaking  of  a  large  quantity  of  lime  is  a  common  cause  of  fire. 


CHLORIDE  OF  CALCIUM.  279 

gypsum  is  supported ;  under  these  arches  the  fuel  is  burnt,  and  its  flame 
is  allowed  to  traverse  the  gypsum,  care  being  taken  that  the  temperature 
does  not  rise  too  high,  or  the  gypsum  is  overburnt,  and  does  not  exhibit 
the  property  of  recombining  with  water.  When  the  operation  is  supposed 
to  be  completed,  the  lumps  are  carefully  sorted,  and  those  which  appear 
to  have  been  properly  calcined  are  ground  to  a  very  fine  powder.  When 
this  powder  is  mixed  with  water  to  a  cream,  and  poured  into  a  mould, 
the  minute  particles  of  calcium  sulphate  combine  with  water  to  reproduce 
the  original  gypsum  (CaS04.2H20),  and  this  act  of  combination  is 
attended  with  a  slight  expansion  which  forces  the  plaster  into  the  finest 
lines  of  the  mould.  If  the  setting  of  plaster  of  Paris  be  watched  with 
the  microscope,  the  gradual  crystallisation  may  be  perceived.  The  ocei'- 
hurnt  plaster  will  not  crystallise  unless  mixed  Avith  good  plaster,  when  the 
crystallisation  pervades  both.  An  addition  of  one-tenth  of  lime  to  the 
plaster  hardens  it  and  acclerates  the  setting. 

Stucco  consists  of  plaster  of  Paris  (occasionally  coloured)  mixed  with  a 
solution  of  size  ;  certain  cements  used  for  building  purposes  (Keene's  and 
Keating's  cements)  are  prepared  from  burnt  gypsum,  which  has  been 
soaked  in  a  solution  of  alum  and  again  burnt ;  and  although  the  plaster 
thus  obtained  takes  much  longer  to  set  than  the  ordinary  kind,  it  is  much 
harder,  and  therefore  takes  a  good  polish. 

Plaster  of  Paris  is  much  damaged  by  long  exposure  to  moist  air,  from 
which  it  regains  a  portion  of  its  water,  and  its  property  of  setting  is  so  far 
diminished. 

Precipitated  calcium  sulphate  is  used  by  paper-makers  under  the  name 
oi  pearl  hardener. 

CaSO^  forms  the  mineral  anhydrite,  a  bed  of  which,  when  exposed  to 
the  air  in  a  railway  cutting,  has  been  known  to  increase  in  bulk  by  absorb- 
ing water  to  such  an  extent  as  to  disturb  the  stability  of  the  sides  of  the 
cutting. 

Calcium  chloride  (CaClo)  has  been  mentioned  as  the  residue  left  in 
the  preparation  of  ammonia.  The  pure  salt  may  be  obtained  by  dissolving 
pure  calcium  carbonate  (white  marble)  in  hydrochloric  acid,  and  evaporat- 
ing the  solution,  when  prismatic  crystals  of  the  composition  CaCl^-BAq. 
are  obtained.  When  these  are  heated  they  melt,  and  at  about  390°  F. 
are  converted  into  a  white  porous  mass  of  CaCl9.2Aq.,  which  is  much 
used  for  drying  gases.  At  a  higher  temperature,  fused  calcium  chloride, 
free  from  water,  is  left ;  this  is  very  useful  for  removing  water  from  some 
liquids.  A  saturated  solution  of  calcium  chloride  boils  at  355°  F.,  and 
is  sometimes  used  as  a  convenient  bath  for  obtaining  a  temperature  above 
the  boiling-point  of  water.  In  consequence  of  the  attraction  of  calcium 
chloride  for  water,  surfaces  wetted  with  a  solution  of  the  salt  never  get 
dry.  Eope  mantlets,  for  the  protection  of  gunners,  are  saturated  with  it 
to  prevent  their  taking  fire. 

When  calcium  hydrate  is  boiled  with  a  strong  solution  of  calcium 
chloride,  it  is  dissolved,  and  the  filtered  solution  deposits  prismatic  crystals 
of  calcium  oxi/chloride,  CaCl2.3CaO.l6Aq.,  which  are  decomposed  by 
pure  water. 

Ccdcium  sidphide  (CaS)  has  lately  acquired  some  importance,  on  account 
of  its  presence  in  Balmain's  Lvminous  Paint.  Its  property  of  shining 
in  the  dark  after  the  exposure  to  a  bright  light  was  observed  by  Canton 
in  1761 ;  his  so-called  phosphorus  was  obtained  by  strongly  heating  oyster- 


^80  ATOMIC  HEATS. 

shells  with  sulphur.  The  phosphorescence  is  not  due  to  slow  oxidation, 
since  a  specimen  which  has  been  kept  for  more  than  a  century  in  a 
sealed  tube  still  exhibits  it. 

197.  General  review  of  the  metals  of  the  alkaline  eartlis, — Barium, 
strontium,  and  calcium  form  a  highly  interesting  natural  group  of  metals 
related  to  each  other  in  a  most  remarkable  manner.  They  exhibit  a 
marked  gradation  in  their  attraction  for  oxygen ;  barium  is  more  readily 
tarnished  or  oxidised,  even  in  dry  air,  than  strontium,  and  strontium  more 
readily  than  calcium.  The  hydrates  of  the  metals  exhibit  a  similar 
gradation  in  properties ;  barium  hydrate  does  not  lose  its  water,  however 
strongly  it  may  be  heated,  whereas  the  hydrates  of  strontium  and  calcium 
are  decomposed  at  a  red  heat.  Then  barium  hydrate  and  strontium 
hydrate  are  far  more  soluble  in  water  than  calcium  hydrate  (which  requires 
about  700  parts  of  water  to  dissolve  it),  and  all  these  three  exhibit  a  very 
decided  alkaline  reaction  which  entitles  them  to  the  name  of  alkaline  earths. 

Among  the  other  compounds  of  these  metals,  the  sulphates  may  be 
named  as  presenting  a  gradation  of  a  similar  description ;  for  barium 
sulphate  may  be  said  to  be  insoluble  in  water,  strontium  sulphate  dissolves 
to  a  very  slight  extent,  and  calcium  sulphate  is  rather  more  soluble. 

The  manner  in  which  these  metals  are  associated  in  nature  is  also  not 
without  its  significance ;  for  if  two  of  them  are  found  in  the  same 
mineral,  they  will  usually  be  those  which  stand  next  to  each  other  in 
the  group  ;  thus  strontium  carbonate  is  found  together  with  barium 
carbonate  in  witherite,  whilst  calcium  carbonate  is  associated  with  strontium 
sulphate  in  celestine.  Again,  strontium  carbonate  is  often  found  with 
calcium  carbonate  in  arragonite. 

198.  Relation  between  specific  heats  and  atomic  weights — Atomic  heats. 
— Since  the  specific  volumes  of  the  vapours  of  these  metals  have  not  been 
ascertained,  recourse  is  had  to  their  specific  heat3  in  order  to  ascertain 
their  atomic  weights.  It  will  be  remembered  that  the  specific  heat  of 
a  substance  is  the  quantity  of  heat  required  to  raise  it  1°  in  tempera- 
ture, as  compared  with  the  quantity  of  heat  required  to  raise  an  equal 
weight  of  water  1° ;  or,  more  concisely,  the  quantity  of  heat  required 
to  raise  one  part  by  weight  of  the  substance  1°  (refeired  to  water  as  the 
unit). 

Thus,  the  specific  heats  of  potassium,  sodium,  and  lithium  are,  respec- 
tively, 0-1696,  0'2934,  and  0*9408  ;  these  numbers  representing  the 
relative  quantities  of  heat  required  to  raise  one  part  by  weight  of  each 
of  these  metals  1°  in  temperature,  supposing  that  an  equal  weight  of 
water  would  be  raised  1°  by  a  quantity  of  heat  expressed  by  one.  No 
simple  relation  can  be  traced  between  these  numbers,  but  if  the  quan- 
tities of  heat  be  calculated  which  are  required  to  raise  atomic  weights  of 
these  elements  1°,  the  case  will  be  difierent. 

If  0*1696  be  the  quantity  of  heat  required  to  raise  one  part  by  weight 
of  potassium  1°;  0*1696  x  39,  or  6*61,  will  represent  the  quantity  of  heat 
required  to  raise  39  parts  (1  atom)  of  potassium  1°.  In  the  same  way, 
0*2934  X  23,  or  6*75,  is  the  quantity  of  heat  required  to  raise  23  parts 
(1  atom)  of  sodium  1° ;  and  0*9408  x  7,  or  6*59,  is  the  quantity  required 
to  raise  7  parts  (1  atom)  of  lithium  1°.  Allowing  for  experimental  error  in 
the  determination  of  the  specific  heats,  these  numbers,  6*61,  6*75,  and 
6*59,  may  be  regarded  as  representing  the  same  quantities  of  heat,  and 


MAGNESIUM.  281 

they  are  the  atomic  heats  of  these  metals,  that  is,  the  relative  quantities 
of  heat  required  to  raise  an  atom  of  each  1°  in  temperature. 

The  atomic  heat,  therefore,  which  is  common  to  these  three  metals  may 
be  represented  by  the  mean  of  the  three  numbers,  or  6  "65. 

The  experiments  which  have  been  made  to  determine  the  specific  heats 
of  those  elements  which  can  be  obtained  in  a  similar  physical  condition, 
lend  strong  support  to  the  belief  that  the  atomic  heats  of  all  elements 
belonging  to  the  same  group  are  identical,  and  even  hold  out  a  prospect 
of  the  identity  of  the  atomic  heats  of  a  great  majority  of  the  elementary 
bodies. 

A  similar  relation  has  been  observed  between  the  atomic  heats  of  com- 
pound bodies  belonging  to  the  same  group  ;  thus,  if  the  specific  heats  of 
the  chlorides  of  potassium,  sodium,  and  lithium  be  multiplied  by  the 
atomic  weights  of  those  chlorides,  the  product  in  each  case  will  approach 
very  nearl}^  to  the  number  12 '69.  If  these  chlorides  be  allowed  to  con- 
tain one  atom  of  each  of  their  constituents,  and  it  be  supposed  that  the 
atomic  heats  of  these  constituents  are  identical,  the  half  of  this  number 
(or  6-34)  should  represent  the  atomic  heat  of  the  alkali-metals,  and,  in 
fact,  it  does  nearly  coincide  with  that  number. 

The  specific  heats  of  barium,  strontium,  and  calcium  have  not  been 
determined,  and  therefore  their  atomic  heats  cannot  be  directly  ascer- 
tained. 

The  specific  heats  of  the  chlorides  of  barium,  strontium,  and  calcium 
have  been  ascertained  to  be  represented  by  the  numbers  0*0900,  O'llSO, 
and  0'1686  respectively.  Now,  the  atomic  heats  of  the  chlorides,  obtained 
by  multiplying  their  atomic  weights  into  their  specific  heats,  would  be 
expressed  by  the  mean  number  18-72  ;  dividing  this  by  3,  the  presumed 
number  of  atoms  in  the  chloride,  we  obtain  the  number  6-24  for  the 
atomic  heat  of  each  of  the  elements,  which  agrees  very  well  with  that 
calculated  for  the  alkali-metals. 

MAGXESirjM. 

Mg"=24-3  parts  by  weight. 

199.  Magnesium  is  found,  like  calcium,  though  less  abundantly,  in 
each  of  the  three  natural  kingdoms.  Among  minerals  containing  this 
metal,  those  with  which  we  are  most  familiar  are  certain  combinations  of 
silica  and  magnesia  (silicates  of  magnesia)  known  by  the  names  of  talc, 
steatite  or  French  chalk,  asbestos,  and  meerschaum,  which  always  contains 
Avater.  Magnesite  is  a  carbonate  of  magnesium.  !Most  of  the  minerals 
containing  magnesium  have  a  remarkably  soapy  feeL  The  compounds  of 
magnesium,  which  are  employed  in  medicine,  are  derived  either  from  the 
mineral  dolomite  or  magnesian  limesto7ie  which  contains  the  carbonates 
of  magnesium  and  calcium,  or  from  the  magnesium  sulphate  which  is 
obtained  from  sea  water  and  from  the  waters  of  many  mineral  springs. 

Metallic  magnesium  has  acquired  some  importance  during  the  last  few 
years  as  a  source  of  light.  When  the  extremity  of  a  wire  of  this  metal 
is  heated  in  a  tiame,  it  takes  fire,  and  burns  with  a  dazzling  white  light, 
becoming  converted  into  magnesia  (MgO).  If  the  burning  wire  be  plunged 
into  a  bottle  of  oxygen,  the  combustion  is  still  more  brilliant.  The  light 
emitted  by  burning  magnesium  is  capable  of  inducing  chemical  changes 
similar  to  those  caused  by  sunlight,  a  circumstance  turned  to  advantage 


282  SULPHATE  OF  MAGNESIA.      " 

for  the  production  of  photographic  pictures  by  night.  Attempts  have 
been  made  to  introduce  magnesium  as  an  illuminating  agent  for  general 
purposes,  but  the  large  quantity  of  solid  magnesia  produced  in  its  com- 
bustion forms  a  very  serious  obstacle  to  its  use.  The  metal  is  extracted 
from  magnesium  chloride  (see  p.  118)  by  fusing  it  with  sodium,  using 
sodium  chloride  and  calcium  fluoride  to  promote  the  fusibility  of  the 
mass. 

On  a  small  scale,  magnesium  may  be  prepared  by  mixing  900  grs.  of  magnesium 
chloride  with  150  grs.  of  calcium  fluoride,  1.50  of  fused  sodium  chloride,  and  150  of 
sodium  cut  into  slices  (see  p.  119).  The  mixture  is  thrown  into  a  red  hot  earthen 
crucible,  which  is  then  covered  again  and  heated.  When  the  action  appears  to  have 
terminated,  the  fused  mass  is  stirred  with  an  iron  rod  to  promote  the  union  of  the 
globules  of  magnesium.  It  is  then  poured  upon  an  iron  tray,  allowed  to  solidify, 
broken  up,  and  the  globules  of  magnesium  separated  from  the  slag  ;  they  may  be 
collected  into  one  globule  by  throwing  them  into  a  melted  mixture  of  chlorides  of 
magnesium  and  sodium  and  fluoride  of  calcium. 

In  most  of  its  physical  and  chemical  characters,  magnesium  resembles 
zinc,  though  its  colour  more  nearly  approaches  that  of  silver ;  in  ductility 
and  malleability  it  also  surpasses  zinc.  It  is  nearly  as  light,  however, 
as  calcium,  its  specific  gravity  being  1  'T^  It  fuses  below  a  red  heat, 
and  may  be  distilled  like  zinc.  Cold  water  has  scarcely  any  action 
upon  magnesium ;  even  when  boiled  it  oxidises  the  metal  very  slowly. 
In  the  presence  of  acids,  however,  it  is  rapidy  oxidised  by  water. 
Solution  of  ammonium  chloride  also  dissolves  it,  owing  to  the  tendency 
of  the  magnesium  salts  to  form  double  salts  with  those  of  ammonium ; 
4NH4Cl  +  Mg  =  (NH4)2MgCl4  +  H2  +  2NH3.  Magnesium  is  one  of  the 
few  elements  which  unite  directly  with  nitrogen  at  a  high  temperature. 
The  magnesium  nitride,  MggNg,  has  been  obtained  in  transparent  crystals, 
and  is  evidently  composed  after  the  type  2NH3,  so  that  it  is  not  surprising 
that  the  action  of  water  upon  it  gives  rise  to  magnesia  and  ammonia; 
Mg^Ng  +  3  HgO  =  2NH3  +  3MgO. 

If  a  foot  of  magnesium  tape  be  burnt  in  air,  the  residue  evolves  much 
ammonia  when  boiled  with  water. 

The  sulphate  of  magnesia  or  magnesium  sulphate,  so  well  known  as 
Epsom  salts,  is  sometimes  prepared  by  calcining  dolomite  to  expel  the 
carbonic  acid  gas,  washing  the  residual  mixture  of  lime  and  magnesia 
with  water  to  remove  part  of  the  lime,  and  treating  it  with  sulphuric 
acid,  which  converts  the  calcium  and  magnesium  into  sulphates ;  and  since 
calcium  sulphate  is  almost  insoluble  in  water,  it  is  readily  separated  from 
the  magnesium  sulphate  which  passes  into  the  solution,  and  is  obtained  by 
evaporation  in  prismatic  crystals,  having  the  composition  MgSO^HgO.  6Aq. 
The  preparation  of  Epsom  salts  from  sea  water  has  already  been  alluded 
to  (p.  261).  In  some  parts  of  Spain  magnesium  sulphate  is  found  in 
large  quantities  (like  nitre  in  hot  climates)  as  an  efflorescence  upon  the 
surface  of  the  soil.  This  sulphate,  as  well  as  that  contained  in  well-waters, 
appears  to  have  been  produced  by  the  action  of  the  calcium  sulphate, 
originally  present  in  the  water,  upon  magnesian  limestone  rocks ; 
MgCOg  +  CaSO^  =  MgSO^  +  CaCOg. 

The  water  of  constitution  in  the  magnesium  sulphate  may  be  displaced 
by  the  sulphate  of  an  alkali-metal  without  alteration  in  its  crystalline  form; 
a  double  sulphate  of  magnesium  and  potassium  (MgSO^.Kg^O^GAq.), 
and  a  similar  salt  of  ammonium  may  be  thus  obtained.  The  mineral 
pohjlialite    (ttoXv's,   many,    oAs,   salt)   is   a   remarkable    salt,   containing 


CHLORIDE  OF  MAGNESIUM.  283 

^rgSO^.K2S042CaS04,2H20.*  Water  decomposes  it  into  its  constituent 
salts. 

The  preparation  commonly  used  in  medicine  under  the  name  of  mag- 
nesia, is  really  a  basic  magnesium,  carbonate,  or  a  compound  of  magnesium 
carbonate  with  magnesium  hydrate  and  water,  in  the  porportions  expressed 
by  the  formula,  5MgC03.2Mg(HO)2.7Aq.  It  is  obtained  by  mixing  boil- 
ing solutions  of  magnesium  sulphate  and  sodium  carbonate,  when  one- 
fourth  of  the  carbon  dioxide  is  expelled  in  the  state  of  gas  ;  the  white 
precipitate  is  thrown  upon  a  cloth  strainer,  well  washed,  and  dried  in 
rectangular  moulds. 

Another  process  for  preparing  magnesium  carbonate  consists  in  heating 
magnesian  limestone  to  low  redness,  so  as  to  decompose  the  magnesium 
carbonate  which  it  contains,  and  exposing  it,  under  pressure,  to  the  action 
of  water  and  carbonic  acid,  which  dissolves  the  magnesia  and  leaves  the 
calcium  carbonate.  On  boiling  the  solution,  to  expel  the  excess  of  car- 
bonic acid  gas,  the  magnesium  carbonate  is  precipitated. 

By  moderately  heating  the  carbonate,  its  water  and  carbonic  acid  gas 
are  expelled,  and  pure  or  calcined  magnesia  (MgO)  is  left,  which  is  very 
slightly  soluble  in  water  and  feebly  alkaline. 

The  mineral  periclase  consists  of  magnesia  in  a  crystallised  form.  Mag- 
nesia combines  with  water  to  form  a  hydrate,  Mg(H0)2,  but  not  with 
evolution  of  heat,  as  in  the  cases  of  baryta,  strontia,  and  lime.  Crys- 
tallised magnesium  hydrate  constitutes  the  mineral  binicite.  Magnesia, 
like  lime,  is  remarkable  for  its  infusibility. 

It  has  recently  been  noticed  that  calcined  magnesia,  when  mixed  with 
water,  solidifies  after  a  time  into  a  very  hard,  compact  mass  of  magnesium 
hydrate,  and  may  serve,  like  plaster  of  Paris,  for  taking  casts.  Dolomite 
calcined  below  redness  also  sets  to  a  very  hard  mass  with  water. 

The  magnesiu7n  orthophosphate,  Mg3(P04)2  enters  into  the  composi- 
tion of  bones,  and  the  phosphate  of  magnes:ium  and  ammonium,  or  triple 
pthosphate  (MgNHj^HPO^),  is  found  in  calculi  stud  in  the  minerals  guanite 
and  siruvite. 

Magnesium  borate  composes  the  mineral  boracite;  hydrohoracite  is  a 
hydrated  borate  of  calcium  and  magnesium. 

Serpentine  and  olivine  are  silicates  of  magnesia  and  ferrous  oxide. 
Some  of  the  varieties  of  serpentine  are  employed  for  preparing  the  com- 
pounds of  magnesium,  for  they  are  easily  decomposed  by  acids  with 
separation  of  silica. 

Pearl  spar  is  a  crystallised  carbonate  of  calcium  and  magnesium. 

Magnesium  chloride  is  important  as  the  source  of  metallic  magnesium. 
It  is  easily  obtained  in  solution  by  neutralising  hydrochloric  acid  with 
magnesia  or  its  carbonate,  but  if  this  solution  be  evaporated  in  order  to 
obtain  the  dry  chloride,  a  considerable  quantity  of  the  salt  is  decomposed 
by  the  water  at  the  close  of  the  evaporation,  leaving  much  magnesia 
mixed  with  the  chloride  {MgCl2  +  H^O  =  2HC1  +  MgO).  This  decomposi- 
tion may  be  prevented  by  mixing  the  solution  with  three  parts  of 
cliloride  of  ammonium  for  every  part  of  magnesia,  when  a  double  salt, 
MgCl2.2NH4Cl,  is  formed,  which  may  be  evaporated  to  dryness  without 
decomposition,  and  leaves  fused  magnesium  chloride  when  further  heated, 
the    ammonium   chloride   being   volatilised.     The    magnesium   chloride 

*  Polyhalite  and  kifserite,  MgS04,H„0,  are  found  in  the  salt-beds  of  Stassfurth.  Kainite, 
from  the  same  locality,  isKaSO^.MgSO^.MgCla.SAq. 


284  ZINC. 

absorbs  moisture  very  rapidly  from  the  air,  and  is  very  soluble  in  water. 
Like  all  the  soluble  salts  of  magnesium,  it  has  a  decidedly  bitter  taste. 
When  magnesia  is  moistened  with  a  strong  solution  of  magnesium 
chloride,  it  sets  into  a  hard  mass  like  plaster  of  Paris,  apparently  from  the 
formation  of  an  oxy chloride,  MgO.MgClg.  It  may  be  mixed  with  several 
times  its  weight  of  sand,  and  will  bind  it  firmly  together. 

ZINC. 

Zu"  =  65  parts  by  weight. 

200.  Zinc  occupies  a  high  position  among  useful  metals,  being  peculiarly 
fitted,  on  account  of  its  lightness,  for  the  construction  of  gutters,  water- 
pipes,  and  roofs  of  buildings,  and  possessing  for  these  purposes  a  great 
advantage  over  lead,  since  the  specific  gravity  of  the  latter  metal  is  about 
11*5,  whilst  that  of  zinc  is  only  6 '9.  For  such  applications  as  these, 
where  great  strength  is  not  required,  zinc  is  preferable  to  iron,  on  account 
of  its  superior  malleability  ;  for  although  a  bar  of  zinc  breaks  under 
the  hammer  at  the  ordinary  temperature,  it  becomes  so  malleable  at 
250°  F.  as  to  admit  of  being  rolled  into  thin  sheets.  This  malleability 
of  zinc  when  heated  was  discovered  only  in  the  commencement  of  this 
century,  until  which  time  the  only  use  of  the  metal  was  in  the  manufac- 
ture of  brass.  When  zinc  is  heated  to  400°  F.,  it  again  becomes  brittla 
The  easy  fusibility  of  zinc  also  gives  it  a  great  advantage  over  iron,  as 
rendering  it  easy  to  be  cast  into  any  desired  form;  indeed,  zinc  is 
surpassed  in  fusibility  (among  the  metals  in  ordinary  use)  only  by  tin 
and  lead,  its  melting-point  being  below  a  red  heat,  and  usually  estimated 
at  770°  F.  Zinc  is  also  less  liable  than  iron  to  corrosion  under  the 
influence  of  moist  air,  for  although  a  bright  surface  of  zinc  soon 
tarnishes  when  exposed  to  the  air,  it  merely  becomes  covered  with  a  thin 
film  of  zinc  oxide  (passing  gradually  into  basic  carbonate,  by  absorp- 
tion of  carbonic  acid  from  the  air)  which  protects  the  metal  from  further 
action. 

The  great  strength  of  iron  has  been  ingeniously  combined  with  the 
durability  of  zinc,  in  the  so-called  galvanised  iron,  which  is  made  by  coat- 
ing clean  iron  with  melted  zinc,  thus  affording  a  protection  much  needed 
in  and  around  large  towns,  where  the  sulphurous  and  sulphuric  acids 
arising  from  the  combustion  of  coal,  and  the  acid  emanations  from 
various  factories,  greatly  accelerate  the  corrosion  of  unprotected  iron. 
The  iron  plates  to  be  coated  are  first  thoroughly  cleansed  by  a  process 
which  will  be  more  particularly  noticed  in  the  manufacture  of  tin-plate, 
and  are  then  dipped  into  a  vessel  of  melted  zinc,  the  surface  of  which  is 
coated  with  sal  ammoniac  (ammonium  chloride)  in  order  to  dissolve  the 
zinc  oxide  which  forms  upon  the  surface  of  the  melted  metal,  and  might 
adhere  to  the  iron  plate  so  as  to  prevent  its  becoming  uniformly  coated 
with  the  zinc*  A  more  firmly  adherent  coating  of  zinc  is  obtained  by 
first  depositing  a  thin  film  of  tin  upon  the  surface  of  the  iron  plate  by 
galvanic  action,  and  hence  the  name  galvanised  iron. 

The  ores  of  zinc  are  found  pretty  abundantly  in  England,  chiefly  in 
the  Mendip  Hills  in  Somersetshire,  at  Alston  Moor  in  Cumberland,  in 

*  The  sal  ammoniac  acts  upon  the  heated  zinc  according  to  the  equation,  Zn  +  2NH4C1 
=  ZnC']o4-2NH3+H2,  and  the  zinc  chloride  which  is  formed  dissolves  the  oxide  from  the 
surface  of  the  metal,  producing  zinc  oxychloride. 


EXTRACTION  OF  ZINC.  285 

CorQwall,  and  Derbyshire,  but  the  greater  part  of  the  zinc  used  in  this 
country  is  imported  from  Belgium  and  Germany,  being  derived  from  the 
ores  of  Transylvania,  Hungary,  and  Silesia. 

Metallic  zinc  is  never  met  with  in  nature.  Its  chief  ores  are  calamine 
or  zinc  carbonate  (ZnCOg),  blende  or  zinc  sulphide  (ZnS),  and  red  zinc  ore, 
in  which  zinc  oxide  (ZnO)  is  associated  with  the  oxides  of  iron  and 
manganese. 

Calamine  is  so  called  from  its  tendency  to  form  masses  resembling  a 
bundle  of  reeds  [calamus,  a  reed).  It  is  found  in  considerable  quantities 
in  Somersetshire,  Cumberland,  and  Derbyshire.  A  compound  of  car- 
bonate with  hydrate  of  zinc,  ZnCOg.  2Zn(HO)2,  is  found  abundantly  in 
Spain.  The  mineral  known  as  electric  calaiaine  is  a  silicate  of  zinc 
(•2ZnO.SiOo.H.20).  Blende  derives  its  name  from  the  German  Llenden, 
to  dazzle,  in  allusion  to  the  brilliancy  of  its  crystals,  which  are  gene- 
rally almost  black  from  the  presence  of  iron  sulphide,  the  true  colour  of 
pure  zinc  sulphide  being  white.  Blende  is  found  in  Cornwall,  Cumber- 
land, Derbyshire,  Wales,  and  the  Isle  of  Man,  and  is  generally  associated 
with  galena  or  lead  sulphide,  which  is  always  carefully  picked  out  of  the 
ore  before  smelting  it,  since  it  would  become  converted  into  lead  oxide, 
which  corrodes  the  earthen  crucibles  employed  in  the  process. 

In  England  the  extraction  of  zinc  from  its  ores  is  carried  on  chiefly  at 
Swansea,  Birmingham,  and  Sheiiield.  Before  extracting  the  metal  from 
these  ores,  they  are  subjected  to  a  preliminary  treatment  Avhich  brings 
them  both  to  the  condition  of  zinc  oxide.  For  this  purpose  the  calamine 
is  simply  calcined  in  a  reverberatory  furnace,  in  order  to  expel  carbonic 
acid  gas ;  but  the  blende  is  roasted  for  ten  or  twelve  hours,  with  constant 
stirring,  so  as  to  expose  fresh  surfaces  to  the  air,  when  the  sulphur  passes 
off  in  the  form  of  sulphurous  acid  gas,  and  its  place  is  taken  by  the 
oxygen,  the  ZnS  becoming  ZnO.  The  extraction  of  the  metal  from  this 
zinc  oxide  depends  upon  the  circumstance  that  zinc  is  capable  of  being 
distilled  at  a  bright  red  heat,  its  boiling-point  being  1904°  F. 

The  facility  with  which  this  metal  passes  olf  in  the  form  of  vapour  is 
seen  when  it  is  melted  in  a  ladle  over  a  brisk  fire,  for  at  a  bright  red 
heat  abundance  of  vapour  rises  from  it,  which,  taking  fire  in  the  air, 
burns  with  a  brilliant  greenish-white  light,  throwing  off  into  the  air 
numerous  white  flakes  of  light  zinc  oxide  (the  philosopher's  wool,  or  nil 
album  of  the  old  chemists). 

The  distillation  of  zinc  may  be  effected  on  the  small  scale  in  a  black-lead  crucible 
(A,  fig.  238)  about  5  inches  high  and  3  in  diameter,  A  hole  is  drilled  through  the 
bottom  with  a  round  file,  and  into  this  is  fitted  a  piece  of  wrought-iron  gas-pipe  (B) 
about  9  inches  long  and  1  inch  wide,  so  as  to  reach  nearly  to  the  top  of  the  inside  of 
the  crucible.  Any  crevices  between  the  pipe  and  the  sides  of  the  hole  are  carefully 
stopped  up  with  fireclay  moistened  with  solution  of  borax.  A  few  ounces  of  zinc 
are  introduced  into  the  crucible,  the  cover  of  which  is  then  carefully  cemented  on 
with  fireclay  (a  little  borax  being  added  to  bind  it  together  at  a  high  temperature), 
and  the  hole  in  the  cover  is  stopjied  up  with  fireclay.  The  crucible  having  been 
kept  for  several  hours  in  a  warm  place,  so  that  the  clay  may  dry,  it  is  j^laced  in  a 
cylindrical  furnace  with  a  hole  at  tlie  bottom,  through  which  the  iron  pipe  may  pass, 
and  a  lateral  opening  into  which  is  inserted  an  iron  tube  (0)  connected  with  a  forge 
bellows.  Some  lighted  charcoal  is  thrown  into  the  furnace,  and  when  this  has  been 
blown  into  a  blaze,  the  furnace  is  filled  up  with  coke  broken  into  small  pieces.  The 
fire  is  then  blown  till  the  zinc  distils  freely  into  a  vessel  of  water  placed  for  its  recep- 
tion.    Four  ounces  of  zinc  may  be  easily  distilled  in  half  an  hour. 

English  method  of  extracting  zinc. — The  zinc  oxide,  obtained  as  above 


286 


EXTRACTION  OF  ZINC  FROM  ITS  ORES. 


from  calamine  or  blende,  is  mixed  with  about  half  its  weight  of  coke  or 
anthracite  coal.  This  mixture  is  introduced  into  large  crucibles  (fig.  239) 
with  a  hole  in  the  bottom  through  which  passes  a  short  wide  iron  pipe 
destined  for  the  passage  of  the  vapour  of  zinc.  These  crucibles  are 
about  4  feet  high  by  2\  feet  wide.  Some  large  pieces  of  coke  are  first 
introduced  into  them  to  prevent  the  charge  from  passing  into  the  iron 
pipes,  and  when  they  have  been  charged  with  the  above  mixture,  their 
covers  are  cemented  on,  and  they  are  heated  in  furnaces  somewhat 
resembling  those  of  a  glass-house,  each  furnace  receiving  six  crucibles, 
which  generally  contain,  in  all,  one  ton  of  roasted  ore.  When  the  mixture 
in  the  crucibles  is  heated  to  redness,  it  begins  to  evolve  carbonic  oxide 


Fig.  238. — Distillation  of  zinc. 


Fig.  239. — English  zinc  furnace. 


produced  by  the  combination  of  the  carbon  with  the  oxygen  from  the  zinc 
oxide.  This  gas  burns  with  a  blue  flame  at  the  mouth  of  the  iron  pipe; 
but  at  a  bright  red  heat  the  metallic  zinc  which  has  been  thus  liberated 
is  converted  into  vapour,  and  the  greenish-white  flame  of  burning  zinc  is 
perceived  at  the  orifice.  When  this  is  the  case,  about  8  feet  of  iron  pipe 
are  joined  on  to  the  short  piece,  in  order  to  condense  the  vapour  of  zinc, 
which  falls  into  a  vessel  placed  for  its  reception.  The  dist'dlation  occupies 
about  sixty  hours,  and  the  average  yield  is  about  35  parts  of  zinc  from 
100  of  ore,  a  considerable  quantity  of  zinc  being  left  behind  in  the  form 
of  zinc  silicate  (electric  calamine),  which  is  reduced  with  difiiculty  by 
distillation  with  carbon. 

The  zinc  thus  obtained,  however,  is  mixed  with  a  considerable  quantity 
of  zinc  oxide,  and  with  other  foreign  matters  carried  over  from  the 
crucibles.  It  is,  therefore,  again  melted  in  a  large  iron  pan,  and  allowed 
to  rest,  in  order  that  the  dross  may  rise  to  the  surface ;  this  is  skimmed 
off,  to  be  worked  over  again  in  a  fresh  operation,  and  the  metal  is  cast 
into  ingots,  which  are  sent  into  commerce  under  the  name  of  spelter. 

Belgian  process  for  the  extraction  of  zinc. — At  the  Vieille-Montagne 
works,  near  Liege,  calamine  is  exposed  to  the  rain  for  several  months  in 
order  to  wash  out  the  clay ;  it  is  then  calcined  to  expel  the  water  and 
carbonic  acid  gas,  the  zinc  oxide  so  obtained  being  mixed  with  half  its 


EXTKACTION  OF  ZINC  IN  SILESIA. 


287 


Fig.  240.— Belgian 
zinc  furnace. 


weiglit  of   coal  dust,  and  distilled  in  fireclay  cylinders  (C,  fig.    240), 

holding  about  40  lbs.  each,  and  set  in  seven  tiers  of  six  each  in  the 

same  furnace,  the  vapour  of  zinc  being  conveyed  by 

a   short   conical   iron   pipe  (B)  into   a  conical  iron 

receiver  (D),  which  is  emptied  every  two  hours  into 

a  large  ladle,  from  which   the   zinc  is    poured  into 

ingot  moulds.     Each  distillation  occupies  about  twelve 

hours.     The  advantage   of    this   particular   mode    of 

arranging  the  cylinders  is,  that  it  economises  fuel  by 

allowing  the  poorer  ores,  which  require  less  heat  to 

distil  all  the  zinc  from  them,  to  be  introduced  into 

the  upper  rows  of  cylinders  farthest  from  the  fire  (A). 

There  are  two  varieties  of  Belgian  ore,  one  containing 

33  and  the  other  46  per  cent,  of  zinc,  but  a  large 

proportion  of  this  is  in  the  form  of  silicate,  which  is 

not  extracted  by  the  distillation. 

Silesian  process  for  extracting]  zinc. — In  Silesia  the 
zinc  oxide  obtained  by  the  calcination  of  calamine  is 
mixed  with  fine  cinders,  and  distilled  in  arched  earthen  retorts  (A,  fig. 
241),  into  which  the  charge  is  introduced  through  a  small  door  (B),  which 
is  then  cemented  up.    The 

retorts  are  arranged  in  a      A. 

double  row  in  the  same 
furnace  (fig.  242),  and  the 
vapour  of  zinc  is  con- 
densed in  a  bent  earthen- 
ware pipe  attached  to  each 
retort,  and  having  an  opening  (C)  near  the  bend,  which  is  kept  closed, 
unless  it  is  necessary  to  clear  out  the  pipe.  In  regard  to  the  consumption 
of  fuel,  this  process  is  far 
more  economical  than 
that  followed  in  this 
country.  The  Silesian 
zinc  is  remelted,  before 
casting  into  ingots,  in 
clay  instead  of  iron  pots, 
since  melted  zinc  always 
dissolves  iron,  and  a  very 
small  quantity  of  that 
metal  is  found  to  injure 
zinc  when  required  for 
rolling  into  sheets.  Fig-  242.— Silesian  zinc  furnace. 

A  small  quantity  of  lead  always  distils  over  together  with  the  zinc, 
and  since  this  metal  also  interferes  with  the  rolling  of  zinc  into  sheets,  a 
portion  of  it  is  separated  from  zinc  intended  for  this  purpose,  by  melting 
the  spelter,  in  large  quantity,  upon  the  hearth  of  a  reverberatory  furnace, 
the  bed  of  which  is  inclined  so  as  to  form  a  deep  cavity  at  the  end  nearest 
the  chimney.  The  specific  gravity  of  lead  being  11*4,  whilst  that  of 
zinc  is  6-9,  the  former  accumulates  chiefly  at  the  bottom  of  the  cavity, 
and  the  ingots  cast  from  the  upper  part  of  the  melted  zinc  will  contain 
but  little  lead,  since  zinc  is  not  able  to  dissolve  more  than  1-2  per  cent, 
of  that  metal. 


Fig.  241. 


288  COMPOUNDS  OF  ZINC. 

Ingots  of  zinc,  when  broken  across,  exhibit  a  beautiful  crystalline  frac- 
ture, which,  taken  in  conjunction  with  tlie  bluish  colour  of  the  metal, 
enables  it  to  be  easily  identified. 

The  spelter  of  commerce  is  liable  to  contain  lead,  iron,  tin,  antimony, 
arsenic,  copper,  cadmium,  magnesium,  and  aluminium.  Belgian  zinc  is 
usually  purer  than  the  English  metal. 

Zinc  being  easily  dissolved  by  diluted  acids,  it  is  necessary  to  be  care- 
ful in  employing  this  metal  for  culinary  purpo.?es,  since  its  soluble  salts 
are  poisonous. 

It  will  be  remembered  that  the  action  of  diluted  sulphuric  acid  upon 
zinc  is  employed  for  the  preparation  of  hydrogen.  Pure  zinc,  however, 
evolves  hydrogen  very  slowly,  since  it  becomes  covered  with  a  number  of 
hydrogen  bubbles  which  protect  it  from  further  action;  but  if  a  piece  of 
copper  or  platinum  be  made  to  touch  the  zinc  beneath  the  acid,  these 
metals,  being  electro-negative  towards  the  zinc,  will  attract  the  electro- 
positive hydrogen,  leaving  the  zinc  free  from  bubbles  and  exposed  on  all 
points  to  the  action  of  the  acid,  so  that  a  continuous  disengagement  of 
hydrogen  is  maintained.  As  a  curious  illustration  of  this,  a  thin  sheet  of 
platinum  or  silver  foil  may  be  shown  to  sink  in  diluted  sulphuric  acid, 
until  it  comes  in  contact  with  a  piece  of  zinc,  when  the  bubbles  of  hydro- 
gen bring  it  up  to  the  surface.  The  lead,  iron,  &c.,  met  with  in  commer- 
cial zinc,  are  electro-negative  to  the  zinc,  and  thus  serve  to  maintain  a 
constant  evolution  of  hydrogen. 

A  coating  of  metallic  zinc  may  be  deposited  upon  copper  by  slow  galvanic 
action,  if  the  copper  be  immersed  in  a  concentrated  solution  of  jwtash,  at 
the  boiling-point  of  water,  in  contact  with  metallic  zinc,  when  a  portion  of 
the  latter  is  dissolved  in  the  form  of  oxide,  with  evolution  of  hydrogen, 
and  is  afterwards  precipitated  on  the  surface  of  the  electro-negative  copper. 

Zinc  oxide  (ZnO). — Zinc  forms  but  one  oxide,  which  is  known  in 
commerce  as  zinc-white  or  Chinese  rchite,  and  is  prepared  by  allowing  the 
vapour  of  the  metal  to  burn  in  earthen  chambei-s  through  which  a  current 
of  air  is  maintained.  This  zinc-white  is  sometimes  used  for  painting 
in  place  of  white  lead  (lead  carbonate),  over  which  it  has  the 
advantages  of  not  injuring  the  health  of  the  persons  using  it,  and  of 
being  unaffected  by  sulphuretted  hydrogen,  an  important  consideration 
in  manufacturing  towns  where  that  substance  is  so  abundantly  supplied 
to  the  atmosphere.  Unfortunately,  however,  the  zinc  oxide  does  not 
combine  with  the  oil  of  the  paint  as  lead  oxide  does,  and  the  paint 
is  consequently  more  liable  to  peel  off.  The  zinc  oxide  has  the  charac- 
teristic property  of  becoming  yellow  when  heated,  and  white  again  as 
it  cools.  It  is  sometimes  used  in  the  manufacture  of  glass  for  optical 
purposes. 

Zinc  oxide  forms  a  soluble  compound  with  potash,  in  this  respect 
resembling  alumina,  and  therefore  metallic  zinc,  like  aluminium,  is  dis- 
solved by  boiling  with  solution  of  potash,  hydrogen  being  disengaged 
from  the  water,  the  oxygen  of  which  combines  with  the  zinc. 

Zinc  sulphate  or  white  vitriol,  which  is  employed  in  medicine,  and  more 
extensively  in  calico-printing,  is  prepared  by  roasting  blende  (zinc  sulphide, 
ZnS)  at  a  low  temperature,  when  it  combines  with  oxygen  to  form  ZnSO^.' 
After  roasting,  the  mass  is  treated  with  water,  which  dissolves  the  sulphate, 
and  yields  it  again,  on  evaporation,  in  prismatic  crystals  having  the 
formula  ZnSO^H^O.eAq. 


CADMIUM — GLUCINUM.  i  289 

Zinc  pTiospkate,  combined  with  water,  composes  the  mineral  hopeite, 
Zn3(PO,),.4Aq. 

Ziric  chloride  (ZnClg),  prepared  by  dissolving  zinc  in  hydrochloric  acid, 
is  known  in  commerce  as  Burnett's  disinfecting  fluid,  since  it  is  capable 
of  absorbing  hydrosulphuric  acid,  ammonia,  and  other  offensive  products 
of  putrefaction,  and  arrests  the  decomposition  of  wood  and  animal 
substances.  By  evaporating  its  solution,  the  zinc  chloride  is  obtained  in 
a  fused  state,  and  solidifies  on  cooling  into  white  deliquescent  masses.  It 
has  a  very  powerful  attraction  for  water. 

Zinc  chloride  is  sometimes  made  from  pyrites  containing  blende.  This 
is  biu-nt  as  usual  to  furnish  SOg  for  the  manufacture  of  sulphuric  acid, 
when  the  ZnS  is  converted  into  ZnSO^  which  is  extracted  from  the  spent 
pyrites  by  water,  and  decomposed  with  sodium  chloride,  when  NagSO^ 
is  deposited  in  crystals,  leaving  ZnClg  in  solution. 

When  zinc  oxide  is  moistened  with  a  strong  solution  of  zinc  chloride, 
an  oxychloride  is  formed,  which  soon  sets  into  a  hard  mass,  forming  a  very 
useful  stopping  for  teeth. 

CADMIUM. 

Cd"=112  parts  by  weight. 

201.  This  metal  is  found  in  small  quantities  in  the  ores  of  zinc,  its 
presence  being  indicated  during  the  extraction  of  that  metal  (page  286) 
b}*  the  appearance  of  a  brown  flame  (brown  blaze)  at  the  commencement 
of  the  distillation,  before  the  characteristic  zinc  flame  is  seen  at  the  orifice 
of  the  iron  tube.  Cadmium  is  more  easily  vaporised  than  zinc,  boiling 
at  1580°  F.,  so  that  the  bulk  of  it  is  found  in  the  first  portions  of  the 
distilled  metal.  If  the  mixture  of  cadmium  and  zinc  be  dissolved 
in  diluted  sulphuric  acid,  and  the  solution  treated  with  hydrosulphuric 
acid  gas,  a  bright  yellow  precipitate  of  cadmium  sulphide  (CdS)  is 
obtained,  which  is  employed  in  painting  under  the  name  of  cadmia. 
By  dissolving  this  in  strong  hydrochloric  acid  and  adding  ammonium 
carbonate,  cadmium  carbonate  (CdCOg)  is  precipitated,  from  which 
metallic  cadmium  may  be  extracted  by  distillation  with  charcoal. 

Although  resembling  zinc  in  its  volatility  and  its  chemical  relations,  in 
appearance  it  is  much  more  similar  to  tin,  and  emits  a  crackling  sound 
like  that  metal  when  bent.  Like  tin,  also,  it  is  malleable  and  ductile  at 
the  ordinary  temperature,  and  becomes  brittle  at  about  180°  F.  It  is  as 
fusible  as  tin,  becoming  liquid  at  442°  F.,  so  that  it  is  useful  for  making 
fusible  alloys.  An  alloy  of  3  parts  of  cadmium  with  16  of  bismuth,  8 
of  lead,  and  4  of  tin,  fuses  at  140°  F.  In  its  behaviour  with  acids  and 
alkalies  cadmium  is  similar  to  zinc,  but  the  metal  is  easily  distinguished 
from  all  others  by  its  yielding  a  characteristic  chestnut-brown  oxide 
when  heated  in  air.     This  oxide  (CdO)  is  the  only  oxide  of  cadmium. 

Cadmium  iodide  (Cdl.,),  obtained  by  the  action  of  iodine  upon  the 
metal  in  the  presence  of  water,  is  employed  in  photography. 

GLUCmUM. 

Gl"  =  9  "2  parts  by  weight. 

202.  This  comparatively  rare  metal  (which  derives  its  name  from  the  sweet  taste  of 
its  salts,  jAvKvs,  sweet)  is  found  associated  with  silica  and  alumina  in  the  emerald, 
which  is  a  double  silicate  of  alumina  and  glucina,  AloOa.SSiOo.SCGlO.SiO^),  and 
appears  to  owe  its  colour  to  the  presence  of  a  minute  quantity  of  oxide  of  chromium. 

T 


290  ALUMINIUM. 

The  more  common  mineral  beryl  has  a  similar  composition,  but  is  of  a  paler  green 
colour,  apparently  caused  by  iron.  Chrysoberyl  consists  of  glucina  and  alumina, 
also  coloured  by  iron.  The  earlier  analysts  of  these  minerals  mistook  the  glucina 
for  alumina,  which  it  resembles  in  forming  a  gelatinous  precipitate  on  adding  ammonia 
to  its  solutions,  but  it  is  a  stronger  base  than  alumina,  and  is  therefore  capable  of 
displacing  ammonia  from  its  salts,  and  of  being  dissolved  by  them.  Ammouium 
carbonate  is  employed  to  separate  the  glucina  from  alumina,  since  it  dissolves  the 
glucina  in  the  cold,  forming  a  double  carbonate  of  glucinum  and  ammonium,  from 
which  the  glucinum  carbonate  is  precipitated  on  boiling.  Glucina  (GIO)  is  inter- 
mediate in  properties  between  alumina  and  magnesia,  resembling  the  latter  in  its 
tendency  to  absorb  carbonic  acid  from  the  air,  and  to  form  soluble  double  salts  with 
the  salts  of  ammonium,  and  so  much  resembling  alumina  in  the  gelatinous  form  of 
its  hydrate,  its  solubility  in  alkalies,  and  the  sweet  astringent  taste  of  its  salts,  that 
it  w^as  formerly  regarded  as  a  sesquioxide  like  alumina. 
The  metal  itself  is  very  similar  to  aluminium. 

ALUMINIUAr. 

A\"'  =  27  parts  by  weight. 

203.  Aluminium  is  the  representative  of  the  class  of  metals  usually 
styled  metals  of  the  earths  proper,  and  including  also  glucinum,  thorinura, 
yttrium,  zirconium,  erbium,  terbium,  cerium,  lanthanium,  and  didymium, 
but  of  these  aluminium  is  the  only  metal  having  any  claim  to  our  atten- 
tion on  the  ground  of  its  practical  importance. 

Aluminium  is  distinguished  among  metals,  as  silicon  is  among  non- 
metallic  bodies,  for  its  immense  abundance  in  the  solid  mineral  portion 
of  the  earthy  to  which,  indeed,  it  is  almost  entirely  confined,  for  it  is 
preseut  in  vegetables  and  animals  in  so  small  quantity  that  it  can  scarcely 
be  regarded  as  forming  one  of  their  necessary  components.  Church  has, 
however,  recently  found  it  in  certain  cryptogamous  plants,  especially  in 
the  Lycopodiums ;  the  ash  of  Lycopodium  alpinum  yielding  one-third  of 
its  weight  of  alumina. 

One  of  the  oldest  rocks,  which  appears  to  have  originally  formed  the 
basis  of  the  solid  structure  of  the  globe,  is  that  known  as  granite.  This 
mineral,  which  derives  its  name  from  its  conspicuous  granvlar  structure, 
is  a  mixture,  in  variable  proportions,  of  quartz,  felspar,  and  mica,  tinged 
of  various  colours  by  the  presence  of  small  quantities  of  the  oxides  of 
iron  and  manganese. 

Quartz,  which  forms  the  translucent  or  transparent  grains  in  the  granite, 
consists  simply  of  silica;  felspar,  the  dull  cream-coloured  opaque  part, 
is  a  combination  of  silica  with  oxides  of  aluminium  and  potassium,  its 
composition  being  represented  by  the  formula  KgO.SSiOgjAlgOg.SSiOg. 

Mica,  so  named  from  the  glittering  scales  which  it  forms  in  the  granite, 
is  also  a  double  silicate  of  alumina  and  potash,  but  the  alumina  is  very 
frequently  displaced  by  fenic  oxide,  and  the  potash  by  magnesia. 
'  Ey  the  long-continued  action  of  air  and  water,  the  granite  rock  is 
gradually  crumbled  down  or  disintegrated,  an  effect  which  must  be 
ascribed  to  a  concurrence  of  mechaaical  and  chemical  causes.  Mechani- 
cally, the  rock  is  continually  worn  down  by  variations  of  temperature, 
by  the  congelation  of  water  within  its  'minute  pores,  the  rock  being 
gradually  split  by  the  expansion  attendant  upon  such  congelation. 
Chemically,  the  action  of  water  containing  carbonic  acid  would  tend  to 
remove  the  potash  from  the  felspar  and  mica  in  the  form  of  carbonate  of 
potash,  whilst  the  silicate  of  alumina  and  the  quartz  would  subsequently 
be  separated  by  the  action  of  water;  the  former,  being  so  much  lighter, 


COMPOSITION  OF  CLAY. 


291 


would  be  soon  washed  away  from  the  heavy  quartz,  and  when  again 
deposited,  would  constitute  clay. 

Although  clay,  therefore,  always  consists  mainly  of  silicate  of  alumina, 
it  generally  contains  some  uncombined  silicic  acid,  together  with  variable 
(quantities  of  lime,  of  oxide  of  iron,  &c.,  which  give  rise  to  the  numerous 
varieties  of  clay. 

Composition  of  Olay. 


Chinese  Kaolin. 

Fireclay. 
(Stotu'bi-idge.) 

Pipeclay. 

Silica,         .... 

Alumina,   . 

Water,       .... 

Oxide  of  iron,     . 

Lime,         .... 

Magnesia, 

Potash,     ( 

Soda,         i          ■         ■         ■ 

50-5 

337 

11-2 

1-8 

6-8 
1-9 

64-1 

23-1 

10-0 

1-8 

'6'-9 

537 

32-0 

12-1 

1-4 

0-4 

i          99-9                  99-9 

99-6 

The  silicate  of  alumina  also  constitutes  the  chief  portion  of  several 
other  very  important  mineral  substances,  among  which  may  be  mentioned 
slate,  fuller  s  earth,  and  pumice-stone.  Marl  is  clay  containing  a  consider- 
able quantity  of  carbonate  of  lime.  Loam  is  also  an  impure  variety  of 
clay.  The  different  varieties  of  ochre,  as  well  as  umber  and  sienna,  are 
simply  clays  coloured  by  the  oxides  of  iron  and  manganese. 

Alum,  which  is  the  chief  compound  of  aluminium  employed  in  the  arts, 
is  always  obtained  either  from  clay  or  slate,  but  there  are  several  processes 
by  which  it  may  be  manufactured. 

The  simplest  process  is  that  in  which  pipeclay,  or  some  other  clay  con- 
taining very  little  iron,  is  calcined,  ground  to  powder,  and  heated  on  the 
hearth  of  a  reverberatory  furnace  with  half  its  weight  of  sulphuric  acid, 
until  it  becomes  a  stiff  paste,  which  is  then  exposed  to  air  for  several 
weeks.  During  this  time  the  alumina  of  the  clay  is  acted  on  by  the 
sulphuric  acid  to  form  aluminium  sulphate,  which  may  be  obtained  by 
washing  the  mass  with  water,  when  the  sulphate  dissolves,  and  the 
undissolved  silica  (still  retaining  a  portion  of  the  alumina)  is  left.  When 
the  solution  containing  the  aluminium  sulphate  is  evaporated  to  a  syrupy 
consistence  and  allowed  to  cool,  it  solidifies  into  a  white  crystalline  mass, 
which  is  used  by  dyers  under  the  erroneous  name  of  concentrated  alum, 
or  cake-alum,  and  contains  about  47*5  per  cent,  of  the  dry  salt.  The 
aluminium  sulphate  can  be  obtained  in  crystals  containing  AlgSSO^.lSAq.,* 
but  there  is  considerable  difficulty  in  obtaining  these  crystals  on  account 
of  the  extreme  solubility  of  the  salt.  It  is  on  account  of  this  circumstance 
that  the  aluminium  sulphate  is  usually  converted  into  alum,  which  admits 
of  very  easy  crystallisation  and  purification.  In  order  to  transform  the 
sulphate  into  alum,  its  solution  is  mixed  with  potassium  sulphate,  when, 
by  suitable  evaporation,  beautiful  octahedral  crystals  are  obtained,  having 
the  composition  AlK(S04)2.12Aq. 

Alum  is  more  commonly  prepared  from  the  mineral  termed  alum  shale, 

*  The  mineral  alunogen  found  in  New  South  Wales  has  this  composition  (Liversidge). 
It  forms  fibrous  masses  like  satin-spar,  and  occurs  in  sandstone  rocks. 


292  MANUFACTURE  OF  ALUM. 

which  contains  silicate  of  alumina,  together  with  a  considerable  quantity 
of  finely  divided  iron  pyrites  and  some  bituminous  matter.  This  shale 
is  coarsely  broken  up,  and  built  into  long  pyramidal  heaps,  together  with 
alternate  layers  of  coal,  unless  the  shale  should  happen  to  contain  a  suffi- 
cient amount  of  bitumen.  These  heaps  are  set  fire  to  in  several  places, 
and  are  partly  smothered  with  spent  ore  in  order  to  prevent  too  great  a 
rise  of  temperature.  During  this  slow  roasting  of  the  heap,  the  iron 
pyrites  (FeSg)  loses  half  its  sulphur,  which  is  converted  by  burning  into 
sulphurous  acid  gas  (SOg),  and  this,  in  contact  with  the  porous  shale  and 
the  atmospheric  oxygen,  becomes  converted  into  SO3  (p.  202).  This 
latter  combines  with  the  alumina  to  produce  sulphate  of  alumina.  The 
roasted  heap  is  then  allowed  to  remain  for  some  months  exposed  to  the 
air,  and  moistened  from  tim.e  to  time,  in  order  to  promote  the  absorption 
of  oxygen  by  the  sulphide  of  iron  (FeS),  and  its  conversion  into  sulphate 
of  iron  (FeSO^).  The  heap  is  afterwards  lixiviated  with  water,  which 
dissolves  out  the  sulphates  of  aluminium  and  iron,  together  with  some 
magnesium  sidphate,  which  has  also  been  formed  in  the  process.  When 
this  crude  alum  liquor  is  evaporated  to  a  certain  extent,  a  large  quantity 
of  ferrous  sulphate  (green  vitriol)  crystallises  out,  and  the  liquid  from 
which  these  crystals  have  separated  is  then  mixed  with  so  much  solu- 
tion of  potassium  chloride  as  a  preliminary  experiment  has  shown  to  be 
necessary  to  yield  the  largest  amount  of  alum.  The  potassium  chloride 
is  obtained  as  soap-boiler's  waste,  and  as  the  refuse  from  saltpetre  refineries 
and  glasshouses.  The  ferrous  sulphate  still  left  in  the  solution  is  decom- 
posed by  the  potassium  chloride,  yielding  ferrous  chloride,  and  potassium 
sulphate,  which  combines  which  the  aluminium  sulphate  to  form  alum. 
If  there  be  much  magnesium  sulphate  in  the  liquor,  it  is  subsequently 
obtained  in  crystals  and  sent  into  the  market. 

Where  ammonium  sulphate  can  be  obtained  at  a  cheap  rate  (as  in 
the  neighbourhood  of  the  gas-works),  it  is  very  commonly  substituted 
for  the  potassium  chloride,  when  ammonia-alum  is  obtained  instead  of 
potash-alum.  The  former  is  similar  in  all  respects  to  the  latter  salt,  except 
that  it  contains  the  hypothetical  metal  ammonium  (NHJ  in  place  of  potas- 
sium, and  its  formula  is,  therefore,  A1NH4(S04)2. 1 2 Aq. 

For  all  the  uses  of  alum,  in  dyeing  and  calico-printing,  in  paper-making, 
and  in  the  manufacture  of  colours,  ammonia-alum  answers  quite  as  well 
as  potash-alum,  and  hence  both  these  salts  are  sold  under  the  common 
name  of  alum. 

These  alums  are  the  representatives  of  an  important  class  of  double 
sulphates,  containing  a  monatomic  and  a  triatomic  metal.  They  all  con- 
tain 12  molecules  of  water  of  crystallisation,  and  their  crystalline  form  is 
that  of  the  cube  or  octahedron. 

The  solution  of  alum  is  acid  to  test-papers.  When  solution  of  sodium 
carbonate  is  added  to  it  by  degrees,  a  precipitate  of  aluminium  hydrate  is 
formed,  which,  at  first,  is  redissolved  on  stirring.  The  solution  to  which 
sodium  carbonate  has  been  added  as  long  as  the  precipitate  re-dissolves, 
is  used  under  the  name  of  basic  alum  in  dyeing,  because  stuffs  immersed  in 
it  become  impregnated  with  alumina,  which  serves  as  a  mordant  to  attract 
and  fix  the  colouring-matter  when  the  stuff  is  transferred  to  a  dye-bath. 

Aluminium  sulphate  is  superseding  alum  in  many  applications ;  being 
jirepared  by  treating  clay  or  Bauxite  (see  p.  294)  with  sulphuric  acid,  and 
precipitating  the  iron  either  as  ferric  arsenite  or  as  Prussian  blue. 


ALUMINIUM.  293 

Alumina. — When  ammonia-alum  is  strongly  heated,  it  leaves  a  white 
insoluble  earthy  substance  which  is  alumina  itself  (AlgOg),  and  differs 
widely  from  the  metallic  oxides  which  have  been  hitherto  considered, 
by  the  feebly  basic  character  which  it  exhibits.*  K^ot  only  is  alumina 
destitute  of  alkaline  properties,  but  it  is  not  even  capable  of  entirely 
neutralising  the  acids,  and  hence  both  aluminium  sulphate  and  alum  are 
exceedingly  acid  salts. 

Pure  crystallised  alumina  is  found  in  nature  as  the  mineral  corundum, 
distinguished  by  its  extreme  hardness,  in  which  it  ranks  next  to  the 
diamond.  An  opaque  and  impure  variety  of  corundum  constitutes  the 
very  useful  substance  emery.  The  ruby  and  sapphire^  consist  of  nearly 
pure  alumina ;  spinelle  is  a  compound  of  magnesia  with  alumina, 
MgO.AlgOgj  whilst  in  the  topaz  the  alumina  is  associated  with  silica  and 
aluminium  fluoride.  The  mineral  diaspore  is  a  hydrate  of  alumina 
(Al20g.2H20),  so  named  from  its  falling  to  powder  when  heated  {Siacnropa, 
dispersion). 

The  artificially  prepared  aluminium  hydrate  is  characterised  by  its  gelatinous 
appearance.  If  a  little  alum  be  dissolved  in  warm  water,  and  some  ammonia  added  to 
the  solution,  the  ammonia  will  combine  with  the  sulphuric  acid,  whilst  the  alumina 
will  unite  with  water  to  form  a  semi-transparent  gelatinous  mass  of  hydrate  of 
alumina  ;  AlgOg.SHoO  or  Al2(H0)g.  "When  washed  and  dried  it  shrinks  very  much, 
and  forms  a  mass  resembling  gum.  The  hydrate  has  a  giBat  attraction  for  most 
colouring  matters,  with  which  it  forms  insoluble  compounds  called  lakes.  Thus,  if 
a  solution  of  alum  be  mixed  with  infusion  of  logicood,  and  a  little  ammonia  added, 
the  aluminium  hydrate  will  form,  with  the  colouring  matter,  a  purplish-red  lake, 
which  may  be  filtered  off,  leaving  the  solution  colourless.  This  property  is  turned 
to  advantage  iu  calico-printing,  where  the  compounds  of  alumina  are  largely  used  as 
mordants. 

Aluminium  chloride. — If  the  alumina  obtained  by  calcining  ammonia- 
alum  be  intimately  mixed  with  charcoal,  and  strongly  heated  in  an  earthen 
tube  or  retort  through  which  a  stream  of  well-dried  chlorine  is  passed, 
the  oxygen  of  the  alumina  is  abstmcted  by  the  charcoal,  to  form  car- 
bonic oxide,  whilst  the  chlorine  combines  with  the  aluminium,  yielding 
aluminium  chloride  (AloClg)  which  passes  off  in  vapour,  and  may  be 
condensed,  in,  an  appropriate  receiver,  as  a  white  crystalline  solid — 

AI2O3  +  C3  -f  Clfi  =  AI2CI6  +  SCO. 

This  formation  of  aluminium  chloride  is  possessed  of  some  interest,  as 
an  example  of  the  decomposition  of  a  compound  body  by  the  co-operation 
of  two  elements,  neither  of  which  alone  would  be  able  to  decompose  the 
compound ;  neither  carbon  nor  chlorine  would,  alone,  decompose  alumina, 
however  high  the  temperature,  but  when  the  attraction  of  the  carbon  for 
the  oxygen  is  added  to  that  of  the  chloiine  for  the  aluminium,  the  decom- 
position is  easily  effected.  Aluminium  chloride  is  also  obtained  by 
heating  clay  in  a  mixture  of  hydrochloric  acid  gas  and  vapour  of  carbon 
disulphide.      The  silica  of  the  clay  is  converted  into  silicon  tetrachloride 

(Sicg. 

*  The  great  absorption  and  disappearance  of  heat  during  the  evaporation  of  the  water 
and  ammonia  from  this  alum,  has  led  to  its  emplojTuent  for  filling  the  space  bet\yeen  the 
double  walls  of  fire-proof  safes,  which  may  become  red  hot  outside,  whilst  the  inside  is 
kept  below  the  seorching-pomt  of  paper. 

t  Small  crystals  of  alumina  resembling  natural  sapphire  have  been  obtained  by  the 
action  of  vapour  of  aluminium  fiuoride  upon  boracic  anhydride  at  a  high  temperature. 
By  adding  a  little  chromium  fluoride,  crystals  similar  to  rubies  and  emeralds  have  been 
produced. 


294  ALUMINIUM. 

An  impure  solution  of  aluminium  chloride  is  sold  as  a  disinfectant 
under  the  name  of  chloralum. 

204.  Aluminium. — In  order  to  obtain  this  interesting  metal,  it  is  only 
necessary  to  pass  the  aluminium  chloride  in  the  state  of  vapour  over 
heated  sodium,  which  removes  the  chlorine  in  the  form  of  sodium  chloride, 
leaving  the  aluminium  as  a  white  malleable  metal  about  as  hard  as  zinc, 
and  fusing  at  a  somewhat  lower  temperature  than  silver.  For  the 
(extraction  of  aluminium  upon  the  large  scale,  the  alumina  is  not  prepared 
from  alum,  but  from  the  mineral  known  as  Bauxite,  which  contains 
alumina,  together  with  peroxide  of  iron  and  silica.*  This  mineral  is 
heated  with  soda-ash  (see  page  263),  when  carbonic  acid  gas  escapes,  and 
the  silica  and  alumina  combine  with  soda  to  form  silicate  of  soda,  and  a 
soluble  compound  of  alumina  with  soda,  which  is  generally  called  alumi- 
nate  of  soda,  and  has  the  composition  SNa^CAlgOg.  On  treating  the 
mass  with  water,  an  insoluble  silicate  of  alumina  and  soda  is  left,  whilst 
the  aluminate  of  soda  is  dissolved,  and  is  obtained  as  an  infusible  muss 
when  the  solution  is  evaporated.  This  aluminate  of  soda  is  largely  used 
by  calico-printers  as  a  mordant.  To  obtain  alumina  from  it,  the  solution 
is  neutralised  with  hydrochloric  acid,  which  converts  the  sodium  into 
chloride,  and  precipitates  the  alumina  as  hydrate  of  alumina  (AI2O3.3H2O). 
As  the  next  step  towards  the  preparation  of  aluminium,  the  hydrate  of 
alumina  is  mixed  with  charcoal  and  common  salt,  made  up  into  balls, 
dried,  and  strongly  heated  in  earthen  cylinders  through  which  dry  chlorine 
is  passed.  The  carbon  abstracts  the  oxygen  from  the  alumina,  forming 
carbonic  oxide,  whilst  the  aluminium  combines  with  the  chlorine,  and  the 
aluminium  chloride  so  formed  combines  with  the  chloride  of  sodium, 
and  distils  over  as  the  double  chlonde  of  aluminium  and  sodium 
(Al2Clg.2NaCl).  This  salt  is  then  mixed  with  a  proper  proportion  of 
metallic  sodium,  and  heated  in  a  reverberatory  furnace,  when  the  sodium 
combines  with  the  chlorine  of  the  aluminium  chloride,  leaving  the  metal 
to  separate  in  a  fused  state  beneath  the  melted  sodium  chloride,  which 
protects  it  from  oxidation.  The  aluminium  may  be  rolled  into  sheets  or 
drawn  into  wire.  Commercial  aluminium  has  been  found  to  contain 
from  3  to  7  "5  per  cent,  of  iron.  Silicon  is  also  present  in  it,  as  much  as 
1 4  per  cent,  having  been  found  in  one  sample. 

Aluminium  is  much  more  sonorous  than  most  other  metals.  A  bar  of 
it  suspended  from  a  string,  and  struck  with  a  hammer,  emits  a  clear 
musical  sound.  It  is  remarkable  as  being  the  lightest  metal  capable  of 
resisting  the  action  of  air  even  in  the  presence  of  moisture.  Its  specific 
gmvity  is  2"5.  This  lightness  renders  it  valuable  for  the  manufacture  of 
small  weights,  such  as  the  grain  and  its  fractions,  since  these,  when  made 
of  aluminium,  are  more  than  three  times  as  large  as  when  made  of  brass, 
and  nearly  nine  times  as  large  as  platinum  weights  of  the  same  denomina- 
tion. It  is  also  employed  for  ornamental  purposes,  for  though  not  so 
brilliant  as  silver,  it  is  not  blackened  by  sulphuretted  hydrogen,  which  so 
easily  affects  that  metal  (page  196). 

Another  characteristic  feature  of  aluminium  is  its  comparative  resistance 
to  the  action  of  nitric  acid  even  at  a  boiling  heat.     No  other  metal  com- 

*  Tliis  mineral  is  found  at  Baux,  near  Aries,  in  the  south  of  France,  and  in  Antrim, 
Ireland  ;  it  contains  silica  13  to  17  per  cent.,  alumina  60  to  65,  peroxide  of  iron  4  to  8, 
water  15  to  17.  When  mixed  with  about  3  per  cent,  of  clay  and  6  per  cent,  of  graphite  it 
i.s  said  to  form  an  excellent  lining  lor  steel-melting  furnaces. 


MINERAL  SILICATES  OF  ALUMINA.  295 

monly  met  with,  except  platinum  and  gold,  is  capable  of  resisting  the 
action  of  nitric  acid  to  the  same  extent  Hydrochloric  acid,  however, 
which  will  not  attack  gold  and  platinum,  dissolves  aluminium  with 
facility,  converting  it  into  aluminium  chloride,  with  disengagement  of 
hydrogen ;  Alg  +  6HC1  =  Al^Clg  +  Hg .  Solutions  of  potash  and  soda  also 
easily  dissolve  it,  forming  the  so-called  aluminates  of  those  alkalies ; 
thus  SK'aHO  -I-  Al  =  XagAlOg  +  H^.  Even  when  very  strongly  heated 
in  air,  aluminium  is  oxidised  to  a  very  slight  extent,  probably  because 
the  coating  of  alumina  which  is  formed  remains  infusible  and  protects 
the  metal  beneath  it.  For  a  similar  reason,  apparently  aluminium  de- 
composes steam  slowly,  even  at  a  high  temperature. 

Aluminium  decomposes  water  in  the  cold,  if  some  aluminium  iodide 
be  present;  hydrogen  being  set  free  and  the  aluminium  hydrate  pro- 
duced. 

"When  aluminium  is  fused  with  nine  times  its  weight  of  copper,  it  forms 
an  alloy  very  similar  to  gold  in  appearance,  but  almost  as  strong  as  iron. 
This  alloy  was  strongly  recommended  to  replace  gold  for  ornamental  pur- 
poses, but  it  does  not  retain  its  brilliancy  so  completely  as  that  metal. 
Aluminium  does  not  unite  with  mercury  or  with  melted  lead,  both  of 
which  are  capable  of  dissolving  nearly  all  other  metals. 

205,  Mineral  silicates  of  alumina.' — Many  of  the  chemical  formulae  of 
minerals  which  contain  silicates  of  alumina  associated  with  the  silicates 
of  other  metallic  oxides,  are  complicated,  from  the  circumstance  that  a 
part  of  the  aluminium  is  often  replaced  by  iron,  which,  in  the  form  of 
sesquioxide  (Fe.^Og),  is  isomorphous  with  it,  and  therefore  capable  of  re- 
placing it  without  altering  the  crystalline  form  and  general  character 
of  the  mineral  In  a  similar  manner,  the  other  metals  present  in  the 
mineral  may  be  exchanged  for  isomorphous  representatives ;  thus  there 
are  two  well-known  felspars,  potash-felspar  [orthodase)  and  soda-felspar 
(albite),  having  the  formulae  KgO.AlgOg.GSiOg  and  NagO.AlgOg.GSiOg. 
These  minerals  are  sometimes  mingled  in  one  and  the  same  crystal 
(potash-albite  or  pei'icline)  without  bearing  any  definite  equivalent  pro- 
portion to  each  other ;  the  formula  of  such  a  mineral  would  be  written 
(KNa)20.Al2036Si02. 

Porplujry  has  the  same  chemical  composition  as  felspar. 

Mica,  again,  is  composed  essentially  of  magnesia,  alumina,  and  silica 
(4MgO.Al203. 43102),  but  part  of  the  magnesium  is  so  constantly  re- 
placed by  potassium  and  iron  (as  FeO),  and  part  of  the  aluminium  by 
iron  (as  Fe203),  that  the  general  formula  for  mica  must  be  written 
4(K2MgFe)0.(AlFe)203.4Si02. 

Garnet  is  essentially  a  double  silicate  of  alumina  and  lime,  but  often 
contains  magnesium,  iron,  or  manganese,  replacing  part  of  the  calcium, 
and  iron  replacing  part  of  the  aluminium,  being  written — 

3(CaMgFeMn)0.(AlFe)203.3Si02 . 

This  mineral  is  sometimes  formed  artificially  in  the  slag  of  the  iron  blast- 
furnaces. 

Chlorite,  a  very  important  vari<\ty  of  rock,  is  a  double  silicate  of 
alumina  and  magnesia,  with  variations  as  expressed  by  the  formula — 

4(MgFe)0. (AlFe)203. 2Si02.  SHgO  . 


296  PHOSPHATE  OF  ALUMINA. 

Basalt  is  a  felspathic  rock  containing  crystals  of  augite — 
4(CaMgre)0.5Si02. 

Cyanite,  Kyanite,  or  Disthene,  is  a  silicate  of  alumina  (AlgOg-SiOg),  a 
crystal  of  which  points  north  and  south  when  freely  suspended. 

Gneiss  is  chemically  composed  like  granite,  but  the  mica  is  arranged  in 
regular  layers.  Trap  rock  contains  felspar  together  with  hornblende, 
which  consists  of  silicates  of  alumina,  lime,  magnesia,  and  oxide  of  iron. 
Hornblende  is  sometimes  found  replacing  the  mica  in  granite,  forming 
the  rock  called  syenite. 

Lava,  from  volcanoes,  consists  essentially  of  ferrous,  calcium  and 
aluminium  silicates ;  the  presence  of  a  considerable  proportion  of  potassium 
and  of  phosphoric  acid  renders  the  soil  formed  by  the  weathering  of  lava 
very  fertile. 

Lapis  lazuli,  the  valuable  mineral  which  furnishes  the  natural  ultra- 
marine used  in  painting,  consists  chiefly  of  silica  and  alumina,  which  con- 
stitute respectively  45  and  32  per  cent,  of  it,  but  there  are  also  present 
9  per  cent,  of  soda,  6  per  cent,  of  sulphuric  acid,  about  1  per  cent,  of  sul- 
phur, and  a  somewhat  smaller  quantity  of  iron,  together  with  a  variable 
proportion  of  lime.  The  cause  of  its  blue  colour  is  not  understood,  since 
neither  of  its  predominant  constituents  is  concerned  in  the  production  of 
such  a  colour  in  other  cases.  In  consequence  of  the  rarity  of  the  mineral, 
the  natural  ultramarine  bears  a  very  high  price,  but  the  artificial  ultra- 
marine is  manufactured  in  very  large  quantities  at  a  low  cost,  and  forms 
a  very  good  imitation.  One  of  the  processes  for  preparing  it  consists  in 
heating  to  bright  redness  in  a  covered  crucible,  for  three  or  four  hours, 
an  intimate  mixture  of  100  parts  of  pure  white  clay  (kaolin),  100  of  dried 
carbonate  of  soda,  60  of  sulphur,  and  12  of  charcoal  This  would  be 
expected  to  yield  a  mixture  of  silicate  of  soda,  aluminate  of  soda,  and 
sulphide  of  sodium,  the  two  first  being  white,  and  the  latter  yellow  or 
brown,  but  the  mass  is  found  to  have  a  green  colour  (green  ultramarine). 
It  is  finely  powdered,  washed  with  water,  dried,  mixed  with  a  fifth  of  its 
weight  of  sulphur,  and  gently  roasted  in  a  thin  layer  till  the  sulphxxr  has 
burnt  ofi",  this  operation  being  repeated,  with  fresh  additions  of  sulphur, 
until  the  residue  has  a  fine  blue  colour.  In  the  opinion  of  some  chemists, 
the  presence  of  a  small  proportion  of  iron  is  essential  to  the  blue  colour, 
Avhile  others  believe  the  colour  to  be  due  to  sodium  sulphide  or  tbio- 
sulphate,  or  both.*  Ultramarine  is  a  very  permanent  colour  under  ordinary 
conditions  of  exposure  to  the  air  and  light,  but  acids  bleach  it  at  once, 
with  separation  of  gelatinous  silica  and  evolution  of  sulphuretted  hydrogen. 
Blue  writing  paper  is  often  coloured  with  ultramarine,  so  that  its  colour 
is  discharged  by  acids  falling  upon  it  in  the  laboratory.  Chlorine  also 
bleaches  ultramarine.     Starch  is  often  coloured  blue  with  this  substance. 

Phosp)hate  of  alumina  or  aluminium  phosphate  is  found  naturally  in 
several  forms.  It  occurs  in  large  quantities  in  the  West  India  Islands. 
Turquoise  is  a  hydrated  aluminium  phosphate  (AlPOJ,  owing  its  colour 
to  the  presence  of  oxide  of  copper,  f  Wavellite  has  the  composition 
3AI0O3.2P2O5.  None  of  the  earlier  analysts  detected  the  phosphoric  acid 
in  this  mineral,  on  account  of  the  difficulty  in  separating  it  from  the 

*  Heumann  assigns  to  ultramarine  the  formula  2Na2Al2Si208.Na2S2. 
t  False  or  bone  turquoise  is  fossil  ivory,  owing  its  colour  to  the  presence  of  the  natural 
blue  phosphate  of  iron. 


GALLIUM.  297 

alumina,   so  that  even  in   comparatively  modern  chemical  works  it  is 
described  as  a  hydrate  of  alumina. 

206.  Thorinum  is  present  in  a  rare  Norwegian  mineral  thorite,  where  it  is  asso- 
ciated with  silica,  lime,  magnesia,  and  other  metallic  oxides.  The  metal  itself  is 
similar  to  aluminium,  but  its  oxide  thorina  appears  to  be  a  protoxide  (ThO),  and 
differs  from  alumina  and  glucina  in  being  insoluble  in  th^  alkalies  (potash,  for 
example),  though  it  dissolves  in  potassium  carbonate.  Moreover,  the  sulphate  of 
thorina  is  sparingly  soluble  in  hot  water,  so  that  it  is  precipitated  on  boiling  its 
solution.     Thorina  is  remarkable  for  its  high  specific  gravity  (9 '4). 

207.  Yttrium  and  Erbium  are  very  rare  metals  found  in  gadolinite,  a  mineral 
silicate  occurring  at  Ytterby  in  Sweden,  and  containing  beside  these,  glucinum, 
cerium,  and  iron.  Their  oxides  yttria  (YO)  and  erhia  resemble  thorica  in  being 
insoluble  in  the  alkalies,  but  soluble  in  their  carbonates  ;  j^ttria  is  white,  but  erbia 
has  a  yellow  colour.     The  salts  of  yttria  and  erbia  are  colourless. 

Tcrbia  is  an  earth  very  similar  to  yttria,  with  which  it  is  associated  in  the  mineral 
Samarskite. 

Ytterbium  is  another  metal  recently  found  in  gadolinite. 

208.  Lanthanium  (from  XavOivu,  to  escape  notice)  is  also  found  in  cerite,  but  it 
differs  from  cerium  in  forming  only  one  oxide  (La.203),  which  is  white  in  the  hydrated, 
but  buS  in  the  anhydrous  state.  When  a  mixture  of  nitrates  of  cerium  and  lantha- 
nium  is  calcined,  sesquioxide  of  cerium  and  oxide  of  lanthanium  are  left,  and  may  be 
separated  by  treatment  with  nitric  acid,  diluted  with  100  parts  of  water,  which 
dissolves  only  the  latter. 

209.  DiDYMiUM  (Bi^vfxos,  tvnn)  is  very  similar  to  lanthanium,  which  is  associated 
with  it  in  cerite.  It  also  forms  but  one  oxide*  (DigOj),  which  is  violet  when  hydrated, 
and  brown  when  anhydrous.  It  is  insoluble  in  potash.  The  salts  of  didymium  are 
either  pink  or  violet.  Their  solutions  have  a  remarkable  power  of  absorbing  some  of 
the  rays  of  the  spectrum,  so  that  the  spectroscope  affords  a  very  delicate  test  for  this 
metal,  t 

210.  Zirconium  exists  in  the  rare  minerals  zircon  and  hyacinth,  in  which  its  oxide 
zirconia  (ZrO.2)  is  combined  with  silicic  acid.  Zirconia  is  somewhat  similar  to 
alumina,  but  it  is  insoluble  in  potash,  and  dissolves  in  potassium  carbonate.  Its  sul- 
phate, moreover,  is  decomposed  by  boiling  with  potassium  sulphate,  which  removes 
part  of  the  sulphuric  acid,  and  precipitates  basic  zirconium  sulphate.  Metallic 
zirconium  somewhat  resembles  amorphous  silicon,  but  it  decomposes  water  slowly  at 
the  boiling-point,  and  has  not  been  fused. 

Zirconia,  matle  into  a  paste  with  solution  of  boracic  acid,  and  strongly  heated  in 
iron  moulds,  yields  masses  which  become  even  more  brilliantly  luminous  than  lime 
when  heated  in  the  flame  of  the  oxyhydrogen  blowpipe  {zirconia  light). 

211.  Gallium  is  found  in  veiy  small  quantities  in  certain  ores  of  zinc,  particularl}'' 
in  the  blende  from  Bensberg  in  the  Pyrenees.  The  roasted  ore  is  treated  with  enough 
sulphuric  acid  to  dissolve  nearly  all  the  zinc.  The  residue  containing  the  gallium  is 
dissolved  in  sulphuric  acid,  and  the  solution  partly  precipitated  with  sodium  car- 
bonate. The  precipitate  containing  all  the  gallium  and  part  of  the  zinc,  is  dissolved 
in  sulphuric  acid,  largely  diluted  and  boiled,  to  precipitate  the  titanic  acid.  The 
solution  is  mixed  with  acid  ammonium  acetate,  and  treated  with  hydrosulphuric  acid. 
The  precijiitate,  containing  zinc  and  gallium,  is  dissolved  in  sulphuric  acid,  and  again 
partially  precipitated  with  sodium  carbonate,  which  gives  a  deposit  rich  in  gallium  ; 
this  is  dissolved  in  exactly  the  required  quantity  of  sulphuric  acid,  diluted  and  boiled, 
when  basic  gallium  sulphate  is  deposited ;  on  dissolving  this  in  potash  and  decom- 
posing the  solution  by  the  galvanic  current,  the  gallium  is  deposited  on  the  negative 
pole. 

Gallium  is  a  hard  white  metal  of  sp.  gr.  5  "9,  remarkable  for  its  low  fusing- point 
(30°  C,  86°  F.),  so  that  it  melts  with  the  heat  of  the  hand.  It  will  remain  liquiil 
when  cooled  far  below  this  temperature,  but  solidifies  when  touched  with  a  piece  of 
the  solid  metal. 

•  According  to  Frerichs,  two,  viz.,  DiO  and  Di^Os,  to  which  Brauner  has  added  DioOj. 

+  The  mineral  rhabdophane  foimd  in  Cornwall,  and  formerly  believed  to  contain  zinc 
sulphide,  has  been  shown  by  Hartley  to  be  a  hydrated  phosphate  of  cerium,  didymium, 
lanthanium,  and  yttrium,  with  the  general  formula  R"T04.H20. 


298  URANIUM. 

It  is  not  oxidised  by  dry  air  fintil  heated  nearly  to  redness,  and  the  oxidation  is 
then  only  superficial.  Nitric  acid  scarcely  acts  upon  it  in  the  cold,  but  dissolves  it 
on  heating.  Hydrochloric  acid  dissolves  it,  with  evolution  of  hydrogen.  Potash  has 
a  similar  action. 

Gallium  forms  two  chlorides,  GaClj  and  Ga.2Cl8  ;  they  are  very  fusible,  volatile,  and 
deliquescent. 

Gallium  sulphate  is  very  soluble  in  water  ;  the  solution  deposits  a  basic  salt  when 
boiled.  It  combines  with  ammonium  sulphate  to  form  an  alum,  the  solution  of 
which  is  also  precipitated  by  boiling. 

Ammonia  precipitates  solutions  of  gallium,  but  the  precipitate  is  more  easily  soluble 
in  excess  than  in  the  case  of  aluminium.  Ammonium  sulphide  gives  a  precipitate 
only  if  zinc  be  present,  when  the  gallium  is  precipitated  together  with  the  zinc. 
Potash  gives  a  precipitate  which  dissolves  easily  in  excess.  Potassium  ferrocyanide 
produces  a  white  precipitate. 

The  most  delicate  test  for  gallium  is  the  production  of  two  violet  bands  in  the 
spectrum,  when  an  induction  spark  passes  from  the  positive  terminal  of  a  secondary 
coil  to  the  surface  of  the  solution  under  examination  into  which  the  negative  terminal 
of  the  coil  is  made  to  dip. 

From  the  description  of  its  properties,  it  will  be  seen  that  gallium  bears  consider- 
able resemblance  to  aluminium,  and  it  is  probable  that  its  oxide  has  the  formula 
Ga,03. 

212.  IxDiUM  is  the  name  of  a  metal  which  has  recently  been  discovered,  with  the 
help  of  the  spectroscope,  in  a  specimen  of  blende  from  Freiberg.  Its  name  refers  to 
an  indigo  blue  line  in  the  spectrum.  The  examination  of  the  metal  is  as  yet  imper- 
fect, but  it  is  white,  malleable,  and  dissolves,  like  zinc  and  cadmium,  in  hydrochloric 
acid.  Its  specific  gravity  is  7  "42.  Fusing-point  176°  C.  Less  easily  converted  into 
vapour  than  zinc  or  cadmium.  Indium  dissolves  in  HCl,  forming  InCls,  in  HNOs, 
forming  In(N03).„  and  in  H2SO4,  forming  In2(S04)3  which  crystallises  with  QHjO. 

Ammonia  produces,  in  solutions  of  indium,  a  white  precipitate,  In(0H)3 ;  insoluble 
in  excess.  Ammonium  carbonate  gives  a  precipitate  soluble  in  excess  and  reprecipi- 
tated  by  boiling.  To  extract  indium  from  the  Freiberg  zinc,  the  metal  is  boiled 
with  dilute  sulphuric  acid,  employed  in  such  quantity  as  to  leave  part  of  the  zinc 
undissolved,  together  with  indium  and  lead.  The  residue  is  dissolved  in  nitric  acid, 
the  lead  and  cadmium  precipitated  by  hydrosulphuric  acid,  the  latter  expelled  by 
boiling,  and  the  oxide  of  indium  precipitated  from  the  solution  by  barium  carbon- 
ate. When  this  precipitate  is  dissolved  in  hydrochloric  acid,  and  excess  of  ammonia 
added,  the  white  indium  hydrate  is  precipitated,  and  may  be  reduced  by  healing  in 
hydrogen. 

At  a  bright  red  heat  it  bums  with  a  violent  blue  flame,  yielding  a  yellow  oxide  of 
indium,  IfigOs- 

The  atomic  weight  of  indium  is  113*4. 

213.  Cerium  is  found  in  gadolinite,  but  more  abundantly  in  cerite,  which  is 
essentially  a  silicate  of  cerium.  Phosphate  of  cerium  {cryptoHte)  has  also  been  found 
in  brown  apatite.  The  mineral  fluocerite  is  CcjFg,  and  fliiocerine  is  an  oxyfluoride. 
This  metal  has  been  employed  medicinally,  in  the  form  of  oxalate  of  cerium. 
It  forms  two  basic  oxides,  cermts  oxide,  CegOg,  which  forms  colourless  salts,  and 
eerie  oxide,  CeOj,  which  is  yellow,  and  gives  yellow  or  red  salts.  In  this  respect 
cerium  more  nearly  resembles  iron  than  aluminium.  These  oxides  of  cerium  are 
insoluble  in  the  alkalies  ;  cerous  oxide  is  easily  precipitated  from  its  salts  by  oxalic 
acid  in  the  form  of  the  oxalate  mentioned  above.  Ceric  oxide  does  not  appear  to 
form  a  corresponding  chloride,  but  yields  cerous  chloride  and  free  chlorine  when 
heated  with  hydrochloric  acid.     Tetrafiuoride  of  cerium,  CeF4,  has  been  obtained. 

214.  Uranium. — This  is  a  rare  metal,  never  employed  in  the  metallic  state,  but  in 
the  form  of  sesquioxide  (U2O3)  and  black  oxide  (2U0.  U2O3),  for  imparting  yellow  and 
black  colours  respectively  to  glass  and  porcelain.  The  chief  source  of  these  compounds 
is  the  mineral  pitch-blevde,  which  contains  a  large  proportion  of  black  oxide  of 
uranium,  together  with  silica,  iron,  copper,  lead,  and  arsenic.  In  its  chemical 
relations  uranium  presents  some  similarity  to  iron  and  manganese.  It  forms  two 
distinct  oxides,  UO  and  U2O3,  of  which  the  fonner  is  decidedly  basic,  whilst  the 
latter  is  capable  of  acting  both  as  an  acid  and  a  base.  The  bright  greenish-yellow 
colour  of  the  salts  of  the  sesquioxide  of  uranium  is  characteristic  of  the  metal,  and 
glass  coloured  with  this  oxide  exhibits  the  remarkable  optical  effect  of  fluorescence  in 
a  very  high  degree. 


IKON. 


299 


The  uranic  salts  (derived  from  U2O3)  are  reduced  to  urauous  salts  (derived  from 
UO)  by  tlie  action  of  liglit  in  tlie  presence  of  organic  substances. 

The  vapour-densities  of  the  tetrachloride  and  tetrabromide  of  uranium  lead  to  240 
(instead  of  120)  as  the  atomic  weight  of  this  metal. 

IRON. 

Fe"  =  56  parts  by  weight. 

215.  This  most  useful  of  all  metals  is  one  of  those  most  widely  and 
abundantly  diffused  in  nature.  It  is  to  be  found  in  nearly  all  forms  of 
rock,  clay,  sand,  and  earth,  its  presence  in  these  being  commonly  indi- 
cated by  their  colours,  for  iron  is  the  commonest  of  natural  mineral 
colouring  ingredients.  It  is  also  found,  though  in  small  proportion,  in 
plants,  and  in  larger  quantity  in  the  bodies  of  animals,  especially  in  the 
blood,  which  contains  about  0*5  per  cent,  of  iron  in  very  intimate  associ- 
ation with  its  colouring  matter. 

But  iron  is  very  rarely  found  in  the  metallic  state  in  nature,  being 
almost  invariably  combined  either  with  oxygen  or  sulphur. 

Metallic  iron  is  met  with,  however,  in  the  meteorites  or  metallic  masses, 
sometimes  of  enormous  size,  and  of  unknown  origin,  which  occasionally 
fall  upon  the  earth.  Of  these  iron  is  the  chief  component,  but  there  are 
also  generally  present  cobalt^  nickel,  chromium,  manganese,  copper,  tin, 
magnesium,  carbon,  phosphorus,  and  sulphur. 

The  chief  forms  of  combination  in  which  iron  is  found  in  sufficient 
abundance  to  render  them  available  as  sources  of  the  metal,  are  shown  in 
the  following  table  : — 

Ores  of  Iron. 


Common  Name. 

Chemical  Name. 

Composition. 

Magnetic  iron  ore 

Ferroso-ferric  oxide 

Fe304 

Red  heematite 

Ferric  oxide 

re,03 

Si)ecular  iron 

Brown  hematite 

Ferric  hydrate 

2Fe203.3H20 

Spathic  iron  ore 

Ferrous  carbonate 

FeCOs 

Clay  iron-stone 

Ferrous  carbonate  with  clay 

Blackband 

J  Ferrous  carbonate  with  clay  and 
1      bituminous  matter 

Iron  pyrites 

Bisulphide  of  iron 

FeSa 

These  ores  are  frequently  associated  with  extraneous  minerals,  some  of 
the  constituents  of  which  are  productive  of  injury  to  the  quality  of  the 
iron.  It  is  worthy  of  notice  that  scarcely  one  of  the  ores  of  iron  is 
entirely  free  from  sulphur  and  phosphorus,  substances  which  will  be  seen 
to  have  a  very  serious  influence  on  the  quality  of  the  iron  extracted  from 
them,  and  the  presence  of  which  increases  the  difficulty  of  obtaining  the 
metal  in  a  marketable  condition. 

The  following  table  illustrates  the  general  composition  of  the  most 
important  English  ores  of  iron,  with  reference  to  the  proportions  of  iron, 
and  of  those  substances  which  materially  influence  the  character  of  the 
iron  extracted  from  the  ore,  viz.,  manganese  (present  as  oxide  or  car- 
bonate), phosphorus  (present  as  phosphates),  and  sulphur  (present  as 
bisulphide  of  iron).  The  maximum  and  minimum  quantities  found  in 
each  ore  are  specified. 


300 


ORES  OF  IRON. 


British  Iron  Ores.* 


In  100  parts. 


Clay  iron-stone  from  coal-measures, 
Clay  iron-stone  from  the  lias, 
lirown  haemaiite,   .... 
Red  liiematite,        .... 
Spathic  ore 

Magnetic  ore,         .... 


Max. 

43-30 
49-17 
63-04 
69-10 
49-78 


Min. 

L'0-95 
17-34 
11 -9S 
47-47 
13-98 


Oxide  of 

Manganese, 

MnO. 


Max.  I  Min. 


3-30 
1-30 
1-60 
1-13 
12-64 


0-46 

0 

ti-ace 
trace 

1-93 


Phosphoric 
Anhydride, 


Max. 

1-42 
5-05 
3-17 
trace 
0-22 


Min. 

0-07 
0 
0 

trace 
0 


Bisulphide 

of  Iron 
(Pyrites). 


Max. 

1-21 
1-60 
0-30 
0-06 
0-11 


Min. 

0 
0 
0 
0 
0 


0-07 


No.  of 
Samples 
Analysed. 


From  this  table  it  will  be  gathered  that,  among  the  most  abundant  of 
the  iron  ores  of  this  country,  red  haematite  is  the  richest  and  purest, 
whilst  the  brown  haematite  often  contains  considerable  proportions  of 
sulphur  and  phosphorus,  and  the  spathic  ore,  though  containing  little 
sulphur  and  phosphorus,  often  contains  much  manganese. 

The  argillaceous  ores,  or  clay  iron-stones  found  in  the  lias,  contain  more 
phosphorus  than  those  from  the  coal-measures ;  and  these  latter,  as  a 
general  rule^  contain  more  sulphur  (pyrites)  than  the  former,  although  the 
maximum  in  the  table  does  not  show  this. 

Clay  iron-stone  is  the  ore  from  which  the  largest  quantity  of  iron  is 
extracted  in  England,  since  it  is  found  abundantly  in  the  coal-measures 
of  Staffordshire,  Shropshire,  and  South  Wales;  and  it  is  a  circumstance  of 
great  importance  in  the  economy  of  English  iron-smelting,  that  the  coal 
and  limestone  required  in  the  smelting  process,  and  even  the  fireclay  em- 
ployed in  the  construction  of  the  furnace,  are  found  in  the  immediate 
vicinity  of  the  ore. 

Blackhand  is  the  clay  iron-stone  found  in  the  coal-fields  of  Scotland, 
and  often  contains  between  20  and  30  per  cent,  of  bituminous  matter, 
which  contributes  to  the  economy  of  fuel  in  smelting  it. 

Red  hcematite  (EcgOj)  is  the  most  characteristic  of  the  ores  of  iron, 
occurring  in  hard  shining  rounded  masses,  with  a  peculiar  fibrous  structure 
and  a  dark  red-brown  colour,  whence  the  ore  derives  its  name  {al^a,  blood). 
It  is  found  in  considerable  quantities  in  Lancashire  and  Cornwall,  but 
unfortunately  its  very  compact  structure  is  an  obstacle  to  its  being  smelted 
alone,  so  that  it  is  generally  mixed  with  some  clay  iron-stone,  and  hence 
the  iron  obtained  is  not  so  free  from  sulphur  and  phosphorus  as  if  it  were 
extracted  from  haematite  alone. 

Bed  ochre  is  a  soft  variety  of  this  ore,  containing  a  little  clay. 

Brown  hcematite  (2Fe203.3H20)  is  found  at  Alston  Moor  (Cumberland) 
and  in  Durham,  but  it  is  more  abundant  on  the  Continent,  and  is  the 
source  of  most  of  the  Belgian  and  French  irons.  Pea  iron  ore  and  yellow 
ochre  are  varieties  of  brown  haematite.  The  Scotch  ore,  called  Iddney-form 
clay  iron-stone^  is  really  a  hydrated  sesqnioxide  of  iron. 

Specidar  iron  ore  (Fe._jO.J  (oligist  ore  or  iron-glance),  although  of  the 
same  composition  as  red  haematite,  is  very  different  from  it  in  appearance, 
having  a  steel-grey  colour  and  a  brilliant  metallic  lustre.  The  island  of 
Elba  is  the  chief  locality  where  this  ore  is  found,  but  it  also  occurs  in 
Germany,  France,  and  Russia.  The  excellent  quality  of  the  iron  smelted 
from  this  ore  is  due  partly  to  the  purity  of  the  ore,  and  partly  to  the  cir- 
cumstance that  charcoal,  and  not  coal,  is  employed  in  smelting  it. 

*  This  table  has  hcen  compiled  from  the  analyses  given  in  Percy  On  Iron  and  Steel. 


METALLURGY  OF  IRON".  301 

Magnetic  iron  ore  (Fe^jO^),  of  which  the  loadstone  is  a  variety,  has  a 
more  granular  structure,  and  a  dark  iron-grey  colour.  It  forms  moun- 
tainous masses  in  Sweden,  and  is  also  found  in  Russia  and  North 
America.  It  is  generally  smelted  with  charcoal,  and  yields  an  excellent 
iron.  Iron  sand,  a  peculiar  heavy  black  sand  of  metallic  lustre,  con- 
sists in  great  measure  of  the  magnetic  ore,  but  contains  a  very  large  pro- 
portion of  titanium.  It  is  found  abundantly  in  India,  Nova  Scotia,  and 
New  Zealand;  but  its  fine  state  of  division  prevents  it  from  being  largely 
available  as  a  source  of  iron. 

Spathic  iron  ore  (FeCOg)  is  found  in  abundance  in  Saxony,  and  often 
contains  a  considerable  qiiantity  of  manganese  carbonate,  which  influences 
the  character  of  the  metal  extracted  from  it. 

The  oolitic  iron  ore,  occurring  in  the  Northampton  ooh'te,  contains  both 
hydra  ted  sesquioxide  and  carbonate  of  iron,  together  with  clay. 

Iron  pyrites  (FeS^)  is  remarkable  for  its  yellow  colour,  its  brilliant 
metallic  lustre  and  crystalline  structure,  being  generally  found  either  in 
distinct  cubical  or  dodecahedral  crystals,  or  in  rounded  nodules  of  radiated 
structure.  It  was  formerly  disregarded  as  a  source  of  iron,  on  account  of 
the  difficulty  of  separating  the  sulphur ;  but  since  the  demand  for  iron 
has  so  largely  increased,  an  inferior  quality  of  the  metal  has  been  extracted 
from  the  residue  left  after  burning  the  pyrites  in  the  manufacture  of  oil  of 
vitriol  (page  206),  the  residue  being  first  well  roasted  in  a  lime-kiln  to 
remove  as  much  as  possible  of  the  sulphur. 

The  quantity  of  iron  ore  raised  annually  in  this  country  is  estimated  at 
about  16  million  tons,  of  which  about  9  millions  are  clay  and  calcareous 
iron-stones  (chiefly  the  former)  from  the  lias  formations  of  North  York 
shire,  Lincolnshire,  Northamptonshire,  Oxford,  and  Wiltshire ;  4^  mil- 
lions are  clay  iron-stones  of  the  coal  formations  in  Scotland,  England,  and 
Wales ;  and  about  2^  millions  are  haematites  and  spathic  ores. 

216.  Metallurgy  of  iron. — Iron  owes  the  high  position  which  it  occupies 
among  useful  metals  to  a  combination  of  valuable  qualities  not  met  with 
in  any  other  metal.  Although  possessing  nearly  twice  as  great  tenacity  or 
strength  as  the  strongest  of  the  other  metals  commonly  used  in  the  metallic 
state,  it  is  yet  one  of  the  lightest,  its  specific  gravity  being  only  77,  and 
is  therefore  particularly  well  adapted  for  the  construction  of  bridges  and 
large  edifices,  as  well  as  for  ships  and  carriages.  It  is  the  least  yielding 
or  malleable  of  the  metals  in  common  use,  and  can  therefore  be  relied 
upon  for  aff"ording  a  rigid  support ;  and  yet  its  ductility  is  such  that  it 
admits  of  being  rolled  into  the  thinnest  sheets  and  drawn  into  the  finest 
wire,  the  strength  of  which  is  so  great  that  a  wire  of  yV^^  vach.  in  dia- 
meter is  able  to  sustain  705  pounds,  while  a  similar  wire  of  copper,  which 
stands  next  in  order  of  tenacity,  will  not  support  more  than  385  pounds. 

Being,  with  the  exception  of  platinum,  the  least  fusible  of  useful  metals, 
iron  is  applicable  to  the  construction  of  fire-grates  and  furnaces.  Nor  are 
its  qualifications  all  dependent  upon  its  physical  properties,  for  it  not  only 
enters  into  a  great  number  of  compounds  Avhich  are  of  the  utmost  use  in 
the  arts,  but  its  chemical  relations  to  one  of  the  non-metallic  elements, 
carbon,  are  such,  that  the  addition  of  a  small  quantity  of  this  element 
converts  it  into  steel,  far  surpassing  iron  in  the  valuable  properties  of  hard- 
ness and  elasticity  ;  whilst  a  larger  quantity  of  carbon  gives  rise  to  cast- 
iron,  the  greater  fusibility  of  which  permits  it  to  be  moulded  into  vessels 
and  shapes  which  could  not  be  produced  by  forging. 


302 


EXTRACTION  OF  IRON  FROM  CLAY  IRON-STONE. 


217.  English  process  of  smelting  day  iron-stone. — The  first  step 
towards  the  extraction  of  the  metal  consists  in  calcining  (or  roasting)  the 
ore  in  order  to  expel  water  and  carbonic  acid  gas.  To  effect  this  the  ore 
is  built  up,  together  with  a  certain  amount  of  small  coal,  into  long  pyra- 
midal heaps,  resting  upon  a  foundation  of  large  lumps  of  coal ;  blackband 
often  contains  so  much  bituminous  matter  that  any  other  fuel  is  unneces- 
sary. These  heaps  are  kindled  in  several  places,  and  allowed  to  burn 
slowly  until  all  the  fuel  is  consumed.      This  calcination  has  the  effect  of 


Fig.  243. — Blast-furnace  for  smelting  iron  ores. 

rendering  the  ore  more  porous,  and  better  fitted  for  the  smelting  process. 
If  the  ore  contained  much  sulphur,  a  part  of  it  would  be  expelled  by  the 
roasting  in  the  form  of  sulphurous  acid  gas. 

Sometimes  the  calcination  is  effected  in  kilns  resembling  lime-kilns,  and 
it  is  often  altogether  omitted  as  a  separate  process,  the  expulsion  of  the 
water  and  carbonic  acid  gas  being  then  effected  in  the  smelting-furnace 
itself  as  the  ore  descends. 

The  calcined  ore  is  smelted  in  a  huge  UaM-furnace  (fig.  243)  about 
fifty  or  sixty  feet  high,  built  of  massive  masonry,  and  lined  internally  with 
firebrick.  Since  it  would  be  impossible  to  obtain  a  sufficiently  high 
temperature  with  the  natural  draught  of  this  furnace,  air  is  forced  into  it 
at  the  bottom,  under  a  pressure  of  three  or  four  pounds  upon  the  inch, 
til  rough  three  tuyere  pipes,  the  nozzles  of  which  pass  through  apertures  in 
three  sides  of  the  furnace. 


CHEMICAL  CHANGES  IN  THE  BLAST-FUKNACE.  303 

It  would  be  very  easy  to  reduce  to  the  metallic  state  the  oxide  of  iron 
contained  in  the  calcined  ore,  by  simply  throwing  it  into  this  furnace, 
together  with  a  proper  quantity  of  coal,  coke,  or  charcoal ;  but  the  metallic 
iron  fuses  with  so  great  difficulty,  that  it  is  impossible  to  separate  it  from 
the  clay  unless  this  latter  is  brought  into  a  liquid  state  ;  and  even  then, 
the  fusion  of  the  iron,  which  is  necessary  for  complete  separation,  is  only 
effected  after  it  has  formed  a  more  easily  fusible  compound  with  a  small 
proportion  of  carbon  derived  from  the  fuel. 

ISTow,  clay  is  even  more  difficult  to  fuse  than  iron,  so  that  it  is  neces- 
sary to  add,  in  the  smelting  of  the  ore,  some  substance  capable  of  forming 
with  the  clay  a  combination  which  is  fusible  at  the  temperature  of  the 
furnace.  If  clay  (silicate  of  alumina)  be  mixed  with  limestone  (carbonate 
of  lime),  and  exposed  to  a  high  temperature,  carbonic  acid  gas  is  expelled 
from  the  limestone,  and  the  lime  unites  with  the  clay  forming  a  double 
silicate  of  alumina  and  lime,  which  becomes  perfectly  liquid,  and  when 
cool,  solidifies  to  a  glass  or  slag.  The  limestone  is  here  said  to  act  as  a 
Jiux,  because  it  induces  the  clay  to  flow  in  the  liquid  state.  In  order, 
therefore,  that  the  clay  may  be  readily  separated  from  the  metallic  iron, 
the  calcined  ore  is  mixed  with  a  certain  proportion  of  limestone  before 
being  introduced  into  the  furnace. 

Great  care  is  necessary  in  first  lighting  the  blast-furnace  lest  the  new 
masonry  should  be  cracked  by  too  sudden  a  rise  of  temperature,  and  when 
once  lighted,  the  furnace  is  kept  in  constant  work  for  years  until  in  want  of 
repair.     When  the  fire  has  been  lighted,  the  furnace  is  filled  up  with  coke, 
and  as  soon  as  this  has  burnt  down  to  some  distance  below  the  chimney,  a 
layer  of  the  mixture  of  calcined  ore  with  the  requisite  proportion  of  lime- 
stone is  thrown  upon  it ;  over  this  there  is  placed  another  layer  of  coke, 
then  a  second  layer  of  the  mixture  of  ore  and  flux,  and  so  on,  in  alternate 
layers,  until  the  furnace  has  been  filled  up ;  when  the  layers  sink  down, 
fresh  quantities  of  fuel,  ore,  and  flux  are  added,  so  that  the  furnace  is  kept 
constantly  full.     As  the  air  passes  from  the  tuyere  pipes  into  the  bottom 
of  the  furnace,  it  parts  with  its  oxygen  to  the  carbon  of  the  fuel,  which  it 
converts  into  carbonic  acid  gas  (COg)  ;  the  latter,  passing  over  the  red  hot 
fuel  as  it  ascends  in  the  furnace,  is  converted  into  carbonic  oxide  (CO)  by 
combining  with  an  additional  quantity  of   carbon.     It  is  this  carbonic 
oxide  which  reduces  the  calcined  ore  to  the  metallic  state,  when  it  comes 
in  contact  with  it,  at  a  red  heat,  in  the  upper  part  of  the  furnace,  for 
carbonic  oxide  removes  the  oxygen,  at  a  high  temperature,  from  the  oxides 
of  iron,  and  becomes  carbonic  acid  gas  ;  the  iron  being  left  in  the  metallic 
state.     But  the  iron  so  reduced  remains  disseminated  through  the  mass 
of  ore  until  it  has  passed  down  to  a  part  of  the  furnace  which  is  more 
strongly  heated,  where  the  iron  enters  into  combination  with  a  small  pro- 
portion of  carbon  to  form  cast-iron,  which  fuses  and  runs  down  into  the 
crucible  or  cavity  for  its  reception  at  the  bottom  of  the  furnace.     At  the 
same  time,  the  clay  contained  in  the  ore  is  acted  upon  by  the  lime  of  the 
flux,  producing  a  double  silicate  of  alumina  and  lime,  which  also  falls 
in  the  liquid  state  into  the  crucible,  where  it  forms  a  layer  of  ''slag" 
above  the  heavier  metal.     This  slag,  which  has  five  or  six  times  the  bulk 
of  the  iron,  is  allowed  to  accumulate  in  the  crucible,  and  to  run  over 
its  edge   down  the  incline  upon  which  the  blast-furnace  is  built ;   but 
when  a  sufficient  quantity  of     cast-iron  has  collected  at  the  bottom  of 
the  crucible,  it  is  run  out  through  a  hole  provided  for  the  purpose,  either 


304  THE  HOT  BLAST. 

into  channels  made  in  a  bed  of  sand,  or  into  iron  moulds,  where  it  is  cast 
into  rough  serai-cylindrical  masses  called  pigs,  whence  cast-iron  is  also 
spoken  of  as  pig-iron.  The  temperature  of  the  furnace  is,  of  course, 
highest  in  the  immediate  neighbourhood  of  the  tuyeres  :  the  reduction  of 
the  iron  to  the  metallic  state  appears  to  commence  at  about  two-thirds  of 
the  way  down  the  furnace,  the  volatile  matters  of  the  ore,  fuel,  and  flux 
being  driven  off  before  this  point  is  reached, 

Some  idea  may  be  formed  of  the  immense  scale  upon  which  the  smelt- 
ing of  iron  ores  is  carried  out,  when  it  is  stated  that  each  furnace  con- 
sumes, in  the  course  of  twenty-four  hours,  about  50  tons  of  coal,  30  tons 
of  ore,  6  tons  of  limestone,  and  100  tons  of  air.  The  cast-iron  is  run  off 
from  the  crucible  once  or  twice  in  twelve  hours,  in  quantities  of  five 
or  six  tons  at  a  time.  The  average  yield  of  calcined  clay  iron-stone  is 
35  per  cent,  of  iron. 

The  gases  escaping  from  the  chimney  of  the  blast-furnace  are  highly 
inflammable,  for  they  contain,  beside  the  nitrogen  of  the  air  blown  into 
the  furnace,  a  considerable  quantity  of  carbonic  oxide  and  some  hydrogen, 
together  with  the  carbonic  acid  gas  formed  by  the  action  of  the  carbonic 
oxide  upon  the  ore.  Since  the  carbonic  oxide  and  hydrogen  confer  con- 
siderable heating  power  upon  these  gases,  they  are  employed,  in  some 
iron- works,  for  heating  steam-boilers,  or  for  calcining  the  ore,  or  for  raising 
the  temperature  of  the  blast. 

The  composition  of  the  gas  issuing  from  a  hot-blast  furnace  (fed  with  uncoked 
coal)  may  be  judged  of  from  the  following  table  : — 


Gas  from 

Blast-Furnace. 

Nitrogen,     .         ^ 

.     55 '35  vols 

Carbonic  oxide,    . 

.     25-97     ,, 

Hydrogen,  . 

.       6-73     ,, 

Carbonic  acid  gas, 

.      7-77    ,. 

Marsh  gas, 

.       3-75     ,, 

Oleiiant  gas, 

.       0-4«     „ 

100-00     „ 

The  carbonic  oxide,  of  course,  renders  these  gases  highly  poisonous,  and  fatal  acci« 
dents  occasionally  happen  from  this  cause. 

Although  the  bulk  of  the  nitrogen  present  in  the  air  escapes  unchanged  from  tlie 
furnace,  it  is  not  improbable  that  a  portion  of  it  contributes  to  the  formation  of  the 
cyanide  of  potassium  (KCN),  which  is  produced  in  the  lower  part  of  the  furnace,  the 
potassium  being  furnished  by  the  ashes  of  the  fuel. 

The  Jwt  Mast — On  considering  the  enormous  quantity  of  air  which 
passes  through  the  blast-furnace,  it  will  be  seen  that  it  occasions  the  loss 
of  a  considerable  amount  of  heat.  In  order  to  economise  the  fuel,  hot-^ 
blast  furnaces  are  fed  with  air  of  which  the  temperature  is  raised  to  about 
600°  F.,  by  passing  it  through  heated  iron  pipes  or  over  hot  firebricks 
before  allowing  it  to  enter  the  blast-furnace.  The  higher  temperature 
which  is  thus  attained  permits  the  use  of  uncoked  coal,  which  would  not 
have  given  enough  heat  in  a  cold-blast  furnace,  and  the  same  quantity  of 
ore  may  be  smelted  with  less  than  half  the  coal  formerly  employed,  since 
the  blast  may  be  heated  by  means  of  the  waste  heat  of  the  furnace.  It 
appears,  however,  that  the  hot-blast  iron  is  inferior  in  quality  to  that 
obtained  from  the  same  ore  in  a  cold-blast  furnace,  and  this  is  generallj-^ 
explained  by  referring  to  the  larger  quantity  of  sulphur  contained  in  the 
raw  coal ;  to  the  circumstance,  that  the  cast-iron  being  exposed  to  a  much 


SLAG  FROM  CAST-IRON.  305 

higher  temperature  in  the  hot-blast  furnace  is  more  liable  to  receive  and 
retaia  a  larger  amount  of  foreign  substances ;  and  (most  important  of 
all)  to  the  custom  of  extracting  iron  in  a  hot-blast  furnace  from  slags 
obtained  in  the  subsequent  processes  of  the  iron-manufacture,  which  could 
not  be  smelted  in  a  cold-blast  furnace.  These  slags  always  contain  sulphur 
and  phosphorus,  and  therefore  yield  an  inferior  quality  of  iron.  Hence  the 
distinction  commonly  drawn  between  mine  iron  extracted  from  the  ore 
without  admixture  of  slags,  and  cinder  iron  (or  kentledge)  in  the  preparation 
of  which  slag  or  cinder  has  been  employed. 

The  sLig  from  the  blast  furnace  is  essentially  a  glass  composed  of  a 
double  silicate  of  aluminium  and  calcium,  the  composition  of  which  varies 
much  according  to  the  nature  of  the  earthy  matters  in  the  ore,  and  the 
composition  of  the  flux.  Its  colour  is  generally  grey,  streaked  with  blue, 
green,  or  brown. 

1'he  nature  of  the  flux  employed  must,  of  course,  be  modified  according 
to  the  composition  of  the  earthy  substances  (or  gangue)  present  in  the  ore. 
Where  this  consists  of  clay  (silicate  of  alumina)  the  addition  of  lime 
(which  is  sometimes  added  in  the  form  of  limestone  and  sometimes  as 
quicklime)  will  provide  for  the  formation  of  the  double  silicate  of  alumina 
and  lime.  But  if  the  iron-ore  happened  already  to  contain  limestone,  an 
addition  of  clay  would  be  necessary,  or  if  quartz  were  present,  consisting 
of  silica  only,  both  lime  and  alumina  (in  the  form  of  clay)  will  be  neces- 
sary as  a  flux.  It  is  sometimes  found  economical  to  employ  a  mixture  of 
ores  containing  different  kinds  of  gangue,  so  that  one  may  serve  as  a  flux 
to  the  other.  If  a  proper  proportion  of  lime  were  not  added,  a  portion  of 
the  oxide  of  iron  would  combine  with  the  silica  and  be  carried  off  in  the 
slag ;  but  if  too  large  a  quantity  of  lime  be  employed,  it  will  diminish  the 
fusibility  of  the  slag,  and  prevent  the  complete  separation  of  the  iron  from 
the  earthy  matter.  The  most  easily  fusible  slag  which  can  be  formed  by 
the  action  of  lime  upon  clay  has  the  composition  6CaO. AlgOg.QSiOg ; 
but  in  English  furnaces,  where  coal  and  coke  are  employed,  it  is  found 
necessary  to  employ  a  larger  proportion  of  lime  to  convert  the  sulphur  of 
the  fuel  into  calcium  sulphide,  so  that  the  slag  commonly  has  a  composi- 
tion more  nearly  represented  by  the  formula,  12Ca0.2Al203.9Si02,  which 
would  express  a  compound  of  6  molecules  of  normal  calcium  silicate  with 
1  molecule  of  normal  aluminium  silicate,  6Ca.,Si04.Al^(Si04)3. 

Since  iron,  manganese,  and  magnesium  are  commonly  found  occupying 
the  place  of  a  portion  of  the  calcium,  a  more  general  forijiula  for  the  slag 
from  English  Ijlast-furnaces  would  be  6(CareMnMg)2Si04.Al4(Si04)3. 

A  fair  impression  of  the  ordinary  composition  of  the  slag  from  blast- 
furnaces is  conveyed  by  the  following  table  : — 

Slag  from  Blast-Fumace. 

Silica, 43-07 

Alumina,         ........  14 '85 

Lime, 28-92 

ilagfnesia,        ........  5 '87 

O.mle  of  iron  (FeO), 2-35 

Oxide  of  mangauese  (MnO),    .         .         .         .         .  1'37 

Potash, 1-84 

Sulphide  of  calcium,        ......  1  '90 

Phosphoric  acid,      . trace 

100-17 

U 


306  COMPOSITION  OF  CAST-IRON. 

These  slags  are  sometimes  run  from  the  blast-furnace  into  iron  mouldsy 
in  which  they  are  cast  into  blocks  for  rough  building  purposes.  The 
presence  of  a  considerable  proportion  of  potash  has  led  to  experiments 
upon  their  employment  as  a  manure,  for  which  purpose  they  have  been 
blown  out,  when  liquid,  into  a  finely -divided  frothy  condition  fit  for 
grinding  and  applying  to  the  soil  By  blowing  steam  through  the  slag  it 
is  converted  into  a  substance  resembling  spun  glass,  and  used  under  the 
name  of  mineral  cotton,  for  packing  round  steam-pipes,  &c. 

218.  Cast-Iron  is,  essentially,  composed  of  iron  with  from  2  to  5  per 

cent,  of  carbon,  but  always  contains  other  substances  derived  either  from 
the  ore  or  from  the  fuel  employed  in  smelting  it  •  On  taking  into  con- 
sideration the  energetic  deoxidising  action  in  the  blast-furnace,  it  is  not 
surprising  that  portions  of  the  various  oxygen  compounds  exposed  to  it 
should  part  with  their  oxygen^  and  that  the  elements  thus  liberated 
should  find  their  way  into  the  cast-iron.  In  this  way  the  silica  is  reduced, 
and  its  silicon  is  found  in  cast-iron  in  quantity  sometimes  amounting 
to  3  or  4  per  cent.  Haematite  pig  is  usually  rich  in  silicon,  from  the 
presence  of  silica  in  an  easily  reducible  condition  in  the  ore.  Sulphur 
and  phosphorus  are  also  generally  present  in  cast-iron,  but  in  very  much 
smaller  quantity ;  their  presence  diminishes  its  tenacity,  and  the  smelter 
endeavours  to  exclude  them  as  far  as  possible,  though  a  small  quantity  of 
phosphorus  appears  to  be  rather  advantageous  for  some  castings,  since  it 
augments  the  fusibility  and  fluidity  of  the  cast-iron.  The  sulphur  is 
chiefly  derived  from  the  coal  or  coke  employed  in  smelting,  and  for  this 
reason  charcoal  would  be  preferable  to  any  other  fuel  if  it  could  be 
obtained  at  a  sufficiently  cheap  rate.  The  iron-works  of  America  and 
those  of  the  European  continent  enjoy  a  great  advantage  in  this  respect  over 
those  of  England.  The  phosphorus  is  obtained  chiefly  from  the  phos- 
phoric acid  existing  in  the  ore  or  in  the  flux.*  It  appears  to  exist  in  the 
iron,  at  least  in  some  cases,  as  Fe^P.  The  proportion  of  phosphorus  taken 
up  by  the  cast-iron  increases  with  the  temperature  of  the  blast-furnace. 
Manganese,  amounting  to  1  or  2  per  cent.,  is  often  met  with  in  cast-iron, 
having  been  reduced  from  the  oxide  of  manganese,  which  is  generally 
found  in  iron  ores.  Other  metals,  such  as  chromium,  cobalt,  &c.,  are  also 
occasionally  present,  though  in  so  small  quantities  as  to  be  of  no  importance 
in  practice. 

The  following  table  exhibits  the  largest  and  smallest  proportion  of  the 
various  elements  determined  in  the  analysis  of  upwards  of  a  hundred 
specimens  of  cast-iron  : — 

Composition  of  Cast-Iron.^ 

Maximum.     Minimum. 


Carbon, 

4-81 

1  -04  per  cent 

Silicon, 

4-77 

008 

Sulphur,    . 

1-06 

0-00 

Phosphorus, 

1-87 

trace       ,, 

Manganese, 

6-08 

trace       ,, 

Iron, 

In  order  to  understand  the  difference  observed  in  the  several  varieties 
of  cast-iron,  it  is  necessary  to  consider  the  peculiar  relations  between  iron 
and  carbon.     Iron  fused  in  contact  with  carbon  is  capable  of  combining 

*  Phosphorus,  in  the  form  of  phosphates,  is  sometimes  found  in  coal. 
+  Compiled  from  Percy  On  Iron  and  iiteel. 


GREY,  MOTTLED,  AND  WHITE  IRON. 


307 


with  nearly  6  per  cent,  of  that  element,  to  form  a  white,  brilliant,  and 
brittle  compound,  which  may  be  represented  pretty  nearly  as  composed 
of  Fe^C.  Under  certain  circumstances,  as  this  compound  of  iron  and 
carbon  cools,  a  portion  of  the  carbon  separates  from  the  iron,  and  remains 
disseminated  throughout  the  mass  in  the  form  of  minute  crystalline  par- 
ticles very  much  resembling  natural  graphite.  If  a  broken  piece  of  iron 
containing  these  scales  be  examined,  the  fracture  will  be  found  to  exhibit 
a  more  or  less  dark  grey  colour,  due  to  the  presence  of  the  uncombined 
carbon,  and  for  this  reason  a  cast-iron  in  which  a  portion  of  the  carbon 
has  thus  separated  is  commonly  spoken  of  as  grey  iron,  whilst  that  in 
which  the  whole  of  the  carbon  has  remained  in  combination  with  the 
metal  exhibits  a  white  fracture,  and  is  termed  white  iron  or  bright  iron. 
Intermediate  between  these  is  the  variety  known  as  mottled  iron,  which 
has  the  appearance  of  a  mixture  of  the  grey  and  white  varieties. 

The  ditferent  condition  of  the  carbon  in  the  two  varieties  of  cast-iron  is 
rendered  apparent  when  the  metal  is  dissolved  in  diluted  sulphuric  or 
hydrochloric  acid,  for  any  carbon  which  exists  in  the  uncombined  state 
will  then  be  left,  whilst  that  which  had  been  in  combination  with  the 
iron  passes  off  in  the  form  of  peculiar  compounds  of  carbon  and  hydrogen, 
which  impart  the  disagreeable  odour  perceived  in  the  gas  evolved  when 
the  metal  is  dissolved  in  an  acid. 

The  properties  of  these  two  varieties  of  cast-iron  are  widely  different, 
grey  iron  being  so  soft  that  it  may  be  turned  in  a  lathe,  whilst  the  white 
iron  is  extremely  hard,  and  of  higher  specific  gravity.  Again,  although 
white  iron  fuses  at  a  lower  temperature  than  grey  iron,  the  latter  is  far 
more  liquid  when  fused,  and  is  therefore  much  better  fitted  for  casting. 

Although  the  presence  of  uncombined  carbon  is  the  chief  point  which 
distinguishes  grey  from  white  iron,  other  differences  are  commonly  observed 
in  the  composition  of  the  two  varieties.  The  white  iron  usually  contains 
less  silicon  than  grey  iron,  but  a  larger  proportion  of  sulphur.  White 
iron  also  usually  contains  a  much  larger  quantity  of  manganese. 

The  difference  in  the  composition  of  these  three  varieties  of  cast-iron  is 
shown  in  the  followinor  table  : — 


Grey. 

Mottled. 

White.    ■ 

Iron,     .... 

•     90-24 

89-31 

89-86 

Combined  carbon, 

1-02 

1-79 

2-46 

Graphite, 

2-64 

1-11 

0-87 

Silijon, 

3-06 

2-17 

1-12 

Sulphur, 

1-14 

1-48 

2-52 

Phosphorus, 

0-93 

1-17 

0-91 

Manganese,  . 

0-83 

1-60 

2-72 

99-86 

98-63 

100-46 

As  might  be  expected,  it  is  not  easy  to  tell  where  a  cast-iron  ceases  to 
be  grey  and  begins  to  be  mottled,  or  where  the  mottled  iron  ends  and 
white  iron  begins.  There  are,  in  fact,  eight  varieties  of  cast-iron  in  com- 
merce, distinguished  by  the  numbers  one  to  eight,  of  which  No.  1  is  dark 
grey,  and  contains  the  largest  proportion  of  graphite,  which  diminishes  in 
the  succeeding  numbers  up  to  Xo.  8,  Avhich  is  the  whitest  iron,  the  inter- 
mediate numbers  being  more  or  less  mottled. 

The  particular  variety  of  cast-iron  produced  is  to  some  extent  under 


308  KEFINING  CAST-IRON. 

the  control  of  the  smelter ;  a  furnace  in  good  order  appearing  usually  to 
yield  grey  iron,  whilst  a  defective  furnace,  or  one  supplied  with  too  small 
a  proportion  of  fuel,  will  commonly  give  a  white  iron.  But  the  metal 
sometimes  varies  considerably  at  different  levels  in  the  crucible  of  the 
furnace,  so  that  pigs  of  different  degrees  of  greyness  are  obtained  at  the 
same  tapping. 

Mottled  cast-iron  surpasses  both  the  other  varieties  in  tenacity,  and  is 
therefore  preferred  where  this  quality  is  particularly  desirable. 

The  dark  grey  iron  used  for  casting,  known  as  foundry-iron,  is  produced 
at  a  higher  temperature,  by  supplying  the  blast-furnace  with  a  larger  pro- 
portion of  fuel  than  is  employed  in  making  the  lighter  forge-iron  destined 
for  conversion  into  wrought-irou.  The  extra  consumption  of  fuel,  of 
course,  renders  the  foundry-iron  more  expensive.  When  a  furnace  is 
worked  with  a  low  charge  of  fuel  to  produce  a  white  iron,  a  larger  quan- 
tity of  iron  is  lost  in  the  slag,  sometimes  amounting  to  5  per  cent,  of 
the  metal,  whilst  the  average  loss  in  producing  grey  iron  does  not  exceed 
2  per  cent.  Ores  containing  a  large  proportion  of  manganese  are  generally 
found  to  yield  a  white  iron. 

AVhen  grey  iron  is  melted,  the  particles  of  graphite  to  which  its  grey 
colour  is  due  are  dissolved  by  the  liquid  iron,  and  if  it  be  poured  into 
a  cold  iron  mould  so  as  to  solidify  it  as  rapidly  as  possible,  the  external 
portion  of  the  casting  will  present  much  of  the  hardness  and  appear- 
ance of  white  iron,  the  sudden  cooling  having  prevented  the  separation 
of  the  graphite.  This  affords  the  explanation  of  the  process  of  chill- 
casting,  by  which  shot,  &c.,  made  of  the  soft  fusible  grey  iron,  are  made 
to  acquire,  externally,  a  hardness  approaching  that  of  steeL  It  is  a  com- 
mon practice  to  produce  compound  castings,  that  portion  of  the  mould 
where  chilling  and  consequent  hardness  is  required  being  made  of  thick 
cast-iron,  and  the  other  part,  which  is  to  give  a  tougher  and  a  softer  casting, 
of  sand. 

"When  white  pig-iron  is  melted  at  an  extremely  high  temperature  (in  a 
Siemens'  furnace)  and  slowly  cooled,  it  becomes  grey. 

The  specific  gravity  of  cast-iron  varies  between  6*92  (grey)  and  7*53 
(white),  and  lis  fusing-point  is  somewhat  below  3000°  F. 

Eecent  experiments  throw  some  doubt  upon  the  existence  of  carbon  in  a  state  of 
actual  chemical  combination  in  cast-iron.  It  has  been  found  that,  when  acting  upon 
mercuric  chloride,  white  cast-iron  generates  considerably  more  heat  than  pure  iron  ; 
this  would  indicate  that  absorption  of  heat  had  taken  place  in  the  fonnation  of  white 
cast-iron  (which  contained  4  per  cent,  of  "combined"  carbon),  whereas,  had  the 
carbon  combined  chemically  with  the  iron,  generation  of  heat  should  have  taken 
place.  On  the  other  hand,  it  was  found  by  the  same  method,  that  manganese  and 
carbon  do  generate  heat,  and  therefore  enter  into  true  chemical  combination.  This 
fact  may  have  some  bearing  upon  the  use  of  manganese  in  the  manufacture  of  steel. 

Conversion  of  Cast- Iron  into  Bar  or  Wrought-Iron. 

219.  In  order  to  convert  cast-iron  into  bar-iron,  it  is  necessary  to  reduce 
it  as  far  as  possible  to  the  condition  of  pure  iron,  by  removing  the  carbon, 
silicon,  and  other  substances  associated  with  it.  This  purification  is 
effected  upon  the  principle,  that  when  cast-iron  is  strongly  heated  in  con- 
tact with  oxide  of  iron,  its  carbon  is  evolved  in  the  form  of  carbonic  oxide, 
whilst  the  silicon,  also  combining  with  the  oxygen  from  a  part  of  the 
oxide  of  iron,  is  converted  into  silica,  which  unites  with  another  portion 
of  the  oxide  to  form  a  fusible  slag  easily  separated  from  the  metaL 


REFINIXG  CAST-IRON. 


309 


The  most  important  of  the  processes  employed  for  the  conversion 
of  pig-iron  into  bar-iron,  is  that  known  as  the  puddling  process,  but 
this  is  sometimes  preceded  by  the  process  of  refining,  which  will  therefore 
be  first  described. 

Refining  cast-iron. — This  process  consists  essentially  in  exposing  the 
metal,  in  the  fused  state, 
to  the  action  of  a  blast 
of  air.  The  refinery 
(figs.  244,  245)  is  a 
rectangular  trough  with- 
double  walls  of  cast-iron, 
between  which  cold 
water  is  kept  circulating 
to  prevent  their  fusion. 
This  trough  is  about  3| 
feet  long  by  2|  wide, 
and  usually  lined  with 
fireclay ;  on  each  side 
of  it  are  arranged  three 
tuyere  pipes  for  the  sup- 
ply of  air,  inclined  at  an 
angle  of  2b''  to  30°  to 
the  bottom  of  the  fur- 


Fig.  244. — Hearth  for  refining  pig-iron. 


nace,  which  is  fed  with  coke,  unless  the  very  best  iron  is  required,  as  for 
the  manufacture  of  tin-plate,  when  charcoal  is  generally  used  in  the 
refinery. 

This  furnace  having  been  filled  to  a  certain  height  with  fuel,  five  or  six 
pigs  of  iron  (from  20  to  30  cwt.)  are  arranged  symmetrically  upon  it,  and 
covered  with  coke,  a  blast  of  air  being  forced  in  through  the  tuyeres, 
under  a  pressure  of  about  3  lbs.  upon  the  inch.  In  about  a  quarter  of 
an  hour  the  metal  begins 
to  fuse  gradually,  and  to 
trickle  down  through  the 
fuel  to  the  bottom  of 
the  refinery,  a  portion  of 
the  iron  being  converted 
into  oxide  in  its  descent, 
by  the  air  issuing  from 
the  tuyere  j^ipes.  When 
the  whole  of  the  metal 
has  been  fused,  the  air 
is  still  allowed  to  play 
for  some  time  upon  its 
surface,  when  the  fused 
metal  appears  to  boil 
in  consequence  of  the 
escape  of  bubbles  of 
carbonic  oxide. 

After  about  two  hours  the  tap-hole  is  opened,  and  the  molten  metal 
run  out  into  a  flat  cast-iron  mould  kept  cold  by  water,  in  order  to  chill 
the  metal  and  render  it  brittle.  The  plate  of  refined  iron  thus  obtained 
is  usually  about  2  inches  thick.     The  slag  [ai  finery  cinder)  is  generally 


pig-iron. 


310 


THE  PUDDLING  PROCESS. 


I 


received  in  a  separate  mould;  its  composition  may  be  generally  expressed 
by  the  formula  2FeO.Si02,  the  sHica  having  been  derived  from  the  silicon 
contained  in  the  cast-iron. 

The  change  effected  in  the  composition  of  the  iron  by  the  process  of 
refining  will  be  apparent  from  the  following  table  : — 


Refined  Iron, 


Iron, . 
Carbon, 
Silicon, 
Sulphur, 


95-14 
3  07 
0-63 
0-16 


Phosphorus, 
Manganese, 
Slag,    .         . 


0-73 
trace 
0-44 


The  carbon,  therefore,  is  not  nearly  so  much  diminished  as  the  silicon, 
which  is  in  some  cases  reduced  to  Yirth  of  its  former  proportion  by  the 
refining  process.  Half  of  the  sulphur  is  also  sometimes  removed,  being 
found  in  the  slag  as  sulphide  of  iron.  The  phosphorus  is  not  removed  to 
the  same  extent  in  the  refining  process,  though  some  of  it  is  converted 
into  phosphoric  acid,  which  may  be  found  in  the  finery  cinder. 

The  further  purification  of  the  metal  could  not  be  effected  in  the 
re6nery,  since  the  fusibility  of  the  iron  is  so  greatly  diminished  as  it 
approaches  to  a  pure  state,  that  it  could  not  be  retained  in  a  fluid  condi- 
tion at  the  temperature  attainable  in  this  furnace,  and  a  more  spacious 
hearth  is  required  upon  which  the  pasty  metal  may  be  kneaded  into  close 
contact  with  the  oxide  of  iron  which  is  to  complete  the  oxidation  and 
separation  of  the  carbon.  For  this  reason  the  metal  is  transferred  to  the 
puddling  furnace. 

The  puddling  process  is  carried  out  in  a  reverberatory  furnace  (figs.  246, 
247)  connected  with  a  tall  chimney  provided  with  a  damper,  so  as  to  admit 
of  a  very  perfect  regulation  of  the  draught.    A  bridge  of  firebrick  between 


Fig.  246.  — Puddling  furnace. 

the  grate  and  the  hearth  prevents  the  contact  of  the  coal  with  the  iron  to 
be  puddled.  The  hearth  is  composed  either  of  firebrick  or  of  cast-iron 
plates,  covered  with  a  layer  of  very  infusible  slag,  and  cooled  by  a  free 
circulation  of  air  between  them.  This  hearth  is  about  6  feet  in  length  by 
4  feet  in  the  widest  part  near  the  grate,  and  2  feet  at  the  opposite  end; 
it  is  slightly  inclined  towards  the  end  farthest  from  the  grate,  and  finishes 
in  a  very  considerable  slope,  at  the  lowest  point  of  which  is  the  fioss-hole 


THE  PUDDLING  PROCESS. 


311 


for  the  removal  of  the  slag.  Since  the  metal  is  to  attain  a  very  high 
temperature  in  this  furnace  (estimated  at  3000°  F.),  it  is  usually  covered 
with  an  iron  casing,  so  as  to  prevent  any  entrance  of  cold  air  through 
chinks  in  the  brickwork. 

About  5  cwt.  of  the  fine  metal  is  broken  up  and  heaped  upon  the 
hearth  of  this  furnace,  together  with  about  1  cwt.  of  iron  scales  (black 
oxide  of  iron,  FcgO^),  and  of  hammer-slag  (basic  silicate  of  iron,  obtained 
in  subsequent  operations),  which  are  added  in  order  to  assist  in  oxidising 
the  impurities.  When  the  metal  has  fused,  the  mass  is  well  stirred  or 
puddJed,  so  that  the  oxide  of  iron  may  be  brought  into  contact  with 


rig.  247.  — Puddling  furnace. 

every  part  of  the  metal,  to  effect  the  oxidation  of  the  impurities.  The 
metal  now  appears  to  boil,  in  consequence  of  the  escape  of  carbonic  oxide, 
and  in  about  an  hour  from  the  commencement  of  the  puddling,  so  much 
of  the  carbon  has  been  removed  that  the  fusibility  of  the  metal  is  con- 
siderably diminished,  and  instead  of  retaining  a  fused  condition  at  the 
temperature  prevailing  in  the  furnace,  it  assumes  a  granular,  sandy  or  dry 
state,  spongy  masses  of  pure  iron  separating  or  coming  to  nature  in  the 
fused  mass.  The  puddling  of  the  iron  is  continued  until  the  whole  has 
assumed  this  granular  appearance,  when  the  evolution  of  carbonic  oxide 
ceases  almost  entirely,  showing  that  the  removal  of  the  carbon  is  nearly 
completed.  The  damper  is  now  gradually  raised  so  as  to  increase  the 
temperature  and  soften  the  particles  of  iron,  in  order  that  they  may  be 
collected  into  a  mass;  and  the  more  easily  to  effect  this,  a  part  of  the 
slag  is  run  olf  through  the  floss-hole.  The  workman  then  collects  some 
of  the  iron  upon  the  end  of  the  paddle,  and  rolls  it  about  on  the  hearth 
until  he  has  collected  a  sort  of  rough  ball  of  iron,  weighing  about  half  a 
hundredweight.  When  all  the  iron  has  been  collected  into  balls  in  this 
way,  they  are  placed  in  the  hottest  part  of  the  furnace,  and  pressed  occa- 
sionally with  the  paddle,  so  as  to  squeeze  out  a  portion  of  the  slag  with 
which  their  interstices  are  filled.  The  doors  are  then  closed  to  raise  the 
interior  of  the  furnace  to  a  very  high  temperature,  and  after  a  short  time, 
when  the  balls  are  sufficiently  heated,  they  are  removed  from  the  furnace, 
and  placed  under  a  steam  hammer,  which  squeezes  out  the  liquid  slag, 
and  forces  the  softened  particles  of  iron  to  cohere  into  a  continuous  oblong 
mass  or  hloom,  which  is  then  passed  between  rollers,  by  which  it  is  ex- 
tended into  bars.     These  bars,  however  (Rough  or  Puddled,  or  No.  1  Bar), 


312  TAP-CINDER  FROM  PUDDLING  FURNACE. 

are  always  hard  and  brittle,  and  are  only  fit  for  such  constructions  as  rail- 
way bars,  where  hardness  is  required  rather  than  great  tenacity.  In  order 
to  improve  this  latter  quality,  the  rough  bars  are  cut  up  into  short  lengths, 
which  are  made  into  bundles,  and  after  being  raised  to  a  high  tempera- 
ture in  the  mill-fiuiiace,  are  passed  through  rollers,  which  weld  the 
several  bars  into  one  compound  bar,  to  be  subsequently  passed  through 
other  rollers  until  it  has  acquired  the  desired  dimensions.  By  thus  fagot- 
ing or  piling  the  bars,  their  texture  is  rendered  far  more  uniform,  and 
they  are  made  to  assume  a  fibrous  structure,  which  greatly  increases 
their  strength  {Merchant  Bar,  or  No.  2  Bar).  To  obtain  the  best,  or  No. 
3  Bar,  or  icire-iron,  these  bars  are  doubled  upon  themselves,  raised  to  a 
welding  heat,  and  again  passed  between  rollers.  These  repeated  rollings 
have  the  effect  of  thoroughly  squeezing  out  the  slag  which  is  mechanically 
entangled  among  the  particles  of  iron  in  the  rough  bars,  and  would  pro- 
duce flaws  if  allowed  to  remain  in  the  metal.  A  slight  improvement 
appears  also  to  be  effected  in  the  chemical  composition  of  the  iron  during 
the  rolling,  some  of  the  carbon,  silicon,  phosphorus,  and  sulphur,  still 
retained  by  the  puddled  iron,  becoming  oxidised,  and  passing  away  as 
carbonic  oxide  and  slag. 

The  following  table  exhibits  the  change  in  chemical  composition  which 
takes  place  in  pig-iron  when  puddled  (without  previous  refining)  and 
rolled  into  wire-iron: — 

Effect  of  Puddling  and  Forging  on  Cast-iron. 


In  100  parts. 

Carljon. 

SiUcon. 

Sulphur. 

Phosphonis. 

Grey  pig-iron, 
Puddled  bar,       . 
Wire-iron,  . 

2-275 
0-296 
0-111 

2-7-20      1      0-301 
0-120      !      0-134 
0-088      !      0-094 

0-645 
0-139 

0-117 

1 

About  90  parts  of  bar-iron  are  obtained  from  100  of  refined  iron  by 
the  puddling  process,  the  difference  representing  the  carbon  which  has 
passed  off"  as  carbonic  oxide,  and  the  silicon^  sulphur,  phosphorus,  and 
iron,  which  have  been  removed  in  the  slag  or  tap-cinder,  this  being 
essentially  a  silicate  of  protoxide  and  peroxide  of  iron,  varying  much  in 
composition  according  to  the  character  of  the  iron  employed  for  puddling, 
and  the  proportions  of  iron-scale  and  hammer-slag  introduced  into  the 
furnace.  Of  course,  also,  the  material  of  which  the  hearth  is  composed 
will  influence  the  composition  of  the  slag.  The  following  table  affords 
an  illustration  of  its  percentage  composition : — 


Tap-Cinder  from  Puddling  Furnace. 

Protoxide  of  iron  (FeO),  .  57-67 

Peroxide  of  iron  (FegOj),  .  13  53 

Silica,         .         .         .  ,  8-32 

Phosphoric  acid,          .  .  7-29 


Sulphide  of  iron,  .  .       7  07 

Lime,    .         .         .  .4-70 

Oxide  of  manganese,  .       0  78 

Magnesia,      .         .  .0-26 


The  lime  in  the  above  cinder  was  probably  derived  from  the  hearth 
of  the  furnace,  which  is  sometimes  lined  with  that  material  to  assist  in 
removing  the  sulphur. 

When  pig-iron  is  puddled  without  undergoing  the  refining  process,  it 
becomes  much  more  liquid  than  refined  iron,  and  the  process  is  some- 


THE  BESSEMER  PROCESS. 


313 


times  described  as  the  pig-boiling  process,  whilst  refined  iron  undergoes 
dri/  jmddHng. 

It  will  be  observed  that  this  process  of  puddling  is  attended  with  some 
important  disadvantages;  it  involves  a  great  expenditure  of  manual 
labour,  and  of  a  most  exhausting  kind;  the  very  high  temperature  to 
which  the  puddler  is  exposed  renders  him  liable  to  lung  disease,  and 
cataract  is  not  uncommonly  caused  by  the  intense  light  from  the  glowing 
iron;  the  wear  and  tear  of  the  puddling  furnace  is  veiy  considerable,  and 
since  it  receives  only  ten  or  eleven  charges  of  about  5  cwts.  each  in 
the  course  of  twenty-four  hours,  it  is  necessary  to  work  five  or  six 
puddling  furnaces  at  once,  in  order  to  convert  into  bar-iron  the  whole  of 
the  cast-iron  turned  out  from  a  single  blast-furnace.  These  considera- 
tions have  led  to  several  attempts  to  improve  the  puddling  process  by 
employing  revolving  furnaces  and  other  mechanical  arrangements  to 
supersede  the  heavy  manual  labour,  and  even  to  dispense  with  it 
altogether  by  forcing  the  air  into  the  molten  iron.  The  most  generally 
known  of  the  processes  devised  for  this  purpose  is  that  of  Bessemer, 
which  consists  in  running  the  melted  cast-iron  into  a  huge  crucible,  and 
forcing  air  up  through  it  under  considerable  pressure,  thus  combining  the 
purifying  influence  of  the  blast  of  air 
in  the  refinery  with  the  mechanical 
agitation  effected  in  the  puddling 
furnace.  Bessemer's  converting  vessel 
(fig.  248)  is  a  large,  nearly  cylindrical, 
crucible  of  wrought-iron,  lined  with 
ganister,  having  thirty  or  more  open- 
ings of  about  |th  inch  in  diameter 
(A)  at  the  bottom,  through  which  air 
is  blown  at  a  pressure  of  15  or  20 
lbs.  upon  the  inch.  This  vessel  is 
sometimes  large  enough  to  receive  10 
tons  of  cast-iron  for  a  charge.  The  metal  having  been  melted  in  a 
separate  furnace,  is  run  into  the  converting  vessel,  the  blast  being  already 
turned  on  so  that  the  liquid  iron  may  not  run  into  the  air  tubes.  The 
iron  burns  vividly,  and  the  oxide  of  iron  produced  is  diff'used  in  a  melted 
state  through  the  mass  of  metal  by  the  rapid  current  of  air.  This  oxide 
of  iron  acts  upon  the  silicon  and  carbon  in  the  cast-iron,  converting  the 
latter  into  carbonic  oxide,  which  burns  with  flame  at  the  mouth  of  the 
converter,  and  the  former  into  silica,  which  enters  into  the  slag,  and  is 
carried  up  as  a  froth  to  the  surface  of  the  liquid  iron.  The  blast  of  air 
or  hloti)  is  continued  for  about  twenty  minutes,  when  the  disappearance 
of  the  flame  of  carbonic  oxide  indicates  the  completion  of  the  process ; 
but  the  remaining  purified  iron  is  not  pasty  as  in  the  puddling  furnace, 
being  retained  in  a  perfectly  liquid  condition  by  the  high  temperature 
resulting  from  the  combustion  of  part  of  the  iron,  so  that  the  metal  may 
be  run  out  into  moulds  by  tilting  the  converting  vessel,  which  is  usually 
hung  upon  trunnions.  In  this  way  about  85  parts  of  bar-iron  are 
obtained  from  100  of  pig-iron. 

Although  so  great  an  economy  of  time  and  labour  would  result  from 
the  application  of  Bessemer's  process,  it  has  not  superseded  the  puddling 
process,  because  it  does  not  remove  the  sulphur  and  phosphorus  from  the 
pig-iron,   so  that  only  the  best  varieties  of  that  material,  extracted  from 


Fig.  248. — Bessemer's  converting 
vessel. 


314 


COMPOSITION  OF  BAK-IRON. 


haematite  or  magnetic  ore,  yield  a  bar-iron  of  good  quality  when  purified 
in  this  way.*  Moreover,  the  process  is  applicable  only  to  grey  iron  rich 
in  carbon  and  silicon,  which  is  more  expensive  than  the  light  forge  irons 
treated  in  the  puddling  furnace.  Its  application  to  the  manufacture  of 
steel  will  be  noticed  hereafter.  The  effect  of  the  Bessemer  process  upon 
a  particular  specimen  of  pig-iron  is  shown  in  the  table  : — 


In  100  parts  of  Pig-iron. 

Before. 

After. 

Carbon,  ..... 
Silicon,            .... 
Sulphur,          .... 
Phosphorus     .... 

3-309 
0-595 
0-485 
1-012 

0-218 
none 
0-402 
1-102 

In  Dankes^  rotating  puddling  furnace  the  pig-iron  is  run  into  a 
cylindrical  chamber  lined  with  a  mixture  of  haematite  and  lime.  Air  is 
supplied  by  a  fan,  and  the  cylinder  is  revolved  so  as  to  bring  the  metal 
thoroughly  into  contact  with  the  oxides  of  iron  which  form  part  of  the 
charge,  as  in  the  ordinary  puddling  process.  The  charge  of  about  600 
lbs.  is  turned  out  in  a  single  ball,  which  is  further  treated  as  usual.  In 
Crajnpton's  furnace  a  very  high  temperature  is  produced  by  a  blast  of  air 
containing  coal-dust  in  suspension. 

Composition  of  har-iron.- — Even  the  best  bar-iron  contains  from  0"1  to 
0-3  per  cent,  of  carbon,  together  with  minute  proportions  of  silicon, 
sulphur,  and  phosphorus.  Perfectly  pure  iron  is  inferior  in  hardness  and 
tenacity  to  that  which  contains  a  small  proportion  of  carbon. 

Bar-iron  is  liable  to  two  important  defects,  which  are  technically  known 
as  cold-shortness  and  red-shortness.  Cold-short  iron  is  brittle  at  ordinary 
temperatures,  and  appears  to  owe  this  to  the  presence  of  phosphorus,  of 
which  element  0-5  percent,  is  sufficient  materially  to  diminish  the  tenacity 
of  the  iron.  "When  the  iron  is  liable  to  brittleness  at  a  red  heat,  it  is 
termed  red-short  iron,  and  a  very  little  sulphur  is  sufficient  to  affect  the 
quality  of  the  iron  in  this  respect. 

Thei-e  is  much  difference  of  opinion  as  to  the  true  causes  of  the 
variation  in  the  strength  of  wrought-iron,  and  this  is  not  surprising  when 
we  reflect  upon  the  number  of  circumstances  which  may  be  reasonably 
expected  to  exert  some  influence  upon  it  Not  only  the  proportions 
of  carbon,  silicon,  sulphur,  phosphorus,  and  manganese  may  be  supposed 
to  affect  the  quality  of  the  iron,  but  the  state  of  combination  in  which 
these  elements  exist  in  the  mass  is  not  unlikely  to  cause  a  difference. 
It  also  appears  certain  that  the  mechanical  structure,  dependent  upon 
the  arrangement  of  the  particles  composing  the  mass  of  metal,  has  at 
least  as  much  influence  upon  the  tenacity  of  the  iron  as  its  chemical 
composition. 

The  best  bar-iron,  if  broken  slowly,  always  exhibits  a  fibrous  structure, 
the  particles  of  iron  being  arranged  in  parallel  lines.  This  appears  to 
contribute  greatly  to  the  strength  of  the  iron,  for  when  it  is  wanting,  and 
the  bar  is  composed  of  a  confused  mass  of  crystals,  it  is  weaker  in  pro- 
portion to  the  size  of  the  crystals.  The  presence  of  phosphorus  is  said  to 
favour  the  formation  of  large  crystals,  and  hence  to  produce  cold-shortness. 

*  By  lining  the  converter  with  basic  bricks  made  by  calcining  a  mixture  of  magnesian 
limestone  and  ferric  oxide,  the  removal  of  phosphorus  has  been  effected  in  the  Bessemer 

process. 


MANUFACTURE  OF  STEEL. 


315 


There  is  some  reason  to  believe  that  the  fihrous  is  sometimes  exchanged 
for  the  crystalline  texture  under  the  influence  of  frequent  vibrations, 
as  in  the  case  of  railway  axles,  girders  of  suspension-bridges,  &c. 

Considering  the  difficult  fusibility  of  bar-iron,  it  is  fortunate  that  it 
possesses  the  property  of  being  welded,  that  is,  of  being  united  by  ham- 
mering when  softened  by  heat.  It  is  customary  first  to  sprinkle  the 
heated  bars  with  sand  or  clay  in  order  to  convert  the  superficial  oxide  of 
iron  into  a  liquid  silicate,  which  will  be  forced  out  from  between  them  by 
hammering  or  rolling,  leaving  the  clean  metallic  surfaces  to  adhere. 


Mandfactdrb  op  Steel. 

220.  Steel  differs  from  bar-iron  in  possessing  the  property  of  becoming 
very  hard  and  brittle  when  heated  to  redness,  and  then  suddenly  cooled 
by  being  plunged  into  water.  Perfectly  pure  iron,  obtained  by  the 
electrotype  process,  is  not  hardened  by  sudden  cooling ;  but  all  bar-iron 
which  contains  carbon  does  exhibit  this  property  in  a  greater  or  less 
degree  according  to  the  proportion  of  carbon  present.  It  does  not 
become  decidedly  steely,  however,  until  the  carbon  amounts  to  0*15  per 
cent.  The  hardest  steel  contains  about  1'2  per  cent,  of  carbon,  and  when 
the  proportion  reaches  1  '4  per  cent,  it  begins  to  assume  the  properties  of 
white  cast-iron.  Bar-iron  may,  therefore,  be  converted  into  steel  by  the 
addition  of  about  1  per  cent,  of  carbon,  and,  conversely,  cast-iron  is 
converted  into  steel  when  the  quantity  of  carbon  contained  in  it  is 
reduced  to  that  amount,*  There  are  thus  two  processes  by  which  steel 
may  be  produced;  but  that  which  is  employed  almost  exclusively  in  this 
country  consists  in  combining  bar-iron  with  the  requisite  amount  of  carbon 
by  what  is  technically  known  as  cementation,  the  bars  being  imbedded 
in  charcoal  and  exposed  for  several  days  to  a  high  temperature. 

The  operation  is  effected  in  large  chests  of  firebrick  or  stone,  about  10 
or  12  feet  long  by  3  feet  wide  and  3  feet  deep. 

Two  of  these  chests  are  built  into  a  dome-shaped  furnace  {converting 
furnace,  fig.  249),  so  that  the  flame  may  circulate  round  them,  and  the 


Fig.  249.— Furnace  for  converting  bar-iron  into  steel. 

furnace  is  surrounded  with  a  conical  jacket  of  brickwork  in  order  to  allow 
a  steady  temperature  to  be  maintained  in  it  for  some  days.     The  charcoal 

*  Many  metallurgists  are  of  opinion  that  manganese  has  an  influence  similar  to  that  of 
carbon  in  converting  iron  into  steel. 


316  BLISTERED  STEEL. 

is  ground  so  as  to  pass  through  a  sieve  of  ^  inch  mesh,  and  spread  in  an 
even  layer  upon  the  bottom  of  the  chests.  Upon  this  the  bars  of  iron, 
which  must  be  of  the  best  quality,  are  laid  in  regular  order,  a  small 
interval  being  left  between  them,  which  is  afterwards  filled  in  with  the 
charcoal  powder,  with  a  layer  of  which  the  bars  are  now  covered;  over 
this  more  bars  are  laid,  then  another  layer  of  charcoal,  and  so  on  until  the 
chest  is  filled.  Each  chest  holds  5  or  6  tons  of  bars.  One  of  the  bars  is 
allowed  to  project  through  an  opening  in  the  end  of  the  chest,  so  that 
the  workmen  may  withdraw  it  from  time  to  time  and  judge  of  the  progress 
of  the  operation.  The  whole  is  covered  in  with  a  layer  of  about  6  inches 
of  damp  clay  or  sand. 

The  fire  is  carefully  and  gradually  lighted,  lest  the  chests  should  be 
split  by  too  sudden  application  of  heat,  and  the  temperature  is  eventually 
raised  to  about  the  fusing-point  of  copper  (2000°  F.),  at  which  it  is  main- 
tained for  a  period  varying  with  the  quality  of  steel  which  it  is  desired  to 
obtain.  Six  or  eight  days  suffice  to  produce  steel  of  moderate  hardness  ; 
but  the  process  is  continued  for  three  or  four  days  longer  if  very  hard 
steel  be  required.  The  fire  is  gradually  extinguished,  so  that  the  chests 
are  about  ten  days  in  cooHng  down. 

On  opening  the  chests  the  bars  are  found  to  have  suffered  a  remarkable 
change  both  in  their  external  appearance  and  internal  structure.  They 
are  covered  with  large  blisters,  obviously  produced  by  some  gaseovis  sub- 
stance raising  the  softened  surface  of  the  metal  in  its  attempt  to  escape. 
It  is  conjectured  that  the  blisters  are  caused  by  carbonic  oxide  produced 
by  the  action  of  the  carbon  upon  particles  of  slag  accidentally  present 
in  the  bar.  On  breaking  the  bars  across,  the  fracture  is  found  to  have 
a  finely  granular  structure,  instead  of  the  fibrous  appearance  exhibited 
by  bar-iron.  Chemical  analysis  shows  that  the  iron  has  combined  with 
about  1  per  cent,  of  carbon,  and  the  most  remarkable  part  of  the  result 
is  that  this  carbon  is  not  only  found  in  the  external  layer  of  iron,  which 
has  been  in  direct  contact  with  the  heated  charcoal,  but  is  also  present 
in  the  very  centre  of  the  bar.  It  is  this  transmission  of  the  solid  carbon 
through  the  solid  mass  of  iron  which  is  implied  by  the  term  cementation. 
The  chemistry  of  the  process  probably  consists  in  the  formation  of  car- 
bonic oxide  from  the  small  quantity  of  atmospheric  oxygen  in  the  chest, 
and  the  removal  of  one-half  of  the  carbon  from  this  carbonic  oxide,  by 
the  iron,  which  it  converts  into  steel,  leaving  carbonic  acid  gas  (2C0  —  C 
=  COo)  to  be  reconverted  into  carbonic  oxide  by  taking  up  more  carbon 
from  the  charcoal  (C02  +  C  =  2CO),  which  it  transfers  again  to  the  iron. 
Experiment  has  shown  that  soft  iron  is  capable  of  absorbing  mechanically 
4  "15  volumes  of  carbonic  oxide  at  a  low  red  heat,  so  that  the  action  of 
the  gas  upon  the  metal  may  occur  throughout  the  substance  of  the  bar. 
The  carbonic  oxide  is  retained  unaltered  by  the  iron  after  cooling,  unless 
the  bar  is  raised  to  the  temperature  required  for  the  production  of  steeL 

The  blistered  steel  obtained  by  this  process  is,  as  would  be  expected, 
far  from  uniform  either  in  composition  or  in  texture ;  some  portions  of  the 
bar  contain  more  carbon  than  others,  and  the  interior  contains  numerous 
cavities.  In  order  to  improve  its  quality  it  is  subjected  to  a  process  of 
fagoting  similar  to  that  mentioned  in  the  case  of  bar-iron ;  the  bars  of 
blistered  steel,  being  cut  into  short  lengths,  are  made  up  into  bundles, 
Avhioh  are  raised  to  a  welding  heat,  and  placed  under  a  tilt-hammer, 
weighing  about  2  cwt.,  which  strikes  two  or  three  hundred  blows  in  a 


HAEDENIXG  OF  STEEL.  317 

minute  ;  in  this  way  the  se\eral  bars  are  consolidated  into  one  compound 
bar,  which  is  then  extended  under  the  hammer  till  of  the  required 
dimensions.  The  bars,  before  being  hammered,  are  sprinkled  with  sand, 
Avhich  combines  with  the  oxide  of  iron  upon  the  surface,  and  forms 
a  vitreous  layer  which  protects  the  bar  from  further  oxidation.  The 
steel  which  has  been  thus  hammered  is  much  denser  and  more  uniform 
in  composition;  its  tenacity,  malleability,  and  ductility  are  greatly  in- 
creased, and  it  is  fitted  for  the  manufacture  of  shears,  files,  and  other 
tools.  It  is  commonly  known  as  shear  steel.  Double  shear  steel  is 
obtained  by  breaking  the  tilted  bars  in  two,  and  welding  these  into  a 
compound  bar. 

The  best  variety  of  steel,  however,  which  is  perfectly  homogeneous  in 
composition,  is  that  known  as  cad-steel,  to  obtain  which  about  30  lbs.  of 
blistered  steel  are  broken  into  fragments,  and  fused  in  a  fireclay  or  plum- 
bago crucible,  heated  in  a  wind-furnace,  the  surface  of  the  metal  being 
protected  from  oxidation  by  a  little  glass  melted  upon  it.  The  fused 
steel  is  cast  into  ingots,  several  crucibles  being  emptied  simultaneously 
into  the  same  mould.  Cast-steel  is  far  superior  in  density  and  hardness 
to  shear  steel,  but  since  it  is  exceedingly  brittle  at  a  red  heat,  great  care 
is  necessary  in  forging  it.  It  has  been  found  that  the  addition,  to  100 
parts  of  the  cast-steel,  of  one  part  of  a  mixture  of  charcoal  and  oxide  of 
manganese,  produces  a  fine-grained  steel  which  admits  of  being  cast  on  to 
a  bar  of  wrought-iron  in  the  ingot-mould,  so  that  the  tenacity  of  the  latter 
may  compensate  for  the  brittleness  of  the  steel  when  the  compound  bar 
is  forged,  the  wrought-iron  forming  the  back  of  the  implement,  and  the 
steel  its  cutting  edge. 

This  addition  of  manganese  to  the  cast-steel  (Heath's  patent)  has  effected 
a  great  reduction  in  its  cost,  allowing  the  use  of  blister  steel  made  from 
British  bar-iron^  whereas,  before  its  introduction,  only  the  expensive  iron 
of  Swedish  or  Eussian  make  could  be  employed.  But  little  manganese 
passes  into  the  steel,  the  bulk  of  it  going  into  the  slag,  and  apparently 
carrying  the  sulphur  and  phosphorus  with  it. 

After  the  steel  has  been  forged  into  the  shape  of  any  implement,  it  is 
hardened  by  being  heated  to  redness,  and  suddenly  chilled  in  cold  Avater, 
or  oil,*  or  mercury.  It  can  thus  be  rendered  nearly  as  hard  as  diamond, 
at  the  same  time  increasing  slightly  in  volume  (sp.  gr.  of  cast-steel  7 '93 ; 
after  hardening,  7 '66).  The  chemical  difference  between  hard  and  soft 
steel  appears  to  be  of  the  same  kind  as  that  between  grey  and  white  cast- 
iron  (page  307),  the  greater  proportion  of  the  carbon  in  hard  steel  being  in 
combination  with  the  metal,  while  in  soft  steel  the  greater  part  seems  to 
be  in  intimate  mechanical  admixture  with  the  iron,  for  it  is  left  undis- 
solved on  treating  the  steel  with  an  acid.  If  the  hardened  steel  be  heated 
to  redness,  and  allowed  to  cool  slowly,  it  is  again  converted  into  soft  steel, 
but  by  heating  it  to  a  temperature  short  of  a  red  heat,  its  hardness  may 
be  proportionally  reduced.  This  is  taken  advantage  of  in  annealing  the 
steel  or  "  letting  it  down  "  to  the  proper  temper.  The  very  hardest  steel 
is  almost  as  brittle  as  glass,  and  totally  unfit  for  any  ordinary  use,  but 
by  heating  it  to  a  given  temperature  and  allowing  it  to  cool,  its  elasticity 
may  be  increased  to  the  desired  extent,  without  reducing  its  hardness 
below  that  required  for  the  implement  in  hand.     On  heating  a  steel  blade 

*  Chilling  in  oil  cools  the  steel  less  suddenly,  on  account  of  the  lower  specific  heat  of  oil, 
and  therefore  does  not  render  it  so  hard  and  brittle.     It  is  often  spoken  of  as  toughening. 


318 


TEMPERING  OF  STEEL. 


gradually  over  a  flame,  it  will  acquire  a  light  yellow  colour  when  its  tem- 
perature reaches  430°  F.,  from  the  formation  of  a  thin  film  of  oxide ;  as 
the  temperature  rises  the  thickness  of  the  film  increases,  and  at  470°  a 
decided  yellow  colour  is  seen,  which  assumes  a  brown  shade  at  490°, 
becomes  purple  at  520'',  and  blue  at  550°.  At  a  still  higher  temperature 
the  film  of  oxide  becomes  so  thick  as  to  be  black  and  opaque.  Steel 
which  has  been  heated  to  430°,  and  allowed  to  cool  slowly,  is  said  to  be 
tempered  to  the  yellow,  and  is  hard  enough  to  take  a  very  fine  cutting 
edge,  whilst,  if  tempered  to  the  blue,  at  550°,  it  is  too  soft  to  take  a  very 
keen  edge,  but  has  a  very  high  degree  of  elasticity.  The  following  table 
indicates  the  tempering  heats  for  various  implements  : — 

Tempering  of  Steel. 


Temperature,  F. 

Colour. 

Implements  thus  tempered. 

430°  to  450° 

Straw-yellow. 

Razors,  lancets. 

470° 

Yellow. 

Pen-knives. 

490° 

Brown-yellow. 

Large  shears  for  cutting  metal. 

510° 

Brown-purple. 

Clasp-knives. 

620° 

Purple. 

Trtble-knives. 

530°  to  570° 

Blue. 

Watch-springs,  sword-blades. 

If  a  knife  blade  be  heated  to  redness  its  temper  w  spoilt,  for  it  is  con- 
verted into  soft  steel. 

In  general,  the  steel  implements  are  ground  after  being  tempered,  so 
that  they  are  not  seen  of  the  colours  mentioned  above,  except  in  the  case 
of  watch  springs. 

A  steel  blade  may  be  easily  distinguished  from  iron  by  placing  a  drop  of 
diluted  nitric  acid  upon  it,  when  a  dark  stain  is  produced  upon  the  steel, 
from  the  separation  of  the  carbon. 

Some  small  instruments,  such  as  keys,  gun-locks,  «fec.,  which  are 
exposed  to  considerable  wear  and  tear  by  friction,  and  require  the  external 
hardness  of  steel  without  its  brittleuess,  are  forged  from  bar-iron,  and 
converted  externally  into  steel  by  the  process  of  case-hardening,  which 
consists  in  heating  them  in  contact  with  some  substance  containing  carbon 
(such  as  bone-dust,  yellow  prussiate  of  potash,  &c.),  and  afterwards  chiU- 
iiig  in  water.  A  process  which  is  the  reverse  of  this  is  adopted  in  order 
to  increase  the  tenacity  of  stirrups,  bits,  and  similar  articles  made  of  cast- 
iron  ;  by  heating  them  for  some  hours  in  contact  with  oxide  of  iron  or 
manganese,  their  carbon  and  silicon  are  removed  in  the  forms  of  carbonic 
oxide  and  sUica,  and  they  become  converted  into  malleable  cast-iron. 

The  opinion  that  steel  owes  its  properties  entirely  to  the  presence  of 
carbon  is  not  universally  entertained.  Some  chemists  believe  that  nitro- 
gen (or  some  analogous  element)  is  an  indispensable  constituent,  but  the 
proportion  of  nitrogen  found  in  steel  is  too  minute  to  warrant  this  sup- 
position. Titanium  is  alleged  by  some  authorities  to  have  an  important 
influence  upon  the  quality  of  steel,  but  this  also  appears  to  be  a  doubtful 
matter.  Bar-iron  may  be  converted  into  steel  by  being  kept  at  a  high 
temperature  in  an  atmosphere  of  coal  gas,  from  which  it  abstracts  carbon. 

Bessemer  steel  was  originally  produced  by  arresting  the  purification  of 
cast-iron  in  Bessemer's  process  (page  313),  as  soon  as  the  carbon  had 
diminished  to  about  1  per  cent.,  when  the  steel  was  poured  out  in  the 


BESSEMER  STEEL.  319 

fused  state,  i.e.,  in  the  form  of  cast-steel.  A  steel  of  better  quality, 
however,  has  been  obtained  by  continuing  the  purification  until  liquid 
bar-iron  remains  in  the  converter,  and  introducing  the  proper  proportion 
of  carbon  in  the  form  of  a  peculiar  description  of  white  cast-iron  known 
as  Spiegel-eisen  (mirror  iron),  which  crystallises  in  lustrous  tabular  crystals, 
and  contains  large  proportions  of  carbon  and  manganese,  being  obtained 
by  smelting  spathic  iron  ore  rich  in  manganese,  with  charcoal  as  fuel. 
The  Spiegel-eisen  is  added,  in  a  melted  state,  to  the  Bessemer  iron  before 
jjouring  from  the  converter. 

The  composition  of  a  sample  of  Spiegel-eisen  smelted  from  a  spathic  ore, 
found  near  Musen  in  Prussia,  is  here  given  : — 

Iron,        .         .         .         82 -86     I     Silicon,    ...  I'OO 

Manganese,       .         .         10  "/l     |     Carbon,   .         .         .  4 "32 

Ferro-manganese,  which  is  also  employed  in  the  manufacture  of  steel, 
is  extracted  from  certain  manganese  ores,  and  contains  about  74  per  cent, 
of  manganese,  5  per  cent,  of  carbon,  and  1  per  cent,  of  silicon.  Since  the 
pig-iron  obtained  from  clay  ironstones  is  not  well  adapted  for  conversion 
into  Bessemer  steel,  large  quantities  of  haematite  are  imported  for  this 
manufacture  from  Bilbao  (Spain),  Elba,  Algeria,  &c. 

Siemens-Martin  steel  is  made  by  melting  together,  in  a  Siemens'  regene- 
rative furnace,  pig-iron  rich  in  manganese,  and  puddled  iron,  together  with 
steel-scrap  and  ferromanganese,  some  magnetic  iron  ore  being  also  some- 
times added  as  an  oxidising  agent  to  diminish  the  carbon.  Samples  of 
this  steel  were  found  to  contain,  in  100  parts — 

Carbon,      .... 
Manganese, 

The  soft  variety  was  prepared  for  boiler-plates. 

Puddled  steel  is  obtained  by  arresting  the  puddling  process  at  an  earlier 
stage  than  usual,  so  as  to  leave  a  proportion  of  carbon  varying  from  0*3 
to  1  '0  per  cent. 

Natural  steel  or  German  steel  results  in  a  similar  way,  from  the  incom- 
plete purification  of  cast-iron  in  the  refinery.  The  presence  of  manganese 
in  the  iron  is  favourable  to  its  production. 

Krupp's  cast-steel,  manufactured  at  Essen  near  Cologne,  and  employed 
for  ordnance,  shells,  &c.,  is  a  puddled  steel  made  from  haematite  and 
spathic  ore,  smelted  with  coke.  The  iron  thus  obtained  contains  much 
manganese,  which  is  removed  in  the  puddling  process.  Krupp's  steel 
contains  about  1'2  per  cent,  of  combined  carbon,  and  is  fused  with  a 
little  bar-iron  for  casting  ordnance.  The  fusion  is  effected  in  black  lead 
crucibles  holding  30  lbs.  each,  of  which  as  many  as  1200  are  emptied 
simultaneously  into  the  mould  for  the  largest  castings.  A  casting  of 
1 6  tons  requires  about  400  men,  who  act  together  in  well-disciplined  gangs, 
so  that  the  stream  of  molten  metal  shall  flow  continuously  along  the  gut- 
ters into  the  mould.  Such  large  castings  must  be  allowed  to  cool  very 
gradually,  so  that  they  are  kept  surrounded  with  hot  cinders,  sometimes 
for  two  or  three  months,  till  required  for  forging. 

221.  Direct  extraction  of  wrouglit-iron  from  the  ore. — "Where  very  rich 
and  pure  ores  of  iron,  such  as  haematite  and  magnetic  iron  ore,  are  obtain- 
able, and  fuel  is  abundant,  the  metal  is  sometimes  extracted  without 
being  converted  into  cast-iron.     It  is  probable  that  the  iron  of  antiquity 


lard. 

Medium. 

Soft. 

■Ql 

•35 

•16 

•40 

•18 

•14 

820 


EXTKACTION  OF  WROUGHT-IRON  FROM  THE  ORE. 


was  extracted  in  this  way,  for  it  is  doubtful  whether  cast-iron  was  known 
to  the  ancients,  and  the  slag  left  from  old  iron-works  does  not  indicate 
the  use  of  any  flux.  Some  works  of  this  description  are  still  in  operation 
in  the  Pyrenees,  where  the  Catalan  process  is  employed.  The  crucible  is 
lined  at  the  sides  with  thick  iron  plates,  and  at  the  bottom  with  a  refrac- 
tory stone.  A  quantity  of  red  hot  charcoal  is  thrown  into  it,  and  the 
space  above  this  is  temporarily  divided  into  two  compartments  by  a 
shovel.  The  compartment  nearest  to  the  pipe  through  which  the  blast 
enters  is  charged  with  charcoal,  and  the  other  compartment  with  the 
calcined  ore  in  small  pieces.  The  shovel  is  then  withdrawn,  and  a 
gradually  increasing  current  of  air  supplied,  fresh  ore  and  fuel  being  added 
as  they  sink  down.  One  part  of  the  oxide  of  irpn  is  reduced  to  the 
metallic  state  by  the  carbonic  oxide,  and  the  rest  combines  with  the  silica 
present  in  the  ore  to  form  a  slag.     After  about  five  hours  the  spongy 


Fig.  250. — Catalan  forge  for  smelting  iron  ores. 


masses  of  bar-iron  are  collected  into  a  ball  upon  the  end  of  an  iron  rod, 
and  hammered  into  a  compact  mass  like  the  metal  obtained  in  the 
puddling  furnace.  The  blowing  machine  employed  in  the  Pyrenees  is 
one  in  which  the  fall  of  water  from  a  cistern  down  a  long  wooden  pipe, 
sucks  in,  through  lateral  apertures,  a  supply  of  air  which  it  carries  down 
with  it  into  a  box,  from  which  the  pressure  of  the  column  of  water 
projects  it  with  some  force  through  the  blast-pipe,  the  water  escaping 
from  the  box  through  another  aperture. 

In  the  North  American  hloomery  forges  a  modernised  form  of  the  same 
process  is  adopted. 


EXTRACTION  OF  IRON  IN  THE  LABORATORY. 


321 


Fig.  251.— Sefstrom  furnace. 


The  wrought-iron  produced  by  this  process  always  contains  a  larger 
proportion  of  carbon  than  puddled  iron,  and  is  therefore  somewhat  steely 
iu  character. 

222.  Extraction  of  iron  on  the  small  scale. — Iu  the  laboratory,  iron  may  be  extracted 
from  hsematite  in  the  following  manner : — A  fireclay  crucible  (A,  fig.  251),  about  3 
inches  high,  is  filled  with  charcoal  powder,  rammed  down  in  successive  layers  ;  a 
smooth  conical  cavity  is  scooped  in  the  char- 
coal, and  a  mixture  of  100  grs.  red  haematite, 
25  grs.  chalk,  and  25  grs.  pipeclay,  is  intro- 
duced into  it ;  the  mixture  is  covered  with  a 
layer  of  charcoal,  and  a  lid  placed  on  the 
crucible,  which  is  heated  in  a  Sefstrom  blast- 
furnace,* fed  with  coke  in  small  pieces,  for 
about  half  an  hour.  On  breaking  the  cold 
crucible  a  button  of  cast-iron  will  be  obtained. 

Nearly  pure  iron  may  be  prepared  by  fusing 
the  best  wire-iron  with  about  one-fifth  of  its 
weight  of  pure  ferric  oxide,  to  oxidise  the 
carbon  and  silicon  which  it  contains.  Some 
powdered  green  glass,  perfectly  free  from  lead,  must  be  employed  as  a  flux,  and  the 
crucible  (with  its  cover  well  cemented  on  with  fireclay)  exposed  for  an  hour  to  a  very 
high  temperature.     A  silvery  button  of  iron  will  then  be  obtained. 

223.  Chemical  properties  of  iron. — In  its  ordinary  condition  iron  is 
unaffected  by  perfectly  dry  air,  but  in  the  presence  of  moisture  and  carbonic 
acid  gas  it  is  gradually  converted  into  hydrated  ferric  oxide  (2Fe203.3H20) 
or  rust.  The  water  is  decomposed,  and  ferrous  carbonate  formed 
(Fe -1- HgO -1- CO2  =  FeCOg  +  Hg) ;  this  is  dissolved  by  the  carbonic  acid 
present,  and  the  solution  rapidly  absorbs  oxygen  from  the  air,  deposit- 
ing the  ferric  oxide  in  a  hydrated  state,  2FeC03  +  0  -  FcgOg  +  2CO2. 
When  iron  nails  are  driven  into  a  new  oaken  fence,  a  black  streak  will 
soon  be  observed  descending  from  each  nail,  caused  by  the  formation  of 
tannate  of  iron  (ink)  by  the  action  of  the  tannic  acid  in  the  wood  upon 
the  solution  of  carbonate  of  iron  formed  from  the  nails.  The  diffusion  of 
iron-mould  stains  through  the  fibre  of  wet  linen  by  contact  with  a  nail,  is 
also  caused  by  the  formation  of  solution  of  carbonate  of  iron.  The  iron 
in  clialyheate  waters  is  also  generally  present  in  the  form  of  carbonate 
dissolved  in  carbonic  acid,  and  hence  the  rusty  deposit  which  is  formed 
when  they  are  exposed  to  the  air.  Iron  does  not  rust  in  water  containing 
a  free  alkali,  or  alkaline  earth,  or  an  alkaline  carbonate. 

Concentrated  sulphuric  and  nitric  acids  do  not  act  upon  iron  at  the 
ordinary  temperature,  though  they  dissolve  it  rapidly  when  diluted. 
Even  when  boiling,  strong  sulphuric  acid  acts  upon  it  but  slowly. 
When  iron  has  been  immersed  in  strong  nitric  acid  (sp.  gr.  1  "45),  it  is 
found  to  be  unacted  upon  when  subsequently  placed  in  diluted  nitric 
acid,  unless  previously  wiped ;  it  is  then  said  to  have  assumed  the  passive 
state.  If  iron  wire  be  placed  in  nitric  acid  of  sp.  gr.  1'35,  it  is  acted 
upon  immediately,  but  if  a  piece  of  gold  or  platinum  be  made  to  touch  it 
beneath  the  acid,  the  iron  assumes  the  passive  state,  and  the  action 
ceases  at  once.  A  state  similar  to  this,  the  cause  of  which  has  not  yet 
been  satisfa(;torily  explained,  is  sometimes  assumed  by  the  other  metals, 
though  in  a  less  marked  degree.     In  the  case  of  iron  it  has  been  attributed 

*  This  very  useful  furnace,  shown  in  section  in  fig.  251,  consists  of  two  iron  cylinders 
with  a  space  (B)  between  them,  into  which  air  is  forced  through  the  tube  C  by  a  double- 
action  bellows.  The  inner  cylinder  has  a  fireclay  lining  (D),  through  which  foiu"  or  six 
copper  tubes  (E)  admit  the  blast  into  the  fuel. 


322  OXIDES  OF  IRON. 

to  the  formation  of  a  coating  of  the  magnetic  oxide,  which  is  sparingly 
soluble  in  strong  nitric  acid. 

224.  Oxides  of  iron. — Three  compounds  of  iron  with  oxygen  are  known 
in  the  separate  state — 

Protoxide  of  iron,  or  ferrous  oxide,     .         .         .         FeO 
Sesquioxide  or  peroxide  of  iron,  or  ferric  oxide,   .         FegOg 
Magnetic  oxide,  or  ferroso-ferric  oxide,         .         .         ^^z^i 

Ferrous  oxide  is  little  known  in  the  separate  state  on  account  of  the 
readiness  with  which  it  absorbs  oxygen  and  forms  ferric  oxide.  If  a 
little  potash  or  ammonia  be  added  to  a  solution  of  the  green  sulphate  of 
iron  (FeSO^),  a  whitish  precipitate  of  ferrous  hydrate  is  formed,  which 
immediately  absorbs  oxygen,  and  is  converted  into  the  dingy  green 
ferroso-ferric  hydrate;  on  exposing  this  to  the  air,  it  absorbs  more 
oxygen  and  becomes  brown  ferric  hydrate.  This  disposition  of  the 
ferrous  hydrate  to  absorb  oxygen  is  turned  to  advantage  when  a  mixture 
of  ferrous  sulphate  with  lime  or  potash  is  employed  for  converting  blue 
into  white  indigo.     The  ferrous  oxide  is  a  strong  base. 

Peroxide  or  red  oxide  of  iron  has  been  already  noticed  among  the  ores 
of  iron,  and  has  also  been  referred  to  as  occurring  in  commerce  under  the 
names  of  colcothar,  jeweller's  rouge,  and  Venetian  red,  which  are  obtained 
by  the  calcination  of  the  green  sulphate  of  iron ;  2FeS04  =  FcgOg  +  SOg 
+  SO3.  The  hydrated  peroxide  (2Fe203.3H20),  obtained  by  decompos- 
ing a  solution  of  ferric  chloride  with  an  alkali,  forms  a  brown  gelatinous 
]3recipitate,  which  is  easily  dissolved  by  acids ;  but  if  it  be  dried  and 
heated  to  dull  redness,  it  exhibits  a  sudden  glow,  and  is  converted  into  a 
modification  which  is  dissolved  with  great  difficulty  by  acids,  although 
it  has  the  same  composition  as  the  soluble  form  which  has  not  been 
strongly  heated.  When  the  ferric  oxide  is  heated  to  whiteness,  it 
loses  oxygen,  and  is  converted  into  magnetic  oxide  of  iron,  SFegOg 
=  2Fe304  +  0.  Existing  as  it  does  in  all  soils,  ferric  oxide  is  believed  to 
fulfil  the  purpose  of  oxidising  the  organic  matter  in  the  soil,  and  convert- 
ing its  carbon  into  carbon  dioxide,  to  be  absorbed  by  the  plant :  the 
ferric  oxide  being  thus  reduced  to  ferrous  oxide,  which  is  oxidised  by  the 
air,  and  fitted  to  perform  again  the  same  office.  Ferric  oxide,  like  alumina, 
is  a  weak  base,  and  even  exhibits  some  tendency  to  play  the  part  of  an 
acid  towards  strong  bases,  though  not  in  so  marked  a  degree  as  alumina. 

Magnetic  or  hlack  oxide  of  iron  is  generally  regarded  as  a  compound  of 
ferrous  oxide  with  ferric  oxide  (FeO.FegOg),  a  view  which  is  confirmed 
by  the  occurrence  of  a  number  of  minerals  having  the  same  crystalline 
form  as  the  native  magnetic  oxide  of  iron,  in  which  the  iron,  or  part  of 
it,  is  displaced  by  other  metalfe.  Thus,  spinelle  is  MgO.AloOg;  Frank- 
Unite,  ZnO.FegOg ;  chrome-iron  ore,  FeO.CrgOg.  The  natural  magnetic 
oxide  was  mentioned  among  the  ores  of  iron,  and  this  oxide  has  been 
seen  to  be  the  result  of  the  action  of  air  or  steam  upon  iron  at  a  high 
temperature.  The  hydrated  magnetic  oxide  of  iron  (FcgO^.HgO)  is 
obtained  as  a  black  crystalline  powder  by  mixing  1  molecule  of  ferrous 
sulphate  with  1  molecule  of  ferric  sulphate,  and  pouring  the  mixture 
into  a  slight  excess  of  solution  of  ammonia,  which  is  afterwards  boiled 
with  it.  Magnetic  oxide  of  iron,  when  acted  upon  by  acids,  yields  mix- 
tures of  ferrous  and  ferric  salts,  so  that  it  is  not  an  independent  basic  oxide. 


PERRIU  ACID.  323 

The  very  stable  character  of  Fe304  has  led  to  its  application  for  protect 
ing  irou  from  rust.  When  superheated  steam  is  passed  over  the  red  hot 
metal,  a  very  dense  strongly  adherent  film  of  Fe^O^  is  produced,  which 
effectually  protects  the  metal  {Barffs  process).  A  similar  coating  is  pro- 
duced by  the  action  of  a  mixture  of  air  and  carbonic  acid  gas  {Bower's 
process). 

When  iron  filings  are  strongly  heated  with  nitre,  and  the  mass  treated  with  a  little 
water,  a  fine  purple  solution  of  potassium  ferrate  is  obtained.  A  better  method  of 
preparing  this  salt  consists  in  suspending  1  part  of  freshly  precipitated  ferric  oxide 
in  50  parts  of  water,  adding  30  parts  of  solid  potassium  hydrate,  and  passing  chlorine 
till  a  slight  effervescence  commences;  Fe,O3  +  Clg  +  10KHO  =  6KCl  +  2(K2FeO4) 
+  5H2O  ;  the  ferrate  forms  a  black  precipitate,  being  insoluble  in  the  strongly  alkaline 
solution,  though  it  dissolves  in  pure  water  to  form  a  purple  solution,  which  is  decom- 
posed even  by  dilution,  oxygen  escaping,  and  hydrated  feme  oxide  being  precipi- 
tated. A  similar  decomposition  takes  place  on  boiling  a  strong  solution,  or  on  adding 
an  acid  with  a  view  to  liberate  the  ferric  acid.  The  ferrates  of  barium,  strontium, 
and  calcium  are  obtained  as  tine  red  precipitates  when  solutions  of  their  salts  are 
mixed  with  potassium  ferrate. 

225.  Frotos7iIp7iate  of  iron,  copperas,  green  vitriol  or  fen'ous  sulphate, 
is  easily  obtained  by  heating  1  part  of  iron  wire  with  1^  parts  of  strong 
sulphuric  acid,  mixed  with  4  times  its  weight  of  water,  until  the  whole 
of  the  metal  is  dissolved,  when  the  solution  is  allowed  to  crystallise.  Its 
manufacture  on  the  large  scale  by  the  oxidation  of  iron  pyrites  has  been 
already  referred  to.  It  forms  fine  green  rhomboidal  crystals,  having  the 
composition  reSO4.H2O.6Aq. 

The  colour  of  the  crystals  varies  somewhat,  from  the  occasional  presence 
of  small  quantities  of  ferric  sulphate,  re2(S04)3.  It  dissolves  very  easily 
in  twice  its  weight  of  cold  water,  yielding  a  pale  green  solution.  When 
the  commercial  sulphate  of  iron  is  boiled  with  water,  it  yields  a  brown 
muddy  solution,  in  consequence  of  the  decomposition  of  the  ferric  sulphate 
contained  in  it,  with  precipitation  of  a  basic  sulphate.  Ferrous  sulphate 
has  a  great  tendency  to  absorb  oxygen,  and  to  become  converted  into 
ferric  sulphate.  Thus,  the  ordinary  crystals  when  exposed  to  air  gradually 
become  brown,  and  are  converted  into  a  mixture  of  the  normal  and  basic 
ferric  sulphates. 

This  disposition  to  absorb  oxygen  renders  the  ferrous  sulphate  useful 
as  a  reducing  agent ;  thus,  it  is  employed  for  precipitating  gold  in  the 
metallic  state  from  its  solutions.  But  its  chief  use  is  for  the  manufacture 
of  ink  and  black  dyes  by  its  action  upon  vegetable  infusions  containing 
tannic  acid,  such  as  that  of  nut-galls.  This  application  will  be  more 
particularly  noticed  hereafter. 

The  salt  FeSO^.SOg  is  obtained  in  minute  prismatic  crystals  when  a 
saturated  solution  of  ferrous  sulphate  is  added  to  an  excess  of  strong 
sulphuric  acid.* 

Sulphate  of  sesquioxide  of  iron,  or  persulphate  of  iron,  ot  ferric  sulphate, 
is  found  in  Chili  as  a  white  silky  crystalline  mineral,  coquimhite,  having 
the  composition  Fe2(S04)3.9Aq. 

Ferrous  and  ferric  phosphates  are  found  associated  in  the  mineral 
known  as  vivianite  or  native  Prussian  blue. 

226.  Sesquichloride  or  perchloride  of  iron,  ov  fen'ic  chloride  {¥efi\^, 
is  obtained  in  beautiful  dark  green  crystalline  scales  when  iron  wire  is 
heated  in  a  glass  tube  through  which  a  cnrrent  of  dry  chlorine  is  passed, 

*  Bolas,  Journal  of  the.  ChemicaZ  Society,  March  1874. 


324  FERRIC  CHLORIDE. 

the  ferric  chloride  passing  off  in  vapour,  and  condensing  in  the  cool  part 
of  the  tube.  The  crystals  almost  instantly  become  wet  when  exposed  to 
air  on  account  of  their  great  attraction  for  water.  Ferric  chloride  may  be 
obtained  in  solution  by  dissolving  iron  in  hydrochloric  acid,  and  convert- 
ing the  ferrous  chloride  (FeClg)  thus  formed  into  ferric  chloride  by  the 
action  of  nitric  and  hydrochloric  acids  (page  172).  A  strong  solution 
yields  crystals  of  Fe2Clg.2Aq.  The  solution  of  ferric  chloride  has  been 
recommended  in  some  cases  as  a  disinfectant,  being  easily  reduced  to 
ferrous  chloride,  and  thus  affording  chlorine  to  unstable  organic  matters  • 
(page  156).  In  contact  with  paper,  FcgClg  becomes  reduced  to  FeC^  when 
exposed  to  light.  A  solution  of  perchl 'ride  of  iron  in  alcohol  is  used  in 
medicine  under  the  name  of  tincture  of  iron. 

Solution  of  ferric  chloride  is  capable  of  dissolving  a  very  large  quantity  of  pure 
freshly  precipitated  ferric  oxide,  nine  molcules  of  Fe-^Oj  being  dissolved  by  one 
molecule  of  FcjClg.  The  solution  of  ferric  oxychloride  thus  obtained  has  a  very  dark 
red  colour,  and  yields  a  very  copious  brown  precipitate  with  common  water,  or  any 
solution  containing  even  a  trace  of  a  sulphate.  By  dialysis,  an  aqueous  solution  of 
ferric  oxide  is  left  in  the  dialyser. 

227.  Atomic  weight  of  iron. — When  iron  is  dissolved  in  hydrochloric 
acid,  28  parts  by  weight  of  iron  combine  with  35 '5  parts  of  chlorine, 
displacing  1  p^t  of  hydrogen.  The  specific  heat  of  iron  and  its  isomor- 
phism with  magnesium,  zinc,  and  cadmium,  show  that  its  atomic  weight 
must  be  represented  by  56,  so  that  iron  is  a  diatomic  or  bivalent  element, 
one  atom  of  iron  being  exchangeable  for  two  atoms  of  hydrogen. 

The  molecular  formula  of  ferric  chloride  has  been  confirmed  by  the 
determination  of  the  specific  gravity  of  its  vapour,  which  has  been  found 
to  be  165  times  that  of  hydrogen.  If,  therefore,  one  volume  (or  one 
atom)  of  hydrogen  be  represented  as  having  a  weight  =  1,  two  volumes 
(or  one  molecule)  of  ferric  chloride  vapour  would  weigh  (165  x  2)  330, 
a  number  nearly  agreeing  with  the  sum  of  two  atoms  of  iron  (112)  and 
six  atoms  of  chlorine  (213*0). 

It  will  be  remarked  that  iron  possesses  a  different  atomicity  accordingly 
as  it  exists  in  ferrous  or  ferric  compounds.  Thus,  in  ferrous  oxide  (FeO) 
and  ferrous  chloride  (FeCl^),  it  occupies  the  place  of  two  atoms  of  hydrogen, 
and  is  diatomic ;  but  in  ferric  oxide  (FcgOg)  and  ferric  chloride  (FcgCl,,) 
each  atom  of  iron  occupies  the  place  of  three  atoms  of  hydrogen,  and  is 
triatomic. 

Some  chemists  designate  the  diatomic  iron  existing  in  ferrous  compounds  by  the 
name  ferrosum  (Fe"),  and  the  triatomic  iron  of  the  ferric  compounds  hyferricum 
( Fe'").  Others  regard  iron  as  a  tetratomic  metal  Fe'",  existing  in  the  ferrous  salts  as 
a  group  of  two  atoms  united  by  two  bonds,  and  in  the  ferric  salts  as  a  group  of  two 
atoms  united  by  one  bond.  On  this  view,  ferrous  chloride  would  be  FejCl4,  or 
Cl^— Fe=:Fe=Cls  and  ferric  chloride  would  be  FejClg,  or  Cls^Fe— Fe^Clj. 

COBALT. 

Co"  =  59  parts  by  weight. 

228.  Some  of  the  compounds  of  cobalt  are  of  considerable  importance 
in  the  arts,  on  account  of  their  brilliant  and  permanent  colours.  It  is 
generally  found  in  combination  with  arsenic  and  sulphur,  forming  tin- 
white  cobalt,  CoAsg,  and  cobalt  glance,  CoASyCoSg,  but  its  ores  also  gene- 
rally contain  nickel,  copper,  iron,  manganese,  and  bismuth. 

The  metal  itself  is  obtained   by  strongly  heating  the  cobalt   oxalate 


COBALT.  325 

(C0C2O4)  in  a  covered  porcelain  crucible.  In  its  properties  it  closely 
resembles  iron,  but  it  is  said  to  surpass  it  in  tenacity. 

Two  oxides  of  cobalt  are  known — the  protoxide  or  cobaltous  oxide, 
CoO,  which  is  decidedly  basic,  and  the  sesquioxide  or  cobaltic  oxide, 
C02O3,  which  is  a  very  feeble  base.  The  protoxide  of  cobalt,  like  those 
of  iron  and  manganese,  tends  to  absorb  oxygen  from  the  air,  and  when 
heated  in  the  air,  becomes  converted  into  CoO.CogOg,  corresponding  to 
the  magnetic  oxide  of  iron.  The  commercial  oxide  of  cobalt,  which  is 
emplayed  for  painting  on  porcelain,  is  obtained  by  roasting  the  ore,  in 
order  to  expel  part  of  the  sulphur  and  arsenic,  dissolving  it  in  hydro- 
chloric acid,  and  precipitating  the  sesquioxide  of  iron  by  the  careful 
addition  of  lime,  when  the  remaining  arsenic  is  also  precipitated  as  ferric 
arseniate.  Hydrosulphuric  acid  is  passed  through  the  acid  solution  to 
precipitate  the  bismuth  and  copper,  leaving  the  cobalt  and  nickel  in 
solution.  The  latter,  having  been  boiled  to  expel  the  excess  of  hydro- 
sulphuric  acid,  is  neutralised  with  lime  and  mixed  with  solution  of 
chloride  of  lime,  which  precipitates  the  sesquioxide  of  cobalt  as  a  black 
powder,  leaving  the  oxide  of  nickel  in  solution,  from  which  it  may  be 
precipitated  by  the  addition  of  lime. 

The  salts  of  cobalt  have  a  fine  red  colour  in  the  hydrated  state,  or  in 
solution,"  but  are  generally  blue  when  anhydrous.  The  cobalt  silicate 
associated  Avith  potassium  silicate  forms  the  blue  colour  known  as  smalt, 
which  is  prepared  by  roasting  the  cobalt  ore,  so  as  to  convert  the  bulk  of 
the  cobalt  into  oxide,  leaving,  however,  a  considerable  quantity  of  arsenic 
and  sulphur  still  in  the  ore.  The  residue  is  then  fused  in  a  crucible  with 
ground  quartz  and  carbonate  of  potash,  when  a  blue  glass  is  formed,  con- 
taining cobalt  silicate  and  potassium  silicate,  whilst  the  iron,  nickel, 
and  copper,  combined  with  arsenic  and  sulphur,  collect  at  the  bottom  of 
the  crucible  and  form  a  fused  mass  of  metallic  appearance  known  as 
speiss,  which  is  employed  as  a  source  of  nickel  The  blue  glass  is  poured 
into  cold  water,  so  that  it  may  be  more  easily  reduced  to  the  fine  powder 
in  which  the  smalt  is  sold.  If  the  cobalt  ore  destined  for  smalt  be  over- 
roasted, so  as  to  convert  the  iron  into  oxide,  this  will  pass  into  the  smalt 
as  a  silicate,  injuring  its  colour. 

Zaffre  is  prepared  by  roasting  a  mixture  of  cobalt  ore  with  two  or  three 
parts  of  sand. 

Tlienard^s  blue  consists  of  cobalt  phosphate  and  aluminium  phosphate, 
and  is  prepared  by  mixing  precipitated  alumina  with  cobalt  phosphate 
and  calcining  in  a  covered  crucible.  The  phosphate  is  obtained  by 
precipitating  a  solution  of  cobalt  nitrate  with  phosphate  of  potassium  or 
sodium. 

Rinman^s  green  is  prepared  by  calcining  the  precipitate  produced  by 
sodium  carbonate  in  a  mixture  of  cobalt  sulphate  with  zinc  sulphate.  It 
is  a  compound  of  the  oxides  of  cobalt  and  zinc. 

Cobaltous  chloride  (CoClg),  obtained  by  dissolving  cobaltous  oxide  in 
hydrochloric  acid,  forms  red  hydrated  crystals,  which  become  blue  when 
part  of  their  water  is  expelled.  If  strong  hydrochloric  acid  be  added  to 
a  red  solution  of  this  salt,  it  becomes  blue  ;  if  enough  water  be  now  added 
to  render  it  pink,  the  blue  colour  may  be  produced  at  pleasure  by  boiling, 
the  solution  first  passing  through  a  neutral  tint.  Chloride  of  cobalt  is 
employed  as  a  synrpathetic  ink,  for  characters  written  with  its  pink  solu- 
tion are  nearly  invisible   till  they  are  held  before  the   fire,   when  they 


326  COMPOUNDS  OF  NICKEL. 

become  blue,  and  resume  their  original  pink  colour  if  exposed  to  the  air : 
a  little  chloride  of  iron  causes  a  green  colour. 

The  cohaltous  sulphide  (CoS)  is  obtained  as  a  black  precipitate  when 
an  alkaline  sulphide  is  added  to  a  solution  of  a  salt  of  cobalt.  A  cohaltic 
sulphide  (C0.2S3)  is  found  in  grey  octahedra,  forming  cobalt  pi/rites.  The 
disulphide  (CoSg)  has  been  obtained  artificially. 

When  ammonia  in  excess  is  added  to  a  solution  of  a  salt  of  cobalt,  a 
deep  red  liquid  is  produced,  which  rapidly  absorbs  oxygen  from  the  air, 
especially  if  ammonium  chloride  be  present,  giving  rise  to  the  production 
of  some  remarkable  and  complex  bases  which  contain  the  elements  of 
ammonia  and  of  different  oxides  of  cobalt. 

NICKEL. 

Ni"  =  59  parts  by  weight. 

229.  Nickel  owes  its  value  in  the  useful  arts  chiefly  to  its  property  of 
imparting  a  white  colour  to  the  alloys  of  copper  and  zinc,  with  which  it 
forms  the  alloy  known  as  German  silver.  Nickel  is  very  nearly  allied  to 
cobalt,  and  generally  occurs  associated  with  that  metal  in  its  ores.  One 
of  the  principal  ores  of  nickel  is  the  Kujjfernickel  or  copper-nickel,  so 
called  by  the  German  miners  because  they  frequently  mistook  it  for  an 
ore  of  copper;  it  has  a  reddish  metallic  appearance,  and  the  formula 
NiAs.  Grey  nickel  ore  or  nickel  glance  is  an  arseniosulphide  of  nickel, 
NiAs2.NiS2.  Arsenical  nickel,  NiAsg,  corresponds  to  tin- white  cobalt. 
The  metal  is  commonly  extracted  from  the  speiss  separated  during  the 
preparation  of  smalt  from  cobalt  ores  (page  325) ;  the  oxide  of  nickel 
prepared  by  the  method  described  above,  when  strongly  heated  in  contact 
with  charcoal,  yields  metallic  nickel  containing  carbon. 

Nickel  is  now  extracted  from  an  ore  found  in  New  Caledonia,  which 
contains  silicates  of  nickel,  iron,  &c.  The  ore  is  treated  with  sulphuric 
acid,  and  the  solution  mixed  with  ammonium  sulphate.  On  evaporation, 
nickel  ammonium  sulphate  is  deposited  in  crystals,  which  are  purified  by 
recrystallisation  and  boiled  with  an  alkaline  oxalate.  The  precipitated 
nickel  oxalate  is  decomposed  by  boiling  with  sodium  carbonate,  producing 
sodium  oxalate  which  may  be  used  again,  and  nickel  carbonate  which  is 
reduced  by  charcoal. 

The  pure  metal  is  obtained  by  igniting  the  oxalate,  as  in  the  case  of 
cobalt,  which  it  much  resembles  in  properties. 

The  oxides  of  nickel  correspond  in  composition  to  those  of  cobalt  The 
salts  formed  by  nickelous  oxide  (NiO)  are  usually  green,  and  give  bright 
green  solutions.  The  hydrate  has  a  characteristic  apple  green  colour,  and 
does  not  absorb  oxygen  from  the  air  like  the  cobaltous  hydrate.  The 
greater  facility  with  which  the  latter  is  converted  into  sesquioxide  has 
been  applied  (as  above  described)  to  effect  the  separation  of  the  two 
metals.  Nickelous  oxide  has  been  found  native  in  octahedral  crystals, 
which  have  also  been  obtained  accidentally  in  a  copper-smelting  furnace. 

Nickel  sulphate  (NiSO4.H2O.6Aq.)  forms  fine  green  prismatic  crystals, 
the  water  of  constitution  in  which  may  be  displaced  by  potassium 
sulphate,  forming  the  double  sulphate  of  nickel  and  potassium,  NiSO^. 
Iv2S04.6Aq.,  which  crystallises  so  readily  that  it  was  at  one  time  the 
form  in  which  nickel  was  separated  from  the  other  metals  present  in  its 
ores. 


MANGANESE.  327 

Three  sulphides  of  nickel  are  known — a  suhsidphide,  NigS;  a  proto- 
S7dphide,  ISiB,  found  native  as  capillary  pyrites,  and  obtained  as  a  black 
precipitate  by  the  action  of  an  alkaline  sulphide  upon  a  salt  of  nickel ; 
and  a  disidphide,  l^iSg. 

MANGANESE. 

Mu"  =  55  parts  by  weight. 

230.  Manganese  much  resembles  iron  in  several  particulars  relating  both 
to  its  physical  and  chemical  characters,  and  is  often  found  associated, 
in  small  quantities,  with  the  compounds  of  that  metal  The  metal  itself 
has  not  been  applied  to  any  useful  purpose. 

It  is  obtained  by  reducing  manganous  carbonate  (MnCOg)  with  char- 
coal, at  a  very  high  temperature,  when  a  fused  mass,  composed  of  man- 
ganese combined  with  a  little  carbon  (corresponding  to  cast  iron),  is 
obtained,  which  is  freed  from  carbon  by  a  second  fusion  in  contact  with 
manganous  carbonate. 

Metallic  manganese  is  darker  in  colour  than  pure  iron,  and  very  much 
harder;  it  is  brittle,  and  only  feebly  attracted  by  the  magnet.  It  is 
somewhat  more  easily  oxidised  than  iron. 

231.  Oxides  of  manganese. — Three  distinct  compounds  of  manganese 
with  oxygen  are  known — 

Protoxide  of  manganese,  or  manganous  oxide,    .         .         MnO 
Sesquioxide,  or  manganic  oxide,        ....         MugOg 
Peroxide^  or  manganese  dioxide,        ....         MnOg 

Theperoxide  of  manganese  is  the  chief  form  in  which  this  metal  is  found 
in  nature,  and  is  the  source  from  which  all  other  compounds  of  manganese 
are  obtained.  Its  chief  mineral  form  is  pyrohmte,  which  forms  steel- 
grey  prismatic  crystals  ;  but  it  is  also  found  amorphous,  as  psilomelane, 
and  in  the  hydrated  state  as  wad.  In  commerce  pyrolusite  is  known  as 
black  manganese,  or  simply  manganese,  and  is  largely  imported  from 
Germany,  Spain,  &c.,  for  the  use  of  the  manufacturer  of  bleaching-powder 
and  the  glass-maker.  It  is  also  used  as  a  cheap  source  of  oxygen,  which 
it  evolves  when  heated  to  redness,  leaving  the  red  oxide  of  manganese, 
MugO^.  The  manganese  dioxide  is  an  indifferent  oxide,  and  does  not 
combine  with  acids ;  when  heated  with  strong  sulphuric  acid,  it  loses  half 
its  oxygen,  and  forms  the  manganous  oxide,  which  is  a  powerful  base, 
and  reacts  v/ith  the  sulphuric  acid  to  form  manganous  sulphate ;  MnOg 
-1-  H^SO^  =  MnSO^  +  HgO  +  O.  Since  the  natural  dioxide  contains  ferric 
oxide,  some  ferric  sulphate  is  formed  at  the  same  time ;  but  if  the  mixture 
be  dried  and  heated  to  redness,  the  ferric  salt  is  decomposed,  leaving  ferric 
oxide,  while  the  manganous  sulphate  is  not  decomposed,  and  may  be 
dissolved  out  of  the  mass  by  treatment  with  water.  On  evaporating  the 
solution,  and  allowing  it  to  cool,  it  deposits  light  pink  crystals  of  sulphate 
of  manganese,  MnSO^HgO.iAq. 

This  salt  is  employed  by  the  dyer  and  calico-printer  in  the  production 
of  black  and  brown  colours.  When  a  solution  of  manganous  sulphate  is 
mixed  with  solution  of  chloride  of  lime  (page  155),  it  gives  a  black  pre- 
cipitate of  hydrated  peroxide  of  manganese — 

2MnS0,  +  Ca(C10)2  +  2CaO  =  2MnO,  4-  2CaS0,  +  CaClg. 


328  OXIDES  OF  MANGANESE. 

By  decomposing  a  solution  of  nianganous  sulpliate  with  potash  or  soda, 
a  white  precipitate  of  manganous  hydrate  is  obtained,  which  becomes 
brown  when  exposed  to  the  air,  absorbing  oxygen,  and  becoming  con- 
verted into  manganic  hydrate. 

If  solution  of  manganous  sulphate  be  mixed  with  sodium  carbonate, 
a  white  precipitate  of  manganous  carbonate,  2MnC03.H20,  is  obtained. 
The  pink  crystallised  mineral  manganese  spar  consists  of  manganous 
carbonate  (MnCOg). 

Protoxide  of  manganese  or  manganous  oxide  (MnO)  itself  is  obtained  as 
a  green  powder  by  heating  manganous  carbonate  in  a  tube  through  which 
hydrogen  is  passed  to  exclude  the  air,  which  would  convert  the  protoxide 
into  red  oxide  (MugOJ.  The  protoxide  has  been  obtained  in  transparent 
emerald-green  crystals. 

Sesquioxide  of  manganese  or  manganic  oxide,  crystallised  in  octahedra, 
forms  the  mineral  braunite,  and,  in  combination  with  water,  the  prismatic 
crystals  of  manganite  (MugOg-H.^O),  which  often  occurs  in  the  commercial 
ores  of  manganese.  The  manganic  oxide  is  a  weak  base,  dissolving  ia 
acids  to  form  deep  red  solutions,  which  evolve  oxygen  when  heated, 
leaving  manganous  salts.  The  manganic  sulphate  combines  with  potas- 
sium sulphate  to  form  manganese  alum,  KMn(SO^)2.12Aq.,  corresponding 
in  crystalline  form,  as  in  composition,  to  aluminium  alum.  When 
manganese  dioxide  in  minute  quantity  is  added  to  melted  glass,  it  imparts 
a  purple  colour,  which  is  probably  due  to  the  formation  of  a  manganic 
silicate.  The  amethyst  is  believed  by  some  to  owe  its  colour  to  the  same 
cause. 

Red  oxide  of  manganese  (MngO^)  is  the  most  stable  of  the  oxides  of  this 
metal,  and  is  formed  when  either  of  the  others  is  heated  in  air.  Thus 
obtained,  it  has  a  brown  or  reddish  colour;  but  it  is  found  in  nature  as 
the  black  mineral  hausmannite.  In  composition  it  resembles  the  magnetic 
oxide  of  iron,  but  it  seems  probable  that  its  true  formula  is  2MnO.Mn02, 
for  when  treated  with  diluted  nitric  acid  it  leaves  the  black  hydrated 
dioxide. 

When  a  compound  containing  manganese,  in  however  small  quantity,  is  fused 
on  a  piece  of  platinum  foil  with  sodium  carbonate  (page  114),  a  mass  of  sodium 
nianganate  (Na2Mn04)  is  formed,  which  is  green  while  hot,  and  becomes  blue  ou 
cooling.  The  oxygen  required  to  convert  the  lower  oxides  of  manganese  into  the 
nianganate  has  been  absorbed  from  the  air. 

Potassium  manganate  is  obtained  by  mixing  finely-powdered  manganese 
dioxide  into  a  paste  with  an  equal  weight  of  potassium  hydrate  dissolved 
in  a  little  water,  drying  the  paste,  and  heating  it  to  dull  redness  in  a  glass 
tube,  through  which  oxygen  is  passed  as  long  as  it  is  absorbed.  When 
the  mass  is  treated  with  a  little  cold  water,  it  gives  a  dark  emerald  green 
solution,  and  by  evaporating  this  over  oil  of  vitriol,  in  vacuo,  dark  green 
crystals  of  j^otassiuyn  manganate  (K2Mn04)  are  formed,  which  have  the 
same  crystalline  form  as  those  of  potassium  sulphate.  These  crystals 
dissolve  unchanged  in  water  containing  potash;  but  when  dissolved  in 
pure  water  they  yield  a  red  solution  of  potassium  permanganate,  and  a 
precipitate  of  manganese  dioxide — 

SK^MnO^  -1-  2H2O  =  KjMnaOg  +  MuOg  +  4KH0 . 

The  change  is  more  completely  effected  by  adding  a  little  free  acid,  even 
carbonic   acid.     The   changes   of   colour   thus   produced  have   acquired 


PERMANGANATE  OF  POTASH.  329 

for  the  manganate  the  name  chameleon  mineral.  The  solution  of 
potassium  manganate  (containiug  free  potash)  is  vevj  easily  decomposed 
by  substances  having  an  attraction  for  oxygen.  Thus,  most  organic  sub- 
stances abstract  oxygen  from  it,  and  cause  the  separation  of  brown  man- 
ganic oxide;  filtering  its  solution  through  paper  wiU  even  effect  this 
change.  The  offensive  emanations  from  putrefying  organic  matters  are  at 
once  oxidised  and  rendered  inodorous  by  manganates, 

Sodium  7nanganate  (NagMnO^)  obtained  by  heating  manganese  dioxide 
with  sodium  hydrate,  under  free  exposure  to  air,  is  employed  in  a  state 
of  solution  in  water,  as  Condi/ s  green  disinfecting  fluid.  It  is  also  used 
as  a  bleaching  agent,  and  in  the  preparation  of  oxygen  at  a  cheap  rate. 
Barium  manganate  forms  the  pigment  known  as  Cassel  green. 

Permanganic  add,  H.iMngOg,  has  been  obtained  in  a  hydrated  crystalline  state 
by  decomposing  the  barium  permanganate  with  sulphuric  acid,  and  evaporating 
the  solution  in  vacuo.  It  is  a  brown  substance,  easily  dissolving  in  water  to  a  red 
liquid,  which  is  decomposed  at  about  90°  F.,  evolving  oxj'gen,  and  depositing 
manganese  dioxide. 

When  potassium  permanganate  is  added  to  oil  of  vitriol  +  a  molecule  of  water,  red 
oily  drops  separate,  which  explode  when  heated ;  but,  with  care,  they  may  be  distilled 
off  at  about  60°  C. ,  in  violet  vapours,  which  condense  into  a  very  dark  liquid  which 
immediately  sets  fire  to  combustible  bodies.  This  is  probably  HgMngOg,  of  which  the 
crystalline  body  above  mentioned  is  a  combination  with  water. 

Permanganate  of  potash  or  potassium  permanganate  (RgMugOg)  is 
largely  used  in  many  chemical  operations.  In  order  to  prepare  it,  4  parts 
of  finely -powdered  manganese  dioxide  are  intimately  mixed  with  3|  parts 
of  potassium  chlorate,  and  5  parts  of  potassium  hydrate  dissolved  in  a 
very  little  water.  The  pasty  mass  is  dried,  and  heated  to  dull  redness 
for  some  time  in  an  iron  tray  or  earthen  crucible.  The  potassium  chlorate 
imparts  the  required  oxygen.  On  treating  the  cold  mass  Avith  water, 
potassium  manganate  is  dissolved,  forming  a  dark  green  solution.  This 
is  diluted  with  water,  and  a  stream  of  carbonic  acid  gas  passed  through 
it  as  long  as  any  change  of  colour  is  observed;  3K2Mn04 -f- 2CO2 
=  K^Mn^Og -I- MnOg  +  2K2CO3.  The  precipitated  Mn02  is  allowed  to 
settle,  and  the  clear  red  solution  poured  off  and  evaporated  to  a  small 
bulk.  On  cooling,  it  deposits  prismatic  crystals  of  the  permanganate 
(KgMugOg),  which  are  red  by  transmitted  light,  but  reflect  a  dark  green 
colour.  The  potassium  carbonate,  being  much  more  soluble  in  water,  is 
left  in  the  solution.  Potassium  permanganate  is  remarkable  for  its  great 
colouring  power,  a  very  small  quantity  of  the  salt  producing  an  intense 
purplish-red  colour  in  a  large  quantity  of  water.  Its  solution  in  water  is 
very  easily  decomposed  and  bleached  by  substances  having  an  attraction 
for  oxygen,  such  as  sulphurous  acid  or  a  ferrous  salt.  If  a  very  small 
piece  of  iron  wire  be  dissolved  in  diluted  sulphuric  acid,  the  solution  of 
ferrous  sulphate  so  produced  will  decolorise  a  large  volume  of  weak 
solution  of  the  permanganate,  being  converted  into  ferric  sulphate — 
K2Mn20g  -f  lOFeSO^  +  SHgSO^  =  K2SO4  +  2MnS0^  +  5Fe2(S04)3  -f-  8H2O. 

This  decomposition  forms  the  basis  of  a  valuable  method  for  determining 
the  proportion  of  iron  in  its  ores. 

Many  organic  substances  are  easily  oxidised  by  potassium  permanganate, 
and  this  is  the  case  especially  with  the  offensive  emanations  from  putres- 
cent organic  matter.  Hence  it  is  extensively  used  under  the  name  of 
Cond/s  red  disinfecting  fluid ,  in  cases  where  a  solid  or  liquid  substance  is 
to  be  deodorised. 


330  CHLORIDES  OF  MANGANESE. 

An  alkaline  solution  of  the  permanganate  is  sometimes  used  as  an 
oxidising  agent,  since  it  parts  with  oxygen  when  boiled,  becoming  green 
from  the  production  of  manganate  ;  KgHn^Og  +  2KH0  =  2K2Mn04 
+  HgO  +  0. 

232.  Chlorides  of  manganese. — There  appear  to  be  three  compounds  of 
manganese  with  chlorine,  corresponding  to  three  of  the  oxides,  viz., 
MnClg,  MugClg,  and  MnCl4  ;  but  only  the  first  is  obtainable  in  the  pure 
state,  the  others  forming  solutions  which  are  easily  decomposed  with 
evolution  of  chlorine. 

Tlie  manganous  chloride  (MnClg)  is  obtained  in  large  quantity  as  a  waste  product 
in  the  jireparation  of  chlorine,  for  the  manufacture  of  bleaching-powder.  Since  there 
is  no  useful  application  for  it,  the  manufacturer  sometimes  reconverts  it  into  the  black 
oxide.  As  the  native  binoxide  always  contains  iron,  the  liquor  obtained  by  treating 
it  with  hydrochloric  acid  contains  ferric  chloride  (FeaClg)  mixed  with  chloride  of 
manganese  (MnClg).  In  ordei'to  separate  the  iron,  advantage  is  taken  of  the  circum- 
stance that  sesquioxides  are  weaker  bases  than  the  protoxides,  so  that  if  a  small  pro- 
portion of  lime  be  added  to  the  solution,  the  iron  may  be  precijHtated  as  sesquioxide, 
without  decomposing  the  chloride  of  manganese;  re.2Clg  +  3CaO  =  Fe^Os  +  3CaC1.2. 
The  solution  of  chloride  of  manganese  is  then  mixed  with  chalk,  and  subjected  to  the 
action  of  steam  at  a  pressure  of  about  two  atmospheres.  Carbonate  of  manganese  is 
precipitated  (MnCl2  +  CaC03  =  CaCl2  +  MnC03),  and  when  this  is  dried  and  heated  to 
about  600°  F.  in  a  current  of  moist  air,  carbonic  acid  gas  is  expelled,  and  a  large  pro- 
portion of  the  oxide  of  manganese  is  converted  into  binoxide,  which  may  be  employed 
again  for  the  preparation  of  chlorine. 

According  to  Weldon's  process  (page  148),  the  iron  is  precipitated  as  peroxide  by 
adding  chalk,  which  leaves  the  manganese  in  solution  ;  an  excess  of  lime  is  then 
added  and  air  blown  through  the  mixture  at  about  150°  F.,  when  the  white  precipi- 
tate of  MnO,  formed  at  first,  absorbs  the  oxygen,  and  becomes  a  black  compound  of 
MnOj  with  lime,  which  is  used  over  again  for  the  preparation  of  chlorine.  Unless 
the  lime  is  added  in  excess,  only  MnO.MnOj  is  formed,  so  that  the  excess  of  lime 
displaces  the  MnO  and  allows  it  to  be  converted  into  MnOa.  In  another  process 
Weldon  employs  magnesia  instead  of  lime,  with  the  view  of  afterwards  recovering  the 
chlorine  from  the  chloride  of  m.agnesium,  in  the  form  of  hydrochloric  acid  (see  page 
283),  and  using  the  magnesia  over  again. 

By  dissolving  potassium  permanganate  in  oil  of  vitriol,  and  adding  fragments  of 
fused  sodium  chloride,  a  remarkable  greenish-yellow  gas  is  obtained,  which  gives 
purple  fumes  with  moist  air,  and  is  decomposed  by  water,  yielding  a  red  solution  which 
contains  hydrochloric  and  permanganic  acids.  It,  therefore,  must  contain  manganese 
and  chlorine,  and  is  sometimes  regarded  as  the  perchloride  (MnCly)  ;  but  it  is  more 
probably  an  oxychloride  of  manganese  (see  Chlorochromic  acid).  Care  is  required  in 
its  preparation,  which  is  sometimes  attended  with  explosion. 

CHEOMIUM. 

Cr=52  "5  parts  by  weight. 

233.  This  metal  derives  its  name  from  xpwfxa,  colour,  in  allusion  to  the 
varied  colours  of  its  compounds,  upon  which  their  uses  in  the  arts  chiefly 
depend.  It  is  comparatively  seldom  met  with,  its  principal  ore  being  the 
clirome-iron  ore  (FeO.CrgOg),  which  is  remarkable  for  its  resistance  to  the 
action  of  acids  and  other  chemical  agents.  It  is  chiefly  found  in  the 
Shetland  Islands,  Sweden,  Eussia,  and  the  United  States,  and  is  imported 
for  the  manufacture  of  bichromate  of  potash  {'K.fi.^CvO^,  which  is  one  of 
the  chief  commercial  compounds  of  chromium.  The  ore  is  first  heated  to 
redness  and  thrown  into  water,  in  order  that  it  may  be  easily  ground  to 
a  fine  powder,  which  is  mixed  with  carbonate  of  potash,  chalk  being 
added  to  prevent  the  fusion  of  the  mass,  and  strongly  heated  in  a  current 
of  air  on  the  hearth  of  a  reverberatory  furnace,  the  mass  being  occasionally 


CHROMIC  ACID.  331 

stirred  to  expose  a  fresh  surface  to  the  air.  The  oxide  of  iron  is  thus 
converted  into  sesquioxide,  and  the  sesquioxide  of  chromium  (Cr^Og)  also 
absorbs  oxygen  from  the  air,  becoming  chromic  acid  (CrOg),  which  com- 
bines with  the  potash  to  form  chromate  of  potash  (KgO.CrOg).  !Nitre  is 
sometimes  added  to  hasten  the  oxidation.  On  treating  the  mass  with 
water,  a  yellow  solution  of  chromate  of  potash  is  obtained,  which  is  drawn 
off  from  the  insoluble  residue  of  sesquioxide  of  iron  and  lime,  and  mixed 
with  a  slight  excess  of  nitric  acid — 

2(K20.Cr03)  +  2HNO3  =  K20.2Cr03  +  2KNO3  +  HgO. 

Chromate  of  Bichromate  of 

potash.  potash. 

The  solution,  when  evaporated,  deposits  beautiful  red  tabular  crystals  of 
bichromate  of  potash  (potassium  dichromate)  which  dissolve  in  10  parts  of 
cold  water,  forming  an  acid  solution.  It  is  from  this  salt  that  the  other 
compounds  of  chromium  are  immediately  derived. 

Metallic  chromium  has  received  no  useful  application.  It  has  been 
obtained  in  octahedral  crystals  by  the  action  of  sodium  on  chromic 
chloride,  and  in  a  pulverulent  state  by  the  action  of  potassium.  In 
the  latter  condition  it  is  easily  acted  on  by  acids,  but  the  crystallised 
chromium  is  insoluble  even  in  nitrohydrochloric  acid.  Like  aluminium, 
it  is  more  easily  attacked  by  hydrated  alkalies  at  a  high  temperature, 
evolving  hydrogen  and  producing  chromates.     It  is  remarkably  infusible. 

234.  Oxides  of  Chromium. — Two  oxides  of  chromium  are  known  in 
the  separate  state — the  sesquioxide  or  chromic  oxide,  CrgOg,  and  chromic 
anhydride,  CrOg.  Protoxide  of  chromium  or  chromous  oxide  (CrO)  is 
known  in  the  hydrated  state,  and  perchromic  acid  (HgCrgOg)  is  believed 
to  exist  in  solution. 

Chromic  anhydride  (commonly  called  chromic  acid),  the  most  important 
of  these,  is  obtained  by  adding  to  one  measure  of  a  solution  of  bichromate 
of  potash,  saturated  at  130°  JF.,  one  measure  and  a  half  of  concentrated 
sulphuric  acid,  by  small  portions  at  a  time,  and  allowing  the  solution  to 
cool,  when  chromic  anhydride  crystallises  out  in  fine  crimson  needles, 
which  are  deliquescent,  very  soluble  in  water,  and  decomposed  by  a 
moderate  heat  into  oxygen  and  chromic  oxide.  Chromic  anhydride  is  a 
powerful  oxidising  agent;  most  organic  substances,  even  paper,  will  reduce 
it  to  the  green  chromic  oxide.  A  mixture  of  potassium  dichromate  and 
sulphuric  acid  is  employed  for  bleaching  some  oils,  the  colouring  matter 
being  oxidised  at  the  expense  of  the  chromic  acid,  and  chromic  sulphate 
produced — 

KgCr^O.  +  4H2SO4  =  K2SO,  +  Cr2(SOj3  +  O3   +  4H,0  . 

The  dichromate  itself  evolves  oxygen  when  heated  to  bright  redness,  being 
first  fused,  and  afterwards  decomposed;  2K2Cr207  =  2K2C1O4  +  Cr^Og 
+  O3  .  The  oxidising  effect  of  the  potassium  dichromate,  under  the  action 
of  light,  upon  gelatine  and  albumen,  receives  very  important  applications 
in  photography. 

Chromate  ofj)otash  or  normal  potassium  chromate  (K20.Cr03  or  KgCrOJ, 
is  formed  by  adding  carbonate  of  potash  to  the  red  solution  of  bichromate 
of  potash  until  its  red  colour  is  changed  to  a  fine  yellow,  when  it  is 
evaporated  and  allowed  to  crystallise.  It  forms  yellow  prismatic  crystals 
having  the  same  form  as  those  of  potassium  sulphate,  and  is  far  more 


332  CHROMATES. 

soluble  in  water  than  the  dichromate,  yielding  an  alkaline  solution.  It 
becomes  red  when  heated,  and  fuses  without  decomposition.  Potassium 
chromate  has  been  found  in  some  yellow  samples  of  saltpetre  from 
Chili. 

Terchromate  of  potash  (KgO.SCrOg)  has  been  obtained  in  red  crystals 
by  adding  nitric  acid  to  the  dichromate. 

It  will  be  observed  that  the  chromates  of  potassium  are  rather  excep- 
tional salts.  The  yellow  or  normal  chromate,  KgCrO^,  is  formed  upon 
the  model  of  imaginary  chromic  acid,  HgCrO^.  The  red  chromate  or 
potassium  dichromate  is  not  a  true  acid  salt,  for  it  contains  no  hydrogen; 
it  is  sometimes  called  anhydro-chrowate,  and  written  KgCrO^.CrOg.  The 
terchromate  would  be  K2Cr04.2Cr03. 

Chrome-yellow  is  the  chromate  of  lead  (PbCrO^),  prepared  by  mixing 
dilute  solutions  of  lead  acetate  and  potassium  chromate.  It  is  largely 
used  in  painting  and  calico-printing,  and  by  the  chemist  as  a  source  of 
oxygen  for  the  analysis  of  organic  substances,  since,  when  heated,  it 
fuses  to  a  brown  mass,  which  evolves  oxygen  at  a  red  heat.  Chrome- 
yellow  being  a  poisonous  salt,  its  occasional  use  for  colouring  confectionery 
is  very  objectionable.  Chromate  of  lead  in  prismatic  crystals  forms  the 
rather  rare  red  lead  ore  of  Siberia,  in  which  chromium  was  first 
discovered. 

Orange  chrome  is  a  basic  chromate  of  lead  (PbCrO^.PbO),  and  may  be 
obtained  by  boiling  the  yellow  chromate  with  lime;  2(PbCrOJ  +  CaO 
=  PbCrO^.PbO  +  CaCrO^.  The  calico-printer  dyes  the  stuff  with  yellow 
chromate  of  lead,  and  converts  it  into  orange  chromate  by  a  bath  of  lime- 
water. 

The  colour  of  the  ruby  (crystallised  alumina)  appears  to  be  due  to  the 
presence  of  a  small  proportion  of  chromic  anhydride. 

Sesquioxide  of  chromium  or  chromic  oxide  (Cr^f)^  is  valuable  as  a  green 
colour,  especially  for  glass  and  porcelain,  since  it  is  not  decomposed  by 
heat.  Being  extremely  hard,  it  is  used  in  making  razor-strops.  It  is 
prepared  by  heating  bichromate  of  potash  with  one-fourth  of  its  weight 
of  starch,  the  carbon  of  which  deprives  the  chromic  acid  of  half  its  oxygen, 
leaving  a  mixture  of  chromic  oxide  with  potassium  carbonate,  which  may 
be  removed  by  washing  with  water.  If  sulphur  be  substituted  for  the 
starch,  potassium  sulphate  will  be  formed,  which  may  also  be  removed  by 
water.  When  chromic  oxide  is  strongly  heated,  it  exhibits  a  sudden 
glow,  becomes  darker  in  colour,  and  insoluble  in  acids  which  previously 
dissolved  it  easily ;  in  this  respect  it  resembles  alumina  and  ferric  oxide. 
Like  these  oxides,  the  chromic  oxide  is  a  feeble  base ;  it  is  remarkable 
for  forming  two  classes  of  salts,  having  the  same  composition,  but  differing 
in  the  colour  of  their  solutions,  and  in  some  other  properties.  Thus, 
there  are  two  modifications  of  the  chromic  sulphate — the  green  sulphate, 
Cr.2(S04)3.5Aq.,  and  the  violet  sulphate,  Crg  (80^)3.1 5 Aq.  The  solution 
of  the  latter  becomes  green  when  boiled,  being  converted  into  the  former. 
Chrome  alum  forms  dark  purple  octahedra  (KCr"'(S04)2.12Aq.)  which 
contain  the  violet  modification  of  the  sulphate ;  and  if  its  solution  in 
water  be  boiled,  its  purple  colour  changes  to  green,  and  the  solution 
refuses  to  crystallise.*  The  anhydrous  chromic  sulphate  forms  red 
crystals,  which  are  insoluble  in  water  and  acids.  A  green  basic  chromic 
borate  is  used  in  painting  and  calico-printing,  under  the  name  of  vert 
*  Exposure  to  cold,  it  is  said,  again  converts  it  into  the  crystallisable  violet  form. 


CHLORIDES  OF  CHROMIUM.  383 

de  Guignet,  and  is  prepared  by  strongly  heating  bichromate  of  potash 
with  3  parts  of  crystallised  boracic  acid,  when  potassium  borate  and 
chromic  borate  are  formed,  half  the  oxygen  of  the  CrOg  being  expalled. 
The  potassium  borate  and  the  excess  of  BgOg  are  afterwards  washed 
out  by  water.  By  reducing  an  alkaline  chromate  with  sodium  thio- 
sulphate,  the  compound  Cr.2O3.CrO3  has  been  obtained  as  a  brown  pre- 
cipitate. 

Protoxide  of  chromium  or  chromovs  oxide  (CrO)  is  not  known  in  the 
pure  state,  but  is  precipitated  as  .a  brown  hydrate  when  chromous  chloride 
is  decomposed  by  potash.  It  absorbs  oxygen  even  more  readily  than 
ferrous  oxide,  becoming  converted  in  (CrO.CrgOg)  corresponding  in  com- 
position to  the  magnetic  oxide  of  iron.  Chromous  oxide  is  a  feeble  base ; 
a  double  sulphate  (K2Cr"(SO^)2.6Aq.)  is  known,  which  has  the  same 
crystalline  form  as  the  corresponding  iron  salt  (K2Fe"(SO^)2.6Aq.) ;  it 
has  a  blue  colour,  and  gives  a  blue  solution,  which  becomes  green  when 
exposed  to  air,  from  the  formation  of  chromic  oxide. 

Perchromic  acid  (HgCrgOg)  is  believed  to  exist  in  the  blue  solution 
obtained  by  the  action  of  hydric  peroxide  upon  solution  of  chromic  acid, 
but  neither  the  acid  nor  its  salts  have  been  obtained  in  a  separate  state. 

235.  Chlorides  of  chromium. — The  chromic  chloride  (CrjClg)  obtained  by  passing 
dry  chlorine  over  a  mixture  of  chromic  oxide  with  charcoal,  heated  to  redness  in  a 
glass  tube,  is  converted  into  vapour,  and  condenses  upon  the  cooler  part  of  the  tube 
in  shining  leaflets  having  a  fine  violet  colour.  Cold  water  does  not  affect  them,  but 
boiling  water  slowly  dissolves  them  to  a  green  solution  resembling  that  obtained  by 
dissolving  chromic  oxide  in  hydrochloric  acid. 

Chromaus  chloride  (CrClg)  resuJts  from  the  action  of  hydrogen,  at  a  red  heat,  upon 
chromic  chloride.  Strange  to  say,  it  is  white,  and  dissolves  in  water  to  form  a  blue 
solution,  which  absorbs  oxygen  from  the  air,  becoming  green.  It  is  remarkable  that 
if  the  violet  chromic  chloride  is  suspended  in  water,  and  a  minute  quantity  of  chromous 
chloride  added,  the  former  imtnediately  dissolves  to  a  green  solution,  evolving  heat. 

The  so-called  chlorochromic  acid  (CrO.,Cl2)  is  a  veiy  remarkable  brown-red  liquid, 
obtained  by  distilling  10  parts  of  common  salt  and  17  of  bichromate  of  potash, 
previously  fused  together  and  broken  into  fragments,  with  40  parts  of  oil  of  vitriol — 

KaCrgOy  +  4NaGl  -f  SHaSO,  =  K2SO4  +  2Na2S04  +  SHjO  +  2Cr02Cl2 . 

It  much  resembles  bromine  in  appearance,  and  fumes  very  strongly  in  air,  the  mois- 
ture of  which  decomposes  its  red  vapour,  forming  chromic  and  hydrochloric  acids  ; 
Cr02C1.2-l-2H.,0  =  H2Cr04-f2HCl.  It  is  a  very  powerful  oxidising  and  chlorinating 
agent,  and  inflames  ammonia  and  alcohol  when  brought  in  contact  with  them. 

It  is  occasionally  used  to  illustrate  the  nature  of  illuminating  flames  ;  for  if 
hydrogen  be  passed  through  a  bottle  containing  a  few  drops  of  chlorochromic  acid, 
the  gas  becomes  charged  with  its  vapour,  and,  if  kindled,  bums  with  a  brilliant 
white  flame,  which  deposits  a  beautiful  green  film  of  chromic  oxide  upon  a  cold 
surface. 

The  name  chromic  oxychloride,  applied  to  this  compound,  is  more  correct  than 
chlorochromic  acid,  for  it  is  not  known  to  form  salts.  Whea  chlorochromic  acid  is 
heated,  in  a  sealed  tube,  to  370°  F.,  it  is  converted  into  a  black  solid  body  according 
to  the  equation  SCrO^Cla  =  CI4 -I- CrClg.  2Cr03. 

Chromic  fluoride  (CrFj)  is  another  volatile  compound  of  chromium  obtained 
by  distilling  chromate  of  lead  with  fluor  spar  and  sulphuric  acid  ;  it  is  a  red  gas,  con- 
densible  to  a  red  liquid  at  a  low  temperature.  Water  decomposes  it,  yielding  chromic 
and  hydrofluoric  acids. 

Chromic  sulphide  (CrgSg)  is  formed  when  vapour  of  carbon  disulphide  is  passed 
over  chromic  oxide  heated  to  redness.  It  forms  black  lustrous  scales  resembling 
graphite. 

By  fusing  chromic  hydrate  with  sodium  carbonate  and  sulphur,  sodium  sulpho- 
chromite  Xa._jCr.2S4  is  obtained,  as  a  dark  red  body  insoluble  in  water,  and  not  easily 
attacked  by  hydrochloric  or  sulphuric  acid.  Sulphochromites  of  other  metals  have 
also  been  obtained. 


334  MOLYBDENUM. 

236.  General  review  of  iron,  cobalt,  nickel,  manganese,  and  chromium. — 
Many  points  of  resemblance  will  have  been  noticed  in  the  chemical 
■history  of  these  metals.  They  are  all  capable  of  decomposing  water  at 
a  red  heat,  and  easily  displace  hydrogen  from  hydrochloric  acid.  Each 
of  them  forms  a  base  by  combining  with  one  atom  of  oxygen,  and  these 
oxides  produce  salts  which  have  the  same  crystalline  form.  All  these 
oxides,  except  that  of  nickel,  easily  absorb  oxygen  from  the  air,  and  are 
converted  into  sesquioxides.  The  sesquoxide  of  nickel  is  an  indifferent 
oxide,  while  that  of  cobalt  is  very  feebly  basic;  the  sesquioxide  of 
manganese  is  a  stronger  base,  and  the  basic  properties  of  the  sesquioxides 
of  chromium  and  iron  are  very  decided.  Nickel  does  not  exhibit  any 
tendency  to  form  a  well-marked  acid  oxide,  but  the  existence  of  an  acid 
oxide  of  cobalt  is  suspected ;  and  iron,  manganese,  and  chromium  form 
undoubted  acid  oxides  with  three  atoms  of  oxygen.  Nickel  is  only  known 
to  form  one  compound  with  chlorine ;  cobalt  and  manganese  form,  in  addi- 
tion to  their  protochlorides,  very  unstable  perchlorides  known  only  in 
solution,  but  iron  and  chromium  form  very  stable  volatile  perchlorides. 
The  metals  composing  this  group  are  all  diatomic,*  and  are  found  associated 
in  natural  minerals;  this  is  especially  the  case  with  iron,  manganese, 
cobalt,  and  nickel  They  are  all  attracted  by  the  magnet,  and  require  a 
very  high  temperature  for  their  fusion.  Iron  and  chromium  connect  this 
group  with  aluminium,  their  sesquioxides  being  isomorphous  with  alumina, 
and  their  perchlorides  volatile  like  aluminium  chloride. 

237.  Molybdenum  (Mo  =  96)  derives  its  name  from  fioXv^Saiva,  lend,  on  accouut 
of  the  resemblance  of  its  chief  ore,  Tiwlybdena,  to  black  lead.  Molybdena  is  the 
molybdenum  dvnilphide  (MoSj),  and  is  found  chiefly  in  Bohemia  and  Sweden ;  it  may 
be  recognised  by  its  remarkable  similarity  to  plumbago,  and  by  its  giving  a  blue 
solution  when  boiled  with  strong  sulphuric  acid.  It  is  chiefly  employed  for  the  pre- 
paration of  ammonium  molybdate,  which  is  used  in  teeing  for  phosphoric  acid.  For 
this  purpose  the  disulphide  is  roasted  in  air  at  a  dull  red  heat,  when  SOj  is  evolved, 
and  molybdic  anhydride  (M0O3)  mixed  with  oxide  of  iron  is  left.  The  residue  is 
digested  with  strong  ammonia,  which  dissolves  the  former  as  ammonium,  molyhdaie, 
obtainable  in  prismatic  crystals  (NH4HM0O4)  on  evaporation.  When  a  solution  of 
ammonium  molybdate  is  added  to  a  phosphate  dissolved  in  diluted  nitric  acid,  a 
yellow  precipitate  of  ammxmiuin  phosphomolybdate  >  is  produced,  which  contains 
molybdic  and  phosphoric  acids  combined  with  ammonia,  by  the  formation  of  which 
very  minute  quantities  of  phosphoric  acid  can  be  detected.  If  hydrochloric  acid  be 
added  in  small  quantity  to  a  strong  solution  of  molybdate  of  ammonium,  the  molybdic 
acid  is  precipitated,  but  it  is  dissolved  by  an  excess  of  hydrochloric  acid,  and  if  the 
solution  be  dialysed,  the  molybdic  acid  is  obtained  in  the  form  of  an  aqueous  solution 
which  reddens  blue  litmus,  has  an  astringent  taste,  and  leaves  a  soluble  gum-like 
residue  when  evaporated,  ilolybdic  anhydride  fuses  at  a  red  heat  to  a  yellow  glass, 
and  may  be  sublimed  in  a  current  of  air  in  shining  needles.  In  contact  with  diluted 
hydrochloric  acid  and  metallic  zinc,  it  is  converted  into  a  blue  compound  of  the  com- 
position (MoOg.4Mo03)  which  is  soluble  in  water,  but  is  precipitated  on  adding  a 
saline  solution.  Molybdate  of  lead  (PbMo04)  is  found  as  a  yellow  crystalline  mineral. 
The  molybdic  oxide  (MoOg)  is  basic,  and  forms  dark  red-brown  salts.  Molybdous  oxide 
(MoO)  is  obtained  by  adding  an  alkali  to  the  solution  resulting  from  the  prolonged 
action  of  zinc  upon  a  hydrochloric  solution  of  molybdic  acid.  It  is  a  basic  oxide  which 
absorbs  oxygen  from  the  air. 

Metallic  molybdenum  is  obtained  by  reducing  molybdic  acid  with  charcoal  at  a 
white  heat,  as  a  white  metal,  fusible  with  difiiculty,  unacted  upon  by  hydrochloric 
and  diluted  sulphuric  acids,  but  converted  into  molybdic  acid  by  boiling  with  nitric 
acid.  It  is  rather  a  light  metal,  its  specific  gravity  being  8  "62.  When  heated  in 
chlorine  it  yields  Tnolybdenum  tetrachloride  (M0CI4),  which  forms  a  red  vapour,  and 
condenses  in  crystals  resembling  iodine,  soluble  in  water.     A  dichloride  (MoClj)  is 

*  Chromium,  like  iron,  is  triatomic  in  the  sesquioxides  and  the  compounds  derived  from 
it,  and  iu  chromic  acid  it  must  be  regarded  as  hexatomic. 


VANADIUM.  '  335 

also  known.     The  trisulphide  (M0S3)  and  tctrasulphide  (M0S4)  of  molybdenum  are 
soluble  in  alkaline  sulphides. 

In  addition  to  the  natural  sources  of  molybdenum  above  mentioned,  there  may  be 
noticed  molybdic  ochre  (an  impure  molybdic  acid),  and  the  difficultly  fusible  ma.sses 
called  bear,  from  the  copper  works  in  Saxony,  which  contain  a  large  amount  of 
molybdenum  combined  with  iron,  copper,  cobalt,  and  nickel.  Molybdenum  has  been 
detected  in  the  mud  deposited  by  the  Buxton  thermal  water. 

238.  Vanadium*  (V  =  51'3)  was  originally  discovered  in  certain  Swedish  iron 
ores,  but  its  chief  ore  is  the  vanadiate  of  lead.,  which  is  found  in  Scotland,  Mexico, 
and  Chili.  Vanadic  acid  has  also  been  found  in  some  clays,  in  the  cupriferous  sand- 
stone at  Perm  in  Russia,  and  Alderley  Edge  in  Cheshire.  By  treating  the  vanadiate 
of  lead  with  nitric  acid,  expelling  the  excess  of  acid  by  evaporation,  and  washing 
out  the  lead  nitrate  with  water,  impure  vatwdic  anhijdride  (V„Og)  is  obtained,  which 
may  be  purified  by  dissolving  in  ammonia,  crystallising  the  vanadiate  of  ammonium, 
and  decomposing  it  by  heat,  when  vanadic  anhydride  is  left  as  a  reddish-yellow  fusible 
solid  which  crystallises  on  cooling,  and  dissolves  sparingly  in  water,  giving  a  yellow 
solution.  It  dissolves  in  hydrochloric  acid,  and  if  the  solution  be  treated  with  a  reduc- 
ing agent  (such  as  hydrosulphuric  acid)  it  assumes  a  fine  blue  colour.  If  a  solution 
of  ammonium  vanadiate  be  mixed  with  tincture  of  galls,  it  gives  an  intensely  black 
fluid,  which  forms  an  excellent  ink,  for  it  is  not  bleached  by  acids  (which  turn  it 
blue),  alkalies,  or  chlorine. 

Vanadium  itself  has  been  obtained  by  heating  its  chloride  in  hydrogen,  as  a 
silvery  white  metal.  Berzelius  endeavoured  to  procure  it  by  heating  vanadic  acid 
with  potassium,  but  Roscoe,  who  has  carefully  investigated  the  vanadium  com- 
pounds, has  shown  that  the  apparentlv  metallic  powder  thus  obtained  is  really  an 
oxide  (V2O3). 

239.  The  oxides  of  vanadium  correspond  in  composition  to  those  of  nitrogen. 
VjOg  is  a  basic  oxide,  forming  salts  which  give  lavender-coloured  solutions  ;  these 
absorb  oxygen  rapidly  from  the  air,  and  act  as  powerful  reducing  agents.  V.^Oj  is  a 
black  crystalline  body  resembling  plumbago,  and  capable  of  conducting  electricity, 
obtained  by  heating  vanadic  anhydride  in  a  current  of  hydrogen  ;  it  is  a  basic  oxide. 
V2O4  is  produced  when  V^Og  is  heated  in  air ;  it  also  plays  the  part  of  a  base, 
yielding  blue  salts.  Vanadic  anhydride,  VjOg,  forms  purple  and  green  compounds 
with  the  above  oxides.  Metavanadic  acid,  HVO3,  crystallises  in  beautiful  golden 
scales.  The  yellow  fuming  liquid  formerly  called  chloride  of  vanadium  is  really  an 
oxychloride,  VOCI3.  The  oxychlorides,  V^OgCl,  VOCl,  and  VOCl^,  have  also  been 
obtained.  There  are  two  compounds  of  vanadium  with  nitrogen,  VN  and  VX.2. 
It  will  be  remarked  that  the  composition  of  the  compounds  of  vanadium  connects 
this  metal  with  nitrogen,  phosphorus,  and  arsenic.  Compounds  of  vanadium  are 
now  used  for  blacks  in  calico-printing,  in  conjunction  with  chlorates  and  aniliue 
hydrochlorate. 

BISMUTH. 

Bi"'=.  210  parts  by  weight. 

240.  Bismuth,  though  useful  in  various  forms  of  combination,  is  too 
brittle  to  be  employed  in  the  pure  metallic  state.  It  is  readily  distin- 
guished from  other  metals  by  its  peculiar  reddish  lustre  and  its  highly 
crystalline  structure,  which  is  very  perceptible  upon  a  freshly  broken 
surface ;  large  cubical  (or,  strictly  speaking,  rhombohedral)  crystals  of 
bismuth  are  easily  obtained  by  melting  a  few  ounces  in  a  crucible,  allow- 
ing it  to  cool  till  a  crust  has  formed  upon  the  surface,  and  pouring  out 
the  portion  which  has  not  yet  solidified,  when  the  crystals  are  found 
lining  the  interior  of  the  crucible.  It  is  somewhat  lighter  than  lead  (sp. 
gr.  9 '8),  and  volatilises  more  readily  at  high  temperatures. 

Unlike    most  other  metals,  bismuth  is  found  chiefly  in  the  metallic 

state,  disseminated,  in  veins,  through  gneiss  and  clay-slate.     The  chief 

supply  is  derived  from  the  mines  of  Schneeberg,  in  Saxony,  where  it  is 

associated  with  the  ores  of  cobalt.     Native  bismuth,  together  with  the 

*   Vanadis,  a  Scandinavian  deity. 


336 


BISMUTH. 


Fig.  252. — Extraction  of  bismuth. 


oxides  and  sulphides,  are  found  abundantly  in  Bolivia,  accompanied  by 
tin-stone  and  sometimes  by  silver  and  gold. 

In  order  to  extract  the  metal  from  the  masses  of  earthy  matter  through 
which  it  is  distributed,  advantage  is  taken  of  its  verv  low  fusing-point 

(507°   F.).      The    ore   is 
-^r 'KifM9PiMH^H  broken  into  small  pieces, 

',     y.  w^am^atammmmA  ^^^  introduced  into  iron 

cylinders  which  are  fixed 
in  an  inclined  position 
over  a  furnace  (fig,  252). 
The  upper  opening  of  the 
cyliiiders,  through  which 
the  ore  is  introduced,  is 
provided  with  an  iron 
door,  and  the  lower  open- 
ing is  closed  witli  a  plate 
of  firebrick  perforated  for 
the  escape  of  the  metal, 
■which  flows  out,  when  the  cylinders  are  heated,  into  iron  receiving  pots, 
which  are  kept  hot  by  a  charcoal  fire. 

Commercial  bismuth  generally  contains  considerable  quantities  of 
arsenic,  sulphur,  and  silver ;  it  is  sometimes  cupelled  in  the  same  manner 
as  lead,  in  order  to  extract  the  silver,  the  oxide  of  bismuth  being  after- 
wards again  reduced  to  the  metallic  state  by  heating  it  with  charcoal. 
Pure  bismuth  dissolves  entirely  and  easily  in  diluted  nitric  acid  (sp.  gr. 
1'2);  but  if  it  contains  arsenic,  a  white  deposit  of  bismuth  arseniate  is 
obtained.  Hydrochloric  and  diluted  sulphuric  acids  will  not  act  upon 
bismuth. 

The  chief  use  of  bismuth  is  in  the  preparation  of  certain  alloys  with 
other  metals.  Some  kinds  of  type  metal  and  stereotype  metal  contain 
bismuth,  which  confers  upon  them  the  property  of  expanding  in  the 
mould  during  solidification,  so  that  they  are  forced  into  the  finest  lines 
of  the  impression. 

This  metal  is  also  remarkable  for  its  tendency  to  lower  the  fusing-point 
of  alloys,  which  cannot  be  accounted  for  merely  by  referring  to  the  low 
fusing-point  of  the  metal  itself.  Thus,  an  alloy  of  2  parts  bismuth, 
1  part  lead,  and  1  part  tin,  fuses  below  the  temperature  of  boiling  water, 
although  the  most  fusible  of  the  three  metals,  tin,  requires  a  temperature 
of  442°  F.  An  alloy  of  this  kind  is  used  for  soldering  pewter.  Bismuth 
is  also  employed,  together  with  antimony,  in  the  construction  of  thermo- 
electric piles. 

241.  Oxides  of  bismuth. — Three  compounds  of  bismuth  with  oxygen  have  been 
prepared  ;  bismuthous  oxide  BiO,  bismuthic  oxide  BioOo,  and  bismuthic  anhydride 

BismuthoiLs  oxide  (BiO)  is  obtained  as  a  black  precipitate  by  reducing  bismuthic 
eliloride  with  stannous  chloride  in  the  presence  of  an  excess  of  potash.  It  is  easily 
converted  into  bismuthic  oxide  when  heated  in  contact  with  air. 

Bisviuthic  oxide  (B^Og)  is  the  basic  and  most  important  oxide  of  the  metal.  It 
is  formed  when  bismuth  is  heated  in  air,  or  when  bismuth  nitrate  is  decomposed  by 
heat,  and  is  a  yellow  powder  which  becomes  brown  when  heated,  and  fuses  easily. 
Bismuthic  oxide  forms  the  rare  mineral  bismuth-ochre. 

Bismuthic  anhydride  (BijOj)  is  formed  when  bismuthic  oxide  is  suspended  in  a 
strong  solution  of  potash  through  which  chlorine  is  passed,  when  a  brown  substance 
is  formed  which,  when  treated  with  warm  strong  nitric  acid,  yields  bismuthic  acid 


OXIDES  OF  BISMUTH.  837 

(HBiOa)  as  a  red  powder,  which  becomes  brown  at  120°  C,  losing  HoO  and  becoming 
BigOj.  When  further  heated,  this  loses  O  and  becomes  Bi204,  or  Bi.jOg.BijGj. 
When  heated  with  acids  it  also  evolves  oxygen,  and  forms  salts  of  bismutliic  oxide. 
The  bisniuthates  of  tlie  alkali  metals  are  very  unstable,  being  decomposed  by  water. 

242.  The  only  two  salts  of  bismuth  which  are  known  in  the  arts  ai-e 
the  hanic  nitrate  (trisnitrati'  of  bismuth  or  iiake-Avhite)  and  the  oxychloriih' 
of  bismuth  {pearl -ichite).  The  preparation  of  these  compounds  illustrates 
one  of  the  characteristic  properties  of  the  salts  of  bismuth,  vi/.,  the 
facility  Avith  which  they  are  decomposed  by  water  with  the  production  of . 
insoluble  basic  salts. 

If  bismuth  be  dissolved  in  nitric  acid,  it  acquires  oxygen  from  the 
latter,  and  becomes  bismuthic  oxide,  which  reacts  with  nitric  acid  to  form 
the  bismuthic  nitrate  Bi(X()3)3,  and  this  may  be  obtained  in  prismatic 
crystals  containing  5Aq.  If  the  solution  be  mixed  with  a  large  quantity 
of  water,  it  deposits  a  precipitate  of  flake-white,  Bi(N03)3.2Bi(OH)3,  or 
basic  nitrate  of  bismuth,  the  remainder  of  the  nitric  acid  being  left  in  the 
solution. 

Pearl  white  has  the  composition  2(BiCl3.Bi203).H^O,  and  is  obtained  by 
dissolving  bismuth  in  nitric  acid,  and  pouring  the  solution  into  water  in 
which  common  salt  has  been  dissolved. 

Bis'inulhitc,  which  is,  next  to  native  bismuth,  the  most  important  of  the  bismuth 
ores,  is  composed  of  SBi.jOj.COg.H^O. 

Bismuthic  chloride  (BiClj)  maybe  distilled  over  when  bismuth  is  heated  in  a  current 
of  dry  chlorine  ;  it  is  a  deliquescent  fusible  solid,  easily  dissolved  by  hydrochloric 
acid,  but  decomposed  by  water,  with  formation  of  the  above-mentioned  oxijchloridc  of 
hismutJi ;  3BiCl3+ 3H26  =  BiCl3. 61303  + 6HC1.  This  compound  is  so  insoluble  iii 
water  that  nearly  every  trace  of  bismuth  may  be  preciiiitated  from  a  moderately  acid 
solution  of  the  trichloride  by  ailding  much  water. 

Bismuthous  sulphidr.  (BiS)  is  sometimes  found  in  nature,  but  'more  frecjuently 
bismuthic  sulphide  (BioSj)  or  bism,tith  qloncc,  which  occurs  in  dark  grey  lustrous  prisms 
isomorphous  with  native  sulphide  of  antimony.  It  is  also  obtained  as  a  black  pre- 
(,'ipitate  by  the  action  of  hydrosnlphuric  acid  upon  bismuthic  salts.  Bismuthic  sul- 
phide is  not  soluble  in  diluted  sulphuric  or  hydrochloric  acid,  but  dissolves  easily  in 
nitric  acid.     Bolivite  is  an  oxysulphide,  BijSg.BinOa. 

ANTIMONY. 

Sb"'=120  parts  by  weight. 

243.  Antimony  is  nearly  allied  to  bismuth  in  both  its  physical  and 
chemical  characters.  It  is  even  harder  and  more  brittle  than  that  metal, 
being  easily  reduced  to  a  black  powder.  Its  highly  crystalline  structure 
is  another  very  well-marked  feature,  and  is  at  once  perceived  upon  the 
surface  of  an  ingot  of  antimony,  where  it  is  exhibited  in  beatttiful  f em- 
like  markings  {star  iintimornj).  Its  crystals  belong  to  the  same  system 
(the  rhombohedral)  ;is  those  of  bismuth  and  areenic.  It  is  much  lighter 
than  bismuth  (sp.  gr.  6-715),  and  requires  a  higher  temperature  (SOOT.) 
to  fuse  it,  though  it  is  more  easily  converted  into  vapour,  so  that,  when 
strongly  heated  in  air,  it  emits  a  thick  white  smoke,  the  vapour  l)eing 
oxidised.  Like  bismuth,  it  is  but  little  aftected  by  hydrochloric  or  dilute 
sulphuric  acid,  but  nitric  acid  oxidises  it,  though  it  dissolves  very  little 
of  the  metal,  the  greater  part  being  left  in  the  fonn  of  antimonic  acid. 
The  best  mode  of  dissolving  antimony  is  to  boil  it  Avith  hydrochloric  acid 
and  to  add  nitric  acid  by  degrees. 

Antimony  is  chiefly  found  in  nature  as  (jn-y  antimony  ore  or  sulphide 
of  antimony  (SboSg),  which  occurs  in  Cornwall,  but  much  more  abun- 

Y 


o38  ANTIMONY. 

dantly  in  Hungary.  It  is  found  in  veins  associated  witli  galena,  iron 
pyrites,  quartz,  and  heavy  spar.  In  order  to  purify  it  from  these,  advan- 
tage is  taken  of  its  easy  fusibility,  the  ore  being  heated  upon  the  hearth 
of  a  reverboratory  furnace,  with  some  charcoal  to  prevent  oxidation,  when 
the  sulphide  of  antimony  melts  and  collects  below  the  impurities,  whence 
it  is  run  off  and  cast  into  moulds.  The  product  thus  obtained  is  known 
in  commerce  as  cmde  arttimony,  and  contains  sulphides  of  arsenic,  iron, 
and  lead. 

To  obtain  regulus  of  antimony  or  metallic  antimony,  the  sulphide  of 
antimony  is  sometimes  fused  in  contact  with  refuse  metallic  iron  (such  as 
the  clippings  of  tin-plate),  when  sulphide  of  iron  is  formed,  and  collects 
as  a  fused  slag  upon  the  surface  of  the  melted  antimony  Sb.^S^  -h  Fe<j 
=  '3FeS  -1-  Sb.,.  The  antimony  thus  obtained  always  contains  a  consider- 
able proportion  of  iron. 

A  purer  product  is  procured  by  another  process,  Avhich  consists  in 
roasting  the  sulphide  in  a  reverberatory  furnace  at  a  temperature  insuffi- 
cient to  fuse  it,  for  about  twelve  hours,  when  most  of  the  sulphur  and 
arsenic  are  expelled  as  sulphurous  and  arsenious  oxides,  carrying  with 
them  a  considerable  quantity  of  oxide  of  antimony.  The  roasted  ore 
has  a  brown-red  colour,  and  contains  both  oxide  and  sulphide  of  antimony : 
it  is  mixed  into  a  paste  with  \  its  weight  of  charcoal  saturated  with  a 
strong  solution  of  carbonate  of  soda.  The  mixture  is  strongly  heated  in 
crucibles,  Avhen  the  oxide  of  antimony  is  reduced  by  the  charcoal,  and  a 
portion  of  the  sulphide,  having  been  converted  into  oxide  by  double 
decomposition  with  the  sodium  carbonate  (Sb2S3  4-3Na.3C()3  =  Sb._,0,; 
-f-  SNa^S  +  3C0^),  is  also  reduced,  the  remainder  of  the  sulphide  com- 
bining with  the  sodium  sulphide  to  form  a  slag  which  floats  above  the 
metallic  antimony;  the  latter  is  cast  into  ingots  for  the  market,  and  the 
slag,  known  as  crocus  of  antimony  (chiefly  SNa.^S.Sb.^Sg),  is  employed  for 
the  preparation  of  some  of  the  compounds  of  the  metal. 

On  the  small  scale,  autimoiiy  may  be  extracted  from  the  sulphide  by  fusing  it  iu 
an  earthen  crucible  with  4  parts  of  commercial  potassium  cyanide,  at  a  moderate 
lieat  ;  or  by  mixing  4  parts  of  the  sulphide  with  3  of  bitartrate  of  potash  and  1^  of 
nitre,  and  throwing  the  mixture,  by  small  portions,  into  a  red  hot  crucible,  when 
the  sulpliur  is  oxidised,  and  converted  into  potassium  sulphate,  hy  the  nitre,  which  is 
not  present  in  sufficient  quantity  to  oxidise  the  antimony,  so  that  the  metal  collects 
at  the  bottom  of  the  crucible. 

The  brittleness  of  antimonj""  renders  it  useless  in  the  metallic  state 
except  for  the  construction  of  thermo-electric  piles,  where  it  is  employed 
iu  conjunction  with  bismuth,  Antimony  is  employed,  however,  to 
harden  several  useful  alloys,  such  as  type-metal,  shrapnel-shell  bullets, 
Britannia  metal,  and  pewter. 

Amm-phous  aitiitiiony. — The  ordinary  crystalline  form  of  antimony  may  be  obtained, 
like  copper  and  other  metals,  by  decomposing  solutions  containing  the  metal  by 
transmitting  the  galvanic  current  (the  solution  should  not  contain  more  than  7  per 
cent,  of  antimonious  chloride) ;  but  in  some  cases  the  antimony  is  deposited  from 
very  strong  solutions  in  an  amorphous  condition,  having  properties  very  different 
from  those  of  ordinarj-  antimony.  The  best  mode  of  obtaining  it  in  this  form  is  to 
decompose  a  solution  of  1  part  of  tartar  emetic  (tartrate  of  antimony  and  jiotassium)  in 
4  parts  of  a  strong  solution  of  antimony  trichloride  (obtained  by  heating  hydrochloric 
acid  with  antimony  sulphide  till  it  refuses  to  dissolve  any  more),  by  the  aid  of  three 
cells  of  Smee's  battery,  the  zinc  of  which  is  connected  by  a  copper  wire  with  a  plate 
of  copper  immersed  in  the  antimonial  solution,  whilst  the  jilatiuised  silver  of  the 
battery  is  connected  with  a  plate  of  antimony  iu  the  same  solution,  at  some  little 


OXIDES  OF  ANTIMONY.  339 

distance  from  the  cop]>er  plate.  The  deposit  of  antimony  which  forms  upon  the 
copper  has  a  brilliant  metallic  appearance,  but  is  amorphous,  and  not  crystalline, 
like  the  ordinary  metal.  If  it  be  gently  heated  or  shaiply  struck,  its  temperature 
rises  suddenly  to  about  400°,  and  it  becomes  converted  into  a  form  more  nearly 
resembling  crystalline  antimony.  At  the  same  time,  however,  thick  fumes  of 
antimony  trichloride  are  evolved,  for  this  substance  is  always  present  in  the 
amorphous  antimony  to  the  amount  of  5  or  6  per  cent.,*  so  that,  as  yet,  there  is  not 
sufficient  evidence  to  establish  beyond  a  doubt  the  existence  of  a  pure  amorphous 
form  of  antimony  corresponding  to  amorphous  phosphorus,  however  probable  this 
may  appear  from  the  chemical  resemblance  between  these  elements. 

244.  Oxides  of  antimony. — There  are  two  well-known  oxides  of  anti- 
mony, the  sesquioxide  (SbgOg)  and  antimonic  oxide  (Sb.^Og).  Taroxide 
or  sesqidoxide  of  aniimony,  or  antimonious  oxide,  is  formed  when  anti- 
mony b\irns  in  air,  and  is  prepared  on  a  large  scale  by  roasting  either 
the  metal  or  the  sulphide  in  air,  for  use  in  painting  as  a  substitute 
for  white  lead.  It  is  also  found  in  nature  as  -white  antimony  ore  or 
nalentinite.  Antimonious  oxide  forms  a  crystalline  powder,  usually  com- 
posed of  minute  prisms  having  the  shape  of  the  rarer  form  of  arsenious 
oxide  (page  246),  whilst  occasionally  it  is  obtained  in  crystals  similar  to 
those  of  the  common  octahedral  arsenious  oxide,  with  which,  therefore, 
antimonious  oxide  is  isodimorphous.  The  octahedral  form  appears 
to  be  produced  only  when  the  prismatic  form  is  slowly  sublimed  in 
a  non-oxidising  atmosphere.  The  mineral  exitele  is  prismatic  oxide  of 
antimony,  and  senarmontite  is  the  octahedral  form  of  that  oxide.  AVhen 
heated  in  air  the  oxide  assumes  a  yellow  colour,  afterwards  takes  fire, 
smoulders,  and  becomes  converted  into  the  antimonious  antimoniate 
(Sb203.Sbo05  =  Sbo04),  which  was  formerly  regarded  as  an  independent 
oxide.  The  sesquio.xide  is  insoluble  in  water,  but  acids  dissolve  it, 
forming  salts,  though  its  basic  properties  are  weak,  and  its  salts  rather 
ill  defined.  Potash  and  soda  are  also  capable  of  dissolving  it,  whence  it 
is  sometimes  called  antimonious  anhydride,  corresponding  to  nitrous  anhy- 
dride. Two  crystallised  antimonites  of  sodium  have  been  obtained,  the 
neutral  antimonite  XaSbOo.6Aq.,and  the  terantimoniteXaSbO.,.Sb.,03.  Aq. ; 
the  former  is  sparingly  soluble,  the  latter  almost  insoluble  in  water. 

Antimonic  oxide  (Sb.^Oj)  is  formed  when  antimony  is  oxidised  with 
nitric  acid;  it,  then  forms  a  -white  powder,  which  should  be  well  washed 
and  dried.  When  heated  it  becomes  pale  yellow,  and  is  decomposed  at 
a  high  -temperature,  leaving  Sb203.Sb._,03.  It  is  dissolved  by  solution  of 
potash,  forming  potassium  antimoniate.  Antimonic  acid  HSbO.^,  corre- 
sponding to  nitric  acid,  is  obtained  by  decomposing  antimonic  chloride 
with  water;  SbCl.-f- 3R,0  =  HSbOg  +  SHCl. 

Antimonic  hydrate,  dried  over  sulphuric  acid,  is  SbgUj.SH./).  At 
100°  C.  it  becomes  Sb205.2H20.  At  about  200°,  it  is  Sb^Og.HgO."  These 
may  be  represented,  respectively,  as  HgSbO^,  H^SboO-,  and  HSbOg, 
corresponding  to  ortho-,  pyro-  and  metaphosphoric  acids. 

Potassium  antimoniate  is  made  by  gradually  adding  1  part  of  powdered 
antimony  to  4  parts  of  nitre  fused  in  a  clay  crucible.  The  mass  is 
powdered  and  washed  with  "warm  water  to  remove  the  excess  of  nitre  and 
the  potassium  nitrite,  when  the  anhydrous  potassium  antimoniate  is  left ; 
and  on  boiling  this  for  an  hour  or  two  with  water,  it  becomes  hydi-ated 

*  It  has  been  plausibly  suggested  that  tlie  sudden  rise  of  temperature  may  be  due  to 
the  presence  of  an  antimony  compound  analogous  to  the  so-called  chloride  of  nitrogen,  tlit 
latter  element  V)eing  comiected  with  antimony  by  several  chemical  analogies.  j 


340  ANTIMONIETTED  HYDROGEN. 

and  dissolves.  The  solution,  when  evaporated,  leaves  a  gummy  mass  of 
potassium  antimoniatr,  having  the  composition  2KSb03.5Aq. 

"When  the  solution  of  potassium  antimoniate  is  treated  with  carbonic- 
acid  gas,  a  crystalline  precipitate  of  biantimoniate  (2KSb03.Sb.,05)  is 
obtained.  If  the  antimoniate  be  fused  (in  a  silver  crucible)  with  potassium 
hydrate,  it  becomes  converted  into  mutant imoniaf'-  (K^SboO^),  which  is 
decomposed  by  water  into  potash  and  hintetantimtmiate  (KgHoSbjO-), 
which  may  be  crystallised  from  the  solution.  This  latter  salt  is  valuable 
as  a  test  for  soda,  since  the  sodium  bimetantimouiate,  Na.,H2Sb207,  is 
one  of  the  very  few  salts  of  sodium  which  are  insoluble  in  water,  and  is 
therefore  obtained  as  a  crystalline  precipitate  when  the  potassium  bimet- 
antimouiate is  added  to  a  solution  containing  sodium.  The  solution  of 
potassium  bimetantimouiate  is  gradually  changed  by  keeping,  into  anti- 
moniate, which  does  not  so  readily  precipitate  sodium,  K.,H2Sb.>0- 
=  2KSb0.5-l-H20. 

It  will  be  remarked  that  the  antimoniates  correspond  in  composition 
with  the  metaphosphates,  whilst  the  metantimoniates  represent  the  pyro- 
phosphates. 

Naples  yi'llmr  is  a  compound  of  antimonic  oxide  with  lead  oxide. 

245.  AvHnuniiHted  hf/drotji'ii  (SbHg)  is  obtained,  mixed  with  free 
hydrogen,  when  an  alloy  of  zinc  and  antimony  is  acted  on  by  diluted  sul- 
phuric acid,  or  when  a  solution  of  a  salt  of  antimony  (tartar  emetic,  for 
example)  is  poured  into  a  hydrogen  apparatus  containing  zinc  and  dilute 
sulphuric  acid  (fig.  253).  If  the  gas  be  inflamed  as  it  issues  into  the  air, 
it  burns  Anth  a  livid  flame,  emitting  fumes  of  antimonic  oxide,  and  when 
a  piece  of  glass  or  porcelain  is  depressed  in  the  flame  (fig.  254)  it  becomes 
coated  with  a  black  film  of  metallic  antimony.  A  red  heat  decomposes 
the  gas  into  its  elements,  so  that  if  the  tube  through  which  it  is  passing 
be  heated  with  a  spirit-lamp  (fig.  255),  a  lustrous  black  deposit  of  anti- 


Fig.  253 


V      .>-i  •  Fig.  255. 

rig.  2a4. 

mony  will  be  formed  just  beyond  the  heated  part.  The  composition  of 
antimonietted  hydrogen  is  not  certainly  established,  since  it  has  never 
been  obtained  unmixed  with  hydrogen;  but  it  is  believed  to  contain 
SbH3,  because,  when  passed  into  silver  nitrate,  it  gives  a  black  precipi- 
tate containing  8bAg3.  It  would  then  be  analogous  to  ammonia  (NHg), 
phosphine  (PH.,),  and  arsenietted  hydrogen  (AsHg).  Very  minute 
<juantities  of  antimony  are  detected  in  chemical  analysis  by  converting  it 


,     CHLORIDES  OF  ANTIMONY.  341 

into   this   form,     lu   sunsluiR',   sulphur  decomposes  8bH.^;    28bH3  +  Sg. 
=  Sb,S3  +  SE.p. 

246.  Chlorides  of  antimony. — -Chloritie  and  antimony  combine  readily 
with  evolution  of  heat  and  light ;  the  chlorides  are  among  the  most  im- 
portant compounds  of  this  metal. 

Trichloride  of  antinumij  or  antimoniouH  cliloride  (SbClg)  may  be  pre-' 
pared  by  distilling  three  parts  of  powdered  antimony  with  eight  parts  of 
corrosive  sublimate,  when  calomel  and  an  amalgam  of  antimony  are  left, 
and  the  trichlodde  of  antimony  (boiling  at  433*^  F.)  distils  over — 

Sb,  +  2HgClo  =  SbCla  +  SbHg  +  HgCl. 

It  can  also  be  obtained  by  boiling  powdered  antimony  or  sulphide  of 
antimony  to  dryness  with  strong  sulphuric  acid,  and  distilling  the  anti- 
monious  sulphate  thus  obtained  with  common  salt.  The  trichloride  is  a 
soft  crystalline  fusible  solid,  whence  its  old  name  of  hutter  of  antimony.  It 
may  be  dissolved  in  a  small  quantity  of  water,  but  a  large  quantity  of  water 
decomposes  it,  forming  a  bulky  white  precipitate,  which  is  an  oxychloride- 
of  antimony  (3SbCl3  +  3H,0  =  SbClg.Sb^O.,  -I-  6HC1).  When  hot  water  is 
added  to  a  hot  solution  of  trichloride  of  antimony  in  hydrochloric  acid, 
minute  prismatic  needles  are  deposited,  containing  2SbCl3.5Sb203,  and 
formerly  called  powder  of  Ahjarotli.  The  trichloride  of  antimony,  in  its 
behaviour  with  water,  much  resembles  that  of  bismuth.  Trichloride  of 
antimony  is  occasionally  used  in  surgery  as  a  caustic;  it  also  serves  as  a 
bronze  for  gun-barrels,  upon  which  it  deposits  a  film  of  antimony. 

PentacJiloride  of  antimony  or  antimonic  cldoridc  (SbClj)  is  prepared  by 
heating  coarsely  powdered  antimony  in  a  retort,  through  which  a  stream 
of  dry  chlorine  is  passed  (fig.  213),  the  neck  of  the  retort  being  fitted  into 
an  adapter,  which  serves  to  condense  the  pentachloride.  One  ounce  of 
antimony  will  require  the  chlorine  from  about  6  oz.  of  common  manganese 
and  18  oz.  (measured)  of  hydrochloric  acid.  The  pure  pentachloride  is  a 
colourless  fuming  liquid  of  a  very  suffocating  odour;  it  combines  energeti- 
cally with  a  small  quantity  of  water,  forming  a  crystalline  hydrate,  but 
an  excess  of  water  decomposes  it  into  hydrochloric  and  antimonic  acids, 
the  latter  forming  a  white  precipitate;  SbClj  +  SHoO^HSbOg  4  5HC1. 
Pentachloride  of  antimony  is  employed  by  the  chemist  as  a  chlorinating 
agent;  thus,  olefiant  gas  (CqH^)  when  passed  through  it,  is  converted  into 
Dutch  liquid  (C^H^Clo),  and  carbonic  oxide  into  phosgene  gas,  the  penta- 
chloride of  antimony  being  converted  into  trichloride. 

The  pentachloride  of  antimony  is  the  analogue  of  pentachloride  of  phos- 
phorus, and  a  fhlorosidphide  of  antimony  (SbClgS),  corresponding  to 
chlorosulphide  of  phosphorus,  is  obtained  as  a  white  crystalline  solid  by 
the  action  of  hydrosulphuric  acid  upon  pentachloride  of  antimony. 

247.  SnJphidt's  <f  antitnonij. — A7itimonious, sulphide  or  sesquis^dphide  of 
antimony  (Sb.^Sg)  has  been  noticed  as  the  chief  ore  of  antimony.  It  is  a 
heavy  mineral  (sp.  gr.  4 '63)  of  a  dark  grey  colour  and  metallic  lustre, 
occurring  in  masses  which  are  made  up  of  long  prismatic  needles.  It  fuses 
easily,  and  may  be  sublimed  unchanged  out  of  contact  with  air.  It  is 
easily  recognised  by  heating  it,  in  poM^ler,  with  hydrochloric  acid,  when 
it  evolves  the  odour  of  hydrosulphuric  acid,  and  if  the  solution  be  poured 
into  -vi^ater,  it  deposits  an  orange  precipitate  (page  195).  This  orangt* 
sulphide,  which  has  the  same  composition  as  the  grey  sulphide,  is  also, 


^2  SULPHIDES  OF  ANTIMONY — TIN. 

obtained  by  adding  hydrosulphuric  acid  to  a  solution  of  a  salt  of  antimony 
(for  example,  tartar  emetic)  acidulated  with  hydrochloric  acid.  It  may 
be  converted  into  the  grey  sulphide  by  the  action  of  heat  The  orange 
variety  constitutes  the  antimony  vermilion,  the  preparation  of  which  has 
been  described  at  page  214.  Kative  sulphide  of  antimony  is  employed, 
in  conjunction  with  potassium  chlorate,  in  the  friction-tuhe  for  firing 
cjinnon;  it  is  also  usediu^e?-cwss«'o?i  caps,  together  with  potassium  chlorate 
and  mercuric  fulmina^.  Its  property  of  deflagrating  with  a  bluish-white 
flame  when  heated  -vl^ith  nitre,  renders  it  useful  in  compositions  for 
coloured  fires. 

Glass  of  antimony  is  a  transparent  red  mass  obtained  by  roasting  anti- 
monious  sulphide  in  air,  and  fusing  the  product ;  it  contains  about  8  parts 
of  oxide  and  1  part  of  sulphide  of  antimony. 

Red  antimony  we  is  an  oxysulphide  of  antimony,  Sb.^Og. 28^83. 

Antimonic  sulphide  (SbgSj)  is  obtained  as  a  bright  orange-red  precipitate 
by  the  action  of  hydrosulphuric  acid  upon  a  solution  of  pentachloride  of 
antimony  in  hydrochloric  acid. 

Both  the  sulphides  of  antimony  are  capable-  of  combining  with  tin- 
alkaline  sulphides  to  form  sidphantimonites  and  sulphantimoniate>i 
respectively.  Hence  they  are  easily  dissolved  by  alkalies  and  alkaline 
sulphides.  Even  metallic  antimony,  in  powder,  is  dissolved  when  gently 
heated  with  solution  of  potassium  sulphide  in  which  sulphur  has  been 
dissolved,  any  lead  or  iron  which  may  be  present  being  left  in  the  residue, 
.so  that  the  antimony  may  be  tested  by  this  process  as  to  its  freedom  from 
those  metals. 

Mineral  kennes  is  a  variable  mixture  of  sesquioxide  and  sesquisulphide 
of  antimony,  which  is  deposited  as  a  reddish-brown  powder  from  the  solu- 
tion obtained  by  boiling  sesquisulphide  of  antimony  with  potash  or  soda. 
It  was  formerly  much  valued  for  medicinal  purposes. 

S'ddippa's  salt  is  the  sodium  sulphautimoniate  (NagSbS^.OHpO),  and 
may  be  obtained  in  fine  transparent  tetrahedral  crystals.  This  salt  is 
sometimes  used  in  photography. 

TIK 

iSn  =  118  parts  by  weight. 

248.  Tin  is  by  no  means  so  widely  diffused  as  most  of  the  other  metals 
which  are  largely  used,  and  is  scarcely  ever  found  in  the  metallic  state  in 
nature.  Its  only  important  ore  is  that  known  as  tinstone,  which  is  a 
binoxide  of  tin  Sn02,  and  is  generally  found  in  veins  traversing  quartz, 
granite,  or  slate.  It  is  generally  associated  with  arsenical  iron  pyrites, 
and  with  a  mineral  called  wolfram,  which  is  a  tungstate  of  iron  and 
manganese. 

Tin-stone  is  sometimes  found  in  alluvial  soils  in  tho  form  of  detached 
rounded  masses ;  it  is  then  called  stream  tin  ore,  and  is  much  purer  than 
that  found  in  veins,  for  it  has  undergone  a  natural  process  of  oxidation 
and  levigation  exactly  similar  to  the  artificial  treatment  of  the  impure  ore. 
These  detached  masses  of  stream  tin  ore  are  not  uiifrequently  rectangular 
prisms  with  pyramidal  terminations. 

The  Cornish  mines  furnish  the  largest  supplies  of  tin,  and  those  of 
Malacca  and  Banca  stand  next.  Tin-stone  is  also  found  in  Bohemia, 
Saxony,  and  California.     At  the  Cornish  tin-works  the  purer  portions 


KXTKACTION  OF  TIN. 


34^ 


of  the  ore  are  picked  out  by  hand,  and  the  residue,  Avhish  contains 
quartz  and  other  earthy  impurities,  together  with  copper  pyrites  and 
arsenical  iron  pyrites,  is  reduced  to  a  coarse  powder  in  the  stamp- 
ing-mills, and  washed  in  a  stream  of  water.  The  tin-stone,  being 
extremely  hard,  is  not  reduced  to  so  fine  a  powder  as  the  pyritous 
minerals  associated  with  it,  and  these  latter  are  therefore  more  readily 
carried  away  by  the  stream  of  water  tlian  the  tin-stone.  The  removal 
of  the  foreign  matters  from  the  ore  is  also  much  favoured  by  the 
high  specific  gravity  of  the  biuoxide  of  tin,  wdiich  is  6*5,  whilst  that 
of  sand  or  quartz  is  only  2*7,  so  that  the  latter  would  be  carried  ott" 
by  a  stream  which  would  not  disturb  the  former.  8o  easily  and  com- 
pletely can  this  separation  ))e  efi'ected,  that  a  sand  containing  less 
than  one  per  cent,  of  tin-stone  is  found  capable  of  being  economically 
treated. 

In  order  to  expel  any  arsenic  and  sulphur  which  may  still  remain  in 
the  washed  ore,  it  is  roasted  in  quantities  of  8  or  10  cwts.  in  a 
reverberatory  furnace,  when  the  sulphur  is  disengaged  in  the  form  of 
sulphurous. acid  gas,  and  the  arsenic  in  that  of  arsenious  oxide,  the  iron 
being  left  in  the  state  of  sesquioxide,  and  the  copper  partly  as  sulphate 
of  copper,  partly  as  unaltered  sul 
phide.  To  complete  the  oxidation 
of  the  insoluble  sulphide  of  copper, 
and  its  conversion  into  the  soluble 
sulphate,  the  roasted  ore  is  moistened 
with  water  and  exposed  to  the  air 
for  some  days,  after  which  the 
whole  of  the  copper  may  be  removed 
by  again  washing  with  water. 

A  second  washing  in  a  stream  of 
water  also  removes  the  sesquioxide 
of  iron  in  a  state  of  suspension, 
and  this  is  much  more  easily 
effected  than  when  the  iron  was  in 
the  form  of  pyrites,  since  the  differ- 
ence between  the  specific  gravity 
of  this  mineral  (5"0)  and  that  of 
the  tin-stone  (6"5)  is  far  less  than 
that  between  sesquioxide  of  iron 
and  tin-stone. 

The  ore  thus  purified  contains 
between  60  and  70  per  cent,  of  tin  ; 
it  is  mixed  very  intimately  with 
about  ^  of  powdered  coal,  and  a  little  lime  or  fiuor  spar  to  form  a  fusible 
slag  with  the  earthy  impurities  ;  the  mixture  is  sprinkled  with  water  to 
prevent  its  dispersion  by  the  drauglit  of  air,  and  thrown  on  the  hearth 
(A,  fig.  256)  of  a  reverberatory  furnace,  in  charges  of  between  20  and 
25  cwts. 

The  temperature  is  not  permitted  to  rise  too  high  at  first,  lest  a  portion 
of  the  oxide  of  tin  should  combine  with  the  silica  to  form  a  silicate,  from 
which  the  metal  would  be  reduced  with  difficulty. 

During  the  first  six  or  eight  hours  the  doors  of  the  furnace  are  kept  shut, 
so  as  to  exclude  the  air  and  favour  the  reducing  action  of  the  carbon 


Fig.  256. 


344  rURIFICATION  OF  TIN.  , 

upon  the  binoxide  of  tin,  the  oxygen  of  which  it  converts  into  carbonic 
oxide,  leaving  the  tin  in  the  metallic  state  to  accumulate  upon  the  hearth 
beneath  the  layer  of  slag.  When  the  reduction  is  deemed  complete,  the 
mass  is  well  stirred  with  an  iron  paddle  to  separate  the  metal  from  the 
shig ;  the  latter  is  run  out  first,  and  the  tin  is  tlien  drawn  ofi'  into  an  iron 
pan  (I>),  where  it  is  allowed  to  remain  at  rest  for  the  dross  to  rise  to  the 
surface,  and  is  ladled  out  into  ingot  moulds. 

The  slags  drawn  out  of  the  smelting-fumace  are  carefully  sorted,  those 
which  contain  much  oxide  of  tin  being  worked  \\p  with  the  next  charge 
of  ore,  whilst  those  in  which  globules  of  metallic  tin  are  disseminated  are 
crushed,  so  that  the  metal  may  be  separated  by  washing  in  a  stream  of 
water. 

The  tin,  when  hrst  extracted  from  the  ore,  is  far  from  pure,  being  con- 
taminated with  small  quantities  of  iron,  arsenic,  copper,  and  tungsten. 
In  order  to  purify  it  from  these,  the  ingots  are  piled  into  a  hollow  heap 
near  the  fire-bridge  of  a  reverberatory  furnace,  and  gradually  heated  to  the 
fusing-point,  when  the  greater  portion  of  the  tin  flows  into  an  outer  basin, 
Avhilst  the  remainder  is  converted  into  the  binoxide,  which  remains  as 
dross  upon  the  hearth,  together  with  the  oxides  of  iron,  copper,  and  tung- 
sten, the  arsenic  having  passed  off  in  the  form  of  arsenious  oxide.  Fresh 
ingots  of  tin  are  introduced  at  intervals,  until  about  5  tons  of  the  metal 
have  collected  in  the  basin,  which  is  commonly  the  case  in  about  an  hour 
after  the  commencement  of  the  operation. 

The  specific  gravity  oi  tin  being  very  low  (7"285),  any  dross  which 
may  still  remain  mingled  with  it  does  not  separate  very  readily  ;  to 
obviate  this,  the  molten  metal  is  well  agitated  by  stirring  with  wet 
wooden  poles,  or  by  lowering  billets  of  wet  wood  into  it,  when  the  evolved 
bubbles  of  steam  carry  the  impurities  up  to  the  surface  in  a  kind  of  froth ; 
the  stirring  is  continued  for  about  three  hours,  and  the  metal  is  allowed  to 
remain  at  rest  for  two  hours,  when  it  is  skimmed  and  ladled  into  ingot 
moulds.  It  is  found  that,  in  consequence  of  the  lightness  of  the  metal, 
and  its  tendency  to  separate  from  the  other  metals  with  which  it  is  con- 
taminated, the  ingots  which  are  cast  from  the  metal  first  ladled  out  of  the 
pot  are  purer  than  those  from  the  bottom  ;  this  is  shown  by  striking  the 
hot  ingots  with  a  hammer,  when  they  break  up  into  the  irregular  prismatic 
fragments  known  as  dropped  ox  grain-tin,  the  impure  metal  not  exhibiting 
this  extreme  brittlcness  at  a  high  temperature.  The  tin  imported  from 
Hanca  is  celebrated  for  its  purity  {Straits  tin). 

When  the  tin  ore  contains  wolfram,  it  is  usual  to  purify  it,  before  smelt- 
ing, by  fusion  with  sodium  carbonate  in  a  reverberatory  furnace,  when 
the  tungstic  acid  is  converted  into  sodium  tungstate,  which  is  dissolved  out 
by  water  and  crystallised.     This  salt  finds  an  application  in  calico-printing. 

On  the  small  scale,  tin  may  be  extracted  from  tin-stone  by  fusing  100 
grains  with  20  grains  of  dried  sodium  carbonate,  and  20  of  dri(,'d  borax, 
in  a  crucible  lined  with  charcoal,  exactly  as  in  the  extraction  of  iron  (see 
page  321). 

The  extraction  is  more  easily  effected  by  fusing  100  grains  of  tin- 
stone with  500  grains  of  potassium  cyanide  for  fifteen  minutes  at  a  red  heat 

249.  T)y  its  physical  charactei-s,  tin  is  very  readily  distinguished  from 
other  metals.  If  a  bar  of  tin  be  bent,  it  emits  a  peculiar  crackling  sound. 
With  the  exception  of  lead  and  zinc,  it  is  the  least  tenacious  of  all  the 


ilANUFACTUHE  OF  TIN-PLATK.  345 

inebals  in  common  use  ;  its  ductility  is  therefore  veiy  low,  and  lead  is  the 
only  common  metal  which  it  is  more  difficult  to  draw  into  wiit?  at  the 
ordinary  temperature.     Tin  may,  however,  be  drawn  at  212°  F. 

In  fusibility,  tin  surpasses  all  the  other  common  metals,  becoming 
liquid  at  442°  F.,  but  it  is  not  easily  vaporised.  Its  malleability  is  also 
very  great,  only  gold,  silver,  and  copper  exhibiting  this  quality  in  a  higher 
degree.  This  malleability  is  shown  in  the  manufacture  of  tin-foil,  where 
plates  of  the  best  tin  are  hammered  doAvn  to  a  certain  thinness,  then  cut 
up,  laid  upon  each  other,  and  again  beaten  till  extended  to  the  required 
degree. 

Tiii-platt;  it  must  be  remembered,  is  made  in  a  very  different  wa}',  by 
coating  sheets  of  iron  with  a  layer  of  tin  ;  the  best  kind,  known  as  hlork 
tin,  being  that  which  is  covered  with  the  thickest  layer  of  tin,  and  after- 
wards hammered  upon  a  polished  anvil  in  order  to  consolidate  the  coating 
and  make  it  adhere  more  firml}'.  Tin  being  unaltered  by  exposure  to  air 
at  the  ordinary  tempemture,  will  effectually  protect  the  iron  from  rust  as 
long  as  the  coating  of  tin  is  perfect,  but  as  soon  as  a  portion  of  the  tin  is 
removed  so  as  to  leave  the  iron  exposed,  corrosion  wUl  take  place  very 
rapidly,  because  the  two  metals  form  a  galvanic  couple,  which  will  decom- 
pose the  water  (charged  Av^ith  carbonic  acid)  deposited  upon  them  from 
the  air,  and  the  iron,  having  the  greater  attraction  for  oxygen,  will  be  the 
metal  attacked.  In  the  case  of  galvanised  iron  (coated  with  zinc),  on  the 
contrary,  the  zinc  would  be  the  metal  attacked,  and  hence  the  greater 
durability  of  this  material  under  certain  conditions. 

Fur  the  manufacture  of  tin-plate,  the  very  best  iron  refined  with  char- 
coal (see  page  309)  is  employed,  and  the  most  important  part  of  the  process 
consists  in  cleansing  the  iron  plates  from  every  trace  of  oxide  which  would 
prevent  the  adhesion  of  the  tin.  To  efiiect  this  they  are  made  to  undergo 
several  processes,  of  which  the  most  important  are — (1)  immei-sion  in 
diluted  sulphuric  acid ;  (2)  heating  to  redness ;  (3)  hammering  and  roll- 
ing to  scale  off  the  oxide ;  (4)  steeping  in  sour  bran  ;  (5)  immersion  in 
mixed  diluted  sulphuric  and  hydrochloric  acids  ;  (6)  scouring  Avith  bran ; 
(7)  washing  with  water ;  they  are  then  dried  for  an  hour  in  a  vessel  of 
melted  tallow,  which  prevents  contact  of  air,  and  immei-sed  for  an  hour 
and  a  half  in  melted  tin,  the  surface  of  which  is  protected  from  oxidation 
by  tallow  ;  after  draining,  they  are  dipped  a  second  time  into  the  tin  to 
thicken  the  layer  ;  then  transferred  to  a  bath  of  hot  tallow  to  allow  the 
superfluous  tin  to  run  dow'n  to  the  lower  edge,  whence  it  is  afterwards 
removed  by  liquefying  it  in  a  vessel  of  melted  tin,  and  shaking  it  off  by 
a  sharp  blow.  About  8  lbs.  of  tin  are  required  to  cover  225  plates, 
weighing  112  lbs. 

Terne-platc  is  iron  coated  with  an  alloy  of  tin  and  lead. 

In  tinning  the  interior  of  copper  vessels,  in  order  to  prevent  the  con- 
tamination of  food  with  the  copper,  the  surface  is  first  thoroughly  cleaned 
from  oxide  by  heating  it  and  rubbing  over  it  a  little  sal-ammoniac,  which 
decomposes  any  oxide  of  copper,  converting  it  into  the  volatile  chloride  of 
copper  (CuO-F2XH^Cl  =  CuClo-f-H20-|-2NH3).  A  little  resin  is  then 
sprinkled  upon  the  metallic  surface,  to  protect  it  from  oxidation,  and  the 
melted  tin  is  spread  over  it  with  tow. 

Pins  (made  of  brass  wire)  are  coated  with  tin  by  boiling  them  with 
cream  of  tartar  (bitartrate  of  potash),  common  salt,  alum,  granulated  tin, 
and  water;  the  tin  is  oxidised  at  the  expense  of  the  water,  and  is  then 


346  GUN  METAL. 

«lissolved  by  the  acid  liquid,  from  which  solution  it  is  reduced  by  elec- 
trolytic action,  for  the  tin  is  more  highly  electro-positive  than  tlie  brass, 
and  the  latter  acts  as  the  negative  plate. 

250.  Alloys  of  tin. — The  solder  employed  for  tin  wares  is  an  alloy  of 
tin  and  lead  in  various  proportions,  sometimes  containing  2  parts  of 
tin  to  1  of  lead  (fine  solder),  sometimes  equal  weights  of  the  two  metals 
(common  solder),  and  sometimes  2  parts  of  lead  to  1  of  tin  (coarse  solder). 
All  these  allctys  melt  at  a  lower  temperature  than  tin,  and  therefore,  than 
lead.  In  applying  solder,  it  is  essential  that  the  surfaces  to  be  united  be 
quite  free  from  oxide,  which  Avould  prevent  adhesion  of  the  solder; 
this  is  insured  by  the  application  of  sal-ammoniac,  or  of  hydrochloric 
acid,*  or  sometimes  of  powdered  borax,  remarkable  for  its  ready  fusibility 
and  its  solvent  power  for  the  metallic  oxides. 

Tin  forms  the  chief  part  of  the  alloys  known  as  pewter  and  Britannia 
metal,  the  former  being  composed  of  about  4  parts  of  tin  and  1  of  lead, 
whilst  the  latter  contains,  in  addition  to  the  tin,  comparatively  small 
quantities  of  antimony,  copper,  and  lead.  Another  similar  alloy  is  com- 
posed of  1 2  parts  of  tin,  1  of  antimony,  and  a  little  copper. 

Gun  mftal  is  an  alloy  of  90 '5  parts  of  copper  with  9%5  of  tin,  especially 
valuable  for  its  tenacity,  hardness,  and  fusibility.  In  preparing  this 
alloy,  it  is  usual  to  melt  the  tin,  in  the  hrst  place,  with  twice  its  weight 
of  copper,  when  a  white,  hard,  and  extremely  brittle  alloy  (1iaf>J  mptal)  is 
obtained.  The  remainder  of  the  copper  is  fused  in  a  deoxidising  flame 
on  the  hearth  of  a  reverberatory  furnace,  and  the  hard  metal  thoroughly 
mixed  with  it,  long  wooden  stirrers  being  employed.  A  quantity  of  old 
gun  metal  is  usually  melted  with  the  copper,  and  facilitates  the  mixing  of 
the  metals.  When  the  metals  are  thoroughly  mixed,  the  oxide  is  re- 
moved from  the  surface,  and  the  gun  metal  is  run  into  moulds  made  of 
loam,  the  stirring  being  continued  during  the  running,  in  order  to  prevent 
the  separation,  to  which  this  alloy  is  very  liable,  of  a  white  alloy  contain- 
ing a  larger  proportion  of  tin,  which  has  a  lower  specific  gravity,  and 
would  chiefly  collect  in  the  upper  part  of  the  casting  (forming  tin-spoU). 
In  casting  cannon  (erroneously  called  brass  guns)  the  mould  is  placed 
perpendicularly,  with  the  muzzle  upwards,  the  upper  part  of  the  mould 
being  about  3  feet  longer  than  is  required  for  the  gun,  so  that  a  super- 
fluous cylinder  of  metal  or  dead-head  is  formed,  in  \i'hich  the  separated 
alloy  collects,  together  with  any  oxide  or  dross  which,  may  have  run  out 
with  the  metal;  this  dead-head  is  cut  off"  before  the  gun  is  turned  and 
bored.  The  metal  is  run  into  the  mould  at  a  temperature  as  near  its 
point  of  solidification  as  possible,  so  as  to  diminish  the  chance  of  separa- 
tion. The  purest  commercial  qualities  of  copper  and  tin  are  always 
employed  in  gun  metal 

The  brittle  white  alloy  alluded  to  above  as  hard  metal  appears  to  be  a 
chemical  compound  having  the  formula  SnCu^  (which  requires  31*8  per 
cent,  of  tin,  and  68-2  percent,  of  copper),  though  the  alloy  which  has  the 
highest  density,  and  which  bears  repeated  fusion  without  alteration  in  its 
composition,  corresponds  to  the  formida  SnCug  (38*2  per  cent,  of  tin). 
It  is  probably  one  of  these  alloys  which  forms  the  tin-spots  or  flaws  in 
gun-metal  castings.    '  . 

•  It  is  custoniarj'  to  kill  the  hj'drochloric  acid  by  dissolving  some  ziuc  iu  it.    The 
I  liloride  of  zinc  is  probably  useful  in  protecting  the  work  from  oxidation. 


.  ALLOYS  OF  TIN.  Ml 

Bronze  is  essentially  an  alloy  of  copper  and  tin,  containing  more  tin 
than  giin  metal ;  its  composition  is  varied  according  to  its  application, 
small  quantities  of  zinc  and  lead  being  often  added  to  it.  Bronze  is 
affected  by  changes  of  temperature,  in  a  manner  precisely  the  reverse  of 
that  in  which  steel  is  influenced,  for  it  becomes  hard  and  brittle  when 
allowed  to  cool  slowly,  but  soft  and  malleable  when  quickl}^  cooled. 
The  art  of  making  bronze  was  practised  before  any  progress  had  been 
made  in  working  iron,  and  ancient  weapons  were  very  commonly  of  this 
material. 

Bronze  coin  (substituted  for  the  copper  coinage)  is  composed  of  95 
copper,  4  tin,  and  1  zinc. 

Bell  metal  is  an  alloy  of  about  4  parts  of  copper  and  1  of  tin,  to  which 
lead  and  zinc  are  sometimes  added.  The  metal  of  which  musical  instru- 
ments are  made  generally  contains  the  same  proportions  of  copper  and 
tin  as  bell  metal.  At  a  little  below  a  dark  red  heat,  this  alloy  may  be 
hammered  into  thin  plates,  by  which  Riche  and  Champion  have  succeeded 
in  imitating  the  celebrated  Chinese  gongs. 

Speculum  metal,  employed  for  reflectors  in  optical  instruments,  con- 
sists of  2  parts  of  copper  and  1  of  tin,  to  which  a  little  zinc,  arsenic,  and 
silver  are  sometimes  added  to  harden  it  and  render  it  susceptible  of  a 
high  polish. 

A  superior  kind  of  type  metal  is  composed  of  1  part  of  tin,  1  of  anti- 
mony, and  2  of  lead. 

Tin  is  not  dissolved  by  nitric  acid,-  but  is  converted  into  a  white 
powder,  the  binoxide  of  tin;  hydrochloric  acid  dissolves  it  with  the  aid 
of  heat,  evolving  hydrogen;  but  the  best  solvent  for  tin  is  a  mixture  of 
hydrochloric  with  a  little  nitric  acid.  AVhen  the  metal  is  acted  upon  by 
hydrochloric  acid,  it  assumes  a  crystalline  appearance,  which  has  been 
turned  to  account  for  ornamenting  tin-plate.  If  a  piece  of  common  tin- 
plate  be  rubbed  over  with  tow  dipped  in  a  warm  mixture  of  hydrochloric 
and  nitric  acids,  its  surface  is  very  prettily  diversified  (moire  metallique); 
it  is  usual  to  cover  the  surface  with  a  coloured  transparent  varnish. 

Commercial  tin  is  liable  to  contain  minute  quantities  of  lead,  iron, 
copper,  arsenic,  antimony,  bismuth,  gold,  molybdenum,  and  tungsten. 
Pure  tin  may  be  precipitated  in  crystals  by  the  feeble  galvanic  current 
excited  by  immersing  a  plate  of  tin  in  a  strong  solution  of  stannous 
chloride,  covered  with  a  layer  of  water,  so  that  the  metal  may  be  in  con- 
tact with  both  layers  of  liquid.  ' 

251.  Oxides  of  tin. — Two  oxides  of  this  metal  are  known — the  prot- 
oxide, SnO,  and  the  binoxide,  SnO.,. 

Protoxide  of  tin  (SnO),  or  stannous  oxide,  is  a  substance  of  little 
practical  importance,  obtained  by  decomposing  stannous  chloride  with  in 
alkali.  Its  colour  varies,  according  to  the  mode  of  preparing  it,  from 
black  or  olive-coloured  to  red.  It  is  a  feebly  basic  oxide,  and  therefoiv 
dissolves  in  the  acids ;  it  may  also  be  dissolved  by  a  strong  solution  of 
potash,  but  is  then  easily  decomposed  into  metallic  tin  and  the  binoxide 
which  combines  with  the  potash. 

Binoxide  of  tin  (SnO.,),  or  stannic  oxide,  has  been  mentioned  as  the 
chief  ore  of  tin,  and  is  formed  Avhen  tin  is  heated  in  air.  Tin-stone,  or 
bassiterite,  as  the  natural  form  of  this  oxide  is  called,  occurs  in  very  hard 
square  prisms,  usually  coloured  brown  by  ferric  oxide.     In  its  insolubility 


348  CHLORIDES  OF  TIN. 

in  acids  it  resembles  crystallised  silica,  and,  like  that  substance,  it  forms, 
when  fused  with  alkalies  or  their  carbonates,  compounds  which  are  soluble 
in  water  ;  these  compounds  are  termed  atannatas,  the  binoxide  of  tin  being 
known  as  damiir  anhydrvle. 

Sodium  daniiate  is  prepared,  on  the  large  scale,  for  use  as  a  mordant 
by  calico-printers.  The  prepared  tin  ore  (page  343)  is  heated  with  solu- 
tion of  sodium  hydrate,  and  boiled  down  till  the  temperature  rises  to  500'^ 
or  600°  F. ;  or  the  tin  ore  is  fused  with  sodium  nitrate,  when  the  nitric 
acid  is  expelled.  It  crystallises  easily  in  hexagonal  tables  having  the 
composition  Na.,Sn()3,4Aq.,  which  dissolve  easily  in  cold  water,  and  are 
partly  deposited  again  when  the  solution  is  heated.  Most  normal  salts  of 
the  alkalies  also  cause  a  separation  of  sodium  stannate  from  its  aqueous 
solution.  The  solution  of  sodium  stannate  has,  like  the  silicate,  a  strong 
alkaline  reaction,  and  when  neutralised  by  an  acid,  yields  a  precipitate  of 
stannic  acid,  HgSuO^.  If  the  solution  of  sodium  stannate  be  added  to  an 
excess  of  hydrochloric  acid,  the  stannic  acid  remains  in  solution,  and  if 
the  liquid  be  dialysed  (see  page  114),  a  jelly  is  first  formed,  which 
gradually  liquefies  as  the  sodium  chloride  diffuses  away,  and  ev,entually 
a  pure  aqueous  solution  of  stannic  acid  is  obtained,  which  is  very  easily 
gelatinised  by  the  addition  of  a  minute  quantity  of  hydrochloric  acid,  or 
of  some  neutral  salt.  The  great  similarity  between  stannic  and  silicic 
acids  is  here  very  remarkable.  When  heated,  stannic  acid  is  converted 
into  metastannic  anhydride  (Sn^Ojo). 

Metastannic  acid  HioSn50,5  (dried  at  100°  C.)  is  obtained  as  a  white  crystalline 
hydrate  (with  5Aq.)  wlien  tin  is  oxidised  by  nitric  acid;  when  washed  with  water 
and  dried  by  exposure  to  air,  it  has  the  above  composition.  When  lieated,  it  assumes 
a  yellowish  colour,  and  a  hardness  resembling  that  of  powdered  tin-stone.  Putty 
poicder,  used  for  polishing,  consists  of  metastannic  anhydride ;  as  found  in  commerce 
it  generally  contains  much  oxide  of  lead.  Metastannic  acid  is  insoluble  in  water  and 
diluted  acids,  and  when  fused  witli  hydrated  alkalies,  is  converted  into  a  soluble 
stannate  ;  but  if  boiled  with  solution  of  potash  it  is  dissolved  in  the  form  of  potassium 
metastannate,  which  will  not  crystallise,  like  the  stannate,  but  is  obtained  as  a 
granular  precipitate  by  dissolving  potassium  hydrate  in  its  solution.  This  precipitate 
has  the  composition  KjjO.SnsOiQ.lAq. ;  it  is  very  soluble  in  water,  and  is  strongly 
alkaline.  When  it  is  heated  to  expel  the  water,  it  is  decomposed,  and  the  pota.sh 
may  be  washed  out  with  water,  leaving  metastannic  acid.  The  hydrated  metastannic 
acid  may  be  distinguished  from  stannic  acid  by  the  action  of  stannous  chloride,  which 
converts  it  into  the  yellow  metastannate  of  tin  (SnO.Sn50,„.4Aq.). 

Stannate  of  tin  is  obtained  as  a  yellowish  hydrate  by  boiling  stannous  chloride  with 
hydrated  sesquioxide  of  iron;  FeaO.^-^2SuClg  =  SnO.Sn02  +  2FeCl2.  It  is  sometimes 
written  Sn^Og,  and  called  sesquioxide  of  tin. 

252.  Chlorides  of  tin. — The  two  chlorides  of  tin  correspond  in  com- 
position to  the  oxides. 

Stannous  chloride  or  yrotocldoride  of  tin  (SnClg)  is  much  used  by 
dyers  and  calico-printers,  and  is  prepared  by  dissolving  tin  in  hydrochloric 
acid,  when  it  is  deposited,  on  cooling,  in  lustrous  prismatic  needles 
(SnCl2.2Aq.),  known  as  tin  crystaU  or  salts  of  tin.  The  solution  of  the 
tin  is  generally  effected  in  a  copper  vessel,  in  order  to  accelerate  the 
action  by  forming  a  voltaic  couple,  of  which  the  tin  is  the  attacked  metal. 
When  gently  heated,  the  crystals  lose  their  water,  and  are  partly  de- 
composed, some  hydrochloric  acid  being  evolved  (SnCl., -I- HgO  =  SnO 
-I-2HC1) ;  but  at  a  higher  teuipeiature,  a  great  part  of  the  chloride  may 
be  distilled  in  the  anhydrous  state  ;  the  anhydrous  chloride  is  generally 
prepared  by  distilliug  powdered  tin  with  corrosive  sublimate,  when   it 


SULPHIDES  OF  TIX.  349 

remains  in  the  retort  as  a  brilliant  grey  solid,  which  requires  a  bright  i-ed 
heat  to  convert  it  into  vapour.  When  water  is  poured  upon  the  crystals 
of  stannous  chloride,  they  are  only  partially  dissolved,  a  white  oxychloride 
of  tin  (SnClo.SnO.2Aq.)  being  separated.  A  moderately  dilute  solution 
of  stannous  chloride  absorbs  oxygen  from  the  air,  and  deposits  a  whitt- 
compound  of  stannic  chloride  and  oxide;  2SnCl,  +  O.,  =  SnCl^.Sn().,. 
If  the  solution  contains  much  free  hydrochloric  acid  it  remains  clear, 
being  entirely  converted  into  stannic  chloride.  A  strong  solution  of 
the  chloride  is  not  oxidised  by  the  air,  and  the  weak  solution  may  be 
longer  preserved  in  contact  with  metallic  tin.  Stannous  chloride  has  a 
great  attraction  for  chlorine  as  well  as  for  oxygen,  and  is  frequently 
employed  as  a  deoxidising  or  dechlorinating  agent.  Tin  may  be  preci- 
pitated from  stannous  chloride  by  the  action  of  zinc,  in  the  form  of 
minute  crystals.  A  very  beautiful  tin  tree  is  obtained  by  dissolving 
granulated  tin  in  strong  hydrochloric  acid,  with  the  aid  of  heat,  in  the 
proportion  of  8  measured  oz.  of  acid  to  1000  grs.  of  tin,  diluting  the  solu- 
tion with  four  times  its  bulk  of  water,  and  introducing  a  piece  of  zinc. 

Stannic  chloride,  or  hichJoride,  or  tetrachloride  of  tin  (SnCl^),  is  ob- 
tained in  solution  when  tin  is  heated  with  hydrochloric  and  nitric  acids  : 
for  the  use  of  the  dyer,  the  solution  (nitrormiriate  of  tin)  is  generally 
made  with  chloride  of  ammonium  (sal-ammoniac)  and  nitric  acid.  The 
anhydrous  perchloride  is  obtained  by  heating  tin  in  a  current  of  dry  chlo- 
rine, when  combination  takes  place  with  combustion,  and  the  perchloride 
distils  over  as  a  heavy  (sp.  gr.  2 "28)  colourless  liquid,  volatile  (boiling- 
point,  240°  F.),  and  giving  suffocating  white  fumes  in  the  air.  When 
mixed  with  a  little  Avater,  energetic  combination  takes  place,  and  a 
crystalline  hydrate  (SnCl4.5Aq.)  is  formed,  which  is  decomposed  by  an 
excess  of  water,  with  separation  of  hydrated  stannnic  acid.  Stannic 
chloride  forms  crystallisable  double  salts  with  the  alkaline  chlorides. 
Piid,-  salt,  used  by  dyers,  is  a  compound  of  stannic  chloride  with  chloride 
of  ammonium,  2NH4Cl.SnCl4. 

253.  Sulphidi'K  of  tin. — The  2)t'otOb^dplmh\  or  stan)unu<  .mlphide  (SnS), 
is  found  in  Cornwall  as  ti)i  pyrites,  and  may  be  easily  prepared  by  heating- 
tin  with  sulphur,  when  it  forms  a  grey  crystalline  mass.  It  is  also  ob- 
tained as  a  dark  brown  precipitate  by  the  action  of  hydrosulphuric  acid 
upon  a  solution  of  stannous  chloride.  Stannous  sulphide  is  not  dissolved 
by  alkalies  imless  some  sulphur  be  added,  which  converts  it  into  stannic 
sulphide. 

Bisidphid"  of  tin,  or  stannic  sulphide  (SnSg),  is  commonly  known  as 
mosaic  (/old  or  hronzi'  j^owder,*  and  is  used  for  decorative  purposes.  It  is 
prepared  by  a  curious  process,  which  Avas  devised  in  1771,  and  must  have 
been  the  result  of  a  number  of  trials.  1 2  parts  by  weight  of  tin  are  dis- 
solved in  6  parts  of  mercury ;  the  britth?  amalgam  thus  obtained  is 
l)owtlered  and  mixed  with  7  parts  of  sulphur  and  6  of  sal-ammoniac. 
The  mixture  is  introduced  into  a  Florence  flask,  which  is  gently  heate<l 
in  a  sand-bath  as  long  as  any  smell  of  hydrosulphuric  acid  is  evolved  ; 
the  temperature  is  then  raised  to  dull  redness  until  no  more  fumes  art- 
disengaged.  The  mosaic  gold  is  found  in  beautiful  yeUow  scales  at  the 
bottom  of  the  flask,  and  sulphide  of  mercury  and  calomel  are  deposited  in 

*  Bronze  powder  is  also  niaile  by  powdering  finely  laminated  alloys  of  copper  and  zinc 
a  little  oil  being  used  to  prevent  oxidation. 


350  TITANIUM. 

the  neck.  The  mercury  appears  to  be  used  for  effecting  the  fine  division 
of  the  tin,  and  the  sal-ammoniac  to  keep  down  the  temperature  (by  its 
volatilisation)  below  the  point  at  which  the  bisulphide  of  tin  is  converted 
into  protosulphide. 

Mosaic  gold,  like  gold  itself,  is  not  dissolved  by  hydrochloric  or  nitric 
acid,  but  easily  by  u(jna  rer/ia.  Alkalies  also  dissolve  it  when  heated. 
On  adding  hydrosulphuric  acid  to  a  solution  of  stannic  chloride,  the 
stannic  sulphide  is  obtained  as  a  yellow  precipitate,  which  is  sometimes 
formed  only  on  boiling. 

254.  Titanium  (Ti  =  50  parts  by  weight),  which  stands  in  close  chemical  relation- 
ship to  tin,  used  to  be  described  as  a  very  rare  metal,  but  it  has  lately  been  found  to 
exist  in  considerable  quantity  in  iron  ores  and  clays,  although  no  very  important 
practical  application  has  hitherto  been  found  for  it.  The  form  in  which  it  is  gene- 
rally found  is  titanic  acid  (or  anhydride)  (TiO^),  which  occurs  uncombined  in  the 
minerals  rutile,  anatasc,  and  brookitc,  the  first  of  which  is  isomorphous  with  tin- 
stone, and  is  extremely  hard  like  that  mineral.  In  (jombination  with  oxide  of 
iron,  titanic  acid  is  found  in  iron-sand,  iserine,  or  mcnaccanile  (found  originally 
at  Menaccan  in  Cornwall),  which  resembles  gunpowder  in  appearance,  and  is  now 
imported  in  abundance  from  Nova  Scotia  and  New  Zealand.  Some  specimens  of 
this  mineral  contain  40  per  cent,  of  titanic  acid,  combined  with  protoxide  of  iron. 
To  extraiit  titanic  acid  from  it,  the  finely -ground  mineral  is  fused  with  three  parts 
of  carbonate  of  potash,  when  carbonic  acid  gas  is  expelled  and  titanate  of  potash 
formed ;  on  washing  the  mass  with  hot  water,  this  salt  is  decomposed,  a  part  of  its 
alkali  being  removed  by  the  water,  and  an  acid  titanate  of  potash  left,  mixed  with 
the  oxide  of  iron.  This  is  dissolved  in  hydrochloric  acid,  and  the  solution  evapo- 
rated to  dryness,  when  the  titanic  acid,  and  any  silica  which  may  be  present,  are 
(■ouverted  into  the  insoluble  modifications,  and  are  left  on  digesting  the  residue 
again  with  dilute  hydrochloric  acid  ;  the  residue  is  washed  with  water  (by  decanta- 
tion,  for  titanic  acid  easily  passes  through  the  filter),  dried,  and  fused  at  a  gentle 
heat  with  bisulphate  of  potash.  The  sulphuric  acid  forms  a  soluble  compound  with 
the  titanic  acid  (TiOjSOg),  which  may  be  extracted  by  cold  water,  leaving  the 
silica  undissolved.  The  solution  containing  the  titanic  acid  is  mixed  with  about 
twenty  times  its  volume  of  water,  and  boiled  for  some  time,  when  the  titanic  acid 
is  separated  as  a  white  precii)itate,  exhibiting  a  great  disposition  to  cling  as  a  film 
to  the  surface  of  the  flask  in  which  the  solution  is  boiled,  and  giving  it  the  appear- 
ance of  being  corroded.  The  titanic  acid  becomes  yellow  when  strongly  heated,  and 
white  again  on  cooling ;  it  docs  not  dissolve  in  solution  of  potash  like  silica,  but 
when  fused  with  potash  it  forms  a  titanate,  which  is  decomposed  by  water ;  the 
acid  titanate  of  potash  which  is  left  may  be  dissolved  in  hydrochloric  acid,  and 
if  the  solution  be  neutralised  with  carbonate  of  ammonia,  hydrateil  titanic  acid  is 
precipitated,  very  much  resembling  alumina  in  appearance.  By  dissolving  the 
gelatinous  hydrate  in  cold  hydrochloric  acid,  and  dialysing,  a  solution  of  titanic  acid 
in  water  is  obtained,  which  is  liable  to  gelatinise  spontaneously  if  it  contains  more 
than  1  per  cent,  of  the  acid. 

Titanic  acid  is  employed  in  the  manufacture  of  artificial  teeth,  and  for  imparting 
a  .straw-yellow  tint  to  the  glaze  of  porcelain. 

If  a  mixture  of  titanic  acid  and  charcoal  be  heated  to  redness  in  a  porcelain  tube, 
through  which  dry  chlorine  is  passed,  tetrachloride  of  titanium  (TiCl4)  is  obtained 
as  a  cplourless  volatile  liquid,  very  similar  to  perchloride  of  tin.  By  passing  the 
va[iour  of  the  tetrachloride  of  titanium  over  heated  sodium,  the  metallic  titanium 
is  obtained  in  prismatic  crystals  resembling  specular  iron  ore  in  appearance.  Like 
tin,  it  is  said  to  dissolve  in  hydrochloric  acid  with  liberation  of  hydrogen.  The 
most  remarkable  chemical  feature  of  titanium  is  its  direct  attraction  for  nitrogen, 
with  which  it  combines  when  strongly  heated  in  air.  By  passing  ammonia  gas 
over  titanic  acid  heated  to  redness,  a  violet  powder  is  formed,  which  is  a  nitride  of 
titanium  (TiN.^).  Beautiful  cubes  of  a  copper  colour  and  great  hardness,  formerly 
believed  to  be  metallic  titanium,  are  found  adhering  to  the  slags  of  blast-furnaces 
in  which  titaniferous  iron  ores  are  smelted  ;  these  contain  about  77  per  cent,  of 
titanium,  18  of  nitrogen,  and  rather  less  than  4  of  carbon,  and  are  believed  to  con- 
sist of  a  compound  of  cyanide  with  nitride  of  titanium,  TiCy^.  STi^Ng.  A  similar 
compound  is  obtained  by  passing  nitrogen  over  a  mixture  of  titanic  acid  and  charcoal 
heated  to  whiteness. 


TUNGSTEN.  '  351 

Violet-coloured  ciystals  of  trichloride  of  titanium  (TiClj)  are  obtained  by  passiuw 
hydrogen  charged  with  vapour  of  tetracldoride  ot  titanium  through  a  red  hot  porce 
lain  tube  ;  it  forms  a  violet  solution  in  water,  which  resembles  stannous  chloride  in 
its  reducing  properties. 

When  a  solution  of  titanic  acid  (or  acid  titanate  of  potash)  in  hj'drochloric  acid  is 
acted  on  by  zinc,  a  violet  solution  is  formed,  which  deposits,  after  a  time,  a  blue  (or 
green)  precipitate,  this  appears  to  be  a  sesquioxide  of  titanium  (Ti^Og),  and  rapidly 
absorbs  oxygen  from  the  air,  being  converted  into  titanic  acid.  A  protoxide  of 
titanium  (TiO)  is  said  to  be  obt  lined  as  a  black  powder  when  titanic  acid  is  strongly 
heated  in  a  crucible  lined  with  charcoal. 

Bimdphidr.  of  titanium  is  not  precipitated,  like  bisulphide  of  tin,  when  hydro- 
sulphuric  acid  acts  upon  the  tetrachloride  ;  but  if  a  mixture  of  the  vapour  of 
tetrachloride  of  titanium  with  hydrosulphuric  acid  is  passed  through  a  red  hot  tube, 
greenish-yellow  scales  of  the  bisulphide,  resembling  mosaic  gold,  are  deposited. 

Titanium,  like  tin,  is  classed  among  the  tetratomic  elements. 

255.  Tungsten"  (W  =  184)is  chiefly  found  in  the  mineral  wolfram,  which  occui-s 
often  associated  with  tin-stone,  in  large  brown  shining  prismatic  crystals,  which 
are  even  heavier  than  tin-stone  (sp.  gr.  7 '3),  from  which  circumstance  the  metal 
derives  its  name,  tungsten,  in  Swedish,  meaning  heavy  stone.  The  symbol  (W) 
used  for  tungsten  is  derived  from  the  Latin  name  wolfraviium.  Wolfram  contains, 
the  tungstates  of  iron  and  manganese  in  somewhat  variable  proportions,  but  its 
general  composition  is  expressed  by  the  formula  3FeW04.MnWO^.  Scheelitc,  tung- 
state  of  calcium  (CaW04),  is  another  mineral  in  which  tungsten  is  found.  A  tungstate 
of  copper  has  been  found  in  Chili. 

Tungstate  of  sodium  is  employed  by  calico-printers  as  a  mordant,  and  is  sometimes 
apjilied  to  muslin,  in  order  to  render  it  uninflammable.  It  is  obtained  by  fusing 
wolfram  with  carbonate  of  soda,  an  operation  to  which  tin  ores  containing  this 
mineral  in  large  quantity  are  sometimes  submitted  previously  to  smelting  them. 
Water  extracts  the  sodium  tungstate  which  may  be  crystallised  in  rhomboidal  plates, 
having  the  composition  Xa.,W04.'2Aq.  When  a  solution  of  this  salt  is  mixed  with 
an  excess  of  hydrochloric  acid,  white  hydrated  tungstic  acid  (H2W04.Aq.)  is  pre- 
cipitated, while  hot  solutions  give  a  yellow  precipitate  of  H2WO4  ;  but  if  dilute- 
hydrochloric  acid  be  carefully  added  to  a  5  per  cent,  solution  of  sodium  tungstate- 
in  sufficient  proportion  to  neutralise  the  alkali,  and  the  solution  be  then  dialysed 
(page  114),  the  sodium  chloride  passes  through,  and  a  pure  aqueous  solution  of 
tungstic  acid  is  left  in  the  dialyser.  This  solution  is  unchanged  b}'  boiling,  and 
when  evaporated  to  dryness,  it  forms  vitreous  scales,  like  gelatine,  which  adhere  very 
strongly  to  the  dish.  It  redissolves  in  one-fourth  of  its  weight  of  water,  forming  a 
solution  of  the  very  high  specific  gravity  3  2,  which  is,  therefore,  able  to  float  glass. 
The  solution  has  a  bitter  and  astringent  taste,  and  decomposes  sodium  carbonate 
with  effervescence.  It  becomes  green  when  exposed  to  air,  from  the  deoxidising 
action  of  organic  dust.  When  tungstic  acid  is  heated,  it  loses  water,  and  becomes 
of  a  straw-yellow  colour,  and  insoluble  in  acids.  There  are  at  least  two  modifica- 
tions of  tungstic  acid,  which  bear  to  each  other  a  relation  similar  to  that  between 
stannic  and  meta.stanuic  acids. 

Barium  tungstate  has  been  employed  as  a  substitute  for  white  lead  in  painting. 

The  most  characteristic  property  of  tungstic  acid  is  that  of  yielding  a  blue  oxide 
(WO.,.WOs),  when  placed  in  contact  with  hydrochloric  acid  and  metallic  zinc. 

A  very  remarkable  compound  containing  tungstic  acid  and  soda  is  obtained  when 
bitungstate  of  soda  (Xa.-,0.2WO:j4H.20)  is  fused  with  tin.  If  the  fused  mass  be 
treated  with  strong  potash,  to  remove  free  tungstic  acid,  washed  with  water,  and 
treated  witli  hydrochloric  acid,  yellow  lustrous  cubical  cr3-stals  are  obtained,  whicli 
are  remarkable,  among  sodium  compounds,  for  their  resi-stance  to  the  action  of  water, 
of  alkalies,  and  of  all  acids  except  hydrofluoric.  The  composition  of  these  crystals, 
appears  to  be  NaoO.WO.j.2W03. 

The  tungstoborates  are  remarkalilc  salts  containing  WO3  and  B0O3  combined  with 
metallic  oxides.  Their  solutions  have  a  very  high  specific  gravity  ;  that  of  cadmium 
tungstoborate  has  the  sp.  gr.  3 '6,  and  is  used  to  ett'ect  the  mechanical  separation  of 
minerals  of  different  specific  gi-avities.  Thus,  a  diamond  (.sp.  gr.  3'5)  would  float  ; 
whilst  a  wliite  sapphire  (.sp.  gr.  4*0)  would  sink  in  the  solution.    . 

The  binojide  of  tungsten  (WO.^)  appears  to  be  an  indifl'ereut  oxide,  and  is  obtained 
by  reducing  tungstic  acid  with  hydrogen  at  a  low  red  heat,  when  it  forms  a  browit 
powder  which  is  dissolved  by  boiling  in  solution  of  potash,  hydrogen  being  evolved,, 
and  potassium  tungstate  formed. 


352  NIOBIUM — COPPER. 

Metallic  tmujslcn  is  oljtained  by  reducing  tuugstic  acid  with  charcoal  at  a  white 
heat,  as  au  iron-grej-  infusible  ni'etal  of  sp.  gr.  17 '6,  veiy  hard,  uot  attected  by 
hydrochloric  or  diluted  sulpliuric  acid,  but  converted  into  tungstic  acid  by  the  action 
of  nitric  acid.  When  tungsten  is  dissolved  in  about  t€n  times  its  weight  of  fused 
steel,  it  forms  an  extremely  hard  alloy. 

Wlien  tungsten  is  heated  in  chlorine,  the  ttoufntie  chloride  (WCl^)  sublimes  in 
bronze  coloured  needles  which  are  decompo.sed  by  water.  When  gently  heated  iu 
Jivdrowen,  it  is  converted  into  the  tetrachloride  (WCI4),  but  if  its  vapour  be  mixed 
with  hydrogen  and  passed  through  a  glass  tiibe  heated  to  redness,  metallic  tungsten 
is  obtained  in  a  form  in  which  it  is  not  dissolved,  even  by  aqua  regia,  thougli  it  may 
be  converted  into  pota.ssiuni  tungstate  by  potassium  hypochlorite  mixed  with  potash 
in  excess. 

Bisulphide  o/tuiufstrn  (WSj)  is  a  black  crystalline  substance  resembling  plumbago, 
obtained  by  heating  a  mixture  of  bitungstate  of  potash  with  sulphur,  and  washing 
with  hot  water.  Trisnlphide  of  tungsten  (WS3)  is  a  sulpliur-acid,  obtainable  as  a 
brown'precipitate  by  dissolving  tungstic  acid  in  an  alkaline  sulphide,  and  precipitat- 
ing by  an  acid. 

256.  Xiobium  (Nb==94)  (formerly  (Milled  vMlumbium)  has  been  obtained  from  a 
rare  dark  giey  hard  ciystalline  mineral  known  as  coluvibite,  occurring  in  Massa- 
tthusetts.  This  mineral  contains  niolnc  oxide,  (NbO»)  combined  with  the  oxides  of 
iron  and  manganese. 

The  niobic  oxide  is  extracted  by  a  laborious  process,  and  foims  a  white  i>owder, 
simringly  soluble  in  hydrochloric  acid.  Niobium  itself  has  been  obtained  as  a 
black  )K)wder  insoluble  in  nitric  acid  and  in  aqua  regia,  but  dissolved  by  a  mixturi- 
of  nitric  and  hydrofluoric  acids. 

Tantalum,  formerly  believed  to  be  identical  with  niobium,  occurs  in  the  tantalite 
und  yttrotantalitc  of  Sweden,  whicli  contain  t/mtalk-  oxide  (TaO,)  resembling  niobic 
oxide. 

Niobium  and  tantalum  have  recently  been  found  to  the  aniount  of  2  or  3  per  cent, 
iu  the  tin  ore  of  Montebras. 

COPPER 

t'u"  =  63  "5  parts  by  weight. 

257.  ^Metallic  copper  is  met  with  in  nature  more  abundantly  than 
nudallic  iron,  though  the  compounds  of  the  latter  metal  are  of  more  fre- 
quent occurrence  than  those  of  the  former.*  A  very  important  vein  of 
metallic  copper,  of  excellent  quality,  occurs  near  Lake  Superior  in  North 
America,  from  -which  6000  tons  were  extracted  in  1858.  Metallic  copper 
is  also  sometimes  found  in  Cornwall,  and  rojyjjer  tuiwl,  containing  metalli<; 
copi^er  and  quartz,  is  imported  from  Chili. 

0/'^.s-  of  co]>per. — The  most  important  Englisli  ore  of  copper  is  ropper 
pyrites,  which  is  a  double  sulphide,  containing  copper,  iron,  and  sulphur 
in  the  proportions  indicated  by  the  formula  CuFeS.^.  It  may  be  known 
by  its  beautifvd  brass  yellow  colour  and  metallic  lustre.  Copper  pyrites 
is  found  in  Cornwall  and  Devonshire,  and  is  generally  associated  with 
•arsenical  pyrites  (FeSo-FeAs^),  tin-stone  (Sn( ^g),  quartz,  fluor  spar,  and  clay. 
A  very  attractive  variety  of  copper  pyrites  is  called  varietjated  copj)er  on 
or  pfacncl;  copper,  in  allusion  to  its '  rainbow  colours ;  its  simplest  for- 
mula is  CUgFeSg.     This  variety  is  found  in  Cornwall  and  Killarney. 

Copp^'r  ijlaiire  (CUo8)  is  another  Cornish  ore  of  copper,  of  a  dark  grey 
colour  and  feeble  metallic  lustre. 

Grrij  copper  ore,  also  abundant  in  Cornwall,  is  essentially  a  compound 
of  the  sulphides  of  copper  and  iron  with  those  of  antimony  and  arsenic, 
but  it  often  contains  silver,  lead,  zinc,  anil  sometimes  mercury. 

*  ('oi)per  is  not  at  all  fre<)uently  found  in  animals  or  vegetables  ;  but  Cliurch  has  made 
the  remarkable  observation  that  the  red  colouring  matter  {turncine)  of  the  feathers  of  the 
))laiitain-eater  (tovroni)  contains  as  murli  as  ,i-9  \tvx  cent,  of  copper. 


COPPER  ORES. 


353 


Malachite,  a  basic  carbonate  of  copper,  is  imported  from  Australia 
(Burra  Burra),  and  is  also  found  abundantly  in  Siberia.  Green  malachite, 
the  most  beautifully  veined  ornamental  variety,  has  the  compo&ition 
CuC03,Cu(OH)2,  and  blue  malachite  is  2CuC03.Cu(OH)2. 

Red  copper  ore  (CugO)  is  foxind  in  West  Cornwall,  and  the  black  oxide 
(CuO)  is  abundant  in  the  north  of  Chili. 

258.  The  seat  of  English  copper-smelting  is  at,  Swansea,  which  is 
situated  in  convenient  proximity  to  the  anthracite,  coal  employed  in  the 
furnaces.  The  chemical  process  by  which  copper  is  extracted  from  the 
ore  includes  three  distinct  operations — (1)  the  I'oasting,  to  expel  the 
arsenic  and  part  of  the  sulphur,  and  to  convert  the  sulphide  of  iron  into 
oxide  of  iron ;  (2)  the  fusing  with  silica,  to  remove  the  oxide  of  iron  as 
silicate,  and  to  obtain  tlie  copper  in  combination  with  sulphur  only ;  and 
(3)  the  roasting  of  this  combination  of  copper  with  sulphur,  in  order  to 
expel  the  latter  and  obtain  metallic  copper. 

The  details  of  the  smelting  process  appear  somewhat  complicated, 
because  it  is  divided  into  several  stages  to  allow  of  the  introduction  of  the 
different  varieties  of  ore  to  be  treated.  Thus,  the  first  roasting  process  is 
unnecessary  for  the  oxides  and  carbonates  of  copper,  and  the  fusion  with 
silica  is  not  needed  for  those  ores  which  are  free  from  iron,  so  that  they 
may  be  introduced  at  a  later  stage  in  the  operations. 

(1)  Calcining  or  roasting  the  ore  to  expel  arsenic  and  part  of  the 
sulphur. — The  ores  having  been  sorted,  and  broken  into  small  pieces,  are 


Fig.  257. 

mixed  so  as  to  contain  from  8  to  10  per  cent,  of  copper,  and  roasted,  in 

quantities  of  about  three  tons,  for  at  least  twelve  hours,  on  the  spacious 

hearth  (H,  fig.  258)  of  a  reverberatory 

furnace    (fig.    257),    at    a    temperature 

insufficient  for  fusion,  being  occasionally 

stirred  to    expose   them   freely    to    the 

action  of  the  air,  which  is  admitted  into 

the  furnace  through  an  opening  (0)  in 

the  side  of  the  hearth  upon  which  the 

ore  is   spread.     The   oxygen  of  the  air 

converts  a  part  of  the  sulphur  into  SO^, 

and  the  bulk   of  the   As  into  A&^O.^, 

which  passes  off  in  the  form  of  vapour, 

A  part  of  the  sulphide  of  iron  is  converted 

into  ferrous  sulphate  (FeSO^)  by  absorbing  oxygen  at  an  early  stage  of 

the  process,  and  this  sulphate   is  afterwards  decomposed  at  a  higher 


Fig.  258. 


554 


WELSH  COPPER-SMELTING  PROCESS. 


temperature,  evolving  SOg  and  SO3,  and  leaving  oxide  of  iron.  A  portion 
of  the  sulphide  of  copper  is  also  converted  into  oxide  of  copper  during 
the  Toasting,  so  that  the  roasted  ore  consists  essentially  of  a  mixture  of 
oxide  and  sulphide  of  copper  with  oxide  and  sulphide  of  iron.  Since  the 
sulphide  of  iron  is  more  easily  oxidised  than  sulphide  of  copper,  the 
greater  part  of  the  latter  remains  unaltered  in  the  roasted  ore. 

Durin"  the  roasting  of  copper  ore  dense  white  fumes  escape  from  the 
furnaces.  This  copper  smoke,  as  it  is  termed,  contains  ASgOg,  SOg,  SO3, 
and  HF,  the  latter  being  derived  from  the  fluor  spar  associated  with  the 
ore ;  if  allowed  to  escape,  these  fumes  seriously  contaminate  the  air  in 
the  neighbourhood,  and  copper-smelters  are  endeavouring  to  apply  some 
method  of  condensing,  and  perhaps  turning  them  to  profitable  account. 

(2)  Fusion  for  coarse  metal  to  remove  the  oxide  of  iron  by  dissolving  it 
with  silica  at  a  high  temperature. — The  roasted  ore  is  now  mixed  with 

metal  slag  from  process  4,  and 
with  ores  containing  silica  and 
oxides  of  copper,  but  no  sul- 
phur; the  mixture  is  introduced 
into  the  ore  furnace  (fig.  259), 
and  fused  for  five  hours  at  a 
higher  temperature  than  that 
employed  in  the  previous  opera- 
tion. In  this  process  fiuor  spar 
is  sometimes  added  in  order  to 
increase  the  fluidity  of  the  slag. 
The  oxide  of  copper  acts  upon 
the  sulphide  of  iron  still  con- 
tained in  the  roasted  ore,  with 
formation  of  sulphide  of  copper 
and  oxide  of  iron,  but  since 
there  is  more  sulphide  of  iron 
present  than  the  oxide  of  copper 
can  decompose,  the  excess  of 
sulphide  of  iron  combines  with 
the  sulphide  of  copper  to  form 
a  fusible  compound,  which 
separates  from  the  slag,  and  collects  in  the  form  of  a  matt  or  regulus  of 
coarse  metal,  in  a  cavity  (C)  on  the  hearth  of  the  furnace  :  it  is  run  out 
into  a  tank  of  water  (T)  in  order  to  granulate  it,  so  that  it  may  be  better 
fitted  to  undergo  the  next  operation. 

The  oxide  of  iron  combines  with  the  silica  contained  in  the  charge,  to 
form  a  fusible  ferrous  silicate  (pre furnace  slag),  which  is  raked  out  into 
moulds  of  sand,  and  cast  into  blocks  used  for  rough  building  purposes  in 
the  neighbourhood. 

The  composition  of  the  coarse  metal  corresponds  pretty  closely  with  the 
formula  CuFeSy  It  contains  from  33  to  35  per  cent,  of  copper ;  whilst 
the  original  ore,  before  roasting,  is  usually  sorted  so  that  it  may  contain 
about  8*5  per  cent. 

The  ore-furnace  slag  is  approximately  represented  by  the  formula 
FeO.Si02 ;  but  it  contains  a  minute  proportion  of  copper,  as  is  shown  by 
the  green  efflorescence  on  the  walls  in  which  it  is  used  around  Swansea. 
Fragments  of  quartz  are  seen  disseminated  through  this  slag. 


Fig.  259. 


COPPER- SMELTING  PROCESS.  355 

(3)  Calcination  of  the  coarse  metal  to  convert  the  greater  part  of  the 
ffulphide  of  iron  i7ito  oxide. — The  granulated  coarse  metal  is  roasted  at  a 
moderate  heat  for  twenty-four  hours,  as  in  th-e  first  operation,  so  that  the 
oxygen  of  the  air  may  decompose  the  sulphide  of  iron,  removing  the 
sulphur  as  sulphurous  acid  gas,  and  leaving  the  iron  in  the  form  of 
oxide. 

(4)  Fusion  for  white  metal  to  remove  the  whole  of  the  iron  as  silicate.— 
The  roasted  coarse  metal  is  mixed  with  roaster  and  refinery  slags  from 
processes  5  and  6,  and  with  ores  containing  carbonates  and  oxides  of 
copper,  and  fused  for  six  hours,  as  in  the  second  operation.  Any  sulphide 
of  iron  which  was  left  unchanged  in  the  roasting  is  now  converted  into 
oxide  of  iron  by  the  oxide  of  copper,  the  latter  metal  taking  the  sulphur. 
The  whole  of  the  oxide  of  iron  combines  with  the  silica  to  form  a  fusible 
slag,  the  composition  of  which  is  approximately  represented  by  the  for- 
mula 3Fe0.2Si02. 

The  matt  or  regulus  of  ichite  metal,  which  collects  beneath  the  slag, 
is  nearly  pure  cuprous  sulphide  (CU2S),  half  the  sulphur  existing 
in  the  cupric  sulphide  (CuS)  having  been  removed  by  oxidation  in  the 
furnace.  The  white  metal  is  run  into  sand-moulds  and  cast  into  ingots. 
The  tin  and  other  foreign  metals  usually  collect  in  the  lower  part  of  the 
ingot,  so  that,  for  making  best  selected  copper,  the  upper  part  is  broken  off 
and  worked  separately,  the  inferior  copper  obtained  from  the  lower  part  of 
the  ingot  being  termed  tile-copper.  The  ingots  of  white  metal  often  con- 
tain beautiful  tufts  of  metallic  copper  in  the  form  of  copper  moss. 

The  slag  separated  from  the  white  metal  (metal  slag)  is  much  more  fluid 
than  the  ore-furnace  slag,  and  contains  so  much  silicate  of  copper  that  it 
is  preserved  for  use  in  the  melting  for  coarse  metal. 

(5)  Roasting  the  ichite  metal  to  remove  the  sidphur  and  obtain  blistered 
copper. — The  ingots  of  white  metal  (to  the  amount  of  about  3  tons)  are 
placed  upon  the  hearth  of  a  reverberatory  furnace,  and  heated  for  four 
hours  to  a  tempearture  just  below  fusion,  so  that  they  may  be  oxidised  at 
the  surface,  the  sulphur  passing  off  as  sulphurous  acid  gas,  and  the  copper 
being  converted  into  oxide.  During  this  roasting  the  greater  part  of  the 
arsenic,  generally  present  in  the  fine  metal,  is  expelled  as  As.^Og.  The 
temperature  is  then  raised,  so  that  the  charge  may  be  completely  fused, 
after  which  it  is  lowered  again  till  the  twelfth  hour.  The  oxide  of  copper 
now  acts  upon  the  sulphide  of  copper  to  form  metallic  copper  and  su.1- 
phurous  acid  gas,  which  escapes,  with  violent  ebullition,  from  the  melted 
mass  ;  CuoS  +  2CuO  =  SOo  4-  Cu^.  When  this  ebullition  ceases^  the  tem- 
perature is  again  raised  so  as  to  cause  the  complete  separation  of  the  copper 
from  the  slag,  and  the  metal  is  run  out  into  moulds  of  sand.  Its  name 
of  blister  cojiper  is  derived  from  the  appearance  caused  by  the  escape  of 
the  last  portions  of  SOg  from  the  metal  when  solidifying  in  the  mould. 

The  slag  {roaster  slag)  is  formed  in  this  operation  by  the  combination 
of  a  part  of  the  oxide  of  copper  with  silica  derived  from  the  sand 
adhering  to  the  ingots,  and  from  the  hearth  of  the  furnace.  The  slag 
also  contains  the  silicates  of  iron  and  of  other  metals,  such  as  tin  and  lead, 
which  might  have  been  contained  in  the  white  metal.  This  slag  is  used 
again  in  the  melting  for  white  metal. 

(6)  Refining  to  remove  foreign  meials. — This  process  consists  in  slowly 
fusing  7  or  8  tons  of  the  blistered  copper  in  a  reverberatory  furnace,  so 


16 


POLING  OF  COPPER: 


that  the  air  passing  through  the  furnace  may  remove  any  remaining  sul- 
phur as  sulphurous  acid  gas,  and  may  oxidise  the  small  quantities  of  iron, 
tin,  lead,  &c.,  present  in  the  metal.  Of  course,  a  large  proportion  of  the 
copper  is  oxidised  at  the  same  time,  and  the  cuprous  oxide,  together 
with  the  oxides  of  the  foreign  metals,  combine  with  silica  (from  the  hearth 
or  from  adhering  sand). to  form  a  slag  which  collects  upon  the  surface  of 
the  melted  copper.  A  portion  of  the  cuprous  oxide  is  dissolved  by  the 
ruetallic  copper,  rendering  it  brittle  or  dry  copper. 

(7)  Toughening  or  poling,  to  remove  a  part  of  the  oxygen  and  bring  the 
copper  to  tough-pitch. — After  about  twenty  hours  the  slag  is  skimmed 
from  the  metal,  a  quantity  of  anthracite  is  thrown  over  the  surface  to  pre- 
vent further  oxidation,  and  the  metal  is  poled,  i.e.,  stirred  with  a  pole  of 
young  wood,  until  a  small  sample,  removed  for  examination,  presents  a 
peculiar  silky  fracture,  indicating  it  to  be  at  tough-pitchy  when  it  is  cast 
into  ingots. 

The  chemical  change  during  the  poling  appears  to  consist  in  the  re- 
moval of  the  oxygen  contained  in  the  cuprous  oxide  present  in  the  metal, 
by  the  reducing  action  of  the  combustible  gases  disengaged  from  the  wood. 
The  presence  of  a  small  proportion  of  cuprous  oxide  is  said  to  confer 
greater  toughness  upon  the  metal,  so  that  if  the  poling  be  continued  until 
the  whole  of  the  oxygen  is  removed,  overpoled  copper  of  lower  tenacity  is 
obtained.  On  the  other  hand,  the  brittleness  of  imdeipoled  copper  is  due 
to  the  pi-esence  of  cuprous  oxide  in  too  large  proportion.  Tough-cake 
copper  is  that  which  has  been  poled  to  the  proper  extent. 

When  the  copper  is  intended  for  rolling,  a  small  quantity  (not  exceed- 
ing I  per  cent)  of  lead  is  generally  added  to  it  before  it  is  ladled  into  the 
ingot  moulds.  Apparently  the  oxide  of  lead  formed  by  the  action  of  the 
air  assists  in  removing  some  of  the  impurities  in  the  form  of  slag  {scori- 
fication). 

The  chemical  changes  which  take  place  during  the  above  processes  will 
be  more  clearly  understood  after  inspecting  the  subjoined  table,  which 
exhibits  the  composition  of  the  products  obtained  at  different  stage's  of  the 
process,  these  being  distinguished  by  the  same  numerals  as  were  employed 
in  the  above  description. 


Products  obtained  in  smelting  Ores  of  Copper, 


In  100  parts. 

Ore. 

Roasted 
Ore. 

Coarse 
Uetal. 

Roasfed 
Coarse 
Metal. 

White 
Metal. 

Blister 
Copper. 

Refined 
Copper. 

1 
Tongh- 
pitchl 
Copper. 

Copper,       .         .         .        8-2 
Iron,            .         .         .17-9 
Sulphur,     .         .         .19-9 
Oxygen,      .         .         .   ;      I'O 
Silica,    .     .         .         .   j   34-3 

(1) 
8-6 
17-6 
12-5 
4-5 
34-3 

(2) 
33-7 
33-6 
29-2 

(3) 
33-7 
33-6 
13  0 
110 

(4) 
77-4 

0-7 
21-0 

(5) 

98  0 

0-5 

0-2 

(6) 
99-4 
trace 
trace 

0-4 

(7) 
99-6 
trace 
trace 
003 

Slags. 

Ore 
Furnace 

MetaL    Roaster. 

Refinery 

Oxideof  iron  (FeO), 

Suboxide  of  copper  (CujO), 

Silica, 

(2) 
54-0 

0-5 
45-0 

... 

(4) 
56  0 

0-9 
33-8 

(5) 
280 
16-9 
47-5 

(6) 

3  1 

39-2 

47-4 

EXTRACTION  OF  COPPER  IN  THE  LABORATORY.  357 

Blue  metal  is  the  term  applied  to  the  regulus  of  white  metal  (from  process  4) 
when  it  still  contains  a  considerable  proportion  of  sulphide  of  iron,  in  consequence 
of  a  deficient  supply  of  oxide  of  copper  in  the  furnace.  Fimple  metal  is  obtained  in 
the  same  operation  when  the  oxide  of  copper  is  in  excess,  so  that  a  portion  of  the 
copper  is  reduced,  as  in  process  5,  with  evolution  of  sulphurous  acid  gas,  which  pro- 
duces the  pimply  appearance  in  escaping.  The  reduced  copper  gives  a  reddish  colour 
to  the  pimple  copper.  Coarse  copiper  is  a  similar  intermediate  stage  between  white 
metal  and  blistered  copper.  Tile  copper  is  that  extracted  from  the  bottoms  of  the 
ingots  of  white  metal,  when  the  tops  have  been  detached  for  making  best  select 
copper.  Rosette  or  rose  copper  is  obtained  by  running  water  upon  the  toughened 
metal,  so  as  to  enable  the  metal  to  be  removed  in  films.  Anglesea  or  Mo7ia  copper  is 
a  very  tough  copper,  reduced  by  metallic  iron  from  the  blue  water  of  the  copper 
mines,  which  contains  sulphate  of  copper. 

A  new  method  {Holhvay's  process)  has  recently  been  proposed  for  the  treatment  of 
cupreous  pyrites,  which  consists  in  blowing  air  through  it  in  a  melted  state  in  a 
Bessemer's  converter  (p.  313),  when  the  combustion  of  the  suljihur  maintains  a  very 
high  temperature,  and  the  bulk  of  the  copper  sinks  to  the  bottom  as  a  regulus,  con- 
taining comparatively  small  quantities  of  iron  and  sulphur,  whilst  the  iron  is  converted 
into  oxide,  which  forms  a  slag  with  silica,  added  for  that  purpose.  The  copper 
regulus  contains  all  the  silver  and  gold  present  in  the  pyrites.  It  is  proposed  to 
utilise  the  SO.,  resulting  from  the  combustion  of  the  sulphur,  by  converting  it  into 
H,S04. 

259.  For  the  purpose  of  illustration,  copper  may  be  extracted  from  copper  pyrites 
on  the  small  scale  in  the  following  manner  : — 

200  grains  of  the  powdered  ore  are  mixed  M'ith  an  equal  weight  of  dried  borax, 
and  fused  in  a  covered  earthen  crucible  (of  about  8  oz.  capacity),  at  a  full  red  heat 
for  about  half  an  hour.  The  earthy  matters  associated  with  the  ore  are  dissolved 
by  the  borax,  and  the  pure  copper  pyrites  collects  at  the  bottom  of  the  crucible.  The 
contents  of  the  latter  are  poured  into 
an  iron  mould  (scorifying  mould,  fig. 
260),  and  when  the  mass  has  set,  it 
is  dipped  into  water.  The  semi- 
metallic  button  is  then  easily  detached 
from  the  slag  by  a  gentle  blow ;  it  is 
weighed,  finely  powdered  in  an  iron 
mortar,  and  introduce<l  into  an 
earthen  crucible,  which  is  placed 
obliquely  over  a  dull  fire,  so  that  it 
may  not  become  hot  enough  to  fuse  ^^S-  260. 

the    ore,    which   should    be    stirred 

occasionally  with  an  iron  rod  to  promote  the  oxidation  of  the  sulphur  by  the  air. 
When  the  odour  of  SOo  is  no  longer  perceptible,  the  crucible  is  placed  in  a  Sefstrbm's 
blast-furnace  (fig.  251),  and  exposed  for  a  few  minutes  to  a  bright  red  heat,  in 
order  to  decompose  the  sulphates  of  iron  and  copper.  When  no  more  white  fumes 
of  SO.)  are  perceived,  the  crucible  is  lifted  from  the  fire,  held  over  the  iron  mortar, 
and  the  roasted  ore  quickly  scraped  out  of  it  with  a  steel  spatula.  This  mixture  of 
tlie  oxides  of  copper  and  iron  is  reduced  to  a  fine  powder,  mixed  with  600  grains 
of  dried  carbonate  of  soda  and  60  grains  of  powdered  charcoal,  returned  to  the 
same  crucible,  covered  with  200  grains  of  dried  borax,  and  heated  in  a  Sefstrom's 
furnace  for  twenty  minutes.  The  crucible  is  then  allowed  to  cool  partly,  plunged 
into  water  to  render  it  brittle,  and  carefully  broken  to  extract  the  button  of  metallic 
copper,  which  is  weighed  to  ascertain  the  amount  contained  in  the  original  ore. 

260.  Effect  of  impurities  upon  the  quality  of  copper. — The  information 
possessed  by  chemists  upon  this  subject  is  still  very  limited.  It  has  been 
already  mentioned  that  the  presence  of  a  small  proportion  of  cuprous 
oxide  in  commercial  copper  is  found  to  increase  its  toughness.  It  is 
believed  that  copper,  perfectly  free  from  metallic  impurities,  is  not  im- 
proved in  quality  by  the  presence  of  the  oxide,  but  that  this  substance 
has  the  effect  of  counteracting  the  red-shortness  (see  page  314)  of  com- 
mercial copper,  caused  by  the  presence  of  foreign  metals. 

SuJplmr,  even  in  minute  proportion,  appears  seriously  to  injure  the 
malleability  of  copper. 


358  PROPERTIES  OF  COPPER. 

Arsenic  is  almost  invariably  present  in  copper,  very  frequently  amount- 
ing to  0-1  per  cent.,  and  does  not  appear  to  exercise  any  injurious  influence 
in  this  proportion ;  indeed,  its  presence  is  sometimes  stated  to  increase 
the  malleability  and  tenacity  of  the  metal. 

Phosphonis  is  not  usually  found  in  the  copper  of  commerce.  When 
inirposely  added  in  quantity  varying  from  0*12  to  0*5  per  cent,  it  is  found 
to  increase  the  hardness  and  tenacity  of  the  copper,  though  rendering  it 
somewhat  red-short.  Phosphor-bi'onze  is  a  very  hard  compound  of  this 
description. 

Ti7i,  in  minute  proportion,  is  also  said  to  increase  the  toughness  of 
copper,  though  any  considerable  proportion  renders  it  brittle. 

Antimony  is  a  very  objectionable  impurity,  and  is  by  no  means  uncom- 
mon in  samples  of  copper. 

Nickel  is  believed  to  injure  the  quality  of  copper  in  which  it  occurs. 

Bismuth  and  silver  are  very  generally  found  in  marketable  copper,  but 
their  effect  upon  its  quality  has  not  been  clearly  determined. 

All  impurities  appear  to  affect  the  malleability  and  tenacity  of  copper 
more  perceptibly  at  high  than  at  low  temperatures. 

The  conducting  power  of  copper  for  electricity  is  affected  in  an  extra- 
ordinary degree  by  the  presence  of  impurities.  Thus,  if  the  conducting 
power  of  chemicall}'  pure  copper  be  represented  by  100,  that  of  the  very 
pure  native  copper  from  Lake  Superior  has  been  found  to  be  93,  that  of 
the  copper  extracted  from  the  malachite  of  the  Burra  Burra  mines  in 
South  Australia  was  89,  whilst  that  of  Spanish  copper,  remarkable  for 
containing  much  arsenic,  was  only  14. 

Ptire  copper  is  obtained  by  decomposing  a  solution  of  pure  sulphate  of 
copper  by  the  galvanic  current,  as  in  the  electrotype  process.  If  the 
negative  wire  be  attached  to  a  copper  plate  immersed  in  the  solution,  the 
pure  copper  may  be  stripped  off  this  plate  in  a  sheet. 

261.  Properties  of  copiper. — The  most  prominent  character  which 
confers  upon  copper  so  high  a  rank  among  the  useful  metals  is  its  mal- 
leability, which  allows  it  to  be  readily  fashioned  under  the  hammer,  and 
to  be  beaten  or  rolled  out  into  thin  sheets  ;  among  the  metals  in  ordinary 
use,  only  gold  and  silver  exceed  copper  in  malleability,  and  the  com- 
parative scarcity  of  those  metals  leads  to  the  application  of  copper  for 
most  purposes  where  great  malleability  is  requisite. 

Although,  in  tenacity  or  strength,  copper  ranks  next  to  iron,  it  is  still 
very  far  inferior  to  it,  for  a  copper  wire  of  -y^  inch  in  diameter  will  support 
only  385  lbs.,  while  a  similar  iron  wire  will  carry  705  lbs.  without 
breaking  ;  and  in  consequence  of  its  inferior  tenacity,  copper  is  less  ductile 
than  iron,  and  does  not  admit  of  being  so  readily  drawn  into  exceedingly 
thin  wires. 

The  comparative  ease  with  which  copper  may  be  fused,  allows  it  to  be 
cast  much  more  readily  than  iron ;  for  it  will  be  remembered  that  the 
latter  metal  can  be  liquefied  only  by  the  highest  attainable  furnace  heat, 
whereas  copper  can  be  fused  at  about  1300°  C.  (2372°  F.),  a  temperature 
generally  spoken  of  as  a  bright  red  heat. 

As  being  the  most  sonorous  of  metals,  copper  has  been,  from  time 
immemorial,  employed  in  the  construction  of  bells  and  musical  instru 
nients.  The  readiness  with  which  it  transmits  electricity  is  turned  to 
account  in  telegraphic  communication,  its  conducting  power  being  almost 


I 


EFFECT  OF  SEA  WATER  UPON  COPPER.        -  359 

equal  to  that  of  silver,  which  is  the  best  of  electric  conductors.  In 
conducting  power  for  heat,  copper  is  surpassed  only  by  silver  and  gold. 

Copper  is  not  so  hard  as  iron,  and  is  somewhat  heavier,  the  specific 
gravity  of  cast  copper  being  8 '92,  and  that  of  hammered  or  drawn 
copper  8 "95. 

The  resistance  of  copper  to  the  chemical  action  of  moist  air  gives  it  a 
great  advantage  over  iron  for  many  uses,  and  the  circumstance  that  it  does 
not  decompose  water  in  presence  of  acids  enables  it  to  be  employed  as 
the  negative  plate  in  galvanic  couples. 

262.  Effect  of  sea  icatei'  upon  copper. — "When  copper  is  placed  in  a 
solution  of  salt  in  water,  no  perceptible  action  takes  place ;  but  in  the 
course  of  time,  if  the  air  be  allowed  access,  it  becomes  covered  with  a 
green  coating  of  oxychloride  of  copper  (CuCl2.3CuO.4H2O),  the  action 
probably  consisting,  first,  in  the  conversion  of  the  copper  into  oxide  by 
the  air,  and  afterwards  in  the  decomposition  of  the  oxide  by  the  sodium 
chloride;  4CuO  +  2XaCl  +  H20  =  CuCl2.3CuO  + 2XaH0.  The  surface 
of  the  copper  is  thus  corroded,  and  in  the  case  of  a  copper-bottomed 
ship,  the  action  of  sea  water  not  only  occasions  a  great  waste  of  copper, 
but  roughens  the  surface  of  the  sheathing,  and  affords  points  of  attach- 
ment to  barnacles,  &c.,  which  injure  the  speed  of  the  vessel.  Many 
attempts  have  been  made  to  obviate  this  inconvenience.  Zinc  has  been 
fastened  here  and  there  to  the  outside  of  the  copper,  placing  the  latter 
in  an  electro-negative  condition;  the  copper  has  been  coated  with  various 
compositions,  but  with  very  indifferent  success.  Muntz  metal  or  yelloio 
sheathinrj,  or  malleable  brass,  an  alloy  of  3  parts  of  copper  and  2  parts 
of  zinc,  has  been  employed  with  some  advantage  in  place  of  copper,  for 
it  is  very  much  cheaper  and  somewhat  less  easily  corroded ;  but  the 
difficulty  is  by  no  means  overcome.  Copper  containing  about  0'5  per 
cent,  of  i^hosphorus  is  said  to  be  corroded  by  sea  water  much  less  easily 
than  pure  copper. 

263.  Danger  attending  the  use  of  copper  vessels  in  cooking  food. —  The 
use  of  copper  for  culinary  vessels  has  occasionally  led  to  serious  conse- 
quences, from  the  poisonous  nature  of  its  compounds,  and  from  ignorance 
of  the  conditions  under  which  these  compounds  are  formed.  A  perfectly 
clean  surface  of  metallic  copper  is  not  affected  by  any  of  the  substances 
employed  in  the  preparation  of  food,  but  if  the  metal  has  been  allowed  to 
remain  exposed  to  the  action  of  the  air,  it  becomes  covered  with  a  film  of 
oxide  of  copper,  and  this  subsequently  combines  with  water  and  carbonic 
acid  gas  derived  from  the  air  to  produce  a  basic  carbonate  of  copper,* 
which,  becoming  dissolved,  or  mixed  with  the  food  prepared  in  these 
vessels,  confers  upon  it  a  poisonous  character.  This  danger  may  be 
avoided  by  the  use  of  vessels  which  are  perfectly  clean  and  bright,  but 
even  from  these,  certain  articles  of  food  may  become  contaminated  "with 
copper,  for  this  metal  is  much  more  likely  to  be  oxidised  by  the  air  when 
in  contact  with  acids  (vinegar,  juices  of  fruits,  &c.),  or  with  fatty  matters, 
or  even  with  common  salt ;  and  if  oxide  of  copper  be  once  formed,  it  wiU 
be  readily  dissolved  by  such  substances.  Hence  it  is  usual  to  coat  the 
interior  of  copper  vessels  with  tin,  Avhich  is  able  to  resist  the  action  of 
the  air,  even  in  the  presence  of  acids  and  saline  mattei-s. 

*  Often  erroneously  called  verdigris,  which  is  really  a  basic  acetate  of  copper. 


360  ALLOYS  OF  COPPER. 

264,  Useful  alloys  of  copper  with  other  metals. — The  most  important 
alloys  of  which  copper  is  a  predominant  constituent  are  the  following :  — 

Brass — 64  copper,  36  zinc. 

Muntz  metal — 60  to  64  copper,  40  to  36  zinc. 

German  silver — 51  copper,  30'5  zinc,  18 "5  nickel 

Aich  or  Gedge's  metal — 60  copper,  38  "2  zinc,  1*8  iron. 

Sterro-metal — 55  copper,  42*4  zinc,  0*8  tin,  1*8  iron. 

Bell  metal — 78  copper,  22  tin. 

Speculum  metal — 66-6  copper,  33*4  tin. 

Bronze — 80  copper,  4  tin,  16  zinc. 

Gun  metal — 90*5  copper,  9*5  tin, 

Bronze  coinage — 95  copper,  1  zinc,  4  tin. 

Aluminium  bronze — 90  copper,  10  aluminium. 
Brass  is  made  by  melting  copper  in  a  crucible,  and  adding  rather  more 
than  half  its  weight  of  zinc.  It  is  difficult  to  decide  whether  brass  is  a 
true  chemical  compound  or  a  mere  mechanical  mixture  of  copper  and 
zinc,  because  it  is  capable  of  dissolving  either  of  those  metals  when  in  a 
state  of  fusion.  The  circumstance  that  it  can  be  deposited  by  decom- 
posing a  solution  containing  copper  and  zinc  by  the  galvanic  current, 
would  appear  to  indicate  that  it  is  a  chemical  compound,  and  its  physical 
properties  are  not  such  as  would  be  expected  from  a  mere  mixture  of  its 
constituents.  A  small  quantity  of  tin  is  added  to  brass  intended  for 
door  plates,  which  renders  the  engraving  much  easier.  When  it  has  to 
be^turned  or  filed,  about  2  per  cent,  of  lead  is  usually  added  to  it,  in 
order  to  prevent  it  from  adhering  to  the  tools  employed.  Brass  cannot 
be  melted  without  losing  a  portion  of  its  zinc  in  the  form  of  vapour. 
When  Exposed  to  frequent  vibration  (as  in  the  suspending  chains  of  chan- 
deliers) it  suffers  an  alteration  in  structure  and  becomes  extremely  brittle. 
The  solder  used  by  braziers  consists  of  equal  weights  of  copper  and  zinc. 
In  order  to  prevent  ornamental  brass-work  from  being  tarnished  by  the 
action  of  air,  it  is  either  lacquered  or  bronzed.  Lacqtieiincj  consists 
simply  in  varnishing  the  brass  with  a  solution  of  shellac  in  spirit, 
coloured  with  dragon's  blood.  Bronzing  is  effected  by  applying  a  solution 
of  arsenic  or  mercury,  or  platinum,  to  the  surface  of  the  brass.  By  the 
action  of  arsenious  oxide  dissolved  in  hydrochloric  acid,  upon  brass,  the 
latter  acquires  a  coating  composed  of  arsenic  and  copper,  which  imparts  a 
bronzed  appearance,  the  zinc  being  dissolved  in  place  of  the  arsenic,  which 
combines  with  the  copper  at  the  surface.  A  mixture  of  corrosive  sub- 
limate (mercuric  cliloride  HgCla)  and  acetic  acid  is  also  sometimes 
employed,  when  the  mercury  is  displaced  by  the  zinc,  and  precipitated 
upon  the  surface  of  the  brass,  with  which  it  forms  a  bronze-like  amalgam. 
For  bronzing  brass  instruments,  such  as  theodolites,  levels,  &c.,  a  solu- 
tion of  chloride  of  platinum  is  employed,  the  zinc  of  the  brass  precipi- 
tating a  very  durable  film  of  metallic  platinum  upon  its  surface  (PtCl^ 
+  Zng  =  Pt -I- 2ZnCl2).  Aich  metal  is  a  kind  of  brass  containing  iron, 
and  has  been  employed  for  cannon,  on  account  of  its  great  strength.  At 
a  red  heat  it  is  very  malleable. 

Sterro  metal  (oreppos,  strong)  is  another  variety  of  brass  containing  iron 
and  tin,  said  to  have  been  discovered  accidently  in  making  brass  with 
the  alloy  of  zinc  and  iron  obtained  during  the  process  of  making  gal- 
vanised iron  (page  284).  It  possesses  great  strength  and  elasticity,  and 
is  used  by  engineers  for  the  pumps  of  hydraulic  presses. 


OXIDES  OF  COPPER.  361 

Aluminium  bronze  has  been  already  noticed,  and  the  alloys  of  copper 
and  tin  have  been  described  under  the  latter  metal. 

A  very  hard  white  alloy  of  77  parts  of  zinc,  17  of  tin,  and  6  of  copper, 
is  sometimes  employed  for  the  bearings  of  the  driving-wheels  of  loco- 
motives. 

Iron  and  steel  are  coated  with  a  closely  adherent  film  of  copper,  by 
placing  them  in  contact  \nih.  metallic  zinc  in  an  alkaline  solution  of  oxide 
of  copper,  prepared  by  mixing  sulphate  of  copper  with  tartrate  of  potash 
and  soda,  and  caustic  soda.  The  copper  is  thus  precipitated  upon  the 
iron  by  slow  voltaic  action,  the  zinc  being  the  attacked  metal.  By 
adding  a  solution  of  stannate  of  soda  to  the  alkaline  copper  solution,  a 
deposit  of  bronze  may  be  obtained. 

265.  Oxides  of  Copper. — Two  oxides  of  copper  are  well  known  in  the 
separate  state,  viz.,  the  suboxide  CugO,  and  the  oxide  CuO.  Another 
oxide,  Cu^O,  has  been  obtained  in  a  hydrated  state,  and  there  is  some 
evidence  of  the  existence  of  an  acid  oxide. 

The  black  oxide  of  copper  (cnpric  oxide),  CuO,  is  the  black  layer  which 
is  formed  upon  the  surface  of  the  metal  when  heated  in  air.  It  is  employed 
by  the  chemist  in  the  ultimate  analysis  of  organic  substances  by  com- 
bustion (page  84),  being  prepared  for  this  purpose  by  acting  upon  copper 
with  nitric  acid  to  convert  it  into  cupric  nitrate  (page  137),  and  heating 
this  to  dull  redness  in  a  rough  vessel  made  of  sheet  copper,  when  it 
leaves  the  black  oxide ;  Cu(X03)2  =  2NOo  +  0  -f  CuO.  At  a  higher  tem- 
perature the  oxide  fuses  into  a  very  hard  mass;  but  it  cannot  be  decom- 
posed by  heat.  Oxide  of  copper  absorbs  water  easily  from  the  air,  but  it 
is  not  dissolved  by  water ;  acids,  however,  dissolve  it,  forming  .the  salts 
of  copper,  whence  the  use  of  oil  of  vitriol  and  nitric  acid  for  cleansing 
the  tarnished  surface  of  copper ;  a  blackened  coin,  for  example,  immersed 
in  strong  nitric  acid,  and  thoroughly  washed,  becomes  as  bright  as  when 
freshly  coined.  Silica  dissolves  oxide  of  copper  at  a  high  temperature, 
forming  cupric  silicate,  which  is  taken  advantage  of  in  producing  a  fine 
green  colour  in  glass. 

Hed  oxide  or  suboxide  of  copper  (cuprotis  oxide),  CugO,  is  formed  when 
a  mixture  of  5  parts  of  the  black  oxide  with  4  parts  of  copper  filings 
is  heated  in  a  closed  crucible.  It  may  also  be  prepared  by  boiling  a  solu- 
tion of  cupric  sulphate  with  a  solution  containing  sodium  sulphite  and 
sodium  carbonate  in  equal  quantities,  when  the  suboxide  of  copper  is 
precipitated  as  a  reddish-yellow  powder,  which  should  be  washed,  by 
decantatiou,  with  boiled  water;  2CuS04  +  2ya2C03-HNa9S03  =  Cu20 
-f  3Xa2SO^-h2C02. 

Cuprous  oxide  is  a  feeble  base,  but  its  salts  are  not  easily  ob- 
tained by  direct  action  of  acids,  for  these  generally  decompose  it  into 
metallic  copper  and  cupric  oxide  yielding  cupric  salts.  In  the  moist 
state  it  is  slowly  oxidised  by  the  air.  Ammonia  dissolves  cuprous 
oxide,  forming  a  solution  which  is  perfectly  colourless  until  it  is  allowed 
to  come  into  contact  with  air,  when  it  assumes  a  fine  blue  colour,  be- 
coming converted  into  an  ammdniacal  solution  of  cupric  oxide.  If  the 
blue  solution  be  placed  in  a  stoppered  bottle  (quite  filled  with  it)  with  a 
strip  of  clean  copper,  it  will  gradually  become  colourless,  the  cupric 
oxide  being  again  reduced  to  cuprous  oxide,  a  portion  of  the  copper  being 
dissolved.  \Yhen  copper  filings  are  shaken  Avith  ammonia  in  a  bottle  of 
air,  the  same  blue  solution  is  obtained,  the  oxidation  of  the  copper  being 


362  SULPHATE  OF  COPPER. 

attended  with  a  simultaneous  oxidation  of  a  portion  of  the  ammonia,  and 
its  conversion  into  nitrous  acid,  so  that  the  white  fumes  of  ammonium 
nitrite  are  formed  in  the  upper  part  of  the  bottle.  If  the  blue  solution  be 
poured  into  a  large  quantity  of  water,  a  light  blue  precipitate  of  cupric 
hydrate  is  obtained.  The  ammoniacal  solution  of  cupric  oxide  has  the 
unusual  property  of  dissolving  paper,  cotton,  tow,  and  other  varieties  of 
cellulose,  this  substance  being  reprecipitated  from  the  solution  on  adding 
an  acid. 

Cuprous,  oxide,  added  to  glass,  imparts  to  it  a  fine  red  colour,  which 
is  turoed  to  account  by  the  glass-maker. 

Quadrant  oxide  of  copper,  Cu^O,  has  been  obtained  in  combination  with 
water,  by  the  action  of  stannous  chloride  and  potash  upon  a  cupric  salt. 

Cupric  acid  is  believed  to  be  formed  when  metallic  copper  is  fused 
with  nitre  and  caustic  potash.  The  mass  yields  a  blue  solution  in  water, 
which  is  very  easily  decomposed  with  evolution  of  oxygen  and  precipita- 
tion of  cupric  oxide.  The  existence  of  an  unstable  oxide  of  copper,  con- 
taining more  than  one  atom  of  oxygen,  is  also  rendered  probable  by  the 
circumstance  that  oxide  of  copper  acts  like  manganese  dioxide  in 
facilitating  the  disengagement  of  oxygen  from  potassium  chlorate  by  heat 
(page  33). 

266.  Sulphate  of  copper  or  cupric  sulphate. — The  beautiful  prismatic 
crystals  known  as  blue  vitriol,  blue  stone,  blue  copperas,  or  sulphate  of 
copper,  have  been  already  mentioned  as  formed  in  the  preparation  of 
sulphurous  acid  gas  (page  199),  by  dissolving  copper  in  oil  of  vitriol,  a 
process  which  is  occasionally  employed  for  the  manufacture  of  this  salt. 
A  considerable  supply  of  the  sulphate  is  obtained  as  a  secondary  product 
in  the  process  of  silver-refining  (page  209). 

The  sulphate  of  copper  is  also  manufactured  by  roasting  copper  pyrites 
(FeCuSg)  with  free  access  of  air,  when  it  becomes  partly  converted  into  a 
mixture  of  cupric  sulphate  with  ferrous  sulphate,  FeCuSa  +  03  =  FeSO^ 
-1-  CUSO4.  The  ferrous  sulphate,  however,  is  decomposed  by  the  heat, 
leaving  ferric  oxide  (see  page  322).  When  the  roasted  mass  is  treated 
with  water,  the  ferric  oxide  is  left  undissolved,  but  the  cupric  sulphate 
enters  into  solution,  and  may  be  obtained  in  crystals  by  evaporation. 

These  crystals,  as  they  are  found  in  commerce,  are  usually  opaque, 
but  if  they  are  dissolved  in  hot  water  and  allowed  to  crystallise  slowly, 
they  become  perfectly  transparent,  and  have  then  the  composition 
expressed  by  the  formula  CUSO4.5H2O.  If  the  crystals  be  heated  to 
the  temperature  of  boiling  water,  they  lose  four-fifths  of  their  water,  and 
crumble  down  to  a  greyish-white  powder,  which  has  the  composition 
CuSO^.HgO,  and  if  this  be  moistened  with  water,  it  becomes  very  hot 
and  resumes  its  original  blue  colour.  The  whitish  opacity  of  the  ordinary 
crystals  of  blue  stone  is  due  to  the  absence  of  a  portion  of  the  water  of 
crystallisation.  The  fifth  molecule  of  water  can  be  expelled  only  at  a 
temperature  of  nearly  400°  F.,  and  is  therefore  generally  called  water  of 
constitution  (see  page  42),  the  formula  of  the  crystals  being  then  written 
CuSO4.H2O.4Aq.  The  crystals  dissolve  in  4  parts  of  cold  and  2  parts 
of  boiling  water.     The  solution  reddens  litmus. 

The  sulphate  of  copper  is  largely  employed  by  the  dyer  and  calico- 
printer,  and  in  the  manufacture  of  pigments.  It  is  also  occasionally  used 
in  medicine,  in  the  electrotype  process,  and  in  galvanic  batteries. 

If  a  solution  of  cupric  sulphate  be  mixed  with  an  excess  of  solution 


CHLORIDES  OF  COPPER.  363 

of  potash,  a  blue  precipitate  of  cupric  hydrate,  Cu(OH)jj,  is  produced. 
On  boiling  this  in  the  liquid,  it  loses  water  and  becomes  black  oxide. 
The  paint  known  as  blue  verditer  is  cupric  hydrate  obtained  by  decom- 
posing cupric  nitrate  with  calcium  hydrate. 

When  ammonia  is  added  to  solution  of  cupric  sulphate,  a  basic  sul- 
phate is  first  precipitated,  which  is  dissolved  by  an  excess  of  ammonia 
10  a  dark  blue  fluid.  On  allowing  this  to  evaporate,  dark  blue  crystals 
of  ammonio-cuprics  ulphate,  C\i^O^,^^lS.^,Yl^O,  are  deposited.  They  lose 
their  ammonia  when  exposed  to  the  air. 

A  basic  cupric  sulphate,  CuS04,4Cu(OH)2,  constitutes  the  mineral 
b7'ochantite. 

Sulphate  of  copper  cannot  easily  be  separated  by  crystallisation  from 
the  sulphates  of  iron,  zinc,  and  magnesium,  because  it  forms  double  salts 
with  them,  which  contain,  like  those  sulphates,  seven  molecules  of  water. 
An  instance  of  this  is  seen  in  the  black  vitriol  obtained  from  the  mother- 
liquor  of  the  sulphate  of  copper  at  Mansfeld,  and  forming  bluish-black 
crystals  isomorphous  with  green  vitriol,  FeSO^jTHgO.  The  formula 
of  black  vitriol  may  be  written  (CuMgFeMnCoNi)lS04.7H20,  the  six 
isomorphous  metals  being  interchangeable  without  altering  the  general 
character  of  the  salt. 

Cupric  arsenite  or  Scheele's  green  has  been  mentioned  at  page  241. 

The  basic  phosphates  of  copper  compose  the  minerals  tagilite  and 
libetlienite. 

The  basic  carbonates  of  copper  have  been  noticed  as  forming  the  very 
beautiful  minerals  blue  malachite,  or  chessylite,  and  green  malachite. 

Mineral  green,  CuC03.Cu(OH)2,  has  the  same  composition  as  greea 
malachite,  and  is  prepared  by  mixing  hot  solutions  of  sodium  carbonate 
and  cupric  sulphate.  When  boiled  in  the  liquid,  it  is  gradually  con- 
verted into  black  oxide  of  copper. 

Silicates  of  copper  are  found  in  the  minerals  dioptase,  or  emerald  copper,. 
and  chrysocolla. 

267.  Chlorides  of  copper. — The  chloride  of  copper  (cupric  chloride) 
(CuClg)  is  produced  by  the  direct  union  of  its  elements,  when  it  forms  a 
brown  mass,  which  fuses  easily,  and  is  decomposed  into  chlorine  and  sub- 
chloride  of  copper,  the  latter  being  afterwards  converted  into  vapour. 
When  dissolved  in  water,  it  gives  a  solution  which  is  green  when  concen- 
trated, and  becomes  blue  on  dilution.  The  hydrated  cupric  chloride  is 
readily  prei^ared  by  dissolving  the  black  oxide  in  hot  hydrochloric  acid, 
and  allowing  the  solution  to  crystallise;  it  forms  green  needle-like 
crystals  (CUCI9.2H0O)  which  become  blue  when  dried  in  vacuo  (Hartley). 
A  solution  of  chloride  of  copper  in  alcohol  burns  vvith  a  splendid  green 
flame,  and  the  chloride  imparts  a  similar  colour  to  a  gas  flame. 

Oxychloride  of  copper  (CuCl2.3CuO.4H2O)  is  found  at  Atacama,  in 
prismatic  crystals,  and  is  called  atacamite.  The  paint  Bnmswick  green 
has  the  same  composition,  and  is  made  by  moistening  copper  with  solu- 
tion of  hydrochloric  acid  or  sal-ammoniac,  and  exposing  it  to  the  air  in 
order  that  it  may  absorb  oxygen;  Cu4-|-2HCl-l-3H20-l-04  =  CuCl2. 
3CUO.4H2O.  The  Brunswick  green  of  the  shops  frequently  consists  of  a 
mixture  of  Prussian  blue,  chromate  of  lead,  and  sulphate  of  baryta. 

Subchloride  of  copper  (cuprous  chloride),  CU2CI2,  is  formed  when  fine 
copper  turnings  are  shaken  with  strong  hydrochloric  acid  in  a  bottle  of 


364  COPPER  AND  SULPHUR. 

air  (Cug  +  2HCI  +  O  =  CuaCU  +  Hp).  The  subchloride  dissolves  in  the 
excess  of  hydrochloric  acid,  forming  a  brown  solution,  from  which  water 
precipitates  the  ichite  subchloride  of  copper,  for  this  is  one  of  the  few 
chlorides  insoluble  in  "water.  When  exposed  to  light  it  assumes  a 
purplish-grey  tint.  It  may  be  obtained  in  larger  quantity  by  dissolving 
5  parts  of  black  oxide  of  copper  in  hydrochloric  acid,  and  boiling  with 
4  parts  of  fine  copper  turnings,  the  brown  solution  being  afterwards  pre- 
cipitated by  water.  If  the  solution  be  moderately  diluted  and  set  aside, 
it  deposits  tetrahedral  crystals  of  the  subchloride.  Ammonia  (free  from 
air)  dissolves  the  subchloride  to  a  colourless  liquid,  which  becomes  dark 
blue  by  contact  with  air,  absorbing  oxygen.  The  ammoniacal  solution  of 
cuprous  chloride  is  employed  as  a  test  for  acetylene  (page  93),  which 
gives  a  red  precipitate  with  it.  The  solution  may  be  preserved  in  a 
colourless  state  by  keeping  it  in  a  well-stoppered  bottle,  quite  full,  with 
strips  of  clean  copper.  When  copper,  in  a  finely-divided  state,  is  boiled 
with  solution  of  ammonium  chloride,  the  solution  deposits  colourless 
crystals  of  the  salt,  Cu2C1.2(NH3)2.  If  the  solution  of  this  salt  be  exposed 
to  the  air,  blue  crj^stals  are  deposited,  having  the  formula  CugClg-Cu  Clg. 
4XH3.H.,0,  and  on  further  exposure,  a  compound  of  this  last  salt  with 
ammonium  chloride  is  deposited.  The  solution  of  subchloride  of  copper 
in  hydrochloric  acid  is  employed  for  absorbing  carbonic  oxide  in  the 
analysis  of  gaseous  mixtures.  When  this  solution  is  exposed  to  air  it 
absorbs  oxygen,  and  deposits  the  oxychloride  of  copper.  A  strong  solu- 
tion of  ammonium  or  potassium  chloride  readily  dissolves  the  cuprous 
chloride,  even  in  the  cold,  forming  soluble  double  chlorides.  The  solution 
in  potassium  chloride  does  not  absorb  oxygen  quite  so  easily  as  that  in 
ammonium  chloride. 

268.  Suljihides  of  copper. — Copper  has  a  very  marked  attraction  for 
sulphur,  even  at  the  ordinary  temperature.  A  bright  surface  of  copper 
Foon  becomes  tarnished  by  contact  with  sulphur,  and  hydrosulphuric  acid 
blackens  the  metal.  Finely-divided  copper  and  sulphur  combine  slowly 
at  the  ordinary  temperature,  and  when  heated  together,  they  combine  with 
combustion.  A  thick  copper  wire  burns  easily  in  vapour  of  sulphur 
(page  193).  Copper  is  even  partly  converted  into  sulphides  when  boiled 
with  sulphuric  acid,  as  in  the  preparation  of  sulphurous  acid  gas.  This 
great  attraction  of  copper  for  sulphur  is  taken  advantage  of  in  the  process 
of  liernel  roastimj  for  extracting  the  copper  from  pyrites  containing  as 
little  as  1  per  cent,  of  the  metal.  The  pyrites  is  roasted  in  large  heaps 
(page  190)  for  several  weeks,  when  a  great  part  of  the  iron  is  converted 
into  peroxide,  and  the  copper  remains  combined  with  sulphur,  forming 
a  hard  kernel  in  the  centre  of  the  lumps  of  ore.  This  kernel  contains 
about  5  per  cent,  of  copper,  and  can  be  smelted  with  economy.  Children 
are  employed  to  detach  the  kernel  from  the  shell,  which  consists  of 
peroxide  of  iron  and  a  little  sulphate  of  copper,  which  is  washed  out 
with  water. 

The  suhmlphide  of  copper  or  cuproiis  sulphide  (CugS)  has  been  mentioned 
among  the  ores  of  copper  and  among  the  furnace  products  in  smelting, 
Mhen  it  is  sometimes  obtained  in  octahedral  crystals.  It  is  not  attacked 
by  hydrochloric  acid,  but  nitric  acid  dissolves  it  readily.  Copper  pyrites 
is  believed  to  contain  the  copper  in  the  form  of  cuprous  sulphide,  its  true 
formula  being  CuoS.FegSgj  for  if  the  copper  be  present  as  cupric  sulphide, 


CHARACTERS  OF  LEAD.  365 

CuS,  tlie  iron  must  be  present  as  ferrous  sulphide,  and  the  mineral  would 
have  the  formula  CuS.FeS.  Xow,  FeS  is  easily  attacked  by  dilute  sul- 
phuric or  hydrochloric  acid,  which  is  not  the  case  with  copper  pyrites. 
Nitric  acid,  however,  attacks  it  violently. 

Sulphide  of  copper  or  cupric  sulphide  (CuS)  occurs  in  nature  as  indifio 
copper  or  blue  copper,  and  may  be  obtained  as  a  black  precipitate  by  the 
action  of  hydrosulphuric  acid  upon  solution  of  cupric  sulphate.  When 
this  precipitate  is  boiled  with  sulphur  and  ammonium  sulphide,  it  is 
dissolved  in  small  quantity,  and  the  solution  on  cooling  deposits  fine 
scarlet  needles  containing  a  higher  sulphide  of  copper  combined  with 
sulphide  of  ammonium. 

A  yentasidphide  of  copper  (CuSg)  is  obtained  by  decomposing  cupric 
sulphate  with  potassium  pentasulphide;  it  forms  a  black  precipitate  dis- 
tinguished from  the  other  sulphides  of  copper  by  its  solubility  in  potassium 
carbonate. 

The  sulphides  of  copper,  when  exposed  to  air  in  the  presence  of  water, 
are  slowly  oxidised  and  converted  into  cupric  sulphate,  which  is  dissolved 
by  the  water.  It  appears  to  be  in  this  way  that  the  blue  water  of  the 
copper  mines  is  formed. 

Phosphide  of  copper,  cupric  phosphide  (CugPg),  obtained  as  a  black 
powder  by  boiling  solution  of  cupric  sulphate  with  phosphorus,  has  been 
already  mentioned  as  a  convenient  source  of  phosphine.  Another  phos- 
phide, obtained  by  passing  vapour  of  phosphorus  over  finely-divided  copper 
at  a  high  temperature,  is  employed  in  Abel's  composition  for  magneto- 
electric  fuzes,  in  conjunction  with  cuprous  sulphide  and  potassium 
chlorate. 

Silicon  may  be  made  to  unite  with  copper  by  strongly  heating  finely- 
divided  copper  with  silica  and  charcoal.  A  bronze-like  mass  is  thus 
obtained  containing  about  5  per  cent,  of  silicon.  It  is  said  to  rival  iron 
in  ductility  and  tenacity,  and  fuses  at  about  the  same  temperature  as 
bronze. 

LEAD. 

Pb"  -  207  parts  by  weight. 

269.  Lead  owes  its  usefulness  in  the  metallic  state  chiefly  to  its  soft- 
ness and  fusibility.  The  former  quality  allows  it  to  be  easily  rolled  into 
thin  sheets,  and  to  be  drawn  into  the  form  of  tubes  or  pipes;  it  is  indeed 
the  softest  of  the  metals  in  common  use,  and  at  the  same  time  the  least 
tenacious,  so  that  it  can  only  be  drawn  with  difficulty  into  thin  wire,  and 
is  then  very  easily  broken.  The  ease  with  which  it  makes  a  dark  streak 
upon  paper  shows  how  readily  minute  particles  of  the  metal  may  be 
abraded.  Its  want  of  elasticity  also  recommends  it  for  some  special  uses, 
as  for  deadening  a  shock  or  preventing  a  rebound. 

In  fusibility  it  surpasses  all  the  other  metals  commonly  employed  in 
the  metallic  state,  except  tin,  for  it  melts  at  617°  F.,  and  this  circumstance, 
taken  in  conjunction  with  its  high  specific  gravity  (11  "4),  particularly 
adapts  it  for  the  manufacture  of  shot  and  bullets.  For  one  of  its  extensive 
uses,  however,  as  a  covering  for  roofs,  it  would  be  better  suited  if  it  were 
lighter  and  less  fusible,  for  in  case  of  fire  in  houses  so  roofed,  the  fall  of 
the  molten  lead  frequently  aggravates  the  calamity. 

"With  the  exception,  perhaps,  of  the  ores  of  iron,  none  is  more  abundant 
in  this  country  than  the  chief  ore  of  lead,  galena,  a  sulphide  of  lead  (PbS). 


366 


SMELTING  LEAD  ORES. 


This  ore  might  at  the  first  glance  be  mistaken  for  the  metal  itself,  from  its 
liigh  specific  gravity  and  metallic  lustre.  It  is  found  forming  extensive 
veins  in  Cumberland,  Derbyshire,  and  Cornwall,  traversing  a  limestone 
rock  in  the  two  first  counties,  and  a  clay  slate  in  the  last.  Spain  also 
furnishes  large  supplies  of  this  important  ore. 

Galena  presents  a  beautiful  crystalline  appearance,  being  often  found  in 
large  isolated  cubes,  which  readily  cleave  or  split  up  in  directions  parallel 
to  their  faces.  Blende  (sulphide  of  zinc)  and  copper  pyrites  (sulphide  of 
copper  and  iron)  are  frequently  found  in  the  same  vein  with  galena,  and 
it  is  usually  associated  with  quartz  (silica),  heavy  spar  (barium  sulphate), 
or  fluor  spar  (calcium  fluoride).  Considerable  quantities  of  sulphide  of 
silver  are  often  present  in  galena,  and  in  many  specimens  the  sulphides  of 
bismuth  and  antimony  are  found. 

Though  the  sulphide  is  the  most  abundant  natural  combination  of  lead, 
it  is  by  no  means  the  only  form  in  which  this  metal  is  found.  The  metal 
itself  is  occasionally  met  with,  though  in  very  small  quantity,  and  the 
carbonate  of  lead  (PbC03),  ^ohite  lead  ore,  forms  an  important  ore  in  the 
United  States  and  in  Spain.  The  sulphate  of  lead,  anglesite  (PbSO^),  is 
also  found  in  Australia,  and  is  largely  imported  into  this  country  to  be 
smelted. 

270.  The  extraction  of  lead  from  galena  is  effected  by  taking  advantage 
of  the  circumstance,  that  when  a  combination  of  a  metal  with  oxygen  is 
raised  to  a  high  temperature  in  contact  with  a  sulphide  of  the  same  metal, 
the  oxygen  and  sulphur  unite,  and  the  metal  is  liberated. 

The  ore,  having  been  separated  by  mechanical  treatment  as  far  as  pos- 
sible from  the  foreign  matters  associated  with  it,  is  mixed  with  a  small 
proportion  of  lime,  and  spread  over  the  hearth  of  a  reverberatory  furnace 
(fig.  261),  the  sides  of  which  are  considerably  inclined  towards  the  centre, 
so  as  to  form  a  hollow  for  the  reception  of  the  molten  lead. 


During  the  first  stage  of  the  smelting  process,  the  object  is  to  roast  the 
ore  with  free  access  of  air,  exposing  as  large  a  surface  as  possible,  on  which 
account  the  temperature  is  kept  below  that  at  which  galena  fuses;  indeed, 
during  the  first  two  hours,  no  fuel  is  thrown  into  the  grate,  sufficient  heat 
being  radiated  from  the  sides  of  the  furnace,  which  have  become  red  ho  t 
during  the  smelting  of  the  previous  charge  of  ore.     The  ore  is  stirred  from 


SMELTING  OF  GALENA.  367 

time  to  time,  to  expose  fresh,  surfaces  to  the  action  of  the  atmospheric 
oxygen. 

The  effect  of  this  roasting  is  to  convert  a  portion  of  the  sulphide  of  lead 
(PbS)  into  sulphate  of  lead  (PbSO^),  whilst  another  portion  loses  its 
sulphur,  which  is  evolved  as  sulphurous  acid  gas  (SOo),  and  acquires 
oxygen  in  its  stead,  becoming  converted  into  oxide  of  lead  (PbO).  A 
large  proportion  of  the  galena,  however,  remains  unoxidised.  "When  the 
roasting  is  sufficiently  advanced,  some  fuel  is  thrown  into  the  grate,  some 
rich  slags  from  previous  smeltings  are  thrown  on  to  the  hearth,  the 
damper  is  slightly  raised,  and  the  doors  of  the  furnace  are  closed,  so  that 
the  charge  may  be  heated  to  the  temperature  at  which  the  oxide  and  sul- 
phate of  lead  act  upon  the  unaltered  sulphide,  furnishing  metallic  lead, 
whilst  the  sulphur  is  expelled  in  the  form  of  sulphurous  acid  gas— 

PbS  +  2PbO  =  Pbg  +  SO2,  and  PbS04  +  PbS  =  Pb^  +  2SO2  • 

During  this  part  of  the  operation  the  contents  of  the  hearth  are  con- 
stantly raked  up  towards  the  fire-bridge,  so  as  to  facilitate  the  separation 
of  the  lead,  and  to  cause  it  to  run  down  into  the  hollow  provided  for  its 
reception.  It  is  also  found  that  the  separation  of  the  lead  from  the  slags 
is  much  assisted  by  occasionally  throwing  open  the  doors  to  chill  the 
furnace.  After  about  four  hours  the  charge  is  reduced  to  a  pretty  fluid 
condition,  the  lead  having  accumulated  at  the  bottom  of  the  depressed 
portion  of  the  hearth  with  the  slag  above  it ;  this  slag  consists  chiefly  of 
the  silicates  of  lime  and  oxide  of  lead,  and  would  have  contained  a  larger 
proportion  of  the  latter  if  the  lime  had  not  been  added  as  a  flux  at  the 
commencement  of  the  operation.  In  order  still  further  to  reduce  the 
quantity  of  lead  in  the  slag,  a  few  more  shovelfuls  of  lime  are  now  thrown 
into  the  hearth,  together  with  a  little  small  coal,  the  latter  serving  to 
reduce  to  the  metallic  state  the  oxide  of  lead  displaced  by  the  lime  from 
its  combination  with  the  silica. 

But  since  silicate  of  lime  is  far  less  fusible  than  silicate  of  oxide  of 
lead,  the  effect  of  this  addition  of  lime  is  to  dry  up  the  slags  to  a 
semi-solid  mass,  and  it  will  now  be  seen  that  if  the  whole  of  the  lime  had 
been  added  at  the  commencement  of  the  smelting,  the  diminished  fusibility 
of  the  slag  would  have  opposed  an  obstacle  to  the  separation  of  the  metallic 
lead. 

During  the  last  hour  or  so  the  temperature  is  very  considerably  raised, 
and  at  the  expiration  of  about  six  hours,  when  the  greater  portion  of  the 
lead  is  thought  to  have  separated,  the  slag  is  raked  out  through  one  of  the 
doors  of  the  furnace,  and  the  melted  metal  allowed  to  run  out  through  a 
tap-hole  in  front  of  the  lowest  portion  of  the  hearth,  into  an  iron  basin, 
from  which  it  is  ladled  into  pig-moulds. 

The  rich  slags,  together  with  the  layer  of  subsulphide  of  lead  (PbjS) 
which  forms  over  the  surface  of  the  metal,  are  worked  up  again  with  a 
fresh  charge  of  ore. 

In  the  smelting  of  galena  a  very  considerable  quantity  of  lead  is  carried 
off"  in  the  form  of  vapour ;  and  in  order  to  condense  this,  the  gases  from 
the  furnace  are  made  to  pass  through  flues,  the  aggregate  length  of 
which  is  sometimes  three  or  four  miles,  before  being  allowed  to  escape  up 
the  chimney.  "When  these  flues  are  swept,  many  tons  of  lead  are  recovered 
in  the  forms  of  oxide  and  sulphide. 

In  the  north  of  England  the  smelting  of  lead  ores  is  now  generally 


368 


TREATMENT  OF  HARD  LEAD. 


conducted  in  an  economico-furnace  (fig.  262),  or  small  blast-furnace,  instead 
of  in  the  reverberatory  furnace  described  above.  Air  is  supplied  to  the 
furnace  through  three  blast-pipes  (A),  and  the  ore  and  fuel  being  charged 
in  at  B,  the  lead  runs  into  a  cavity  (C)  at  the  bottom  of  the  furnace, 
whilst  the  slag  flows  over  into  a  reservoir  (D)  outside  the  furnace.  The 
charge  is  sprinkled  with  water  through  the  rose  (E)  fixed  just  above  the 
opening  into  the  chimney  (F),  to  prevent  it  from  being  blown  away  by 
the  current  of  air. 

271.  Some  varieties  of  lead,  particularly  those  smelted  from  Spanish  ores, 
are  known  as  hard  lead,  their  hardness  being  chiefly  due  to  the  presence 
of  antimony ;  and  since  this  hardness  interferes  materially  with  some  of  the 
uses  of  the  metal,  such  lead  is  generally  subjected  to  an  improving  or  cal- 
rining  process,  in  which  the  impurities  are  oxidised  and  removed,  together 
with  a  portion  of  the  lead,  in  the  dross.*  To  effect  this,  6  or  8  tons 
of  the  hard  lead  are  fused  in  an  iron  pot  (P,  fig.  263),  and  transferred  to 


Fig.  262.  Fig.  263. 

a  shallow  cast-iron  pan  (C)  measuring  about  10  feet  by  5.  In  this  pan, 
which  is  set  in  the  hearth  of  a  reverberatory  furnace,  and  is  about  8 
inches  deep  nearest  the  grate  and  9  inches  at  the  other  end,  the  lead 
is  kept  in  fusion  by  the  flame  Vifhich  traverses  it  from  the  grate  G-  to  the 
flue  F,  for  a  period  varying  with  the  degree  of  impurity,  some  specimens 
being  found  sufficiently  soft  after  a  single  day's  calcination,  whilst  others 

*  l"he  following  analyses  illustrate  the  composition  of  hard  lead  : — 


English. 

Spanish. 

Lead,         .... 

Antimony, 

Copper,     .... 

Iron,          .... 

99-27 
0  57 
0-12 
0-04 

95-81 
3-56 
0-32 
0-21 

100-00 

100-00 

pattinson's  desilverising  process. 

must  be  kept  in  a  state  of  fusion  for  three  or  four  weeks.  The  workman 
judges  of  the  progress  of  the  operation  by  a  peculiar  flaky  crystaUine 
appearance  assumed  by  a  small  sample  on  cooling.  When  sufficiently 
purified,  the  metal  is  run  off  and  cast  into  pigs. 

At  first  sight,  it  is  not  intelligible  how  antimony  should  be  removed 
from  lead  by  calcination,  since  lead  is  the  more  easily  oxidised  metal. 
The  result  must  be  ascribed  to  the  tendency  of  antimony  to  form  antimonic 
oxide  (Sb^Og),  which  combines  with  the  oxide  of  lead.  The  dross 
(antimoniate  of  lead)  formed  in  this  process,  when  reduced  to  the  metallic 
state,  yields  an  alloy  of  lead  with  30  or  40  per  cent,  of  antimony,  which 
is  much  used  for  casting  type  furniture  for  printers. 

272.  Extraction  of  silver  from  lead. — The  lead  extracted  from  galena 
often  contains  a  sufficient  quantity  of  silver  to  allow  of  its  being  pro- 
fitably extracted.  Previously  to  the  year  1829,  this  was  practicable  only 
when  the  lead  contained  more  than  1 1  ounces  of  silver  per  ton,  for  the 
only  process  then  known  for  effecting  the  separation  of  the  two  metals 
was  that  of  cupellation,  which  necessitates  the  conversion  of  the  whole 
of  the  lead  into  oxide,  which  is  then  to  be  separated  from  the  silver 
and  again  reduced  to  the  metallic  state,  thus  consuming  so  large  an 
amount  of  labour  that  a  considerable  yield  of  silver  must  be  obtained  to 
pay  for  it. 

By  the  simple  and  ingenious  operation  known  as  Pattinson's  desilverising 
process,  a  very  large  amount  of  the  lead  can  be  at  once  separated  in  the 
metallic  state  with  little  expenditure  of  labour,  thus  leaving  the  remainder 
sufficiently  rich  in  the  more  precious  metal  to  defray  the  cost  of  the  far 
more  expensive  process  of  cupellation,  so  that  3  or  4  ounces  of  silver  per 
ton  can  be  extracted  with  profit.  Pattinson  founded  his  process  upon  the 
observation  that  when  lead  containing  a  small  proportion  of  silver  is 
melted  and  allowed  to  cool,  being  constantly  stirred,  a  considerable 
quantity  of  the  lead  separates  in  the  form  of  crystals  containing  a  very 
minute  proportion  of  silver,  almost  the  whole  of  this  metal  being  left 
behind  in  the  portion  still  remaining  liquid. 

Eight  or  ten  cast-iron  pots,  set  in  brickwork,  each  capable  of  holding 
about  6  tons  of  lead,  are  placed  in  a  row,  with  a  fire-place  underneath 
each  of  them  (fig.  264).  Suppose  that  there  are  ten  pots  numbered 
consecutively,  that  on  the  extreme  left  of  the  workman  being  "No.  1,  and 
that  on  his  extreme  right  No.  10.  About  S  tons  of  the  lead  containing 
silver  are  melted  in  pot  No.  5,  the  metal  skimftied,  and  the  fire  raked  out 
from  beneath  so  that  the  pot  may  gradually  cool,  its  liquid  contents  being 
constantly  agitated  with  a  long  iron  stirrer.  As  the  crystals  of  lead  form, 
they  are  well  drained  in  a  perforated  ladle  (about  10  inches  wide  and  5 
inches  deep)  and  transferred  to  pot  No.  4.  When  about  -fths  of  the 
metal  have  thus  been  removed  in  the  crystals,  the  portion  still  remaining 
liquid,  Avhich  retains  the  silver,  is  ladled  into  pot  No.  6,  and  the  pot  No. 
5,  which  is  now  empty,  is  charged  with  fresh  argentiferous  lead  to  be 
treated  in  the  same  manner. 

When  pots  Nos.  4  and  6  have  received,  respectively,  a  sufficient  quantity 
of  the  crystals  of  lead  and  of  the  liquid  part  rich  in  silver,  their  contents 
are  subjected  to  a  perfectly  similar  process,  the  crystals  of  lead  being 
always  passed  to  the  left,  and  the  rich  argentiferous  alloy  to  the  right. 
As  the  final  result  of  these  operations,  the  pot  No.  10,  to  the  extreme, 
rights  becomes  filled  with  a  rich  alloy  of  lead   and  silver,  sometimes. 

2  a 


370 


CUPELLATION  OF  ARGENTIFEROUS  LEAD. 


containing  300  ounces  of  silver  to  the  ton,  whilst  pot  No  1,  to  the  extreme 
left,  contains  lead  in  which  there  is  not  more  that  |  ounce  of  silver  to  the 
ton.  This  lead  is  cast  into  pigs  for  the  market  The  ladle  used  in  the 
above  operation  is  kept  hot  by  a  small  temper  pot  containing  melted  lead. 
A  fulcrum  is  provided  at  the  edge  of  each  pot,  for  resting  the  ladle 
during  the  shaking  of  the  crystals  to  drain  off  the  liquid  metaL  Any 
copper  present  in  the  lead  is  also  left  with  the  silver  in  the  liquid 
portion. 


Fig.  264. — Pattinson's  desilverising  process. 

273.  In  order  to  extract  the  silver  from  the  rich  alloy,  it  is  subjected 
to  a  process  of  refining,  or  ciipellation,  which  is  founded  upon  the 
oxidation  suffered  by  lead  when  heated  in  air,  and  upon  the  absence  of 
any  tendency  on  the  part  of  silver  to  combine  directly  with  oxygen. 

The  refinery  or  cupelling  furnace  (fig.  265),  in  which  this  operation  is 
performed,  is  a  reverberatory  furnance,  the  hearth  of  which  consists  of  a 
nipel  (C),  made  by  ramming  moist  powdered  bone-ash  mixed  with  a  little 
Avood-asli  into  an  oval  iron  frame  about  4  inches  deep,  and  provided  with 
four  cross-bars  at  the  bottom,  each  about  4  inches  wide.  When  this  frame 
has  been  well  filled  with  bone-ash,  part  of  it  is  scooped  out,  so  as  to  leave 
the  sides  about  2  inches  thick  at  the  top  and  3  inches  at  the  bottom,  the 
l)one-ash  being  left  about  1  inch  thick  above  the  iron  cross-bars. 

The  cupel,  which  is  about  4  feet  long  by  2|  feet  wide,  is  fixed  so  that 
the  flame  from  the  grate  (G)  passes  across  it  into  the  chimney  (B),  and  at 
one  end,  the  nozzle  (N)  of  a  blowing  appai-atus  directs  a  blast  of  air  over 
the  surface  of  the  contents  of  the  cupel.  The  latter  is  carefully  dried  by 
a  gradually  increasing  heat,  and  is  then  heated  to  redness ;  the  alloy  of 
lead  and  silver,  having  been  previously  melted  in  an  iron  pot  (P)  fixed 


PROCESS  OF  CUPELLATION. 


371 


by  the  side  of  the  furnace,  is  ladled  in  through  a  gutter  until  the  cupel 

is  nearly  filled  with  it ;  a  film  of  oxide  soon  makes  its  appearance  upon 

the  surface  of  the  lead,  and  is  fused  by  the  high  temperature.    When  the 

blast  is  directed  upon  the  surface,  it  blows  off  this  film  of  oxide,  and 

supplies  the  oxygen  for  the  formation  of  another  film  upon  the  clean 

metallic  surface  thus  exposed.     A  part  of  the  oxide  of  lead  or  litharge 

thus  formed  is  at  first  absorbed 

by  the  porous  material  of  the 

cupel,  but  the  chief  part  of  it  is 

forced  by  the  blast  through  a 

channel  cut  for  the  purpose  in 

the  opposite  end  to  that  at  which 

the  blast  enters,  and  is  received 

as  it  issues  from  A,  in  an  iron 

vessel  placed  beneath  thefurnace. 

In  proportion  as  the  lead  is  in 

this  manner  removed  from  the 

cupel,  fresh  portions  are  supplied 

from  the  adjoining  melting-pot, 

and    the    process    is   continued 

until  about  5  tons  of  the  alloy 

liave  been  added. 

The  cupellation  is  not  con- 
tinued until  the  whole  of  the 
lead  has  been  removed,  but  until 
only  2  or  3  cwts.  of  that  metal 
are  left  in  combination  with  the 
whole  of  the  silver  (say  1000 
ounces)  contained  in  the  5  tons  of 
alloy.  The  metal  is  run  through 
a    hole    made    in    the    bottom 


Fig.  265. — Cupellation  furnace. 


of  the  cupel,  which  is  then  again  stopped  up  so  that  a  fresh  charge  may 
be  introduced.  The  fumes  of  oxide  of  lead  which  are  freely  evolved 
during  this  process  are  carried  off  by  a  liood  and  chimney  (H)  situated 
opposite  to  the  blast  of  air. 

When  three  or  four  charges  have  been  cupelled,  so  as  to  yield  from 
3000  to  5000  ounces  of  silver  alloyed  with  6  or  8  cwts.  of  lead,  the  removal 
of  the  latter  metal  is  completed  in  another  cupel,  since  some  of  the  silver 
is  carried  off  with  the  last  portions  of  litharge.  The  appearances  indicat- 
ing the  removal  of  the  last  portion  of  lead  are  very  striking ;  the  surface 
of  the  molten  metal,  which  has  been  hitherto  tarnished,  becomes  iridescent 
as  the  film  of  oxide  of  lead  thins  off,  and  afterwards  resplendently  bright, 
and  when  the  cake  of  refined  silver  is  allowed  to  cool,  it  throws  up  from 
its  surface  a  variety  of  .fantastic  arborescent  excrescences,  caused  by  the 
escape  of  oxygen  which  has  been  mechanically  absorbed  by  the  fused 
silver,  and  is  given  off  during  solidification. 

The  litharge  obtained  from  the  cupelling  furnaces  is  reduced  to  the 
metallic  state  by  mixing  it  with  small  coal,  and  heating  it  in  a  furnace 
similar  to  that  employed  in  smelting  galena. 

A  new  process  for  desilverising  lead  consists  in  melting  about  18  tons 
of  the  rich  lead  in  a  cast-iron  pot,  and  stirring  it  with  about  1  per  cent 
of  zinc  for  twenty  minutes ;  on  standing,  the  zinc  rises  to  the  surface, 


372 


USES  OF  LEAD. 


bringing  with  it  the  silver  and  some  lead,  forming  a  solid  crust,  which  is 
removed  and  distilled  in  a  plumbago  crucible  to  recover  the  zinc.  The 
rich  alloy  of  silver  and  lead  remaining  in  the  crucible  is  cupelled  in  the 
usual  way.  The  desilverised  lead  is  freed  from  zinc  by  the  improving 
process  (p.  368). 

274.  On  the  small  scale,  lead  may  easily  be  extracted  from  galena  by  mixing  300 
grains  with  450  grains  of  dried  carbonate  of  soda  and  20  grains  of  charcoal,  intro- 
ducing the  mixture  into  a  crucible,  and  placing  in  it  two  tenpenny  nails,  heads  down- 
wards. The  crucible  is  covered  and  heated  in  a  moderate  fire  for  about  half  an  hour. 
(A  charcoal  fire  in  the  small  furnace,  fig.  131,  page  117,  will  suffice.)  The  remainder 
of  the  nails  is  carefully  removed  from  the  liquid  mass,  which  is  then  allowed  to  cool, 
the  crucible  broken,  and  the  lead  extracted  and  weighed.  In  this  process  the 
sulphur  of  the  galena  is  removed,  partly  by  the  sodium  of  the  carbonate  and  partly 
by  the  iron  of  the  nails,  the  excess  of  carbonate  of  soda  serving  to  flu.x  any  silica 
with  which  the  galena  may  be  mixed. 

Or  300  grs.  of  galena  may  be  mixed  with  600  grs.  of  sodium  carbonate  and  200 
gi"3.  of  nitre  (which  oxidises  the  sulphur),  and  fused  for  half  an  hour. 

To  ascertain  if  it  contains  silver,  the  button  of  lead  is 
placed  on  a  small  bone-ash  cupel  (fig.  266),  heated  in  a 
muflle  (fig.  267),  until  the  whole  of  the  lead  is  oxidised 
and  absorbed  into  the  bone-ash  of  the  cujiel,  leaving  the 
minute  globule  of  silver. 

Small  globules  of  lead  may  be  conveniently  cupelled 
on  charcoal  before  the  blowpipe,  by  pressing  some 
bone-ash  into  a  cavity  scooped  in  the  charcoal,  placing  the  lead  upon  its  surface, 
and  exposing  it  to  a  good  oxidising  flame  (page  109)  as  long  as  it  decreases  in  size. 
If  any  copper  be  present,  the  bone-ash  will  show  a  green  stain  after  cooling.  Pure 
lead  gives  a  yellow  stain. 

275.  Uses  of  lead. — The  employment  of  this  metal  for  roofing,  &c., 
has  been  already  noticed.     Its  fusibility  adapts  it  for  casting  type  for 

printing,  but  it  would  be  far  too  soft  for 
this  purpose ;  accordingly,  type-metal  con- 
sists of  an  alloy  of  4  parts  of  lead  with  1  of 
antimony.  A  similar  alloy  is  used  for  the 
bullets  contained  in  shrapnel  shells,  since 
bullets  of  soft  lead  would  be  liable  to  be 
jammed  together,  and  wotdd  not  scatter  so 
well  on  the  explosion  of  the  shell.  On  the 
other  hand,  rifle  bullets  are  made  of  very 
pure  soft  lead,  in  order  that  they  may  more 
easily  take  the  grooves  of  the  rifle. 

Small  shot  are  made  of  lead  to  which 
about  40  lbs.  of  arsenic  per  ton  has  been 
added.  The  arsenic  dissolves  in  the  lead, 
hardening  it  and  causing  it  to  form  spherical 
drops  when  chilled.  The  fluid  metal  is 
poured  through  a  sort  of  colander  fixed  at 
the  top  of  a  lofty  tower  (or  at  the  mouth  of 
a  deserted  coal  shaft),  and  the  minute  drops 
into  which  it  is  thus  divided  are  allowed  to 
fall  into  a  vessel  of  water,  after  having  been 
chilled  by  the  air  in  their  descent.  They 
are  afterwards  sorted,  and  polished  in  revolv- 
ing barrels  containing  plumbago.  If  too  little  arsenic  is  employed,  the 
shot  are  elongated  or  pyriform;  and  if  the  due  proportion  has  been 
exceeded,  their  form  is  flattened  or  lenticular. 


Fig.  267. 


OXIDES  OF  LEAD.  373 

Common  solder  is  an  alloy  of  equal  weights  of  lead  and  tin,  which  is 
more  fusible  than  either  metal  separately.  Other  alloys  containing  lead 
will  be  noticed  in  their  proper  places. 

Leaden  vessels  are  much  used  in  manufacturing  chemistry,  on  account 
of  the  resistance  of  this  metal  to  the  action  of  acids.  Neither  concentrated 
sulphuric,*  hydrochloric,  nitric,  or  hydrofluoric  acid  will  act  upon  lead 
at  the  ordinary  temperature.  The  best  solvent  for  the  metal  is  nitric 
acid  of  sp.  gr.  1  '2,  since  the  nitrate  of  lead,  being  insoluble  in  an  acid  of 
greater  strength,  would  be  deposited  upon  the  metal,  which  it  would 
protect  from  further  action. 

Lead  is  easily  corroded  in  situations  where  it  is  brought  in  contact 
with  air  highly  charged  with  carbonic  acid  gas,  when  it  absorbs  oxygen, 
forming  oxide  of  lead,  which  combines  with  carbonic  acid  gas  and  water 
to  produce  the  basic  carbonate  of  lead,  PbC0g,Pb(0H)2.  The  lead  of  old 
coffins  is  often  found  converted  into  a  white  earthy-looking  brittle  mass 
of  basic  carbonate,  with  a  very  thin  film  of  metallic  lead  inside  it. 

When  lead  is  exposed  to  the  joint  action  of  air  and  of  the  acetic  acid 
contained  in  beer,  wine,  cider,  &c.,  it  becomes  converted  into  acetate  of 
lead  or  sugar  of  lead,  which  is  very  poisonous.  Hence  the  accidents 
arising  fiom  the  reprehensible  practice  of  sweetening  cider  by  keeping 
it  in  contact  with  lead,  and  from  the  accidental  presence,  in  beer  and 
wine  bottles,  of  shot  which  have  been  employed  in  cleansing  them.  The 
action  of  water  upon  leaden  cisterns  has  been  already  noticed.  Contact 
Avith  air  and  sea-water  soon  converts  lead  into  oxide  and  chloride. 

276.  Oxides  of  Lead. — Four  compounds  of  lead  with  oxygen  are 
known — 


Suboxide  of  lead,         Pb.^O 
Oxide         „  PbO 


Red  oxide  of  lead,        PbgO^ 
Peroxide        „  PbOo 


'2 

The  bright  surface  of  lead  soon  tarnishes  when  exposed  to  the  air, 
becoming  coated  with  a  dark  film,  which  is  believed  to  consist  of  suboxide 
of  lead.  In  a  very  finely-divided  state,  lead  takes 
fire  when  thrown  into  the  air,  and  is  converted 
into  oxide  of  lead. 

The  lead  pyrophorus,  for  exhibiting  the  spontaneous 
combustion  of  lead,  is  prepared  by  placing  some  lead 
tartrate  in  a  glass  tube  closed  at  one  end  (fig.  268), 
drawing  the  tube  out  to  a  narrow  neck  near  the  open  end, 
and  holding  it  nearly  horizontally,  whilst  the  lead  tartrate 
is  heated  with  a  gas  or  spirit  flame  as  long  as  any  fumes 
are  evolved  ;  the  neck  is  then  fused  with  a  blowpipe 
flame  and  drawn  off".  Lead  tartrate  (PbC^H^Og),  when 
heated,  leaves  a  mixture  of  metallic  lead  with  charcoal.  Fig.  268. 

which  prevents   it  from  fusing  into  a   compact  mass. 

This  mixture  may  be  preserved  unchanged  in  the  tube  for  any  length  of  time ;  but 
when  the  neck  is  broken  off  and  the  contents  scattered  into  the  air,  they  inflame  at 
once,  producing  thick  fumes  of  oxide  of  lead.  Lead  tartrate  is  prepared  by  adding 
solution  of  lead  acetate  to  solution  of  tartaric  acid  constantly  stirred,  as  long  as  a 
precipitate  is  formed.  The  precipitated  lead  tartrate  is  collected  upon  a  filter,  washed 
several  times,  and  dried  at  a  gentle  heat. 

Oxide  or  p7'otoxide  of  lead  (phimhous  oxide)  is  prepared  on  a  large  scale 
by  heating  lead  in  air.     When  the  metal  is  only  moderately  heated,  the 

*  It  has  recently  been  found  that  pure  lead  is  slowly  acted  on  by  sulphuric  acid,  hydrogen 
being  evolved.     The  presence  of  a  little  antimony  almost  entirely  prevents  the  action. 


374  EED  LEAD. 

oxide  forms  a  yellow  powder,  which  is  known  in  commerce  as  massicot, 
but  at  a  higher  temperature  the  oxide  melts,  and  on  cooling  forms  a 
brownish  scaly  mass  which  is  called  litharge  {kiBos,  stmie;  Sfyyvpos,  silver), 
probably  because  that  obtained  by  the  alchemists  would  always  furnish  a 
considerable  proportion  of  silver,  which  was  present  in  most  samples  of  lead 
before  the  introduction  of  Pattinson's  process.  The  litharge  of  commerce 
often  has  a  red  colour,  caused  by  the  presence  of  some  red  oxide  of  lead ; 
from  1  to  3  per  cent,  of  finely-divided  metallic  lead  may  also  sometimes 
be  found  in  it.  When  heated  to  dull  redness,  litharge  assumes  a  dark 
brown  colour,  and  becomes  yellow  on  cooling.  At  a  bright  red  heat  it  fuses, 
and  readily  attacks  clay  crucibles,  forming  a  fusible  silicate  of  lead,  and 
soon  perforating  the  sides.  When  boiled  with  distilled  water,  litharge  is 
dissolved  in  small  quantity,  yielding  a  solution  which  is  decidedly  alka- 
line, and  becomes  turbid  when  exposed  to  the  air,  absorbing  carbonic 
acid  gas,  and  depositing  lead  carbonate.  The  presence  of  a  small  quantity 
of  saline  matter  in  the  water  hinders  the  solution  of  the  oxide,  but 
organic  matter,  and  especially  sugar,  favours  it.  Two  definite  white 
hydrates  of  oxide  of  lead,  H20.2PbO  and  HgO.SPbO,  may  be  obtained  by 
precipitating  solutions  of  lead  with  the  alkalies.  Oxide  of  lead  is  a 
powerful  base,  and  has  a  strong  tendency  to  form  basic  salts.  Hot  solu- 
tions of  potash  and  soda  dissolve  it  readily,  and  deposit  it  in  pink  crystals 
on  cooling. 

Litharge,  from  its  easy  combination  with  silica  at  a  high  temperature,  is 
much  used  in  the  manufacture  of  glass  and  in  glazing  earthenware.  The 
assayer  also  employs  it  as  a  flux.  A  mixture  of  litharge  with  lime  is 
sometimes  applied  to  the  hair,  which  it  dyes  of  a  purplish-black  colour, 
due  to  the  formation  of  sulphide  of  lead  from  the  sulphur  existing  in  hair. 
Dhil  mastic,  used  by  builders  in  repairing  stone,  is  a  mixture  of  1  j^art  of 
massicot  with  10  parts  of  brick-dust,  and  enough  linseed  oil  to  form  a 
paste;  it  sets  into  a  very  hard  mass,  which  is  probably  due  partly  to  the 
formation  of  sihcate  of  lead,  and  partly  to  the  di'ying  of  the  linseed  oil  by 
oxidation  favoured  by  the  oxide  of  lead. 

Red  lead  or  minium  is  prepared  by  heating  massicot  in  air  to  about 
600°  F.,  when  it  absorbs  oxygen,  and  becomes  converted  into  red  lead. 
The  massicot  for  this  purpose  is  prepared  by  heating  lead  in  a  rever- 
beratory  furnace  to  a  temperature  insufficient  to  fuse  the  oxide  which  is 
formed,  and  rejecting  the  first  portions,  which  contain  iron  and  other 
metals  more  easily  oxidisable  than  lead  (as  cobalt),  as  well  as  the  last, 
which  contain  copper  and  silver,  less  easily  oxidised  than  lead.  The  inter- 
mediate product  is  ground  to  a  fine  powder  and  suspended  in  water  ;  the 
coarser  particles  are  thus  separated  from  the  finer,  which  are  dried,  and 
heated  on  iron  trays  placed  in  a  reverberatory  furnace,  till  the  requisite 
colour  has  been  obtained.  Minium  is  largely  used  in  the  manufacture  of 
glass,  whence  it  is  necessary  that  it  should  be  free  from  the  oxides  of  iron, 
copper,  cobalt,  &c.,  which  would  colour  the  glass.  It  is  also  employed  as 
a  common  red  mineral  colour,  and  in  the  manufacture  of  lucifer  matches. 

When  minium  is  treated  with  dilute  nitric  acid,  lead  nitrate  Pb(N03)2 
is  obtained  in  solution,  and  peroxide  of  lead  (PbOa)  is  left  as  a  brown 
powder,  showing  that  minium  is  probably  a  compound  of  the  oxide  and 
peroxide  of  lead.  The  minium  obtained  by  heating  massicot  in  air  till  no 
further  increase  of  weight  is  observed,  has  the  composition  2PbO.Pb02 
or  PbgO^,  which  would  appear  to  represent  pure  minium  ;   commercial 


WHITE  LEAD.  375 

minium,  liowever,  has  more  frequently  a  composition  corresponding  to 
3PbO.Pb02,  ^"*  when  this  is  treated  with  potash,  PbO  is  dissolved  out, 
and  2PbO.Pb02  remains.  Minium  evolves  oxygen  at  a  red  heat,  becoming 
PbO,  hence  the  necessity  for  keeping  the  temperature  below  600°  I", 
during  its  preparation. 

Peroxide,  or  hinoxide,  or  puce  oxide  of  lead  {plumbic  oxide),  is  found  in 
the  mineral  kingdom  as  heavy  lead  ore,  forming  black,  lustrous,  six-sided 
prisms.  It  may  be  prepared  from  red  lead  by  boiling  it,  in  fine  powder, 
with  nitric  acid  diluted  with  five  measures  of  water,  washing  and  drying. 
The  binoxide  of  lead  easily  imparts  oxygen  to  other  substances ;  sulphur, 
mixed  with  it,  may  be  ignited  by  friction,  hence  this  oxide  is  a  common 
ingredient  in  lucifer-match  compositions.  Its  oxidising  property  is 
frequently  turned  to  account  in  the  laboratory ;  for  example,  in  absorbing 
sulphur  dioxide  from  gaseous  mixtures  by  converting  it  into  sulphate  of 
lead  ;  PbOg  +  SOg  =  PbSO^.  Binoxide  of  lead  is  not  dissolved  by  dilute 
acids,  and  has  no  basic  properties  ;  indeed,  it  is  sometimes  called  plumbic 
anhydride,  for  it  acts  upon  potassium  hydrate,  yielding  potassium  plumbate 
(KgPbOg.SHgO),  which  has  been  crystallised  from  an  alkaline  solution, 
but  is  decomposed  by  pure  water. 

277.  White  lead  or  ceruse  is  a  carbonate  of  lead,  or,  strictly  speaking,  a 
basic  carbonate,  a  combination  of  lead  carbonate,  PbCOg,  with  variable 
proportions  of  lead  hydrate,  Pb(0H)2.  This  substance  is  a  constantproduct 
of  the  corrosive  action  of  air  and  water  upon  the  metal.  Its  formation  is,  of 
course,  very  much  encouraged  by  the  presence  of  organic  matters  in  a  state 
of  decay,  which  evolve  carbonic  acid  gas. 

White  lead  is  manufactured  on  the  large  scale  by  two  processes,  which 
depend,  however,  upon  the  same  principle ;  this  may  be  stated  as  follows : — 
When  oxide  of  lead  is  brought  in  contact  with  acetic  acid  (H.CgHgOg), 
it  forms  lead  acetate  (sugar  of  lead)  Pb(C2H302)2-  This  salt  is  capable  of 
combining  with  two  molecules  of  lead  oxide,  forming  the  tribasic  lead  acetate, 
Pb(C2H302)2-2PbO,  and  if  this  be  acted  upon  by  carbonic  acid  gas,  the 
lead  oxide  is  converted  into  carbonate,  whilst  the  normal  lead  acetate, 
Pb(C2H302)2,  is  left. 

In  the  older  of  the  two  processes,  commonly  known  as  the  Dutch  pro- 
cess, metallic  lead,  in  the  form  of  square  gratings  cast  from  the  purest 
lead,  is  placed  over  earthen  pots  containing  a  small  quantity  of  common 
vinegar ;  a  number  of  these  pots  being  built  up  into  heaps,  together  with 
alternate  layers  of  dung  or  spent  tan,  the  heaps  are  entirely  covered  up 
with  the  same  material.  The  metal  is  thus  exposed  to  conditions  most 
favourable  to  its  oxidation,  viz.,  a  very  warm  and  moist  atmosphere  pro- 
duced by  the  fermentation  of  the  organic  matters  composing  the  heap,  and 
the  presence  of  a  large  quantity  of  acid  vapour  generated  from  the  acetic 
acid  of  the  vinegar.  The  lead  is  therefore  soon  converted  into  oxide,  a 
portion  of  which  unites  with  the  acetic  acid  to  form  the  tribasic  acetate  of 
lead,  which  is  then  decomposed  by  the  carbonic  acid  gas,  evolved  from 
the  fermenting  dung  or  tan,  yielding  carbonate  of  lead,  which  combines 
with  another  portion  of  the  oxide  of  lead  and  of  water  to  form  the  white 
lead.  The  neutral  acetate  of  lead  left  after  the  removal  of  the  oxide  of 
lead  from  the  tribasic  acetate,  is  now  ready  to  take  up  an  additional  quan- 
tity of  the  oxide,  and  the  process  is  thus  continued  until,  in  the  course  of 
a  few  weeks,  the  lead  has  become  coated  with  a  very  thick  crust  of  white 


376  CHLORIDE  OF  LEAD. 

lead ;  the  heaps  are  then  destroyed,  the  crust  detached',  washed,  to  remove 
adhering  acetate  of  lead,  ground  to  a  paste  with  water,  and  dried.  Rolled 
lead  is  not  so  easily  converted  as  cast  lead. 

The  newer  process  is  a  more  direct  application  of  the  same  principle, 
for  it  consists  in  boiling  acetic  acid  with  an  excess  of  litharge  in  order  to 
produce  the  tribasic  acetate  of  lead,  which  is  afterwards  decomposed  by 
passing  through  it  a  current  of  carbonic  acid  gas  obtained  by  combustion 
or  fermentation,  or  even  by  exhalation  from  the  earth.  The  solution  of 
neutral  acetate  of  lead  is  then  again  boiled  with  litharge,  when  tribasic 
acetate  is  produced,  and  is  again  precipitated  by  the  carbonic  acid  gas. 
The  precipitated  carbonate  of  lead  always  carries  down  with  it  a  variable 
proportion  of  the  hydrate  of  lead.  This  process  is,  of  course,  much  more 
rapid  than  the  old  one,  and  dispenses  with  the  grinding,  which  is  so  in- 
jurious to  the  workmen  ;  but  the  white  lead  so  produced,  being  crystalline, 
has  less  opacity  or  covering-power  {body)  than  that  obtained  by  the  Dutch 
method. 

The  usual  composition  of  white  lead  is  expressed  by  the  formula 
Pb(OH)2.2PbC03,  though  other  basic  carbonates  of  lead  are  often  mixed 
with  it. 

White  lead  being  very  poisonous,  its  use  by  painters  and  others  is  gene- 
rally attended  with  symptoms  of  lead  poisoning,  arising  in  many  cases, 
probably,  from  neglecting  to  wash  the  hands  before  eating,  the  effect  of 
lead  being  cumulative,  so  that  minute  doses  may  show  their  combined 
action  after  many  days.  Diluted  sulphuric  acid  and  solutions  of  the  sul- 
phates of  magnesia  and  the  alkalies  are  sometimes  taken  internally  to 
counteract  its  effect,  since  the  sulphate  of  lead  is  not  poisonous. 

All  paints  containing  lead,  and  cards  glazed  with  white  lead,  are 
blackened  even  by  minute  quantities  of  sulphuretted  hydrogen,  from  the 
production  of  black  sulphide  of  lead.  If  the  blackened  surface  remain 
exposed  to  the  light  and  air,  it  is  bleached  again,  the  sulphide  of  lead 
(PbS)  being  oxidised  and  converted  into  white  sulphate  of  lead  (PbSO^), 
but  this  does  not  take  place  in  the  dark.  A  little  sulphide  of  lead  or 
powdered  charcoal  is  sometimes  mixed  with  commercial  white  lead  to  give 
it  a  bluish  tint. 

The  pure  lead  carbonate  is  found  in  white  crystals  associated  with  galena. 

Lead  sulphate  is  found  in  nature  in  prismatic  and  octahedral  crystals 
of  anglesite  or  lead-vitriol.  It  is  nearly  insoluble  in  diluted  acids,  and  is 
one  of  the  chief  forms  in  which  lead  is  precipitated  from  its  solutions  in 
analytical  operations.  The  minerals  lanarkite  and  leadhillite  are  com- 
pounds of  sulphate  and  carbonate  of  lead.  The  chromates  of  lead  have 
been  already  noticed. 

Lead,  pliosphate,  Pb3(P04)2,  is  occasionally  associated  with  the  car- 
bonate in  the  ores  of  lead. 

278.  Lead  chloride  (PbClg)  forms  the  mineral  termed  horn  lead.  It 
is  one  of  the  few  chlorides  which  are  not  readly  soluble  in  water,  and  is 
precipitated  when  hydrochloric  acid  or  a  soluble  chloride  is  added  to  a 
solution  of  lead.  Boiling  water  dissolves  about  ^^  of  its  weight  of  lead 
cliloride,  and  deposits  it  in  beautiful  shining  white  needles  on  cooling.  It 
fuses  easily,  and  is  converted  into  vapour  at  a  high  temperature.  The 
specific  gravity  of  this  vapour  at  1070°  C.  is  9*64  (theory  requires  9 "62). 

The  lead    oxy chloride  (PbClg-PbO)  is  formed  when  lead  chloride   is 


THALLIUM.  377 

heated  in  air.  It  is  sometimes  employed  as  a  substitute  for  white  lead  in 
painting,  being  prepared  for  this  purpose  by  decomposing  finely-powdered 
galena  with  concentrated  hydrochloric  acid  (PbS-l-2HCl  =  PbCl  +  H2S)^ 
washing  the  resulting  lead  chloride  with  cold  water,  dissolving  it  in  hot 
water,  and  adding  lime-water,  which  precipitates  the  oxychloride;  2PbCl2 
-I-  CaO  =  PbClg-PbO  +  CaCla . 

Turner's  yellow  (Paris  yellow,  patent  yellow,  mineral  yellow)  is  another 
oxychloride  of  lead  (PbClg-TPbO),  prepared  by  heating  a  mixture  of  lith- 
arge and  sal-ammoniac.  It  has  a  fine  golden  yellow  colour,  is  easily  fused, 
and  crystallises  in  octahedra  on  cooling.  The  mineral  meyidipite  is  an 
oxychloride  of  lead  (PbClg.SPbO)  which  occurs  in  colourless  prismatic 
crystals. 

Lead  chlorohromide  (PbBrCl)  has  been  found  in  crystals  resembling  lead 
chloride  among  the  furnace-products  in  smelting  lead  carbonate  ore. 

Lead  iodide  (Pbig)  is  obtained  as  a  bright  yellow  precipitate  on  mix- 
ing solutions  of  nitrate  or  acetate  of  lead  and  potassium  iodide.  If  it 
be  allowed  to  settle,  the  liquid  poured  off,  and  the  precipitate  dissolved 
in  boiling  water  (with  one  or  two  drops  of  hydrochloric  acid),  it  forms  a 
colourless  solution,  depositing  golden  scales  as  it  cools. 

279.  Sulphides  of  lead. — The  subsulphide  (Pb<,S)  has  been  mentioned 
as  produced  in  smelting  galena.  Sulphide  of  lead,  or  galena,  has  been 
described  among  the  ores  of  lead.  It  is  always  obtained  as  a  black 
precipitate  when  hydrosulphuric  acid  or  a  soluble  sulphide  acts  upon 
a  solution  containing  lead,  even  in  minute  proportion. 

A  persulphide  of  lead,  the  composition  of  which  has  not  been  ascer- 
tained, is  formed  as  a  red  precipitate  when  a  solution  of  lead  is  mixed 
with  a  solution  of  an  alkaline  sulphide  saturated  with  sulphur  (or  with 
solution  of  ammonium  sulphide  which  has  been  kept  till  it  has  acquired  a 
red  colour).     It  is  probablj^  1*^85. 

Lead  chlorosulphide  (3PbS.2FbCl2)  is  obtained  as  a  bright  red  pre- 
cipitate when  hydrosulphuric  acid  is  added  in  small  quantity  to  a  solution 
of  lead  chloride  in  hydrochloric  acid. 

Lead  selenide  (PbSe)  occurs  associated  with  the  sulphide  in  some  lead 
ores ;  it  much  resembles  galena,  and  has  the  same  crystalline  form. 

280.  Thallium  (T1  =  204  parts  by  weight).— The  discovery  of  this  metal  in  1861 
was  one  of  the  first  results  of  the  application  of  the  new  method  of  testing  by  obser- 
vation of  coloured  lines  in  the  spectrum  of  a  tlame,  described  at  p.  272.  Crookes  was 
examining  the  spectrum  obtained  by  holding  in  the  flame  of  a  Bunsen  burner  the 
deposit  formed  in  the  flues  of  a  sulphuric  acid  chamber,  in  which  pyrites  was 
employed  as  the  source  of  sulphur.  A  green  line  made  its  appearance  in  the  spectrum, 
which  a  less  acute  and  practised  observer  might  have  mistaken  for  one  of  the  lines 
caused  by  barium  (see  fig.  2-35),  with  which  it  nearly  coincides  in  position ;  but  the 
line  was  much  brighter  than  that  produced  by  barium,  and  on  instituting  a  searching 
analysis  of  the  deposit,  a  metal  was  obtained  which  did  not  agree  in  properties  with 
any  hitherto  described,  and  was  named  thallium,  from  0aK\6s,  a  young  shoot,  in 
allusion  to  the  vernal  green  colour  of  its  spectrum  line.  It  has  since  been  detected 
in  several  mineral  waters  ;  but  the  pyrites  obtained  from  Spain  and  Belgium  appear 
to  be  its  best  source.  From  the  flue-dust  of  the  sulphuric  acid  chambers,  the  metal 
is  extracted  by  a  simple  process,  but  large  quantities  must  be  operated  on  to  obtain 
any  considerable  amount.  The  deposit  is  treated  with  boiling  water,  and  the  solution 
mixed  with  much  strong  hydrochloric  acid,  which  precipitates  the  thallium  as 
thallous  chloride  (TlCl)  ;  this  is  converted  into  acid  thallous  sulphate  (TIHSO4)  by 
treatment  with  sulphuric  acid,  and  this  salt  having  been  purified  by  recrystallisation, 
is  decomposed  by  zinc,  which  precipitates  metallic  thallium  in  a  spongy  form,  fusible 
into  a  compact  mass  in  an  atmosphere  of  coal  gas. 


378  SILVER. 

In  external  characters  thallium  is  very  similar  to  lead  ;  but  it  tarnishes  much 
more  rapidly  when  exposed  to  air,  and  the  streak  which  it  makes  on  paper  soon 
becomes  yellowish,  being  converted  into  thallous  oxide,  Tl^O.  If  a  tarnished  piece  of 
the  metal  be  allowed  to  touch  the  tongne,  a  strongly  alkaline  taste  is  perceived,  for 
the  thallmis  oxide  (TljO)  is  very  soluble  in  water,  so  that  the  tarnished  metal  becomes 
bright  when  immersed  in  water.  If  granulated  thallium  be  exposed  to  moist  air  in 
a  warm  place,  it  absorbs  oxygen  and  carbonic  acid  gas.  On  boiling  with  water  and 
filtering,  the  alkaline  solution  deposits  white  needles  of  tJutllous  carbmiate  (TljCOj), 
and  afterwards  yellow  needles  of  thallous  hydrate  (TIOH).  The  ready  solubility  of 
the  oxide  seemed  to  require  thallium  to  be  classed  among  the  alkali-metals,  a  view 
which  was  encouraged  by  the  circumstance  that  its  specific  heat  proved  it  to  be 
monatomic  like  potassium  and  sodium.  But  thallium  appears  to  be  more  nearly 
related  to  another  monatomic  metal,  silver,  by  the  sparing  solubility  of  its  chloride 
and  the  insolubility  of  its  sulphide.  The  circumstance  that  it  may  be  kept  unaltered 
in  water  and  may  be  precipitated  from  its  salts  by  zinc,  at  once  removes  it  from  the 
group  of  alkali-metals.  The  ready  solubility  of  its  oxide  in  water  is  only  an  exaggera- 
tion of  the  behaviour  of  the  oxides  of  lead  and  silver,  both  of  which  dissolve  slightly 
in  water,  yielding  alkaline  solutions.  Moreover,  its  hydrate  is  far  less  stable  than 
those  of  potassium  and  sodium,  for  it  becomes  TLO  when  dried  in  vacuo  over  oil  of 
vitriol.  Diluted  sulphuric  acid  acts  upon  thallium  as  upon  zinc,  evolving  hydrogen. 
It  is  not  much  afl'ected  by  diluted  nitric  acid  in  the  cold ;  even  on  heating,  the  action 
is  slow  unless  the  acid  is  very  weak.  On  cooling,  the  solution  becomes  filled  with 
needles  of  thallous  nitrate.  Thallium  burns  in  oxygen  with  a  beautiful  green  flame, 
and  the  thallous  chlorate  has  been  recommended  for  the  manufacture  of  green  fires  in 
place  of  barium  chlorate  (see  page  166). 

Thallous  sulphate,  TI2SO4,  is  obtained  by  dissolving  thallium  in  sulphuric  acid 
and  evaporating ;  the  acid  sulphate,  TIHSO4,  first  produced,  being  decomposed  by 
further  heating.  TljjS04  is  isomorphous  with  K^SOj,  and  it  forms  thallous  alum, 
TlAl(S04)2.12Aq.  crystallising  like  potash-alum. 

Thallous  chloride,  TlCl,  resembles  lead  chloride,  being  precipitated  by  adding  HCl 
to  a  solution  of  a  thallous  salt,  and  being  dissolved  by  boiling  water  from  which  it 
crystallises  on  cooling. 

Thallous  iodide,  Til,  is  obtained  as  a  yellow  precipitate  on  adding  potassium  iodide 
to  a  thallous  salt ;  when  dried  and  heated,  it  fuses  to  a  red  liquid  which  remains  red 
after  solidifying,  and  changes,  after  a  time,  to  yellow.  When  spread  on  paper,  the 
yellow  iodide,  becomes  red  when  heated,  and  remains  red  on  cooling,  but  becomes 
yellow  when  rubbed  mth  a  hard  body. 

Thallous  sulphide,  TljS,  is  deposited  as  a  brownish-black  precipitate,  on  adding 
ammonium  sulphide  to  a  thallous  salt. 

Thallic  oxide,  TLOj,  is  obtained  by  adding  sodium  hypochlorite  to  thallous  chloride 
mixed  with  excess  of  sodium  carl>onate.  It  is  a  dark  red  substance,  which  evolves 
oxygen  and  leaves  thallous  oxide  when  heated.  It  is  also  a  basic  oxide,  its  sulphate 
having  the  composition  TI,(S04)3.  HjO.  6Aq. 

TliAxllic  chloride,  TICI3,  is  fornled  by  heating  thallium  in  excess  of  chlorine ;  it  is 
soluble  and  crystallisable. 

Salts  of  thallium,  like  those  of  lead,  are  poisonous. 


SILVER 
Ag*  =  108  parts  by  weight. 

281.  In  silver,  we  meet  with  the  first  metal  hitherto  considered  which 
is  not  capable  of  undergoing  oxidation  in  the  air,  and  this,  in  conjunction 
with  its  beautiful  appearance,  occasions  its  manifold  ornamental  uses, 
which  are  much  favoured  also  by  the  great  malleability  and  ductility 
of  this  metal  (in  which  it  ranks  only  second  to  gold),  for  the  former 
property  enables  it  to  be  rolled  out  into  thin  plates  or  leaves,  so  that  a 
small  quantity  of  silver  suffices  to  cover  a  large  surface,  whilst  its  ductility 
permits  the  wire-drawer  to  produce  that  extremely  thin  silver  wire  which 
is  employed  in  the  manufacture  of  silver  lace. 

Silver,  although  pretty  widely  diffused,  is  found  in  comparatively  small 


LIQUATION — AMALGAMATION. 


379 


quantity,  and  hence  it  bears  a  high  value,  which  adapts  it  for  a  medium 
of  currency. 

As  might  be  expected  from  its  want  of  direct  attraction  for  oxygen, 
silver  is  found  frequently  in  the  metallic  or  native  state,  crystallised  in 
cubes  or  octahedra,  which  are  sometimes  aggregated  together,  as  in  the 
silver-mines  of  Potosi,  into  arborescent  or  dendritic  forms.*  Silver  is 
more  frequently  met  with,  however,  in  combination  with  sulphur,  forming 
the  sulphide  of  silver  (AgoS),  which  is  generally  associated  with  large 
quantities  of  the  sulphides  of  lead,  antimony,  and  iron.  The  largest  sup- 
plies of  silver  are  obtained  from  the  Mexican  and  Peruvian  mines,  but  the 
quantity  furnished  by  Saxony  and  Hungary  is  by  no  means  insignificant. 
The  process  by  which  silver  is  extracted  from  galena  has  been  already 
described  under  the  history  of  lead. 

The  ores  of  copper  (particularly  the  grey  copper  ore)  often  contain  so 
much  silver  as  to  be  worth  working  for  that  metal,  in  which  case  they 
are  smelted  in  the  usual  way,  when  the  copper  obtained  is  found  to  con- 
tain the  whole  of  the  silver  present 
in  the  ore.  The  silver  is  separated 
from  the  copper  by  taking  advantage 
of  the  facility  with  which  the  former 
metal  is  dissolved  by  melted  lead. 
The  process  of  liqioation,  as  it  is 
termed,  consists  in  fusing  the  argenti- 
ferous copper  Avith  about  thrice  its 
weight  of  lead,  and  casting  the  alloy 
thus  obtained  into  cakes  or  discs, 
which  are  afterwards  gradually  heated 
upon  a  hearth  (fig.  269),  so  contrived 
that  the  lead,  which  melts  much  more 
easily  than  the  copper,  may  flow  off 
in  the  liquid  state,  carrying  with  it,  in  the  form  of  an  alloy,  the  silver 
which  was  associated  with  the  copper,  leaving  this  last  metal  in 
porous  masses,  having  the  form  of  the  original  discs,  upon  the  hearth. 
The  lead  and  silver  are  separated  by  the  process  of  cupellation  (page 
370). 

"When  the  extraction  of  the  silver  is  the  main  object  with  which  a 
particular  ore  is  treated,  the  process  of  amalgamation  is  adopted,  in  which 
the  silver  is  dissolved  out  by  means  of  mercury.  At  Freiberg,  the  silver 
is  extracted  by  this  method  from  an  ore  which  contains  silver  sulphide 
together  with  much  iron  pyrites  and  other  metallic  sulphides.  The  ore 
is  mixed  with  a  small  proportion  of  common  salt,  and  roasted  in  a  rever- 
beratory  furnace,  when  the  silver  sulphide  is  converted  into  silver  chloride. 
It  is  then  ground  to  a  very  fine  powder,  which  is  agitated,  in  revolving 
casks,  with  water  and  metallic  iron,  when  the  latter  appropriates  the 
chlorine  and  reduces  the  silver  to  the  metallic  state.  A  quantity  of 
mercury  is  then  introduced  into  the  casks,  and  the  revolution  continued 
for  several  hours;  the  mercury  dissolves  the  silver,  copper,  and  lead,  and 
is  run  out  of  the  barrels  into  stout  linen  strainers,  which  allow  the  excess 
of  fluid  mercury  to  pass  through,  but  retain  the  soft  solid  amalgam  con- 
taining the  silver.     In  order  to  recover  the  silver,  this  amalgam  is  placed 

*  Flight  found  23  per  cent,  of  mercury  in  a  specimen  of  native  silver  from  Kongsberg. 
Other  samples  also  proved  to  be  amalgams. 


Fig.  269.  — Liquatiou  hearth. 


380 


SILVER-PLATING. 


%s^!;&sss%^s%sssK0; 


Fig.  270. 


^ 


in  iron  trays  arranged  one  above  the  other  (fig.  270),  and  covered  with 
an  iron  bell-shaped  receiver  standing  over  water.  By  heaping  burning 
fuel  round  the  upper  part  of  this  dome,  its  temperature  is  raised  sufficiently 
to  convert  the  mercury  into  vapour,  which 
condenses  again  in  the  water,  leaving  the  silver, 
together  with  the  copper  and  lead,  upon  the 
iron  trays.  Finally,  the  silver  is  refined  by 
fusing  it  with  an  additional  quantity  of  lead 
and  subjecting  the  alloy  to  cupellation  (page 
370),  when  the  fused  oxide  of  lead  which  is 
formed  carries  with  it  the  copper,  also  in  the 
form  of  oxide,  leaving  the  silver  in  a  state  of 
purity. 

Various  methods  have  been  devised  to 
supersede  the  amalgamation  process.  For 
example,  the  ores  have  been  roasted  with 
common  salt  to  convert  the  silver  into  chloride, 
which  is  dissolved  out  of  the  mass  by  means 
of  a  strong  solution  of  common  salt,  from 
which  the  silver  is  afterwards  precipitated  in  the  metallic  state  by  copper. 
Sodium  hyposulphite  has  also  been  employed  to  dissolve  out  the  silver 
chloride,  and  the  solution  precipitated  by  sodium  sulphide,  the  resulting 
silver  sulphide  being  roasted  to  remove  the  sulphur  and  leave  metallic 
silver. 

Although  silver  is  capable  of  resisting  the  oxidising  action  of  the  atmo- 
sphere, it  is  liable  to  considerable  loss  by  wear  and  tear  in  consequence 
of  its  softness,  and  is  therefore  always  hardened,  for  useful  purposes,  by 
the  addition  of  a  small  proportion  of  copper.  The  standard  silver  em- 
ployed for  coinage  and  for  most  articles  of  silver  plate  in  this  country, 
contains,  in  1000  parts,  925  of  silver  and  75  of  copper,  whilst  that  used 
in  France  contains  900  of  silver  and  100  of  copper. 

Standard  silver,  for  coining  and  other  purposes,  is  whitened  by  being 
heated  in  air  and  immersed  in  diluted  sulphuric  acid,  which  dissolves  out 
the  oxide  of  copper,  leaving  a  superficial  film  of  nearly  pure  silver.  Dead 
or  frosted  silver  is  produced  in  this  manner.  Oxidised  silver  is  covered 
with  a  thin  film  of  sulphide  by  immersion  in  a  solution  obtained  by 
boiling  sulphur  with  potash. 

The  solder  employed  in  working  silver  consists  of  5  parts  of  silver,  2 
of  zinc,  and  6  of  brass. 

Plated  articles  are  manufactured  from  copper  or  one  of  its  alloys, 
which  has  been  united,  by  rolling,  with  a  thin  plate  of  silver,  the  adhesion 
of  the  latter  being  promoted  by  first  washing  the  surface  of  the  copper 
with  a  solution  of  nitrate  of  silver,  when  a  film  of  this  metal  is  deposited 
upon  its  surface,  the  copper  taking  the  place  of  the  silver  in  the  solution. 
Electro-plating  consists  in  covering  the  surface  of  baser  metals  with  a 
coating  of  silver,  by  connecting  them  with  the  negative  (or  zinc)  pole  of 
the  galvanic  battery,  and  immersing  them  in  a  solution  made  by  dissolving 
silver  cyanide  in  potassium  cyanide;*  the  current  gi-adually  decomposes 
the  silver  cyanide,  and  this  metal  is  of  course  (see  page  9)  deposited  upon 
the  object  connected  with  the  negative  pole,  whilst  the  cyanogen  liberated 

*  A  solution  of  potassium  cyanide  in  10  parts  of  water,  Avith  50  grains  of  silver  chloride 
dissolved  in  each  pint  of  the  liquid,  will  answer  the  purpose. 


PROPERTIES  OF  SILVER.  381 

at  the  positive  (copper  or  platinum)  pole  is  allowed  to  act  upon  a  silver 
plate  with  which  this  pole  is  connected,  so  that  the  silvering  solution  is 
always  maintained  at  the  same  strength,  the  quantity  of  silver  dissolved 
at  this  pole  being  precisely  equal  to  that  deposited  at  the  opposite  pole. 

Brass  and  copper  are  sometimes  silvered  by  rubbing  them  with  a  mix- 
ture of  10  parts  of  silver  chloride,  with  1  of  corrosive  sublimate  (mercuric 
chloride)  and  100  of  bitartrate  of  potash.  The  silver  and  mercury  are 
both  reduced  to  the  metallic  state  by  the  baser  metal,  and  an  amalgam 
of  silver  is  formed,  which  readily  coats  the  surface.  The  acidity  of  the 
bitartrate  of  potash  promotes  the  reduction.  The  surface  to  be  silvered 
should  always  be  cleansed  from  oxide  by  momentary  immersion  in  nitric 
acid,  and  washed  with  water.  For  dry  silveiing,  an  amalgam  of  silver 
and  mercury  is  applied  to  the  clean  surface,  and  the  mercury  is  after- 
wards expelled  by  heat. 

Silvering  upon  glass  is  effected  by  means  of  certain  organic  substances 
which  are  capable  of  precipitating  metallic  silver  from  its  solutions. 
Looking-glasses  have  been  made  by  pouring  upon  the  surface  of  plates  of 
glass  a  solution  containing  silver  tartrate  and  ammonium  tartrate.  On 
heating  the  glass  plates  to  a  certain  temperature,  the  tartrate  is  reduced, 
and  the  metallic  silver  is  deposited  in  a  closely  adhering  film.  Glass  globes 
and  vases  are  silvered  internally  by  a  process  which  is  exactly  similar 
in  principle.  The  coating  is  rendered  more  adherent  by  sprinkling  it 
with  a  weak  solution  of  potassio-mercuric  cyanide,  which  amalgamates  the 
silver. 

Small  surfaces  of  glass  for  optical  purposes  may  be  silvered  in  the  following  manner : — 
Dissolve  one  gramme  of  silver  nitrate  in  20  cubic  centimetres  of  distilled  water,  and 
add  weak  ammonia  carefully  until  the  precipitate  is  almost  entirely  dissolved.  Filter 
the  solution,  and  make  it  up  to  100  cubic  centimetres  with  distilled  water.  Then 
dissolve  2  grammes  of  silver  nitrate  in  a  little  distilled  water,  and  add  it  to  a  litre  of 
boiling  distilled  water.  Add  1  "66  gramme  of  Rochelle  salt  (tartrate  of  potassium  and 
sodium),  and  boil  till  the  precipitated  silver  tartrate  becomes  grey ;  filter  while  hot. 

Clean  the  glass  to  be  silvered  very  thoroughhj  with  nitric  acid,  distilled  water, 
potash,  distilled  water,  alcohol,  distilled  water  ;  place  it  in  a  clean  glass  or  porcelain 
vessel,  with  the  side  to  be  silvered  uppermost.  Mix  equal  measures  of  the  two  silver 
solutions  (cold),  and  pour  the  mixture  in  so  as  to  cover  the  glass,  which  will  be 
silvered  in  about  an  hour.  After  washing,  it  may  be  allowed  to  dry,  and  varnished 
{Instruction  in  Physics  in  the  Lahcrratory  at  South  Kensington). 

Pure  silver  is  easily  obtained  from  standard  silver  by  dissolving  it  in 
nitric  acid,  with  the  aid  of  heat,  diluting  the  solution  with  water,  adding 
solution  of  common  salt  as  long  as  it  produces  any  fresh  precipitate  of 
silver  chloride,  washing  the  precipitate  by  decantation  as  long  as  the 
washings  give  a  blue  tinge  with  ammonia,  and  fusing  the  dried  precipitate 
with  half  its  weight  of  dried  carbonate  of  soda  in.  a  brisk  fire,  when  a 
button  of  silver  will  be  found  on  breaking  the  crucible — 

2AgCl  +  Na^COg  =  Ag,  +  2NaCl  4-  0  -t-  CO^. 
282.  Properties  of  silver. — The  brilliant  whiteness  of  silver  distin- 
guishes it  from  all  other  metals.  It  is  lighter  than  lead,  its  specific 
gravity  being  10"53  ;  harder  than(^d,  but  not  so  hard  as  copper;  more 
malleable  and  ductile  than  any  other  metal  except  gold,  which  it  sur- 
passes in  tenacity.  It  fuses  at  a  somewhat  lower  temperature  than  gold  or 
copper  (about  1900°  F.,  1037°  C),  and  is  the  best  conductor  of  heat  and 
electricity.  It  is  not  oxidised  by  dry  or  moist  air,  either  at  the  ordinary 
or  at  high  temperatures,  but  is  oxidised  by  ozone,  and  tarnished  by  air 


382  OXIDES  OF  SILVER. 

containing  sulphuretted  hydrogen,  from  the  production  of  silver  sulphide, 
which  is  easily  removed  by  solution  of  potassium  cyanide.  It  is  unaffected 
by  dilute  acids,  with  the  exception  of  nitric;  but  hot  concentrated  sul- 
phuric acid  converts  it  into  silver  sulphate,  and  when  boiled  with  strong 
hydrochloric  acid,  it  dissolves  to  a  slight  extent  in  the  form  of  silver 
chloride,  which  is  precipitated  on  adding  water.  The  potassium  and 
sodium  hydrates  do  not  act  on  silver  to  the  same  extent  as  on  platinum 
when  fused  Avith  it ;  hence  silver  basins  and  crucibles  are  much  used  in 
the  laboratory. 

283.  Oxides  of  silver. — There  are  three  compounds  of  silver  "with 
oxygen:  the  suboxide  Ag^O;  the  oxide  AggO;  and  the  peroxide,  probably 
Ag202,  which  is  not  known  in  the  pure  state.  The  oxide  alone  has  any 
practical  interest,  as  being  the  base  of  the  salts  of  silver. 

Silver  oxide  (AggO)  is  obtained  as  a  brown  precipitate  when  solution 
of  silver  nitrate  is  decomposed  by  potash.  It  is  a  powerful  base,  slightly 
soluble  in  water,  to  which  it  imparts  a  weak  alkaline  reaction.  A 
moderate  heat  decomposes  it  into  its  elements.  "When  moist  freshly- 
precipitated  silver  oxide  is  covered  with  a  strong  solution  of  ammonia, 
and  allowed  to  stand  for  some  hours,  it  becomes  black,  and  acquires 
dangerously  explosive  properties.  The  composition  of  this  fulminating 
silver  is  not  accurately  known,  but  it  is  supposed  to  be  a  silver  nitride 
NAg3,  corresponding  in  composition  to  ammonia. 

Silver  yiitrate  (AgNOg),  or  lunar  caustic  (silver  being  distinguished 
as  hina  by  the  alchemists),  is  procured  by  dissolving  silver  in  nitric  acid, 
with  the  aid  of  a  gentle  heat,  evaporating  the  solution  to  dryness,  and 
heating  the  residue  till  it  fuses,  in  order  to  expel  the  excess  of  acid.  For 
use  in  surgery,  the  fused  nitrate  is  poured  into  cylindrical  moulds,  so  as 
to  cast  it  into  thin  sticks ;  but  for  chemical  purposes  it  is  dissolved  in 
water  and  crystallised,  when  it  forms  colourless  square  tables.  The  action 
of  nitrate  of  silver  as  a  caustic  depends  upon  the  facility  with  which  it 
parts  with  oxygen,  the  silver  being  reduced  to  the  metallic  state,  and  the 
oxygen  combining  with  the  elements  of  the  organic  matter.  This  effect 
is  very  much  promoted  by  exposure  to  sunlight,  or  diffused  daylight. 
Pure  silver  nitrate  is  not  changed  by  exposure  to  light,  but  if  organic 
matter  be  present,  a  black  deposit,  containing  finely-divided  silver,  is  pro- 
duced. Thus,  the  solution  of  silver  nitrate  stains  the  fingers  black 
when  exposed  to  light,  but  the  stain  may  be  removed  by  potassium 
cyanide.  If  solution  of  silver  nitrate  be  dropped  upon  paper,  and  exposed 
to  light,  black  stains  will  be  produced,  and  the  paper  corroded.  Silver 
nitrate  is  a  frequent  constituent  of  marking  inks^  since  the  deposit  of 
metallic  silver  formed  on  exposure  to  light  is  not  removable  by  washing. 
The  linen  is  sometimes  mordanted  by  applying  a  solution  of  sodium 
carbonate  before  the  marking  ink,  when  the  insoluble  silver  carbonate  is 
precipitated  in  the  fibre,  and  is  more  easily  blackened  than  the  nitrate, 
f  speiiially  if  a  hot  iron  is  applied.  Marking  inks  without  preparation  are 
made  with  silver  nitrate  containing  an  excess  of  ammonia,  which  appro- 
priates the  nitric  acid,  and  hastens  the  blackening  on  exposure  to  light 
or  heat.  Hair  dyes  often  contain  silver  nitrate.  The  important  use  of 
tliis  salt  in  photography  has  been  noticed  already  (page  212). 

In  order  to  prepare  silver  nitrate  from  standard  silver  (containing  copper),  the 
metal  is  dissolved  in  moderately  strong  nitric  acid,  and  the  solution  evaporated  to 


CHLORIDE  OF  SILVER.  383 

dryness  in  a  porcelain  dish,  when  a  blue  residue  containing  the  nitrates  of  silver  and 
copper  is  obtained.  The  dish  is  now  moderately  heated  until  the  residue  has  fused, 
and  become  uniformly  black,  the  blue  copper  nitrate  being  decomposed  and  leaving 
black  copper  oxide,  at  a  temperature  which  is  insufficient  to  decompose  the  silver 
nitrate.  To  ascertain  when  all  the  copper  nitrate  is  decomposed,  a  small  sample  is 
removed  on  the  end  of  a  glass  rod,  dissolved  in  water,  filtered,  and  tested  with 
ammonia,  which  will  produce  a  blue  colour  if  any  copper  nitrate  is  left.  The  residue 
is  treated  with  hot  water,  the  solution  filtered  from  the  copper  oxide,  and  evaporated 
to  crystallisation. 

284.  Silver  chloride  (AgCl)  is  an  important  compound,  as  being  the 
form  into  which  silver  is  commonly  converted  in  extracting  it  from  its 
ores,  and  in  separating  it  from  other  metals.  It  separates  as  a  white 
curdy  precipitate,  when  solution  of  hydrochloric  acid  or  a  chloride  is 
mixed  with  a  solution  containing  silver.  The  precipitate  is  brilliantly 
white  at  first,  but  soon  becomes  violet,  and  eventually  black,  if  exposed 
to  daylight,  or  more  rapidly  in  sunlight,  the  chloride  of  silver  being  re- 
duced to  subchloride  (Ag2Cl),  with  separation  of  chlorine  (see  page  213). 
The  blackening  takes  place  more  rapidly  in  the  presence  of  an  excess  of 
silver  nitrate  or  of  organic  matter,  upon  which  the  liberated  chlorine  is 
capable  of  acting.  The  silver  chloride  formed  by  suspending  silver  leaf 
in  a  bottle  of  chlorine  gas,  is  not  blackened  by  light.  If  the  white  silver 
chloride  be  dried  in  the  dark,  and  heated  in  a  crucible,  it  fuses  at  about 
500°  F.,  to  a  brownish  liquid,  which  soHdifies,  on  cooling,  to  a  transparent, 
nearly  colourless  mass,  much  resembling  horn  in  external  characters 
{horn  silver) ;  a  strong  heat  converts  it  into  vapour,  but  does  not  decom- 
pose it.  If  fused  silver  chloride  be  covered  with  hydrochloric  acid,  and 
a  piece  of  zinc  placed  upon  it,  it  Avill  be  found  entirely  reduced,  after  a 
few  hours,  to  a  cake  of  metallic  silver ;  the  first  portion  of  silver  having 
been  reduced  in  contact  with  the  zinc,  and  the  remainder  by  the  galvanic 
action  set  up  by  the  contact  of  the  two  metals  beneath  the  liquid. 
Ammonia  readily  dissolves  silver  chloride,  and  the  solution  deposits 
colourless  crystals  of  the  chloride  when  evaporated.  If  the  ammonia  be 
very  strong,  the  solution  deposits  a  crystalline  compound  of  silver  chloride 
with  ammonia.  The  absorption  of  ammoniacal  gas  by  silver  chloride  has 
been  noticed  at  page  127,  and  the  photographic  application  of  the  chloride 
at  page  213. 

Recovery  of  silver  from  old  phoU^grapMc  bath^. — One  of  the  simplest  methods  of 
effecting  this  consists  in  mixing  tlie  liquid  with  solution  of  common  salt  as  long  as 
it  causes  a  fresh  precipitate  of  silver  chloride,  which  is  allowed  to  subside,  washed 
once  or  twice  by  decantation,  mixed  with  a  little  sulphuric  acid,  a  lump  of  zinc 
(spelter)  placed  in  it,  and  left  for  a  day  or  two  to  reduce  the  silver  to  the  metallic 
state.  The  zinc  is  then  taken  out,  and  the  metallic  silver  well  washed  by  decanta- 
tion, first  with  dilute  sulphuric  acid,  to  remove  zinc,  and  afterwards  with  water,  till 
the  washings  are  quitp  tasteless.  It  may  either  be  reconverted  into  nitrate  by  dissolving 
in  nitric  acid  (p.  382),  or  fused  in  an  earthen  crucible  with  a  little  borax. 

From  the  fixing  solutions  containing  sodium  hyposulphite,  the  silver  cannot  be 
precipitated  by  salt,  because  the  silver  chloride  is  soluble  in  the  hyposulphite.  A 
piece  of  sheet  copper  left  in  this  for  a  day  or  two  will  precipitate  the  sUver  at  once  in 
the  metallic  state. 

Subchloride  of  silver  ( Ag._,Cl)  has  been  been  obtained  b}'  the  action  of  ferric  chloride 
upon  metallic "  silver  (Ag4'+FeXl6  =  2Ag2Cl  +  2FeCl2).  It  is  black,  and  insoluble 
in  nitric  acid.  Ammonia  decomposes  it,  dissolving  out  silver  chloride,  and  leaving 
metallic  silver. 

Another  subchloride  of  silver,  Ag4Cl3,  has  been  obtained  as  a  black  powder  by  the 
action  of  hydrocliloric  acid  upon  the  argentous  citrate  prepared  by  reducing  argentic 
citrate  with  hydrogen. 


384  MERCURY. 

Silver  bromide  (AgBr)  is  a  rare  Chilian  mineral.  Associated  with 
silver  chloride,  it  forms  the  mineral  etnholite.  It  much  resembles  the 
chloride,  but  is  somewhat  less  easily  dissolved  by  ammonia. 

Silvei'  iodide  (Agl)  is  also  found  in  the  mineral  kingdom.  It  is 
worthy  of  remark  that  silver  decomposes  hydriodic  acid  much  more  easily 
than  hydrochloric  acid,  forming  silver  iodide,  and  evolving  hydrogen. 
The  silver  iodide  dissolves  in  hot  hydriodic  acid,  and  is  deposited  iri 
crystals  on  cooling.  By  adding  silver  nitrate  to  potassium  iodide  the 
silver  iodide  is  obtained  as  a  yellow  precipitate  which,  unlike  the  chloride, 
does  not  dissolve  in  ammonia.  Silver  iodide  dissolves  in  a  boiling 
saturated  solution  of  silver  nitrate,  and  the  solution,  on  cooling,  deposits 
crystals  having  the  composition  Agl.AgNOg,  which  are  far  more  sensitive 
to  the  action  of  ligbt  than  silver  iodide  itself,  a  circumstance  which  is 
taken  advantage  of  by  photographers.  The  crystals  are  decomposed  by 
water,  with  separation  of  silver  iodide. 

Silver  sulphide  (Ag.^S)  is  found  as  silver  glance,  which  may  be  regarded 
as  the  chief  ore  of  silver ;  it  has  a  metallic  lustre,  and  is  sometimes  found 
in  cubical  or  octahedral  crystals.  The  minerals  known  as  rosiclers  or  red 
silver  ores  contain  sulphide  of  silver  combined  with  the  sulphides  of 
arsenic  and  antimony.  The  black  precipitate  obtained  by  the  action  of 
hydrosulphuric  acid  upon  a  solution  of  silver  is  silver  sulphide.  It  may 
also  be  formed  by  heating  silver  with  sulphur  in  a  covered  crucible. 
Silver  sulphide  is  remarkable  for  being  soft  and  malleable,  so  that  medals 
may  even  be  struck  from  it.  It  is  not  dissolved  by  diluted  sulphuric  or 
hydrochloric  acid,  but  nitric  acid  readily  dissolves  it.  Metallic  silver 
dissolves  silver  sulphide  when  fused  with  it,  and  becomes  brittle  even 
when  containing  only  1  per  cent,  of  the  sulphide. 


MERCUEY. 
Hg"=200  parts  by  weight.* 

285.  Mercury  (quicksilver)  is  the  only  metal  which  is  liquid  at  the 
ordinary  temperature,  and  since  it  requires  a  temperature  of  39°  below 
zero  F.  to  solidify  it,  this  metal  is  particularly  adapted  for  the  construc- 
tion of  thermometers  and  barometers.  Its  high  boiling-point  (662°  F.) 
also  recommends  it  for  the  former  purpose,  as  its  high  specific  gravity 
(13-54)  for  the  latter,  a  column  of  about  30  inches  in  height  being 
able  to  couiiterpoise  a  column  of  atmospheric  air  having  the  same 
sectional  area,  and  a  height  equal  to  that  of  the  atmosphere  above  the 
level  of  the  sea.  The  symbol  for  mercury  (Hg)  is  derived  from  the  Latin 
name  for  this  element,  hydrargyrum  (vSwp,  water,  referring  to  its  fluidity, 
apyvpos,  silver). 

Mercury  is  not  met  with  in  this  country,  but  is  obtained  from  Idria 
(Austria),  Almaden  (Spain),  China,  and  New  Almaden  (California).  It 
occurs  in  these  mines  partly  in  the  metallic  state,  diffused  in  minute 
globules  or  collected  in  cavities,  but  chiefly  in  the  state  of  cinnabar,  which 
is  mercuric  sulphide  (HgS). 

The  metal  is  extracted  from  the  sulphide  at  Idria  by  roasting  the  ore 

*  The  vapour  of  mercury  is  only  100  times  as  heavy  as  hydrogen,  which  would  indicate 
100  as  the  atomic  weight  of  mercury,  but  the  specific  heat  of  mercury  when  multiplied  by 
100  would  give  an  atomic  heat  only  half  that  of  most  other  metals. 


MERCURY.  ggS 

in  a  kiln  (fig.  271),  which  is  connected  with  an  extensive  series  of  con- 
densing chambers  built  of  brickwork.  The  sulphur  is  converted,  by  the 
air  in  the  kiln,  into  sulphurous  acid  gas,  whilst  the  mercury  passes  off  in 
vapour  and  condenses  in  the  chambers. 


WM 


Fig.  271. — Extraction  of  mercury  at  Idria. 

At  Almaden,  the  extraction  is  conducted  upon  the  same  principle,  but 
the  condensation  of  the  mercury  is  effected  in  earthen  receivers  (called 
aliidels)  opening  into  each  other,  and  delivering  the  mercury  into  a  gutter 
which  conveys  it  to  the  receptacles. 

The  cinnabar  is  placed  upon  the  arch  (A,  fig.  272)  of  brickwork,  in 
which  there  are  several  openings  for  the  passage  of  the  flame  of  the  wood 
fire  kindled  at  B ;   this  flame 

ignites  the  sulphide  of  mercury,  a  j| 

which  burns  in  the  air  passing  I 

up   from   below,    forming   sul-  I 

phurous  acid  gas  and  vapour  of         wli^teSW 
mercury  (HgS  +  02  =  Hg  +  HI^^B^^^""*""'^'^"""' 

8O.2),  which  escape  through  the  mfmBSU     y^-^  •>^^^  y 

flue  (F)  into  the  aludels  (C),  wHm       I  I         I 

where    the    chief   part   of    the  ^^^^         .'  ' 

mercury    condenses    and    runs  ^-:«9!^'<r^^^§-5S§%-."..n.-.-t^'v^^    ^ 

down  into  the  gutter  (G).     The  Fig.  272. 

suljihurous    acid     gas     escapes 

through  the  flue  (H),  and  any  mercury  which  may  have  escaped  condensa- 
tion is  collected  in  the  trough  (I)),  the  gas  finally  passing  out  through 
the  chimney  (E),  which  provides  for  the  requisite  draught. 

In  the  Palatinate,  the  cinnabar  is  distilled  in  cast-iron  retorts  with 
lime,  when  the  sulphur  is  left  in  the  residue  as  calcium  sulphide  and 
sulphate,  whilst  the  mercury  distils  over — 

4HgS  -h  4CaO  =  3CaS  +  CaSO^  -F  Hg^.     ,.   .,,    ,;  ; 

The  mercury  found  in  commerce  is  never  perfectly  pure,  as  may  be  shown  by 
scattering  a  little  upon  a  clean  glass  plate,  when  it  tails  or  leaves  a  track  upon  the 
glass,  which  is  not  the  case  with  pure  mercury.  Its  chief  impurity  is  lead,  which 
may  be  removed  by  exposing  it  in  a  thin  layer  to  the  action  of  nitric  acid  diluted 
with  two  measures  of  water,  which  should  cover  its  surface,  and  be  allowed  to  remain 
in  contact  with  it  for  a  day  or  two,  witli  occasional  stirring.  The  lead  is  far  more 
easily  oxidised  and  dissolved  than  the  mercury,  though  a  little  of  this  also  passes 
into  solution.  The  mercury  is  afterwards  well  washed  with  water  and  dried,  first  with 
blotting-paper,  and  then  ))y  a  gentle  heat.  Mercury  is  easily  freed  from  meclianical 
impurities  by  filtering  it  through  a  cone  of  paper,  round  the  apex  of  which  a  few  pin- 
holes have  been  made.  Zinc,  tin,  and  bismuth  are  sometimes  present  in  the  mercury 
0^  coimmeree:  "'■  ^    '■  ' 

2b 


386  USES  OF  MERCURY. 

286.  Although  mercury  in  its  ordinar)-^  condition  is  not  oxidised  by  air 
at  the  common  temperature,  it  appears  to  undergo  a  partial  oxidation 
when  reduced  to  a  fine  state  of  division,  as  in  those  medicinal  prepara- 
tions of  the  metal  which  are  made  by  triturating  it  with  various  sub- 
stances which  have  no  chemical  action  upon  it,  until  globules  of  the  metal 
are  no  longer  visible.  Bluo,  pill  and  grey  powder,  or  hydrargyrum  cnm 
rrefd,  afford  examples  of  this,  and  probably  owe  much  of  their  medicinal 
activity  to  the  presence  of  one  of  the  oxides  of  mercury. 

287.  Uaes  of  mercury.- — One  of  the  chief  uses  to  which  mercury  is 
devoted  is  the  ffilvering  of  InoMng-glasseAi,  which  is  effected  by  means  of 
an  amalgam  of  tin  in  the  following  manner :  a  sheet  of  tin-foil  of  the 
same  size  as  the  glass  to  be  silvered  is  laid  perfectly  level  upon  a  table, 
and  rubbed  over  with  metallic  mercury,  a  thin  layer  of  which  is  after- 
wards poured  upon  it.  The  glass  is  then  carefully  slid  on  to  the  table, 
so  that  its  edge  may  carry  before  it  part  of  the  superfluous  mercury  with 
the  impurities  upon  its  surface  ;  heavy  weights  are  laid  upon  the  glass  so 
as  to  squeeze  out  the  excess  of  mercury,  and  in  a  few  days  the  combina- 
tion of  tin  and  mercury  is  found  to  have  adhered  firmly  to  the  glass ;  this 
coating  usually  contains  about  1  part  of  mercury  and  4  parts  of  tin.  In 
this  and  all  other  arts  in  which  mercury  is  used  (such  as  barometer-mak- 
ing) much  suffering  is  experienced  by  the  operatives,  from  the  poisonous 
action  of  the  mercury. 

The  readiness  with  which  mercury  unites  with  most  other  metals  to 
form  amalgams  is  one  of  its  most  striking  properties,  and  is  turned  to 
account  for  the  extraction  of  silver  and  gold  from  their  ores.  The  attrac- 
tion of  the  latter  metal  for  mercury  is  seen  in  the  readiness  with  which 
it  becomes  coated  with  a  silvery  layer  of  mercury,  whenever  it  is  brought 
in  contact  with  that  metal,  and  if  a  piece  of  gold  leaf  be  suspended 
at  a  little  distance  above  the  surface  of  mercury,  it  will  be  found,  after 
a  time,  silvered  by  the  vapour  of  the  metal  which  rises  slowly  even  at 
the  ordinary  temperature.  From  the  surface  of  rings  which  have  been 
accidentally  whitened  by  mercury,  it  may  be  removed  by  a  moderate 
heat,  or  by  warm  dilute  nitric  acid,  but  the  gold  will  afterwards  require 
burnishing. 

Zinc  plates  are  amalgamated,  as  it  termed,  for  use  in  the  galvanic 
battery,  by  rubbing  the  liquid  metal  over  them  under  the  surface  of  dilute 
sulphuric  acid,  which  removes  the  coating  of  oxide  from  the  surface  of 
the  zinc.  The  amalgam  of  zinc  is  not  acted  on  by  the  diluted  sulphuric 
acid  used  in  the  battery  (see  page  8)  until  the  circuit  is  completed,  so  that 
no  zinc  is  wasted  when  the  battery  is  not  in  use.  An  amalgam  of  6  parts 
of  mercury  with  1  part  of  zinc  and  1  of  tin  is  used  to  promote  the  action 
of  electrical  machines. 

The  addition  of  a  little  amalgam  of  sodium  to  metallic  mercury  gives 
it  the  power  of  adhering  much  more  readily  to  other  metals,  even  to  iron. 
Such  an  addition  has  been  recommended  in  all  cases  where  metallic  sur- 
faces have  to  be  amalgamated,  and  especially  in  the  extraction  of  silver 
and  gold  from  their  ores  by  means  of  mercury. 

Iron  and  platinum  are  the  only  metals  in  ordinary  use  which  can  be 
employed  in  contact  with  mercury  without  being  corroded  by  it.  Mer- 
cury, however,  adheres  to  platinum. 

The  following  definite  compounds  of  mercury  with   other  metals  have  beeii  ol>- 


OXIDES  OF  MERCURY.  38T 

tained  by  combining  them  with  excess  of  mercury,  and  squeezing  out  the  fluid  metal 
by  hydraulic  pressure,  amounting  to  60  tons  upon  the  inch  : — 


Amalgam  of  lead. 

Pb.Hg 

Amalgam  of  zinc, 

Zn,Hg 

,,             silver. 

A^Hg 

,,            copper. 

CuHg 

,,             iron, 

FeHg* 

,,             platinum. 

PtHg, 

The  amalgam  of  silver  (AgHg)  has  been  found  in  nature,  in  dodecahedral  crystals. 

A  very  beautiful  crystallisation  of  the  amalgam  of  silver  {Arbor  DianaR)  may  be 
obtained  in  long  prisms  having  the  composition  Ag^Hg,,  by  dissolving  400  grains  of 
silver  nitrate  in  40  measured  ounces  of  water,  adding  160  minims  of  concentrated 
nitric  acid,  and  1840  grains  of  mercury  ;  in  the  course  of  a  day  or  two  crystals  of  2  or 
3  inches  in  length  will  be  deposited. 

288.  Oxides  of  mercury. — Two  oxides  of  mercury  are  known,  the  sub- 
oxide HggO,  and  the  oxide  HgO  :  both  combine  with  acids  to  form  salts. 

Suboxide  of  mercurij,  black  oxide  or  mercurous  oxide,  HggO,  is  obtained 
by  decomposing  calomel  with  solution  of  potash,  and  washing  with  water 
(Hg^CIg  +  2KH0  =  HggO  +  2KC1  +  H2O).  It  is  very  easily  decomposed, 
by  exposure  to  light  or  to  a  gentle  heat,  into  mercuric  oxide  and  metallic 
mercury. 

Red  oxide  of  mercury  or  mercuric  oxide  (HgO)  is  formed  upon  the 
surface  of  mercury,  when  heated  for  some  time  to  its  boiling-point  in  con- 
tact with  air.  The  oxide  is  black  while  hot,  but  becomes  red  on  cooling. 
It  is  used  under  the  name  of  red  precipitate,  in  ointments,  and  is  prepared 
for  this  purpose  by  dissolving  mercury  in  nitric  acid,  evaporating  the 
solution  to  dryness,  and  gently  calcining  the  mercuric  nitrate,  Hg(iS^03)2, 
until  the  nitric  acid  is  expelled.  The  name  nitric  oxide  of  mercury  refers 
to  this  process.  It  is  thus  obtained,  after  cooling,  as  a  brilliant  red  crys- 
talline powder,  which  becomes  nearly  black  when  heated,  and  is  resolved 
into  its  elements  at  a  red  heat.  It  dissolves  slightly  in  water,  and  the 
solution  has  a  very  feeble  alkaline  reaction.  A  bright  yellow  modification 
of  the  oxide  is  precipitated  when  a  solution  of  corrosive  sublimate  is 
decomposed  by  potash  (HgClg  +  2KH0  =  HgO  -f-  2KC1  -I-  H^O) ;  the  yellow 
variety  is  chemically  more  active  than  the  red. 

When  mercuric  oxide  is  anted  on  by  strong  ammonia,  it  becomes  converted  into  a 
yellowish-white  powder  which  possesses  the  properties  of  a  strong  base,  absorbing 
carbonic  acid  eagerly  from  the  air,  and  combining  readily  with  other  acids.  It  is 
easily  decomposed  by  exposure  to  light,  and,  if  rubbed  in  a  mortar  when  dry,  is 
decomposed  with  slight  detonations,  a  property  in  which  it  feebly  resembles  fulmin- 
ating silver  (p.  382).  The  composition  of  this  substance  is  represented  by  the 
formula  4HgO.2NH3.2H2O,  and  it  is  sometimes  called  ammoniated  mercuric  OdndA. 
When  exposed  in  vacuo  over  oil  of  vitriol,  it  loses  2H.2O,  becoming  4Hg0.2NH3,  but 
if  heated  to  about  260"  F.,  it  becomes  brown  ;titnow  contains  Hg40;,N2H4,  and  may 
be  regarded  as  a  compound  of  mercuric  oxide  with  two  molecules  of  ammonia  in  which 
two  atoms  of  hydrogen  are  displaced  by  mercury  (N.2H4Hg",3HgO). 

Tliis  substance  is  sometimes  called  mcrctiramine  ;  it  forms  salts  with  the  acids. 

By  passing  ammonia  gas  over  the  yellow  oxide  of  mercury  as  long  as  it  is  absorbed, 
and  heating  the  compound  to  about  260°  F.  in  a  current  of  ammonia  as  long  as  any 
water  is  evolved,  a  brown  explosive  powder  is  obtained  which  is  believed  to  be  a 
nitride  of  mercuri/,  N.^Hgg",  representing  a  double  molecule  of  ammonia  in  which  the 
hydrogen  has  been  displaced  by  mercury.  It  yields  salts  of  ammonium  when  decom- 
posed by  acids. 

289.  The  salts  formed  by  the  oxides  of  mercury  with  the  oxygen-acids  are  not  of 
great  practical  importance.     Protonitratc  of  mercury  or  mercurous  nitrate  is  obtained 

*  HgjFe,  has  been  obtained  by  the  action  of  finely-divided  iron  on  sodium-amalgam  in 
presence  of" water. 

+  It  has  been  stated  that  by  heating  it  for  some  time  in  a  current  of  dry  ammonia,  the 
whole  of  the  oxygen  may  be  expelled  as  water,  leaving  the  oxide  of  raercurammonium 
<NHg2")20,  which  is  very  explosive,  and  combine.s  with  water  to  form  a  hydrate  which 
produces  salts  with  the  acids. 


388  CHLORIDES  OF  MERCUftY. 

when  mercury  is  dissolved  in  nitric  acid  diluted  with  5  volumes  of  water  ;  ft  ma]?' 
be  procured  in  crystals  having  the  composition  Hg2(N03)2,2Aq.  The  prismatie 
crystals  which  are  sometimes  sold  aa  protoiiitrate  of  mercury  consist  of  a  basic  nitrate, 
3Hgj(N03)2,Hg20.H20,  prepared  by  actiilg  with  diluted  nitric  acid  upon  mercury 
in  excess.  When  this  salt  is  powdered  In  a  mortar  with  a  little  commoa  salt,  it 
becomes  black  from  the  separation  of  mercurous  oxide — 

3Hg2(N03)j,Hg20.H20  +  6NaCl  =  SHgsCls  +  eNaNOg  +  HgzO  +  HjO ;'  '; 
"but  the  normal  nitrate  is  not  blackened   (Hg2(N03)j  +  *JNaCl=Hg2Clj  +  2NaNO:,). 
These  nitrates  cannot  be  dissolved  in  water  without  partial  decomposition  aqd  pre- 
cipitation of  yellow  basic  nitrates. 

Nitrate  of  mercury  or  mercuric  nitrate  is  fonned  when  mercury  is  dissolved:  with  aji 
excess  of  strong  nitric  acid,  and  the  solution  boiled.  It  is  better  to  prepare  it  by 
saturating  strong  nitric  acid,  diluted  with  an  equal  measure  of  water,  with  mercuric 
oxide.  It  may  be  obtained  in  crystals  of  the  formula  2Hg(N03)2.  ■'^I-  Water  decom- 
poses it,  precipitating  a  yellow  basic  nitrate,  which  leaves  merciuic  oxide  when  Ipng 
washed  with  water. 

Mercuroits  sulphate  (Hg2S04)  is  precipitated  as  a  white  crystalline  po\yder,wheu 
■dilute  sulphuric  acid  is  added  to  a  solution  of  mercurous  nitrate. 
■  Mercuric  suljihate  (HgSO^)  is  obtained  by  heating  2  parts  by  weight  of  mercury 
with  3  parts  of  oil  of  vitriol,  and  evaporating  to  dryness.  Mercurous  sulphate  is  first 
produced,  and  is  oxidised  by  the  excess  of  sulphuric  acid.  It  forms  a  white  crystalline 
powder,  which  is  decomposed  by  water  into  a  soluble  acid  sulphate,  and  an  insoluble 
yellow  basic  sulphate  of  mercury,  HgS04,2HgO,  known  as  turbith  or  turpeth  mineral, 
said  to  have  been  so  named  from  its  resembling  in  its  medicinal  effects  the  root  of  the 
Convolvulus  turpethum. 

290.  Chlorides  of  mercury, — The  chlorides  are  the  most  important 
of  the  compounds  of  mercury,  one  chloride  being  calomel  (HgCl  or  HggClo) 
and  the  other  corrosive  sublimate  (HgClg).  Vapour  of  mercury  burns  in 
•chlorine  gas,  corrosive  sublimate  being  produced.* 

Corrosive  sublimate,  chloride  of  mei'cwy,  hicliloi'ide  or  perehloride  of 
mercury,  or  mercuric  cJdonde,  is  manufactured  by  heating  2  parts  by 
weight  of  mercury  with  3  parts  of  strong  sulphuric  acid,  and  evaporating 
to  dryness,  to  obtain  mercuric  sulphate  (Hg+ 2X12804  =  HgS04  +  2H2<> 
+  SOg),  which  is  mixed  with  1^  part  of  common  salt  and  heated  in 
glass  vessels  (HgS04  +  2]SraCl  =  Na.^S04  +  HgClo),  when  sodium  sulphate 
is  left,  and  the  corrosive  sublimate  is  converted  into  vapour,  condensing 
oa  the  cooler  part  of  the  vessel  in  lustrous  colourless  masses  which  are 
very  heavy  (sp.  gr.  5 "4),  and  have  a  crystalline  fracture.  It  fuses  verjr 
easily  (at  509°  F.)  to  a  perfectly  colourless  liquid,  which  boils  at  563°  F., 
emitting  an  extremely  acrid  vapour,  which  destroys  the  sense  of  smell 
for  some  time.  The  specific  gravity  of  its  vapour  is  140  (H  =  l)  ;  and 
that  calculated  from  the  formula  HgClgis  135-5.  This  vapour  condensps 
in  fine  needles,  or  sometimes  in  octahedra.  Corrosive  sublimate  dissolves 
in  three  times  its  weight  of  boiling  water,  but  requii-es  16  parts  of  cold 
water,  so  that  the  hot  solution  readily  deposits  long  four-sided  prismatic 
crystals  of  the  salt.  It  is  remarkable  that  alcohol  and  ether  dissolve 
.corrosive  sublimate  much  more  easily  than  water,  boiling  alcohol  dissolving 
about  an  equal  weight  of  the  chloride,  and  cold  ether  taking  up  one-third 
of  its  weight.  By  shaking  the  aqueous  solution  with  ether,  the  greater 
part  of  the  corrosive  sublimate  will  be  removed,  and  will  remain  dissolved 
in  the  ether  which  rises  to  the  surface.  Watei'  in  which  sal-ammoniac 
has  been  dissolved  will  take  up  corrosive  sublimate  more  easily  than  pure 
water,  a  soluble  double  chloride  (sal  alemhroth)  being  formed,  which  may 
be  obtained  in  ttibular  crystals  of  the  composition  HgCl2.6NH4Cl,H20. 

*  Two  volumes  of  vapour  of-  corrostve  sublimate  contain  2  volumes  of  meicjiry' vapour 
>(see  note  to  page  384)  and  2  volumes  of  chlorine.  .:..'...       .  .      ,•  -.! 


CALOMEL  OK  MERCUROUS  CHLORIDE.  389 

A  solution  of  corrosive  sublimate  in  water  containing  sal-ammoniac  is  a 
very  efficacious  hug-poison. 

The  poisonous  properties  of  corrosive  sublimate  are  very  marked,  so 
little  as  three  grains  having  been  known  to  cause  death  in  the  case  of  a 
child.  The  white  of  egg  is  commonly  administered  as  an  antidote,  because 
it  is  known  to  form  an  insoluble  compound  with  corrosive  sublimate^  so 
as  to  render  the  poison  inert  in  the  stomach.  The  compound  of  albumen 
with  corrosive  sublimate  is  also  much  less  liable  to  putrefaction  than 
albumen  itself,  and  hence  corrosive  sublimate  is  sometimes  employed  for 
preserving  anatomical  preparations  and  for  preventing  the  decay  of  wood 
(by  combining  with  the  vegetable  albumen  of  the  sap). 

Mercuric  chloride  unites  with  many  other  chlorides  to  form  soluble 
double  salts,  and  with  mercuric  oxide,  forming  several  oxyMorides, 
which  have  no  useful  applications.  , 

White  jyt'ccipitate,  employed  for  destroying  vermin,  is  deposited  when 
a  solution  of  corrosive  sublimate  is  poured  into  an  excess  of  solution  of 
ammonia  :  HgClg  +  2NH3  =  NH^Cl  +  NH2Hg"Cl  {white  precipitate). 

The  true  constitution  of  white  precipitate  has  been  the  subject  of  much  discussion, 
but  the  changes  which  it  undergoes,  under  various  circumstances,,  appear  to  lead  to 
the  conchision  that  it  represents  ammonium  chloride,  NH4CI,  in  which  half  of 
the  hydrogen  has  been  dis])laced  by  mercury.  When  boiled  with  potash,  it  yields 
ammonia  and  mercuric  oxide,  NH2Hg"Cl  +  KHO  =  XH:,  +  HgO  +  KCl.  If  it  be 
boiled  with  water,  it,  is  only  partly  decomposed  in  a  similar  manner,  leaving  a  yellow 
powder  having  the  composition  (NH.,HgCl).  HgO,  produced  according  to  the  equation 
2(NHoHgCl)  +  H2O  =  NH4CI  +  (NHjHgCl).  HgO.  A  compound  corresponding  to  this 
yellow  precipitate,  but  containing  mercuric  chloride  in  place  of  oxide,  is  precipitated 
when  ammonia  is  gradually  added  to  solution  of  corrosive  sublimate  in  large  excess, 
the  result  being  a  compound  of  white  precipitate  with  a  molecule  of  undecomposed 
mercuric  chloride,  (NH2HgCl).HgCU. 

If  white  precii)itate  be  heated  to  about  600°  F.,  it  evolves  ammonia,  and  yields  a 
sublimate  of  ammoniated  mercuric  chloride,  HgClo-NHj,  leaving  a  red  crystalline 
powder  which  is  insoluble  in  water  and  in  diluted  acids,  and  is  unchanged  by  boiling 
with  potash  ;  it  may  be  represented  as  a  compound  of  mercuric  chloride  with 
ammonia,  in  which  the  whole  of  the  hydrogen  has  been  displaced  by  mercury, 
N2Hg/'.2HgCl2. 

When  solution  of  corrosive  sublimate  is  added  to  a  hot  solution  of  sal-ammoniac, 
mixed  with  ammonia,  a  crystalline  deposit  is  obtained  on  cooling  the  liquid,  which 
is  known  as  fusible  white  precipitate,  and  represents  two  molecules  of  ammonium 
clil.oride,  in  which  one-fourth  of  the  hydrogen  has  been  displaced  by  mercury,  its 
composition  being  NoHgHg"Clj.  The  same  compound  is  formed  when  white  precipi- 
tate is  boiled  with  solution  of  sal-ammoniac,  NH2Hg"Cl-f-NH4Cl  =  N2H(.Hg"Cl2. 

The  above  compounds  possess  a  special  interest  for  the  chemist,  as  they  were 
among  the  first  to  attract  attention  to  the  mobility  of  the  hydrogen  in  ammonia, 
which  has  since  been  so  well  exemplified  in  the  artificial  production  of  organic  bases 
by  the  action  of  ammonia  upon  the  iodides  of  the  alcohol-radicals.  The  relation  of 
these  compounds  to  each  other  is  here  exhibited : — 

White  precipitate, NHoHg''Cl 

Produced  with  corrosive  sublimate  in  excess,    .  (NHjHgCl). HgCL, 

by  boiling  with  water,       .         .  (NH2HgCl).HgO 

,,  ,,  sal-ammoniac,  .         .  N2HfiHg"Cl2 

„         by  heating  to  600"  F.,        .         .         .  (N2Hg3".2HgCl2) . 

291.  Calomel,  suhchtoride  or  protochloride  of  mercury,  or  mercuroii^ 
chloride  (HgCl),*  unlike  corrosive  sublimate,  is  insoluble  in  water,  so 

* -That  this  is  the  correct  formula,  and  not  HgoClj,  has  been  recently  proved  by  the 
experiments  of  Fileti  on  the  vapour-density  of  a  mixture  of  mercurous  and  mercuric 
chlorides. 


390  IODIDES   OF  MERCURY. 

that  it  is  precipitated  when  hydrochloric  acid  or  a  soluble  chloride  is 
added  to  mercurous  nitrate.  The  simplest  mode  of  manufacturing  it 
consists  in  intimately  mixing  a  molecular  weight  of  corrosive  sublimate 
with  an  atomic  weight  of  metallic  mercury,  a  little  water  being  added  to 
prevent  dust,  drying  the  mixture  thoroughly,  and  subliming  it ;  HgCU 
+  Hg  =  2HgCl.  But  it  is  more  commonly  made  by  adding  another 
atomic  weight  of  mercury  to  the  materials  employed  in  the  preparation  of 
corrosive  sublimate.  Two  parts  by  weight  of  mercury  are  dissolved,  with 
the  aid  of  heat,  in  3  parts  of  oil  of  vitriol,  and  evaporated  to  dryness ; 
Hg  +  2H2SO4  =  HgSO^  +  SO2  +  2H2O.  The  residue  of  mercuric  sulphate 
is  intimately  mixed  with  two  more  parts  of  mercury,  and  the  mixture 
afterwards  triturated  with  1|  parts  of  common  salt,  until  globules  are  no 
longer  visible.  The  mixture  is  then  heated,  so  that  the  calomel  may 
pass  off  in  vapour,  which  condenses  as  a  translucent  fibrous  cake  on 
the  cool  part  of  the  subliming  vessel,  leaving  sodium  sulphate  behind  ; 
HgS04  +  Hg  +  2NaCl  =  2HgCl  +  Na2S04.  For  medicinal  purposes  the 
calomel  is  obtained  in  a  very  fine  state  of  division  by  conducting  the 
vapour  into  a  large  chamber  so  as  to  precipitate  it  in  a  fine  powder  by 
contact  with  a  large  volume  of  cold  air.  Steam  is  sometimes  introduced 
to  promote  its  fine  division.  Sublimed  calomel  always  contains  some 
corrosive  sublimate,  so  that  it  must  be  thoroughly  washed  with  water 
before  being  employed  in  medicine.  When  perfectly  pure  calomel  is 
sublimed,  a  little  is  always  decomposed  during  the  prcfcess  into  metallic 
mercury  and  corrosive  sublimate. 

Calomel  is  met  Avith  either  as  a  semi-transparent  fibrous  mass,  or  an 
amorphous  powder,  with  a  slightly  yellow  tinge.  It  is  heavier  than 
corrosive  sublimate  (sp.  gr.  7 "IS),  and  does  not  fuse  before  subliming; 
it  may  be  obtained  in  four-sided  prisms  by  slow  sublimation.  Diluted 
acids  wiU  not  dissolve  it,  but  boiling  nitric  acid  gradually  converts  it 
into  mercuric  chloride  and  nitrate,  which  pass  into  solution.  Boiling 
hydrochloric  acid  turns  it  grey,  some  mercury  being  separated,  and 
mercuric  chloride  dissolved.  Mercuric  nitrate  dissolves  it,  forming  mercuric 
chloride  and  mercurous  nitrate.  Alkaline  solutions  convert  it  into 
black  mercurous  oxide,  as  is  seen  in  black-wash,  made  by  treating  calomel 
with  lime-water  (2 HgCl  +  Ca(0H)2  =  Hg/J -I- CaCL^-t-HaO).  Solution  of 
ammonia  converts  it  into  a  grey  compound  (NHgHggCl),  which  is  the 
analogue  of  white  precipitate  (NH2Hg"Cl),  containing  Hg2  in  place 
of  Hg". 

Mercurous  iodide  (Hgl)  is  a  green  unstable  substance,  formed  when  iodine  is 
triturated  with  an  excess  of  mercury  and  a  little  alcohol.  The  beautiful  scarlet 
»ierc«rtc  lorfrrfe  (Hglj)  has  been  noticed  at  p.  178.  Its  vapour  has  the  remarkably 
Jiigh  specific  gravity  15 '68  (air  =  l).     The  iodide  dissolves  in  ether  and  in  alcohol. 

If  mercuric  iodide  be  dissolved  in  potassium  iddide,  the  solution  mixed  with 
potash,  and  some  ammonia  added,  a  brown  precipitate  is  formed,  which  may  be 
represented  by  the  formula  NHg"jI.H.^O;  its  formation  can  be  explained  by  the 
equation,  2Hgl2-t-3KHO  +  NH3  =  NHg2l.HjjO  +  3KI-h'JH20. 

A  solution  of  mercuric  iodide  in  potassium  iodide,  mixed  with  potash,  is  employed 
as  one  of  the  most  delicate  tests  {Nessler's  test)  for  ammonia  in  waters  ;  thi  grain  of 
ammonia  in  lialf  a  pint  of  water  is  distinctly  recognised  by  the  brown-yellow  tinge 
caused  by  this  test. 

292.  Stdphides  of  mercury. — When  mercury  is  triturated  with  sulphur, 
the  black  svhsuljjMde  of  mercurij  or  merairous  mlpJiide  (HgjS)  is 
formed ;    it   was   termed   by   old   writers  Ethiop's   mirieral,  and   is   an 


VKEMILION  OK  MERCURIC  SULPHIDE.  891 

unstable  compound  easily  resolvable  into  metallic  mercury  and  mercuric 
sulphide  (HgS).  The  latter  has  been  mentioned  as  the  principal  ore  of 
mercury,  and  is  important  as  composing  vi'rmilion.  The  native  mercuric 
sulphide,  or  cinnahar,  is  found  sometimes  in  amorphous  masses,  some- 
times crystallised  in  six-sided  prisms  varying  in  colour  from  dark  brown 
to  bright  red.  It  may  be  distinguished  from  most  other  minerals  by  its 
great  weight  (sp.  gr.  8  •2),  and  by  its  red  colour  when  scraped  with  a 
knife.  Neither  hydrochloric  nor  nitric  acid,  separately,  will  dissolve  it, 
but  a  mixture  of  the  two  dissolves  it  as  mercuric  chloride,  with  separa- 
tion of  sulphur.  Some  specimens  of  cinnabar  have  a  bright  red  colour, 
so  that  they  only  require  grinding  and  levigating  to  be  used  as  vermilion ; 
and  if  the  brown  cinnabar  in  powder  be  heated  for  some  time  to  120°  F. 
with  a  solution  of  sulphur  in  potash,  it  is  converted  into  vermilion. 

Of  the  artificial  mercuric  sulphide  there  are  two  varieties,  the  black, 
which  is  precipitated  when  corrosive  sublimate  is  added  to  hydro- 
sulphuric  acid  or  a  soluble  sulphide,  and  the  red  (vermilion),  into  which 
the  black  variety  is  converted  by  sublimation,  or  by  prolonged  contact 
with  solutions  of  alkaline  sulphides  containing  excess  of  sulphur,  though, 
so  far  as  is  known,  the  conversion  is  effected  without  chemical  change, 
the  red  sulphide  having  the  same  composition  as  the  black.  In  Idria 
and  Holland,  6  parts  of  mercury  and  1  of  sulphur  are  well  agitated 
together  in  revolving  casks  for  several  hours,  and  the  black  sulphide 
thus  obtained  is  sublimed  in  tall  earthen  pots  closed  with  iron  plates, 
when  the  vermilion  is  deposited  in  the  upper  part  of  the  pots,  and  is 
afterwards  ground  and  levigated.  The  sublimed  vermilion,  however, 
is  geufirally  inferior  to  that  obtained  by  the  wet  process,  of  which  there 
are  several  modifications.  One  of  the  processes  consists  in  triturating 
300  parts  of  mercury  with  114  parts  of  sulphur  for  two  or  three  hours, 
and  digesting  the  black  product,  at  about  120'  F.,  with  75  parts  of 
caustic  potash  and  400  of  water  until  it  has  acquired  a  line  red 
colour.  The  permanence  of  vermilion  paint  is,  of  course,  attributable  to 
the  circumstance  that  it  resists  the  action  of  light,  of  oxygen,  carbonic 
acid,  aqueous  vapour,  and  even  of  the  sulphuretted  hydrogen,  and  sul- 
phurous or  sulphuric  acid  which  contaminate  the  air  of  towns,  whereas 
the  red  paints  containing  lead  are  blackened  by  sulphuretted  hydrogen, 
and  all  vegetable  and  animal  reds  are  liable  to  be  bleached  by  atmospheric 
oxygen  and  by  sulphurous  acid. 

When  the  black  precipitated  mercuric  sulpliide  is  boiled  with  solution 
of  corrosive  sublimate,  it  is  converted  into  a  white  clilorosul phide  of 
mercurij,  HgCl2.2HgS,  which  is  also  formed  when  a  small  quantity  of 
hydrosulphuric  acid  is  added  to  corrosive  sublimate. 

It  is  remarkable  that  the  molecule  of  vermilion,  HgS,  occupies  3 
volumes  instead  of  2,  containing  2  volumes  of  mercury  vapour  combined 
with  1  volume  of  sul])hur  vapour.  The  anomaly  might  be  explained  on 
the  supposition  that  the  high  temperature  requisite  to  convert  the  ver- 
milion into  vapour  suffices  to  suspend  the  attraction  between  its  elements, 
so  that  the  vapour  of  which  the  specific  gravity  is  taken  is  not  really 
that  of  the  compound  of  mercury  and  sulphur  (which  should  occupy  2 
volumes),  but  a  mixtun'  of  the  2  volumes  of  mercur}'  vapour  and  1 
volume  of  sulphur  vapour,  occupying  3  volumes.  This  view  of  the  tem- 
porary decomposition  of  the  vapour  receives  some  slight  support  from  the 
*:onvertibility  of  the  black  into  the.  red  sulphide  by  sublimation. 


392  EXTRACTION   OF  PLATINUM. 

PLATINUM. 

Pt  =  1 97  •!  parts  by  weight. 

293.  Platinum  (ptathia,  Spanish  diminutive  of  silver)  is  always  found 
in  the  metallic  state  distributed  in  flattened  grains  through  alluvial  de- 
posits similar  to  those  in  -which  gold  is  found ;  indeed,  these  grains  are 
generally  accompanied  by  grains  of  gold,  and  of  a  group  of  very  rare 
metals  only  found  in  platinum  ores,  viz.,  palladium,  iridium,  osmium, 
rhodium,  and  ruthenium.  Eussia  furnishes  the  largest  supply  of  platinum 
from  the  Ural  Mountains,  but  smaller  quantities  are  obtained  from  Brazil, 
Peru,  Borneo,  Austi-alia,  and  California. 

The  process  for  obtaining  the  platinum  in  a  marketable  form  is  rather 
a  chemical  than  a  metallurgic  operation.  The  ore,  containing  the  grains 
of  platinum  and  the  associated  metals,  is  heated  with  a  dilute  mixture 
of  hydrochloric  and  nitric  acids,  by  which  the  platinum  is  converted  into 
perchloride  of  platinum  (PtCl^)  and  dissolved,  whilst  the  iridium  and 
osmium  are  left  in  the  residue.  The  solution  is  then  mixed  with  some 
chloride  of  ammonium,  which  combines  with  the  perchloride  of  platinum 
to  form  a  yellow  insoluble  salt  (ammonio-chloride  of  platinum  2NH4CI. 
PtCl^).*  This  precipitate  is  collected,  washed,  and  heated  to  redness, 
when  all  its  constituents,  except  the  platinum,  are  expelled  in  the  form 
of  gas,  that  metal  being  left  in  the  peculiar  porous  condition  in  which  it 
is  known  as  spongy  j'lcitmum.  To  convert  this  into  compact  platinum  is 
by  no  means  an  easy  task,  on  account  of  the  infusibility  of  the  metal,  for 
it  remains  solid  at  the  very  highest  temperatures  of  our  furnaces.  The 
spongy  platinum  is  finely  powdered  in  a  Avooden  mortar  (as  it  wovdd 
cohere  into  metallic  spangles  in  one  of  a  harder  material)  and  rubbed  to  a 
paste  with  water;  this  paste  is  then  rubbed  through  a  sieve  to  render  it 
perfectly  smooth  and  uniform,  and  introduced  into  a  cyhnder  of  brass,  in 
which  it  is  subjected  to  pressure  so  as  to  squeeze  out  the  water,  and  cause 
the  minute  particles  of  platinum  to  cohere  into  a  somewhat  compact  disk; 
this  disk  is  then  heated  to  Avhiteness,  and  beaten  into  a  compact  metallic 
ingot  by  a  heavy  hammer;  it  is  then  ready  for  forging. 

This  method  is  now  modified  by  fusing  the  ore  with  6  parts  of  lead,  and  treating 
the  alio}-  with  dilute  nitric  acid  (1:8)  which  dissolves  most  of  the  lead,  together  with 
copper,  iron,  palladium,  and  rhodium.  The  residue,  containing  platinum,  lead,  and 
iridium,  is  treated  with  dilute  aqua  regia,  which  leaves  the  iridiunt  undissolved. 
The  lead  is  precipitated  by  sulphuric  acid,  and  the  solution  ot  platinic  chloriile  treated 
as  above. 

Another  process  for  obtaining  platinum  from  its  ores  is  based  upon  the  tendency 
of  this  metal  to  .dissolve  in  melted  lead.  The  platinum  ore  is  fused  in  a  small 
reverberatory  furnace,  with  an  equal  weight  of  sulphide  of  lead  and  the  same  quantity 
of  oxide  of  lead,  when  the  sulphur  and  oxygen  escape  as  sulphurous  acid  gas,  and 
the  reduced  lead  dissolves  the  platinum,  leaving  undissolved  a  very  heavy  alloy  of 
osmium  and  iridium,  which  sinks  to  the  bottom.  The  upper  part  of  the  alloy  of 
lead  and  platinum  is  then  ladled  out  and  cupelled  (page  370),  when  the  latter  metal 
is  left  in  a  spongy  condition,  the  lead  being  removed  in  the  form  of  oxide.  The 
platinum  is  then  fused  by  the  aid  of  the  oxyhydrogen  blowpipe,  in  a  furnace  made  of 
lime  (fig.  273),  whence  it  is  poured  into  an  ingot  mould  made  of  gas  carbon.  The 
melted  platinum  absorbs  oxygen  mechanically  like  melted  silver,  and  evolves  it  again 
on  cooling  (see  page  371).  Platinum  articles  are  now  frequently  made  from  the  fused 
metal,  instead  of  from  that  which  has  been  welded. 

*  Wlien  rhodium  is  present,  the  liquid  from  which  this  precipitate  has  been  deposited 
will  have  a  rose  colour.  The  precipitate  is  then  mixed  with  bisulphate  of  potassium  and 
a  little  bisulphate  of  ammonium,  and  heated  to  redness  in  a  platinum  dish.  The  rhodium 
is  then  converted  into  a  double  sulphate  of  rhodium  and  potassium,  which  may  be  removed 
from  the  spongy  platinum  by  boiling  with  wat«r. 


PROPERTIES  OF  PLATINUM. 


803 


Fig.  273. 


Its  resistance  to  the  action  of  high  temperatures  and  of  most  chemical 
agents,  renders  platinum  of  the  greatest  service  in  chemical  operations. 
It  will  be  remembered  that  platinum  stills  are  employed,  even  on  the 
large  scale,  for  the  concentration  of  sulphuric  acid.  In  the  form  of 
basins,  small  crucibles,  foil,  and  wire,  this 
metal  is  indispensable  to  the  analytical 
chemist.  Unfortunately,  it  is  aofter  than 
silver,  and  therefore  ill  adapted  for  wear, 
and  is  so  heavy  (sp,  gr.  21  "5)  that  even 
small  vessels  must  be  made  very  thin  in  order 
not  to  be  too  heavy  for  a  delicate  balance. 
Since  it  expands  less  than  any  other  metal 
when  heated,  wires  of  platinum  may  be  sealed 
into  glass  without  danger  of  splitting  it  by 
unequal  contraction.  Its  malleability  and 
ductility  are  very  considerable,  so  that  it  is 
easily  rolled  into  thin  foil  and  drawn  into 
fine  wires ;  in  ductility  it  is  surpassed  only 
by  gold  and  silver,  and  it  has  been  drawn, 

by  an  ingenious  contrivance  of  Wollaston's,  into  wire  of  only  aowTT^'^ 
of  an  inch  in  diameter,  a  mile  of  which  (notwithstanding  the  high 
specific  gravity  of  the  metal)  would  only  weigh  a  single  grain.  This 
remarkable  extension  of  the  metal  Avas  effected  by  casting  a  cylinder 
of  silver  around  a  very  thin  platinum  wire  obtained  by  the  ordinary 
process  of  wire-drawing ;  when  the  cylinder  of  silver,  with  the  platinum 
wire  in  its  centre,  was  itself  drawn  out  into  an  extremely  thin  wire,  of 
course  the  platinum  core  would  have  become  inconceivably  thin,  and 
when  the  silver  casing  was  dissolved  off  by  nitric  acid,  this  minute  fila- 
ment of  platinum  was  left.  Platinum  is  sometimes  employed  for  the 
touch-holes  of  fowling-pieces  on  account  of  its  resistance  to  corrosion.  A 
little  iridium  is  sometimes  added  to  platinum  in  order  to  increase  its 
elasticity.  An  alloy  of  4  parts  platinum,  3  parts  silver,  and  1  part  copper 
is  used  for  pens. 

The  remarkable  power  possessed  by  platinum,  of  inducing  chemical 
combination  between  oxygen  and  other  gases,  has  already  been  noticed. 
Even  the  compact  metal  possesses  this  property,  as  may  be  seen  by  heat- 
ing a  piece  of  platinum  foil  to  redness  in  the  flame  of  a  gauze  gas-burner 
nipidly  extinguishing  the  gas,  and  turning  it  on  again,  when  the  cold 
stream  of  gas  will  still  maintain  the  metal  at  a  red  heat, 
in  consequence  of  the  combination  with  atmospheric 
oxygen  at   the  surface  of  the  platinum. 

A  similar  experiment  may  be  made  by  suspending  a 
coil  of  platinum  wire  in  the  flame  of  a  spirit-lamp  (fig. 
274),  and  suddenly  extinguishing  the  flame  when  the 
metal  is  intense!}'  heated,  by  placing  the  mouth  of  a  test- 
tube  over  it;  the  wire  will  continue  to  glow  by  inducing 
the  combination  of  the  spirit  vapour  with  oxygen  on  its 
surface.  By  substituting  a  little  ball  of  spongy  platinum 
for  the  coil  of  platinum  vvite,  and  mixing  some  fragrant  essential  oil  with 
the  spirit,  an  elegant  perfuming  lamp  has  been  contrived.  Upon  the  same 
principle  an  instantaneous  light  apparatus  has  been  made,  in  which  a  jet 
of  hydrogen  gas  is  kindled  by  falling  upon  a  fragment  of  cold  spongy 


Fig.  274. 


'394  OXIDES  OF  PLATINUM. 

platinum,  which  at  once  ignites  it  by  inducing  its  combination  with  the 
oxygen  condensed  within  the  pores  of  the  metal.  Spongy  platinum  is 
obtained  in  a  very  active  form  by  heating  the  ammonio-chloride  of 
platinum  very  gently  in  a  stream  of  coal  gas  or  hydrogen  as  long  as  any 
fumes  of  hydrochloric  acid  are  evolved. 

If  platinum  be  precipitated  in  the  metallic  state  from  a  solution,  it  is 
obtained  in  the  form  of  a  powder,  called  platinum-black,  which  possesses 
this  power  of  promoting  combination  with  oxygen  in  the  highest  perfec- 
tion. This  form  of  platinum  may  be  obtained  by  dissolving  the  metal 
in  aqua  regia,  which  converts  it  into  platinic  chloride  (PtCl^),  evaporating 
the  solution  to  dryness,  and  heating  the  residue  gently  on  a  sand-bath 
as  long  as  it  smells  strongly  of  chlorine.  The  platinous  chloride  (PtClg) 
thus  obtained  is  dissolved  in  a  solution  of  potash  and  heated  with  alcohol, 
when  the  platinum-black  is  precipitated,  and  must  be  filtered  oif,  washed, 
and  dried  at  a  gentle  heat. 

Platinum  in  this  form  is  capable  of  absorbing  800  times  its  volume  of 
oxygen,  which  does  not  enter  into  combination  with  it,  but  is  simply 
condensed  into,  its  pores,  and  is  available  for  combination  with  other  bodies. 
A  jet  of  hydrogen  allowed  to  pass  on  to  a  grain  or  two  of  this  powder  is 
kindled  at  once,  and  if  a  few  particles  of  it  be  thrown  into  a  mixture  of 
hydrogen  and  oxygen,  explosion  immediately  follows.  A  drop  of  alcohol 
is  also  inflamed  when  allowed  to  fall  upon  a  little  of  the  powder. 
Platinum  black  loses  its  activity  after  having  been  heated  to  redness. 
Recent  experiments  by  Berthelot  indicate  that  platinum  black  is  really 
an  oxide. 

Although  platinum  resists  the  action  of  hydrochloric  and  nitric  acids, 
unless  they  are  mixed,  and  is  unaffected  at  the  ordinary  temperature  by 
other  chemical  agents,  it  is  easily  attacked  at  high  temperatures  by  phos- 
phorus, arsenic,  carbon,  boron,  silicon,  and  by  a  large  number  of  the 
metals;  the  caustic  alkalies  and  alkaline  earths  also  corrode  it,  so  that 
some  discretion  is  necessary  in  the  use  of  vessels  made  of  this  costly 
metal.  When  platinum  is  alloyed  with  10  parts  of  silver,  both  metals 
may  be  dissolved  by  nitric  acid. 

29  i.  Oxides  of  platinum. — Only  one  compound  of  platinum  with 
oxygen  is  known  in  the  separate  state,  the  other  having  been  obtained 
in  combination  with  water.  Platinous  oxide,  PtO,  is  precipitated  as  a 
black  hydrate  by  decomposing  platinous  chloride  with  potash,  and 
neutralising  the  solution  with  dilute  sulphuric  acid.  It  is  a  feeble  base,  and 
decomposes  when  heated,  leaving  metallic  platinum.  Platinic  oxide,  PtO.^, 
is  also  a  weak  base,  but  occasionally  plays  the  part  of  an  acid,  whence  it 
is  sometimes  termed  platinic  acid.  Platinate  of  soda  (NagO.SPtOo.GAq.) 
may  be  crystallised  from  a  solution  of  the  hydrated  binoxide  in  soda. 
Platinate  of  lime  is  convenient  for  the  separation  of  platinum  from 
iridium,  which  is  generally  contained  in  the  commercial  metal;  for  this 
purpose,  the  platinum  is  dissolved  in  nitro-hydrochloric  acid,  the  solution 
evaporated  till  it  solidifies  on  cooling,  the  mixed  chlorides  of  iridium  and 
platinum  dissolved  in  water,  and  decomposed  with  an  excess  of  lime 
without  exposure  to  li<jht;  the  platinum  then  passes  into  solution  as 
platinate  of  lime,  and  the  platinic  acid  may  be  separated  from  the  filtered 
sokition,  though  still  in  combination  with  lime,  by  exposure  to  light. 
Acids  dissolve  platinic  oxide,  forming  salts  of  a  brown  colour  Avhich  have 


CHLORIDES  OF  PLATINUM.  395 ■ 

not  been  crystallised.  If  the  oxide  be  dissolved  in  diluted  sulphuric  acid 
and  the  solution  mixed  with  excess  of  ammonia,  a  black  precipitate  of 
fulminating  pZ«fm?(»i  is  obtained,  which  detonates  violently  at  about 
400°  F.  This  compound  is  said  to  have  a  composition  corresponding  to 
the  formula  NoHgPt''.  4H.2O,  or  a  combination  of  water  with  a  double 
molecule  of  ammonia  (ol^g^g),  in  which  4  atoms  of  hydrogen  are  replaced 
by  1  atom  of  tetratomic  platinum. 

Clilorides  of  platinum. — The  percldoride,  ov  platinic  chloride  (PtCl4),  is 
the  most  useful  salt  of  the  metal,  and  may  be  prepared  by  dissolving 
scraps  of  platinum  foil  in  a  mixture  of  four  measures  of  hydrochloric  acid 
with  one  of  nitric  acid  (100  grs.  of  platinum  require  2  measured  ounces 
of  hydrochloric  acid),  evaporating  the  liquid  at  a  gentle  heat  to  the  con- 
sistence of  a  syrup,  redissolving  in  hydrochloric  acid,  and  again  evapor- 
ating to  expel  excess  of  nitric  acid.  The  syrupy  liquid  solidifies,  on 
cooling,  to  a  red-brown  mass,  which  is  very  deliquescent,  and  dissolves 
easily  in  water  or  alcohol  to  a  red  brown  solution.  If  the  concentrated 
solution  be  allowed  to  cool  before  all  the  free  hydrochloric  acid  has  been 
expelled,  long  brown  prismatic  crystals  of  a  combination  of  platinic  chloride 
with  hydrochloric  acid  are  obtained  (PtCl4.2HCl.6Aq).  Platinic  chloride  is 
remarkable  for  its  disposition  to  form  sparingly  soluble  double  chlorides 
with  the  chlorides  of  the  alkali  metals  and  the  hydrochlorates  of  organic 
bases,  a  property  of  great  value  to  the  chemist  iu  effecting  the  detection 
and  separation  of  these  bodies. 

A  good  example  of  this  has  lately  been  afforded  in  the  separation  of 
potassium,  rubidium,  and  caesium.  The  chlorides  of  these  three  metals 
having  been  separated  from  the  various  other  salts  contained  in  the 
mineral  water  in  which  they  occur,  are  precipitated  with  platinic  chloride 
which  forms  combinations  with  all  the  three  chlorides.  The  platino- 
chloride  of  potassium  is  more  easily  dissolved  by  boiling  water  than  those 
of  rubidium  and  caesium,  and  is  removed  by  boiling  the  mixed  precipitate 
with  small  portions  of  water  as  long  as  the  latter  acquires  a  yellow  colour. 
The  remaining  platino-chlorides  of  rubidium  and  caesium  are  then  heated 
in  a  current  of  hydrogen,  which  reduces  the  platinum  to  the  metallic  state, 
and  the  chlorides  may  then  be  extracted  by  water,  in  which  they  are  very 
soluble. 

Platijw-cldoride  of  potassium  (2KCl,PtCl4)  forms  minute  yellow  octa- 
hedral crystals  ;  those  of  rubidium  and  caesium  have  a  similar  composition 
and  crystalline  form. 

Platino -chloride  of  sodium  differs  from  these  in  being  very  soluble  in 
water  and  alcohol ;  it  may  be  crystallised  in  long  red  prisms,  having  the 
composition  2NaCl,PtCl4,6Aq. 

Ammonio-chloridc  of  platimim  (2NH4Cl.PtCl4)  has  been  already  noticed 
as  the  form  in  which  platinum  is  precipitated  iu  order  to  separate  it  from 
other  metals.  It  crystallises,  like  the  potassium-salt,  in  yellow  octahedra, 
which  are  very  sparingly  soluble  in  water  and  insoluble  in  alcohol.  It 
is  the  form  into  which  nitrogen  is  finally  converted  in  analysis  in  order  to 
determine  its  weight.  When  heated  to  redness,  this  salt  leaves  a  residue 
of  spongy  platinum.  Platinic"  chloride  is  sometimes  used  for  browning 
gun-barrels,  &c.,  under  the  name  of  muriate  <f  platina. 

.  Protochloride  of  platinum  or  platinous  chloride  (PtCl^). — Platinic  chloride  may  be 
heated  to  450"  F.  without  decomposition,  but  above  that  temjierature  it  evolves 
chlorine,  and  is  slowly  converted  into  the  platinous  chloride,  which  is  reduced,  at 


.'^96  PLATOSAMINE  COMPOUNDS. 

a  much  higher  temperature,  to  the  metallic  state.  Platinous  chloride  forms  a  dingy 
green  powder,  which  is  insoluble  in  water  and  in  nitric  and  sulphuric  acids,  but 
dissolves  in  hot  hydrochloric  acid,  and  in  solution  of  platinic  chloride,  yielding  in 
the  former  a  bright  red,  in  the  latter  a  very  dark  brown-red  solution.  Its  solution' 
in  hydrochloric  acid  is  not  precipitated  by  potassium  chloride,  but  a  soluble  double 
chloride  (2KCl,PtCl2)  may  be  crystallised  from  the  liquid.  If  ammonium  chloride 
be  added  to  the  hydrochloric  solution,  a  double  salt  2NH4Cl.PtCl2  may  be  obtained 
in  yellow  crystals  by  evaporation.  If,  instead  of  ammonium  chloride,  free  ammonia 
be  added  in  excess  to  the  boiling  solution  of  platinous  chloride  in  hydrochloric  acid, 
brilliant  green  needles  (green  salt  of  Magnus)  are  deposited  on  cooling,  which  con- 
tain the  elements  of  platinous  chloride  and  ammonia  PtCljCNHs)., ;  but  from  the 
behaviour  of  this  compound  with  chemical  agents,  its  true  formula  would  appear  to 
be  NjIIgPfCla,  in  which  the  place  of  2  atoms  of  hydrogen  in  2  molecules  of  .sal- 
ammoniac  is  occupied  by  platinum.  By  heating  this  salt  with  an  excess  of  ammonia, 
the  solution,  on  cooling,  deposits  yellowish-white  prismatic  crystals  of  hydrochlorate 
of  diplatosamine ;  N4HioPt".2H.Cl.Aq.,  the  production  of  which  may  be  represented 
by  the  equation  N.2HgPt"Cl2-i-2NH3=N4HioPt".2HCl.  By  decomposing  a  solution 
of  this  salt  with  silver  sulphate,  the  sulphate  of  diplatosamine  is  obtained ;  N4Hi0Pt". 
2HCl-f  Ag20.S03r:N4HioPt".H20.S03  +  2AgCl. 

When  the  solution  of  diplatosamine  sulphate  is  treated  with  barium  hydrate, 
barium  sulphate  is  precipitated,  and  a  powerfully  alkaline  solution  is  obtained, 
which  yields  crystals  of  diplatosamine  hydrate  N4H]QPt".2HjO,  a  strong  alkali 
which  may  be  regarded  as  a  compound  of  water  with  4  molecules  of  ammonia  (N4HJJ), 
in  M'hich  2  atoms  of  hydrogen  are  replaced  by  platinum.  The  diplatosamine  hydrate 
has  a  strong  resemblance  to  the  alkalies,  eagerly  absorbing  carbonic  acid  from  the 
air,  and  expelling  ammonia  from  its  salts.  When  the  hydrate  of  diplatosamine  is 
heated  to  230°  F.  it  gives  off  water  and  ammonia,  and  becomes  converted  into  a  grey 
insoluble  substance,  which  is  platosamine  hydrate,  N2H4Pt".H20,  and  may  be 
regarded  as  a  compound  of  water  with  a  double  molecule  of  ammonia  (N.2Hb),  ia 
which  one-third  of  the  hydrogen  is  replaced  by  platinum.  This  .substance  is  also  a 
base,  and  forms  salts,  most  of  which  are  insoluble  ;  the  sulphate  of  platosamine, 
N2H4Pt.H2O.SO3.Aq.,  may  be  regarded  as  ammonium  sulphate  {NH4)4S04,  in  which 
2  atoms  of  the  hydrogen  are  replaced  by  platinum.  The  hydrochlorate  of  platosamine 
(N2H4Pt.2HCl)  is  isomeric  with  the  green  salt  of  Magnus,  and  may  be  obtained 
from  that  compound  by  dissolving  it  in  a  hot  solution  of  ammonium  .sulphate 
from  which  it  crystallises  on  cooling.* 

If  the  platosamine  hydrochlorate,  suspended  in  boiling  water,  be  treated  witl^ 
chlorine,  it  is  converted  into  platinamine  hydrochlorate,  N._jH2Pt'''.4HCl,  which  may 
be  represented  as  ammonium  chloride,  in  which  4  atoms  of  hydrogen  have  beeu 
replaced  by  1  atom  of  platinum  in  the  condition  in  which  it  exists  in  PtCl4,  where 
it  is  equivalent  to  H4.  The  conversion  of  the  platosamine  hydrochlorate  into 
platinaniine  hydrochlorate  may  be  represented  by  the  equation,  N.^H4Pt.2HCl-hCl3 
=  N2H2Pt.4HCl.  By  boiling  the  hydrochlorate  of  platinamine  with  silver  nitrate^ 
it  is  converted  mio  jilatinamine  nitrate  N2H2Pt(HN03)4,  and  when  this  is  dissolved 
in  boiling  water  and  decomposed  by  ammonia  the  platinamine  hydrate  (NjH2Pt,4H20), 
is  obtained  in  yellow  prismatic  crystals,  having  the  same  composition  as  that  assigned 
to  fulminating  platinum. 

Several  other  platinum  compounds  derived  from  ammonia  have  been  obtained,  but 
cannot  at  present  be  so  conveniently  classified.  The  following  table  exhibits  the 
composition  of  those  here  enumerated,  the  platinum,  as  it  exists  in  platinous  chloride 
(PtClg),  occupying  the  place  of  2  atoms  of  hydrogen,  being  represented  by  Pt",  and 
the  platinum,  as.it  exists  in  platinic  chloride  (PtCl4)  occupying  the  place  of  4  atoms 
of  hydrogen,  by  Pt''' : — 

Platosamine  hydrate,  .         .         N2H4Pt".H20  ' 

hydrochlorate,        .         N2H4Pt".2HCl 
„  .sulphate,         .        .         N2H4Pt".H2S04Aq. 

Platinamine  hydrate,         .         .         N2H2Pt".4H20 
,,  hydrochlorate,        .         U2H2Pti'.4HCl 

*  The  salts  of  diplatosamine  are  distinguished  from  those  of  platosamine  by  the  action  of 
nitrous  acid,  which  gives  a  fine  blue  or  green  precipitate  or  coloration  with  the  foniier.  For 
the  cause  of  this  change,  and  for  many  other  interesting  points  in  the  history  of  these  pla- 
tinum compounds,  the  reader  is  referred  to  the  elaborate  and  accurate  memoir  by  Hadow.— 
Jmiriml  of  the  Chemical  Society,  August  1866. 


PALLADIUM — RHODIUM.  397 

Diplatosamine  hydrate,      .         .         N4HioPt".2HjO 

,,  hydrochlorate,     .         N4HjoPt".2HCl.A(]. 

„  sulphate,        ,     ,         N^HjoPt^'.  H^SO^ 

Some  of  the  salts  of  dipl^tinaminc  (N.4HgPt''')  have  been  obtained,  this  base  being 
tlerived  from  4  molecules  of  ammonia  in  which  H4  have  been  replaced  by  Pt'^. 

.  The  sulphides  of  platinum  correspond  in  composition  to  the  oxides  and  chlorides, 
and  may  be  obtained  by  the  action  of  hydrosulphuric  acid  upon  the  respective  chlo- 
rides, as  black  .precipitates. 

•295.  Palladium  (Pd  =  106".'))  is  found  in  small  quantity  associated  with  native 
gold  and  platinum.  It  presents  a  great  general  resemblance  to  platinum,  but  is  dis- 
tinguished from  it  by  being  far  more  easily  oxidised,  and  by  its  special  attraction  for 
cyanogen,  with  which  it  forms  an  insoluble  compound.  This  circumstance  is  taken 
advantage  of  in  separating  palladium  from  the  platinum  ores,  for  which  pui-pose  the 
solution  from  Avhicli  the  greater  part  of  the  "platinum  has  been  precipitated  by 
ammonium  chloride  (page  392)  is  neutralised  with  sodium  carbonate,  and  mixed  with 
solution  of  mercuric  cyanide  Hg(CN)2,  when  a  yellowish  precipitate  of  palladium 
cyanide  is  obtained,  yielding  spongy  palladium  when  heated,  which  may  be  welded 
into  a  compact  form  in  the  same  manner  as  platinum.  When  alloyed  with  native 
gold,  palladium  is  separated  by  fusing  the  alloy  with  silver,  and  boiling  it  with  nitric 
acid,  which  leaves  the  gold  undissolved.  The  silver  is  precipitated  from  the  solu- 
tion as  chloride,  by  adding  sodium  chloride,  and  metallic  zinc  is  placed  in  the  liquid, 
which  precipitates  the  palladium,  lead,  and  copper,  as  a  black  powder.  This  is 
dissolved  in  nitric  acid,  and  the  solution  mixed  Avith  an  excess  of  ammonia,  which 
precipitates  the  lead  oxide,  leaving  the  copper  and  palladium  in  solution.  On  adding 
hydrochloric  acid  in  slight  excess,  a  yellow  precipitate  ol  pallctdanmic  hydrochlorate 
(N2H4Pd,2HCl)  is  obtained,  which  leaves  metallic  palladium  when  heated. 

Palladium  is  harder  than  platinum  and  much  lighter  (sp.  gr.  11  o) ;  it  is  malleable 
Mid  ductile  like  that  metal,  and  somewhat  more  fusible,  though  it  cannot  be  melted 
in  an  ordinary  furnace.*  It  is  unchangeable  in  air  unless  heated,  when  it  becomes 
blue  from  superficial  oxidation,  but  regains  its  whiteness  when  further  heated,  the 
oxide  being  decomposed.  Unlike  platinum,  it  may  be  dissolved  by  nitric  acid,  foun- 
\ng  palladium  nitrate,  VA{'^0-^.2,  which  is  sometimes  employed  in  analysis  for  pre- 
cipitating iodine  from  the  iodides,  in  the  form  of  black  palladium  iodide  (Pdlj). 
Palladium  is  useful,  ou  account  of  its  hardness,  lightness,  and  resistance  to  tarnish, 
in  the  construction  of  philosophical  instruments ;  alloyed  with  twice  its  weight  of 
silver,  it  is  used  for  small  weights. 

Of  the  oxides  0/ palladium,  two  correspond  with  those  of  platinum,  and  a  basic 
oxide  (PdO)  has  been  obtained  by  gently  heating  the  dioxide.  Palladia  chloride 
(PdCl^)  is  very  unstable,  being  easily  decomposed,  even  in  solution,  into  palla- 
dious  chloride  (PdClo)  aud  free  chlorine.  Both  the  chlorides  form  double  salts 
with  the  alkaline  chlorides,  those  containing  the  palladious  chloi'ide  (PdClg)  having 
a  dark  green  colour.  Pulverulent  2>aWa^M(m  carbide  is  formed  when  the  metal  is 
heated  in  the  Hame  of  a  spirit-lamp. 

,  296.  Rhodium  (Ro  =  104'3),  another  of  the  metals  associated  with  the  ores  of 
platinum,  has  acquired  its  name  from  the  red  colour  of  many  of  its  salts  {ftohov,  a  rose). 
It  is  obtained  from  the  solution  of  the  ore  in  aqtia  regia  by  precipitating  the  platinum 
with  ammonium  chloride,  neutralising  with  sodium  carbonate,  adding  mercuric 
cyanide  to  separate  the  palladium,  and  evaporating  the  filtered  solution  to  dryness 
AvitTi  excess  of  hydrochloric  acid.  On  treating  the  residue  with  alcohol,  the  double 
chloride  of  rhodium  and  sodium  is  left  undissolved  as  a  red  powder.  By  heating  this 
in  a  tube  through  which  hydrogen  is  passed,  the  rhodium  is  reduced  to  the  metallic 
state,  and  the  sodium  chloride  may  be  washed  out  with  water,  leaving  a  grey  powder 
of  metallic  rhodium,  which  is  fused  by  the  oxyhydrogen  blowpipe  with  greater 
difficulty  than  platinum,  and  forms  a  very  hard  malleable  metal  not  dissolved  even 
by  aqua  rcgict,  although  this  acid  dissolves  it  in  ores  of  platinum,  because  it  is 
alloyed  with  other  metal.s.  If  platinum  be  alloyed  with  30  per  cent,  of  rhodium, , 
however,  it  is  not  affected  bj'  aqua  regia,  which  will  probably  render  the  alloy  useful 
for  chemical  vessels.     Rhodium  may  be  brought  into  solution  by  fusing  it  with  bisul- 

*  Palladium,  at  a  slightly  elevated  temperature,  absorbs,  niechanically,  many  times  its 
volume  of  hydrogen.  Hammered  palladium  foil  condenses  640  times  its  volume  of  hydro- 
gen, below  212°  F.,  though  it  has  not  the  power  of  absorbing  oxygen  or  nitrogen.  Foil 
"KHide  from  fused  palladium  onlv  absorbs  68  times  its  volume  of  hydrogen.— Graham,  Proc. 
fioy.  .S')c.,  June  1866. 


398  OSMIUM-^RUTHENIUM. 

phate  of  potash,  when  sulphurous  acid  gas  escapes,  and  a  double  sulphate  of  rhodium 
and  potassium  is  formed,  which  gives  a  pink  solution  with  water.  Finely-divided 
rhodium  is  oxidised  when  heated  in  air.  It  appears  to  form  two  oxides,  the  prot- 
oxide  {RoO),  which  is  very  little  known,  and  the  sesquioxide  (Ro^Oj),  obtaiued  by  fus- 
ing rhodium  with  potassium  carbonate  and  nitre,  and  washing  the  fused  mass  with 
water,  which  leaves  an  insoluble  compound  of  the  sesquioxide  with  jwtash  ;  on  treat- 
ing this  with  hydrochloric  acid,  the  sesquioxide  of  rhodium  is  left.  It  is  not  decom- 
posed by  heat,  and  is  insoluble  in  acids,  though  it  is  a  basic  oxide,  and  its  salts, 
which  have  a  red   colour,  are  obtained  by  indirect  methods. 

Trichloride  of  rhodium  (R0CI3)  has  a  browuish-black  colour,  and  does  not  crystal- 
lise. Its  aqueous  solution  is  red,  and  it  forms  crystallisable  double  salts  mth  the 
alkaline  chlorides,  which  have  a  fine  red  colour.  The  double  chloride  of  rhodium 
and  sodium  (3NaCl.RoCl3).9Aq.,  is  prepared  by  heating  a  mixture  of  pulverulent 
rhodium  and  .sodium  chloride  in  a  current  of  chlorine.  It  crystallises  in  red  octa- 
hedra.  On  boiling  a  solution  of  trichloride  of  rhodium  with  ammonia  in  excess,  a 
yellow  ammoniated  salt  (R0CI3.5NH3)  may  be  crystallised  out,  from  which  metallic 
rhodium  may  be  obtained  by  ignition. 

With  sulphur,  rhodium  combines  energetically  at  a  high  temperature  ;  a  proto- 
sulphide  and  a  sesquisulphide  have  been  obtained. 

An  alloy  of  gold  with  between  30  and  40  per  cent,  of  rhodium  has  been  found  in 
Mexico. 

297.  O.SMIUM  (Os  =  199)  is  characterised  by  its  yielding  a  very  volatile  acid  oxide 
(osmic  anhydride,  OSO4),  the  vapours  of  which  have  a  very  irritating  odour  [bifi-h, 
odour).  It  occurs  in  the  ores  of  platinum  in  flat  scales,  consisting  of  an  alloy  of 
osmium,  iridium,  ruthenium,  and  rhodium.  This  alloy  is  also  found  associated 
with  native  gold,  and,  being  very  heavy,  it  accumulates  at  the  bottom  of  the  crucible 
in  which  the  gold  is  melted.  The  osmium-  alloy  is  extremely  hard,  and  has  been  used 
to  tip  the  points  of  gold  pens.  When  a  grain  of  it  happens  to  be  present  in  the  gold 
which  is  being  coined,  it  often  seriously  injures  the  die.  When  the  platinum  ore 
is  treated  with  aqua  regia,  this  alloy  is  left  undissolved,  together  with  grains  of 
chrome  iron  ore  and  titanic  iron.  To  extract  the  osmium  from  this  residue,  it  is 
heated  in  a  porcelain  tube  through  which  a  current  of  dry  air  is  passed,  when  the 
osmium  is  converted  into  osmic  anhydride,  the  vapour  of  which  is  carried  forward 
b\-  the  current  of  air  and  condensed  in  bottles  provided  to  receive  it.  The  osmic 
anhydride  forms  colourless  prismatic  crystals  which  fuse  and  volatilise  below  the 
boiling-point  of  water,  yielding  a  most  irritating  vapour  resembling  chlorine.  It  is 
very  soluble  in  water,  giving  a  solution  which  exhales  the  same  odour  and  stains  the 
skin  black  ;  tincture  of  galls  gives  a  blue  precipitate  with  the  solution.  Its  acid 
properties  are  feeble,  for  it  neither  reddens  litmus  nor  decomposes  the  carbonates, 
and  its  salts  are  decomposed  by  boiling  their  solutions.  By  adding  hydrosulphuric 
acid  to  a  solution  of  osmic  acid,  the  osmium  tetrasulphidc  (OsS^)  is  obtained  as  a  black 
precipitate,  and  if  this  be  carefully  dried  and  heated  in  a  crucible  made  of  gas-carbon, 
metallic  osmium  is  obtained  as  a  brittle  mass  (sp.  gr.  21*4),  which  is  not  fused  even 
by  the  oxyhydrogen  blowpipe,  and  is  not  soluble  in  acids.  When  obtaiued  by  other 
processes  in  a  finely-divided  state,  osmium  oxidises  even  at  the  ordinary  temperature, 
and  emits  the  odour  of  osmic  anhydride.  In  thij  state,  also,  it  may  be  dissolved  by 
nitric  acid,  which  converts  it  into  osmic  acid. 

By  dissolving  osmic  anhydride  in  potash  and  adding  alcohol,  the  latter  is  oxidised 
at  the  expense  of  the  potassium  osmiate,  and  rose-coloured  octahedral  crystals  of 
potassium  osmite  (K20804,2Aq.)  are  obtained  ;  the  osmious  acid  has  not  been  isolated. 
A  protoxide  and  a  dioxide  of  osmium  have  been  obtained. 

Osmium  appears  to  form  four  chlorides — dichloride  (OsClj),  ti-ichloride  (OsCl,), 
tetrachloride  (OSCI4),  and  hexachloride  (OsCIg).  The  dichloride  and  tetrachloride  are 
formed  by  the  direct  combination  of  chlorine  with  osmium  ;  the  former  sublimes  in 
green  needles,  which  yield  a  blue  solution  in  water,  soon  absorbing  ox3'gen  from  the 
air  and  becoming  converted  into  tetrachloride.  By  heating  a  mixture  of  pulverulent 
o.smium  with  potassium  chloride  in  a  current  of  chlorine,  a  double  chloride  of  osmium 
and  potassium  (2KCl,OsCl4)  is  obtained,  which  is  sparingly  soluble,  and  crystallises 
in  octahedra  like  the  corresponding  salt  of  platinum.  When  decomposed  with  silver 
nitrate  it  gives  a  dark  green  precipitate  (2AgCl,OsCl4). 

298.  RuTHKN'iUM  (Ru  =  104'2).* — In  the  process  of  exti-acting  osmium  from  the 

*  A  new  mineral  found  in  Borneo,  and  named  laurite,  contains  sulphides  of  rutfacniam 
and  osmium.     It  forms  small  lustrous  granules. 


ANALYSIS  OF  PLATINUM  OEK. 


399 


residue  left  on  treating  the  platinum  ore  with  aqua  reqia,  by  heating  in  a  current  of 
air,  square  prismatic  crystals  of  ruthenium  dioxide  (RuO^)  are  deposited  nearer  to 
the  heated  portion  of  the  tube  than  the  osinic  anhydride,  for  the  dioxide  is  not  itself 
volatile,  being  only  carried  forward  mechanically.  "W  hen  ruthenium  dioxide  is  heated 
in  hydrogen,  iDftalUc  rutlicnium  is  obtained  as  a  hard,  brittle,  almost  infusible  metal, 
which  is  scarcely  affected  even  by  aqua  regia.  The  protoxide  of  ruthcrdum  (RuO)  is 
a  dark  grey  powder  insoluble  in  acids.  The  sesqnioxidc  (RujOg)  and  the  dioxide 
(RuOg)  have  feebly  basic  properties.  The  sesquioxide  is  not  decomposed  by  heat. 
The  anhydrous  dioxide  is  a  greenish-blue  powder.  Muthenic  anhydride  (RuOg)  is 
known  only  in  combination  with  bases. 

299.  Iridium  (Ir  =  197'l),  named  from  Iris,  the  rainbow,  in  allusion  to  the  varied 
colours  of  its  compounds,  has  been  mentioned  above  as  occurring  in  the  insoluble 
alloy  from  the  platinum  ores.  It  is  also  sometimes  found  separately,  and  occasion- 
ally alloyed  with  platinum,  the  alloy  crystallising  in  octahedra,  which  are  even 
heavier  than  platinum  (sp.  gr.  22"3).  If  the  insoluble  osmiridium  alloy  left  by  aqtia 
regia  be  mixed  with  common  salt  and  heated  in  a  current  of  chlorine,  a  mixture  of 
the  sodio-chlorides  of  the  metals  is  obtained,  and  may  be  extracted  by  boiling  water. 
If  the  solution  be  evaporated  and  distilled  with  nitric  acid,  the  osmium  is  distilled 
off  as  osmic  acid,  and  by  adding  ammonium  chloride  to  the  residual  solution,  the 
iridium  is  precipitated  as  a  dark  red-brown  ammonio-coloride,  2NH4Cl.IrCl4,  which 
leaves  metallic  iridium  when  heated.  Like  platinum,  it  then  forms  a  grey  spongy 
mass,  but  is  oxidised  when  heated  in  air,  and  may  be  fused  with  the  oxyhydrogen 
blowpipe  to  a  hard  brittle  mass  (sp.  gr.  22"4),  which  does  not  oxidise  in  air.  Like 
rhodium,  it  is  not  attacked  by  aqua  regia,  unless  alloyed  with  platinum.  The  pro- 
duct of  the  oxidation  of  finely-divided  iridium  in  air  is  the  sesquioxide  (Ir^Og),  which 
is  a  black  powder  used  for  imparting  an  intense  black  to  porcelain  ;  it  is  insoluble 
in  acids.  The  protoxide  (IrO)  is  also  more  easily  acted  upon  bj'  alkalies  than  bj- 
acid.T  ;  its  solution  in  potash  becomes  blue  when  exposed  to  air,  from  the  formation 
of  the  dioxide  (Ir02).  The  trioxide  (IrOs)  is  green.  The  dichloridc  (IrCl.^)  and 
tetrachloride  (IrClj)  of  iridium  resemble  the  corresponding  chlorides  of  platinum  in 
forming  double  salts  with  the  alkaline  chlorides.  There  is  also  a  trichloride  (IrClj), 
the  solution  of  which  has  a  green  colour,  and  gives,  a  yellow  precipitate  with  mer- 
curous  nitrate,  and  a  blue  x*recipitate,  soon  becoming  white,  with  silver  nitrate. 
Iridium  resembles  palladium  in  its  disposition  to  combine  with  carbon  when  heated 
in  the  Hame  of  a  spirit-lamp. 

An  iridio-platinum  alloy  containing  from  15  to  20  per  cent,  of  iridium  has  been 
found  very  useful  for  making  standard  rules  and  weights,  on  account  of  its  indestruc- 
tibility, extreme  rigidity,  hardiies.s,  and  high  density. 

300.  The  following  table  exhibits  a  general  view  of  the  analytical  process  by  which 
the  remarkable  metals  associated  in  the  ores  of  platinum  may  be  separated  from 
each  other,  omitting  the  minor  details  which  are  requisite  to  ensure  the  purity  of 
each  metal  :— 

Analysis  of  the  Ore  of  Platinum. 

Boil  with  aqua  regia. 


Dissolved. 
Platinum,  Palladium,  Rhodium. 

Add  ammonium  chloride. 

Undissolved. 
Iridium,  Osmium,  Ruthenium. 
Clirome  iron,  Titanic  iron,  <fec. 

Heat  in  cuiTent  of  dry  air. 

Precipitated ; 

Platinum 

as 

2NH4CI,  PtCl4. 

Solution  ; 

Neutralise  with  soda  carbonate  ; 

add  mercuric  cyanide. 

VolatllLsed 
Osmium 
as  OsOj. 

Carried 
forward  by 
tlie  cun-ent; 
Ruthenium 

as  RuOj. 

Residue  ; 

Mix  with  sodium 

chloride,  and  heat  in 

current  of  chlorine. 

Treat  with  boiling  water. 

Precipitated  ; 
Palladium 
as  PdCy2. 

Solution  ; 

Evaporate  with 

hydrochloric  acid 

Treat  with  alcohol. 

Insoluble. 

Rhodium 

asSNaCLRoCls. 

Dissolved. 

Iridium 

as2NaCl.IrCl4. 

Residue. 
Titanic  iron. 
Chrome  iron, 

The  group  0^  platinoid  metals  exhibits  some  very  remarkable  features,  and  it  is  to 
be  regretted  that  this  group  is  comparatively  imperfectly  known  in  consequence  of 


400  OtOld. 

the  difficulty  aud  expense  attendant  upon  the  purification  of  the  metals.  Its  mem- 
bers may  be  arranged  in  two  divisions,  the  metals  in  each  agreeing  closely  in  their 
iitomic  freights  and  specific  gravities. 


Atomic  weight. 

Sp.  gi-. 

Atomic  weight. 

Sp.gr. 

Platinum, 

197  1 

21-5 

Palladium,    . 

106-5 

11 

Osmium, 

1990 

22-4 

Rhodium, 

104-3 

11-4 

Iridium, 

197-1 

22-4 

Ruthenium,  . 

104-2 

11-4 

Through  osmium,  this  group  of  elements  is  connected  with  the  group  containing 
antimony,  arsenic,  and  phospnorus,  which  osmium  resembles  in  the  facility  with 
which  it  is  oxidised,  and  in  the  volatility  of  the  oxide  formed.  Palladium  connects 
it  with  mercury  and  silver,  by  its  solubility  in  nitric  acid,  and  its  special  attraction 
for  cyanogen  and  iodine. 

301.  Davyum  is  a  new  metal  which  lias  been  found  in  .small  quantity  in  the  ores 
of  platinum.  It  is  a  silverj'  metal  which  dissolves  in  aqua  rcgia.  The  double 
chloride  of  davyum  and  sodium  is  nearly  insoluble  in  water  and  alcohol,  which  dis- 
tinguishes davyum  from  the  other  platinum  metals.  Its  solutions  give  a  red  colour 
with  potassium  sulphocyanide.     The  specific  gravity  of  the  metal  is  about  9  -4. 

GOLD. 

An  =  196 -6  parts  by  weight. 

30-2.  Gold  is  one  of  those  few  metals  which  are  always  found  in  the 
metallic  state,  and  is  remarkable  for  the  extent  to  Avhich  it  is  distri- 
buted, though  in  small  quantities,  over  the  surface  of  the  earth.  The 
principal  supplies  of  this  metal  are  derived  from  Australia,  California, 
Mexico,  Brazil,  Peru,  and  the  Uralian  Mountains.  Small  quantities 
have  been  occasionally  met  with  in  our  own  islands,  particularly 
at  Wicklow,  at  Cader  Idris  in  Wales,  Leadhills  in  Scotland,  and  in 
CornwalL 

The  mode  of  the  occurrence  of  gold  in  the  mineral  kingdom  resembles 
tliat  of  the  ore  of  tin,  for  it  is  either  found  disseminated  in  the  primitive 
I'ocks,  or  in  alluvial  deposits  of  sand,  which  appear  to  have  been  formed 
by  the  disintegration  of  those  rocks  under  the  continued  action  of  torrents. 
In  the  former  case,  the  gold  is  often  found  crystallised  in  cubes  and  octa- 
hedra,  or  in  forms  derived  from  these,  and  sometimes  aggregated  together 
in  dendritic  or  branch-like  forms.  In  the  alluvial  deposits,  the  gold  is 
usually  found  in  small  scales  (gold  dust),  but  sometimes  in  masses  of  con- 
siderable size  (nuggets),  the  rounded  appearance  of  which  indicates  that 
they  have  been  subjected  to  attrition. 

The  extraction  of  the  particles  of  gold  from  tlie  alluvial  sands  is  effected 
by  taking  advantage  of  the  high  specific  gravity  of  the  metal  (19-3)  which 
causes  it  to  remain  behind,  whilst  the  sand,  which  is  very  much  lighter 
(sp.  gr.  2-6),  is  carried  away  by  water.  This  washing  is  commonly  per- 
formed by  hand,  in  wooden  or  metal  bowls,  in  which  the  sand  is  shaken 
u])  with  water,  and  the  lighter  portipns  dexterously  poured  off,  so  as  to 
leave  the  grains  of  gold  at  the  bottom  <)f  the  vessel.  On  a  somewhat 
larger  scale,  the  auriferous  sand  is  washed  in  a  cradle  or  inclined  wooden 
trough,  furnished  with  rockers,  and  with  an  opening  at  the  lower  end  for 
the  escape  of  the  water.  The  sand  is  thrown  on  to  a  grating  at  the  head 
of  the  cradle,  Avhich  retains  the  large  pebbles,  whilst  the  sand  and  gold 
pass  through,  the  former  being  washed  away  by  a  stream  of  water  which 
is  kept  flowing  through  the  trough. 

When  the  gold  is  disseminated  through  masses  of  quartz  or  other  rock, 
much  labour  is  expended  in  crushing  the  latter  before  the  gold  can  be 


SMELTING  OF  GOLD  ORES.  ;401 

separated.  This  is  effected  either  by  passing  the  coarse  fmguients  between 
lieavy  rollers  of  hard  cast-iron,  or  by  stamping  them,  with  wooden  beams 
shod  "with  iron,  in  troughs  through  which  water  is  kept  continually 
flowing. 

In  some  cases  it  is  found  advantageous  to  smelt  tlie  ore  by  fusing  it 
with  some  substance  capable  of  uniting  with  the  gold,  and  of  being  after- 
wards readily  separated  from  it.  Lead  is  peculiarly  adapted  for  this 
purpose  ;  the  crushed  ore,  being  mixed  with  a  suitable  proportion,  either 
of  metalHc  lead,  or  of  litharge  (oxide  of  lead)  and  charcoal,  or  cA'en  of 
galena  (sulphide  of  lead),  together  with  some  lime  and  oxide  of  iron  or  clay, 
to  flux  the  silica,  is  fused  on  the  hearth  of  a  reverberatory  furnace,  when 
the  fused  lead  dissolves  the  particles  of  gold,  and  collects  beneath  the 
lighter  slag.  The  lead  is  afterwards  separated  from  the  gold  by  cupellation 
(see  page  370). 

In  smelting  the  ores  of  gold  in  Hungary,  the  metal  is  concentrated  by 
means  of  sulphide  of  iron.  The  ore  consists  of  quartz  and  iron  pyrites 
(disulphide  of  iron),  containing  a  little  gold.  On  fusing  the  crushed  ore 
with  lime,  to  flux  the  quartz,  the  pyrites  loses  half  its  sulphur,  and 
becomes  ferrous  sulphide  (FeS),  which  fuses  and  sinks  below  the  slag, 
carrying  Avith  it  the  whole  of  the  gold.  If  this  product  be  roasted  so  as  to 
<'onvert  the  iron  into  oxide,  and  bo  then  again  fused  Avith  a  fresh  portion 
oi  the  ore,  the  oxide  of  iron  Avill  flux  the  quartz,  whilst  the  fresh  portion 
of  sulphide  of  iron  will  cany  down  the  whole  of  the  gold  contained  in 
both  quantities  of  ore.  Tliis  operation  having  been  repeated  until  the 
sulphide  of  iron  is  rich  in  gold,  it  is  fused  with  a  certain  quantity  of  lead, 
which  extracts  tlie  gold  and  falls  to  the  bottom.  The  lead  is  then  cupelled 
in  order  to  obtain  the  gold. 

"When  the  ores  of  lead,  silver,  or  copper  contain  gold,  it  is  always  found 
to  have  accompanied  the  silver  extracted  from  them,  and  is  separated  from 
it  by  a  process  to  be  presently  noticed. 

Gold  is  sometimes  separated  from  the  impurities  remaining  Avith  it  after 
extraction  by  Avashing,  by  the  process  of  amalgamation,  which  consists  in 
shaking  the  mixture  Avith  mercury  in  order  to  dissolve  the  gold-dust,  and 
straining  the  liquid  amalgam  through  chamois  leather,  Avhich  allows  the 
excess  of  mercury  to  jiass  through,  but  retains  the  solid  portion  contain- 
ing the  gold,  from  which  the  mercury  is  then  separated  by  distillation.* 

In  the  Tyrol,  this  process  is  adopted  for  separating  the  gold  from  an 
a\iriferous  iron  pyrites,  b}'  grinding  it  in  a  mill  of  pecuUar  construction, 
Avith  water  and  a  little  mercury,  the  latter  being  alloAA'ed  to  act  upon  suc- 
<-essive  portions  of  ore  until  it  becomes  sufficiently  rich  to  be  strained  and 
distilled. 

Gold,  as  found  in  nature,  is  generally  alloyed  Avith  variable  proportions 
of  silver  and  copper,  the  separation  of  Avhich  is  the  object  of  the  gold 
refiner.  It  may  be  effected  by  means  of  nitric  acid,  Avhich  will  dissolve 
the  silver  and  copper,  provided  that  they  do  not  bear  too  small  a  propor- 
tion to  the  gold.  Sulphuric  acid,  hoAvever,  being  very  much  cheaper,  is 
generally  employed.  The  alio}'  is  fused  and  [)oured  into  water,  so  as  to 
jjranulate  it  and  expose  a  larger  surface  to  the  action  of  the  acid ;  it  is 
then  boiled  with  concentrated  sulphuric  acid  (oil  of  vitriol),  Avhich  con- 

*  A  small  ([uautity  of  sodimii  dissolvetl  in  the  mercury  has  been  found  very  materially 
to  facilitate  the  amalgamation  of  gold  and  silver  ores,  apparently  liecause  the  amalgam 
of  sodium  is  more  highly  electro- j)ositive  than  mercury,  in  relation  to  the  gold.       •        .,   ., 

2  t: 


402  KEFINING  GOLD. 

verts  the  silver  and  the  copper  into  sulphates,  with  evolution  of  sulphur- 
ous acid  gas,  whilst  the  gold  is  left  untouched.  In  order  to  recover  the 
silver  from  the  solution  of  the  sulphates  in  water,  scraps  of  copper  are 
introduced  into  it,  when  that  metal  decomposes  the  sulphate  of  silver, 
producing  sulphate  of  copper,  and  causing  the  deposition  of  the  silver 
in  the  metallic  state. 

Finally,  the  sulphate  of  copper  may  be  obtained  from  the  solution  by 
evaporation  and  crystallisation.  This  process  is  so  effectual  when  the 
proportion  of  gold  in  an  alloy  is  very  small,  that  even  ^\yth  part  of  this 
metal  may  be  profitably  extracted  from  100  parts  of  an  alloy,  and  much 
gold  has  been  obtained  in  this  way  from  old  silver  plate,  coins,  &c.,  which 
were  manufactured  before  so  perfect  a  process  for  the  separation  of  these 
metals  was  known.  On  boiling  old  silver  coins  or  ornaments  with  nitric 
acid,  they  are  generally  found  to  yield  a  minute  proportion  of  gold  in  the 
form  of  a  purple  powder.  But  this  plan  of  separation  is  not  so  successful 
when  the  alloy  contains  a  very  large  quantity  of  gold,  for  the  latter  metal 
seems  to  protect  the  copper  and  silver  from  the  solvent  action  of  the  acid. 
Thus,  if  the  alloy  contains  more  than  Ith  of  its  weight  of  gold,  it  is 
customary  to  fuse  it  with  a  quantity  of  silver,  so  as  to  reduce  the  propor- 
tion of  gold  below  that  point  before  boiling  it  with  the  acid.  Again,  if 
the  alloy  contains  a  large  quantity  of  copper,  it  is  found  expedient  to 
remove  a  great  deal  of  this  metal  in  the  form  of  oxide  by  heating  the  alloy 
in  a  current  of  air. 

Gold  which  is  brittle  and  unfit  for  coining,  in  consequence  of  the  pre- 
sence of  small  quantities  of  foreign  metals,  is  sometimes  refined  by  melt- 
ing it  with  oxide  of  copper  or  with  a  mixture  of  nitre  and  borax,  when 
the  foreign  metals,  with  the  exception  of  silver,  are  oxidised  and  dissolved 
in  the  slag.  Another  process  consists  in  throwing  some  corrosive  sub- 
limate (mercuric  chloride)  into  the  melting  pot,  and  stirring  it  up  with 
the  metal,  when  its  vapour  converts  the  metallic  impurities  into  chlorides, 
which  are  volatilised.  An  excellent  method,  devised  by  F.  B.  MiUer  of 
Sydney,  consists  in  fusing  the  gold  w4th  a  little  borax,  and  passing  chlo- 
rine gas  into  it  through  a  clay  tube.  Antimony,  arsenic,  &c.,  are  carried 
off  as  chlorides,  Avhilst  the  silver,  also  converted  into  chloride,  rises  to  the 
surface  of  the  gold  in  a  fused  state,  afterwards  solidifying  into  a  cake, 
which  is  reduced  to  the  metallic  state  by  placing  it  between  plates  of 
wrought-iron  and  immereing  it  in  diluted  sulphuric  acid. 

Pure  gold,  like  pure  silver,  is  too  soft  to  resist  the  wear  to  which  it  is 
subjected  in  its  ordinary  uses,  and  it  is  therefore  alloyed  for  coinage  in 
this  country. with  ^^yth  of  its  weight  of  copper^  so  that  gold  coin  contains 
1  part  of  copper  and  11  parts  of  gold.  The  gold  used  for  articles  of 
jewellery  is  alloyed  with  variable  proportions  of  copper  and  silver.  The 
alloy  of  copper  and  gold  is  much  redder  than  pure  gold. 

The  degree  of  purity  of  gold  is  generally  expressed  by  quoting  it  as  of 
so  many  carats  fine.  Thus,  pure  gold  is  said  to  be  24  carats  fine  ;  English 
standard  gold  22  carats  fine,  that  is,  contains  22  carats  of  gold  out  of  the 
24.  Gold  of  18  carats  fine  would  contain  18  parts  of  gold  out  of  the  24, 
or  |ths  of  its  weight  of  gold. 

Pure  gold  is  easily  prepared  from  standard  or  jeweller's  gold,  by  dissolving  it  in 
liydroeliloric  acid  mixed  with  one-fourth  of  its  volume  of  nitric  acid,  evaporating  the 
solution  to  a  small  bulk  to  expel  excess  of  acid,  diluting  with  a  considerable  quantity 
of  water,  filtering  from  the  separated  silver  chloride,  and  adding  a  solution  of  green 


PHYSICAL  CHARACTERS  OF  GOLD.  403 

sulphate  of  iron,  •when  the  gold  is  precipitated  as  a  dark  purple  powder,  which  may 
be  collected  on  a  filter,  well  washed,  dried,  and  fused  in  a  small  French  clay  ci-ucible 
with  a  little  borax,  the  crucible  having  been  previously  dipped  in  a  hot  "saturated 
solution  of  borax,  and  dried,  to  prevent  adhesion  of  the  globules  of  gold.  The  action 
of  the  ferrous  sulphate  upon  the  trichloride  of  gold  is  explained  by  the  equation  ; 
2AUCI3  +  6  Fe.,S04  =  Au,  +  Fe/Ilg  +  2Fe.,(S04)3. 

By  employing  oxalic  acid  instead  of  ferrous  sulphate,  and  heating  the  solution,  the 
gold  is  precipitated  in  a  spongy  state,  and  becomes  a  coherent  lustrous  mass  under 
pressure.     The  metal  is  employed  iu  this  form  by  dentists. 

When  standard  gold  is  being  dissolved  in  aqua  rcgia,  it  sometimes  becomes  coated 
with  a  film  of  silver  chloride  which  stops  the  action  of  the  acid  ;  the  liquid  must 
then  be  poured  off,  the  metal  washed,  and  treated  with  ammonia,  which  dissolves 
the  silver  chloride ;  the  ammonia  must  then  be  washed  away  before  the  metal  is 
re]ilaced  in  the  acid.  In  the  case  of  jeweller's  gold,  it  is  advisable  to  extract  as  much 
silver  and  copper  as  possible  by  boiling  it  with  nitric  acid,  before  attempting  to  dis- 
solve the  gold.  Gold  lace  should  be  incinerated  to  get  rid  of  the  cotton  before  being 
treated  with  acid. 

The  genuineness  of  gold  trinkets,  &c.,  is  generally  tested  by  touching  them  with 
nitric  acid,  which  attacks  them  if  they  contain  a  very  considerable  proportion  of 
copper,  producing  a  green  stain,  but  this  test  is  evidently  useless  if  the  surface  be 
gilt.  The  weight  is,  of  course,  a  good  criterion  in  practised  hands,  but  even  these 
have  been  deceiveil  by  bars  of  platinum  covered  with  gold.  The  specific  gravity  may 
be  taken  in  doubtful  cases  ;  that  of  sovereign  gold  is  17  157. 

In  assaying  gold,  the  metal  is  wrapped  in  a  piece  of  thin  paper  together  with  about 
three  times  its  weight  of  pure  silver,  and  added  to  twelve  times  its  weight  of  jmre 
lead  fused  in  a  bone-ash  cupel  (see  page  372)  placed  in  a  mufH^  (or  exposed  to  a 
strong  oxidising  blowpipe  flame),  when  the  lead  and  copper  are  oxidised,  and  the 
fused  oxide  of  lead  dissolves  that  of  copper,  both  being  absorbed  by  the  cupel. 
When  the  metallic  button  no  longer  diminishes  in  size,  it  is  allowed  to  cool,  hammered 
into  a  flat  disk  which  is  annealed  by  being  heated  to  redness,  and  rolled  out  to  a 
thin  plate,  so  that  it  may  be  rolled  up  by  the  thumb  and  finger  into  a  coniette,  which 
is  boiled  with  nitric  acid  (sp.  gr.  118)  to  extract  the  silver  ;  the  remaining  gold  is 
washed  with  distilled  water,  and  boiled  with  nitric  acid  of  sp.  gr.  128,  to  extract  the 
last  traces  of  silver,  after  which  it  is  again  washed,  heated  to  redness  in  a  small 
cnicible,  and  weighed. 

The  stronger  nitric  acid  could  not  be  used  at  first,  since  it  would  be  likely  to  break 
the  cornet  into  fragments  which  could  not  be  so  readily  washed  without  loss.  The 
addition  of  the  three  parts  of  silver  {quartation)  is  made  in  order  to  divide  the  alloy, 
and  permit  the  easy  extraction  of  the  silver  by  nitric  acid,  which  cannot  be  effected 
when  the  gold  predominates. 

303.  The  physical  characters  of  gold  render  it  very  conspicuous  among 
the  metals;  it  is  the  heaviest  of  the  metals  in  common  use,  with  the 
exception  of  platinum,'  its  specific  gravity  heing  19 '3.  In  malleability 
and  ductility  it  surpasses  all  other  metals  ;  the  former  property  is  turned 
to  advantage  for  the  manufacture  of  gold  leaf,  for  which  purpose  a  bar  of 
gold  is  passed  between  rollers  which  extend  it  into  the  form  of  a  riband ; 
this  is  cut  up  into  squares,  which  are  packed  between  layers  of  fine 
vellum,  and  beaten  with  a  heavy  hammer  ;  these  thinner  squares  are  then 
again  cut  up  and  beaten  between  layers  of  gold-beater's  skin  until  they 
are  sufficiently  thin.  An  ounce  of  gold  may  be  thus  spread  over  100 
square  feet ;  282,000  of  such  leaves  placed  upon  each  other  form  a  pile  of 
only  1  inch  high.  These  leaves  will  allow  light  to  pass  through  them, 
and  always  appear  green  or  blue  when  held  up  to  the  light,  though  they 
exhibit  the  ordinary  colour  of  gold  by  reflected  light ;  extremely  thin 
leaves  of  gold,  obtained  by  partially  dissolving  ordinary  gold  leaf  by 
floating  it  on  solution  of  potassium  cyanide,  transmit  a  violet  or  a  red 
light,  according  to  their  thickness,  though  they  still  appear  yellow  by 
reflected  light,  and  if  taken  up  on  a  glass  plate  and  heated  to  about  600° 
F.  they  lose  their  gold  reflection  and  become  ruby-red,  changing  to  green 


404  OXIDES  OF  GOU). 

if  pressed  witli  a  hard  substance.  If  very  finely-divided  gold  be  sus- 
pended in  water,  it  imparts  a  violet  or  red  colour, to  it.  Such  coloured 
fluids  containing  very  minute  particles  of  gold  in  a  state  of  suspension, 
may  be  obtained  by  the  action  of  phosphorus  dissolved  in  ether  upon  a 
very  weak  solution  of  gold  in  aqua  regia;  on  standing  for  a  long  time, 
the  particles  of  finely-divided  gold  are  deposited,  having  the  same  tint  as 
that  which  thoy  i)reviously  exhibited  when  suspended  in  the  liquid;  the 
blue  particles  being  less  minute  are  soonest  deposited,  but  the  red  particles 
require  many  months  to  settle  down.  These  colours  of  finely-divided 
gold  are  taken  advantage  of  in  painting  upon  porcelain,  and  the  Avell- 
known  magnificent  ruby-red  glass  owes  its  colour  to  the  same  cause. 
xl-ffth  of  a  grain  of  gold  is  capable  of  imparting  a  deep  rose  colour  to  a 
cubic  inch  of  fluid. 

The  extreme  ductility  of  gold  is  exemplified  in  the  manufacture  of  gold 
thread  for  embroidery,  in  which  a  cylinder  of  silver  having  been  covered 
•with  gold  leaf,  it  is  drawn  through  a  wire-drawing  plate  and  reduced  to 
the  tliinness  of  a  hair ;  in  this  way  6  ounces  of  gold  are  drawn  into  a 
<iylinder  two  hundred  miles  in  length.  Although  fusing  at  about  the 
.same  temperature  as  copper,  gold  is  seldom  cast,  on  account  of  its  great 
contraction  during  solidification. 

Gold  is  not  ,evon  attected  to  the  same  extent  as  silver  by  exposure  to 
the  atmosphere,  for  sulphuretted  hydrogen  has  no  action  upon  it,  and 
hence  no  metal  is  so  well  adapted  for  coating  surfaces  Avhicli  are  required 
to  preserve  their  lustre. 

The  gold  is  sometimes  applied  to  the  surfaces  of  metals  in  the  form  of 
un  amalgam,  the  mercury  being  afterwards  driven  off  by  heat.  Metals 
may  also  be  gilt  by  means  of  a  boiling  solution  prepared  by  dissolving 
gold  in  aqua  regia,  and  adding  an  excess  of  bicarbonate  of  potash  or  of 
soda.  But  the  most  elegant  process  of  gilding  is  that  of  electro-gilding, 
in  which  the  object  to  be  gilt  is  connected  by  a  wire  with  the  zinc  end 
of  the  galvanic  battery,  and  immersed  in  a  solution  of  cyanide  of  gold  in 
cyanide  of  potassium,  in  which  is  also  placed  a  gold  plate  connected  with 
the  copper  end  of  the  battery,  and  intended,  by  gradually  dissolving,  to 
replace  the  gold  abstracted  from  the  solution  at  the  negative  pole. 

A  gold  crucible  is  very  useful  in  the  laboratory'  for  effecting  the  fusion 
of  substan(!es  with  caustic  alkalies,  which  wouLl  corrode  a  platinum 
<',rucible. 

Wi.  Oxuf('.'<  of  (ji lid. -—Two  compounds  of  gold  with  oxygen  have  been 
<jl)tained,  Auo<  >  and  Au._,().5,  but  neither  of  them  is  of  any  great  practical 
importance. 

Sesqiii oxide,  of  (juld  or  aniic  anhydride  (AuoO,,)  is  prepared  from  the 
solution  of  gold  in  aqua  r<>(jia,  by  boiling  it  with  excess  of  potash,  decom- 
posing the  potassium  aurate  with  sulphuric  acid,  and  purifying  the  auric 
anhydride  by  dissolving  it  in  nitric  acid  and  precipitating  by  water.  It 
forms  a  yellow  precipitate,  which  is  easily  decomposed  by  exposure  to 
light  or  to  a  temperature  of  500°  F.  By  dissolving  it  in  potash  and 
evaporating  in  vacuo,  the  potamnm  aurate  is  obtained  in  yellow  needles 
(KAuOo3A(i.).  Suboxide  of  gold  (Au^O)  forms  a  dark  precipitate  when 
protochloride  of  gold  is  decomposed  by  potash. 

The  chlm-ide^  of  gold  correspond  in  composition  to  the  oxides.  The 
frirldoride  of  gold  or  nun*'  chloride  (AuCl.j)  is  obtained  by  dissolving 


(JHLORIDE.S  OF  GOLD.  AOit 

gold  in  hydrochloric  acid  with  one-fourth  of  its  volume  of  nitric  acid, 
and  evaporating  on  a  water-bath  to  a  small  bulk ;  on  cooling,  yellow  pris- 
matic crystals  of  a  compound  of  the  trichloride  with  hydrochloric  acid 
(AuCl3.HCl.6Aq.)  are  deposited,  from  whicli  the  hydrochloric  acid  may 
be  expelled  by  a  gentle  heat  (not  exceeding  250^  F.),  when  the  trichloride^ 
forms  a  red-brown  deliquescent  mass,  dissolving  very  readily  in  water, 
giving  a  bright  yellow  solution  which  stains  the  skin  and  other  organic' 
matter  purple  when  exposed  to  light,  dejiositing  finely-divided  gold. 
Almo.st  every  substance  capable  of  combining  with  oxygen  reduces  the 
gold  to  the  metallic  state.  The  inside  of  a  perfectly  clean  flask  or  tube 
may  be  covered  with  a  film  of  metallic  gold  by  a  dilute  solution  of  the; 
trichloride  mixed  with  citric  acid  and  ammonia,  and  gently  heated.  The 
facility  with  which  it  deposits  metallic  gold,  and  the  resistance  of  the 
deposited  metal  to  atmospheric  action,  has  rendered  trichloride  of  gold 
very  useful  in  photography^.  Alcohol  and  ether  readily  dissolve  the  tri- 
chloride, the  latter  being  able  to  extract  it  from  its  aqueous  solution. 
Red  crystals  of  trichloride  of  gold  are  sublimed  when  thin  gold  foil  is 
gently  heated  in  a  current  of  chlorine.  Trichloride  of  gold  (like 
platinic  chloride)  forms  crystallisable  compounds  with  the  alkaline 
chlorides  and  with  the  hydrochlorates  of  organic  bases,  and  aifords  great 
help  to  the  chemist  in  defining  these  last.  Aarochlorklc  of  sodium  forms 
reddish-yellow-  prismatic  crystals  (XaCl.  AuCl3,4Aq.),  which  are  sometimes 
sold  for  photographic  purposes. 

Protochlonde  of  gold  or  cmroiis  chloride  (AuCl)  is  obtained  by  gently 
heating  the  trichloride,  Avhen  it  fuses  and  is  decomposed  at  350°  F., 
leaving  the  protochloride,  which  is  reduced  to  metallic  gold  at  about  400^^ 
F.  The  protochloride  is  sparingly  soluble  in  M'ater  and  of  a  pale  yellow 
colour.  IJoiling  water  decomposes  it  into  metallic  gold  and  the  tri- 
chloride. 

Fidminatiiig  gold  is  obtained  as  a  bull'  precipitate  when  ammonia  is 
added  to  solution  of  auric  chloride  ;  its  composition  is  not  well  established, 
but  appears  to  be  Auo03.4XH3,H.^O.  It  explodes  violently  when  gently 
heated. 

The  Sel  d'or  of  the  photographer  is  a  hyposulphite  (thiosulphate)  of  gold 
and  sodium,  Au.2S.203,3Xa,S203,4Aq.,  which  is  obtained  in  fine  white 
needles  by  pouring  a  solution  of  1  part  of  auric  chloride  into  a  solution  of 
3  parts  of  sodium  hyposulphite,  and  adding  alcohol,  in  which  the  double 
salt  is  insoluble.  Its  formation  may  be  explained  by  the  equation, 
SNagS.Pa  +  2AUCI3  =  AU2S2O3,  3Xa.3S203  +  6NaCl  +  2X828406.  It  is 
doubtful  whether  the  above  formula  represents  the  true  constitution  of 
this  salt,  for  it  is  not  decomposed  by  acids  in  the  same  manner  as  ordi- 
nary hyposulphites.  Nitric  acid  causes  the  whole  of  the  gold  to  separate 
in  the  metallic  state. 

Purple  of  Cassius,  which  is  employed  for  imparting  a  rich  red  colour  to 
glass  and  porcelain,  is  a  compound  of  gold,  tin,  and  oxygen,  which  are  be- 
lieved to  be  grouped  according  to  the  fonnula  Au20.Sn02,SnO.Sn02.4Aq.* 
It  may  be  prepared  by  adding  stannous  chloride  to  a  mixture  of  stannic 
chloride  and  auric  chloride ;  7  parts  of  gold  are  dissolved  in  aqua  regia 
and  mixed  with  2  parts  of  tin  also  dissolved  in  aqtia  regia  ;  this  solution 
is  largely  diluted  witli  water,  and  a  weak  solution  of  1  part  of  tin  in 

*  Debray  asserts  that  it  i^i  merely  a  mixture  of  preeipitated  gold  and  stannic  hydrate. 


406  SULPHIDES  OF  GOLD. 

hydrochloric  acid  is  added,  drop  by  drop,  till  a  fine  purple  colour  is  pro- 
duced. The  purple  of  Cassius  remains  suspended  in  water  in  a  very  fine 
state  of  division,  but  subsides  gradually,  especially  if  some  saline  solution 
be  added,  as  a  purple  powder.  The  fresh  precipitate  dissolves  in 
ammonia,  but  the  purple  solution  is  decomposed  by  exposure  to  light, 
becoming  blue,  and  finally  colourless,  metallic  gold  being  precipitated, 
and  stannic  oxide  left  in  solution. 

The  sulphides  of  gold  are  not  thoroughly  known.  When  hydrosul- 
phuric  acid  acts  on  solution  of  auric  chloride,  a  black  precipitate  of 
Au2S,Au2S3,  is  obtained,  which  dissolves  in  alkaline  sulphides.  The 
salt  NagSjAugSjSAq.  has  been  -obtained,  in  colourless  prisms  soluble  in 
alcohol.  The  precipitated  sulphide  of  gold  is  not  dissolved  by  the  acids, 
with  the  exception  of  aqua  regia.  Nitric  acid  oxidises  the  sulphur, 
leaving  metallic  gold.  When  hydrosuljihuric  acid  is  added  to  a  boiling 
solution  of  auric  chloride,  the  metal  itself  is  precipitated — 

SAuClg  +  SHgS  +  I2H2O  =  Aug  +  24HC1  +  SHgSO^. 

A  yellowish-grey  brittle  arsenide  of  gold  (AuAsg)  ^^^  been  found  in 
quartz  in  Australia. 


ON  SOME  OF  THE 

USEFUL  APPLICATIONS  OF  CHEMICAL  PRINCIPLES 
NOT  HITHEETO  MENTIONED. 


CHEMICAL  PRINCIPLES  OF  THE  MANUFACTUEE 
OF  GLASS. 

305.  Glass  is  defined  chemically  to  be  a  mixture  of  two  or  more  sili- 
cates, one  of  which  is  a  silicate  of  an  alkali,  the  other  being  a  silicate  of 
lime,  baryta,  oxide  of  iron,  oxide  of  lead,  or  oxide  of  zinc. 

If  silica  be  fused  with  an  equal  weight  of  carbonate  of  potash  or  soda, 
a  transparent  glassy  mass  is  obtained,  but  this  is  slowly  dissolved  by 
water,  and  would  therefore  be  incapable  of  resisting  the  action  of  the 
weather;  if  a  small  proportion  of  lime  or  baryta,  or  of  the  oxides  of  iron, 
lead,  or  zinc,  be  added,  the  glass  becomes  far  less  easily  affected  by  atmo- 
spheric influences. 

The  most  valuable  property  of  glass,  after  its  transparency  and  per- 
manence, is  that  of  assuming  a  viscid  or  plastic  consistency  when  fused, 
which  allows  it  to  be  so  easily  fashioned  into  the  various  shapes  required 
for  use  or  ornament. 

The  composition  of  glass  is  varied  according  to  the  particular  purpose 
for  which  it  is  intended,  the  materials  selected  being  fused  in  large  clay 
crucibles  placed  in  reverberatory  furnaces,  and  heated  by  a  coal  fire  or  in 
a  gas-furnace. 

Ordinary  iviudow  glass  is  essentially  composed  of  silicate  of  soda  and 
silicate  of  lime,  containing  one  molecule  (13*3  per  cent.)  of  soda,  one 
molecule  (12'9  per  cent.)  of  lime,  and  five  molecules  (69'1  per  cent.)  of 
silica;  it  also  usually  contains  a  little  alumina.  This  variety  (^f  glass 
is  manufactured  by  fusing  100  parts  of  sand  with  about  35  parts  of  chalk 
and  35  parts  of  soda-ash:  a  considerable  quantity  of  broken  window  glass 
is  always  fused  up  at  the  same  time.  Of  course,  the  carbonic  acid  of  the 
chalk  and  of  the  carbonate  of  soda  is  expelled  in  the  gaseous  state;  and  in 
order  that  this  may  not  cause  the  contents  of  the  crucible  to  froth  over 
during  t  he  fusion,  the  materials  are  first  fritted  together,  as  it  is  termed, 
at  a  temperature  insufficient  to  liquefy  them,  when  the  carbonic  acid  gas 
is  evolved  gradually,  and  the  fusion  afterwards  takes  place  without 
effervescence. 

Occasionally  sulphate  of  soda  is  employed  instead  of  the  carbonate, 
when  it  is  usual  to  add  a  small  proportion  of  cliarcoal  in  order  to  reduce 
the  sulphuric  to  the  state  of  sulphurous  oxide,  which  is  far  more  easily 
expelled.     Before  the  glass  is  worked  into  sheets,  it  is  allowed  to  remain 


408  FLINT  GLASS — COLOURED  GLASS. 

at  rest  for  some  time  in  the  fiused  state,  so  that  the  air-bubbles  may 
escape,  and  the  (/laxx-;fal/  or  scum  (consisting  chiefly  of  sulphate  of  soda 
and  chloride  of  sodium),  which  rises  to  the  surface,  is  removed. 

Plate  [iloHS  is  also  chiefly  a  silicate  of  soda  and  lime,  but  it  contains, 
in  addition,  a  considerable  (quantity  of  silicate  of  potash  (74  per  cent,  of 
silicic  acid,  12  of  soda,  5-5  of  potash,  and  5*5  of  lime).  The  purest  white 
sand  is  selected,  and  great  care  is  taken  to  exclude  impurities. 

Crown  (jl(i><>!,  used  for  o})tical  purposes,  contains  no  soda,  since  that 
alkali  has  the  property  of  imparting  a  greenish  tint  to  glass,  which  is  not 
the  case  with  potash.  This  variety  of  glass,  therefore,  is  prepared  by 
fusing  sand  with  carbonate  of  potfish  and  chalk  in  such  proportions  that 
the  glass  may  contain  one  molecule  (22  per  cent.)  of  potash,  one  molecule 
(12-5  per  cent.)  of  lime,  and  four  molecules  (62  per  cent.)  of  silica. 

The  glass  of  which  icinc  boft/ex  are  made  is  of  a  much  cheaper  and  com- 
moner description,  consisting  chiefly  of  silicate  of  lime,  but  containing,  in 
addition,  small  quantities  of  the  silicates  of  the  alkalies,  of  alumina,  and 
of  oxide  of  iron,  to  the  last  of  which  it  owes  its  dark  colour.  It  is  made 
of  the  coarsest  materials,  such  as  common  red  sand  (containing  iron  and 
alumina),  soap-maker's  waste  (containing  lime  and  small  quantities  of 
alkali),  refuse  lime  from  the  gas-works,  clay,  and  a  very  small  proportion^ 
of  rock-salt. 

Flint  ;/lcts>«,  which  is  used  for  table  glass  and  for  ornamental  purposes, 
is  a  double  silicate  of  potash  and  oxide  of  lead,  containing  one  molecule 
(13'67  per  cent.)  of  potash,  one  molecule  (33'28  per  cent.)  of  oxide  of 
lead,  and  six  molecules  (51  "93  per  cent.)  of  silica.  It  is  })rcpared  by 
fusing  300  parts  of  the  purest  white  sand  with  200  parts  of  minium  (red 
oxide  of  lead),  100  parts  of  refined  i)earl-ash,  and  30  parts  of  nitre.  The 
fusion  is  effected  in  crucibles  covered  in  at  the  top  to  prevent  the  access 
of  the  flame,  Avhich  would  reduce  a  portion  of  the  lead  to  the  metallia 
state.  The  nitre  is  added  in  order  to  oxidise  any  accidental  impurities 
which  might  reduce  the  lead. 

The  presence  of  the  oxide  of  lead  in  glass  very  much  increases  its 
fusibility,  and  renders  it  much  softer,  so  that  it  may  be  more  easily  cut 
into  ornamental  forms;  it  also  greatly  increases  its  lustre  and  beauty. 

Baryta  has  also  the  effect  of  increasing  the  fusibility  of  glass,  and  oxide 
of  zinc,  like  oxide  of  lead,  increases  its  brilliancy  and  refracting  power, 
on  whicli  account  it  is  employed  in  some  kinds  of  glass  for  optical  ijur- 
poses.  Glass  of  this  description  is  also  made  by  substituting  boracic  aeid 
for  a  portion  of  the  silica. 

Some  varieties  of  glass,  if  heated  nearly  to  their  melting-point,  and 
allowed  to  cool  slowly,  become  converted  into  an  opaque  very  hard  mass 
resembling  porcelain  {^Reaumur's porcelain).  This  change,  which  is  known 
as  (lemtrification,  is  due  to  the  crystallisation  of  the  silicates  contained  in 
the  mass,  and  by  again  fusing  it,  the  glass  may  be  restored  to  its  original 
transparent  condition. 

In  producing  culoured  i/lass,  advantage  is  taken  of  its  property  of  dis-i 
solving  many  metallic  oxides  with  production  of  peculiar  colours.  It  has 
been  mentioned  above  that  bottle  glass  owes  its  green  colour  to  the  pre- 
sence of  oxide  of  iron ;  and  since  this  oxide  is  generally  found  in  small 
(juantity  in  sand,  and  even  in  chalk,  it  occasionally  happens  that  a  glass 
which  is  required  to  be  perfectly  colourless  turns  out  to  have  a  slight  green 
tinge.     In  order  to  remove  this,  a  small  quantity  of  some  oxidising  agent 


.    POTTERY  AND  POKCELAIX,  409 

is  usually  addod,  in  order  to  convert  the  oxide  of  iron  into  the  sesquioxide, 
which  does  not  impart  any  colour  when  present  in  minute  proportion.  A 
little  nitre  is  sometimes  added  for  this  purpose,  or  some  white  ai-senic, 
which  yields  its  oxygen  to  the  oxide  of  iron,  and  escapes  in  the  form  of 
vapour  of  arsenic;  red  oxide  of  lead  (PbyO^)  may  also  be  employed,  and 
is  reduced  to  oxide  of  lead  (PbO),  which  rt^mains  in  the  glass.  Binoxide 
of  manganese  is  often  added  as  an  oxidising  agent,  being  reduced  to  the 
state  of  oxide  of  manganese  (MnO),  which  does  not  colour  the  glass;  but 
care  is  then  taken  not  to  add  too  much  of  the  binoxide,  for  a  very  minute 
quantity  of  this  substance  imparts  a  beautiful  amethyst  purple  colour  to 
glass. 

Suboxide  of  copper  is  used  to  produce  a  red  glass,  and  the  finest  ruby 
glass  is  obtained,  as  already  mentioned  at  page  404,  by  the  addition  of  a 
little  gold.  The  oxides  of  antimony  impart  a  yellow  colour  to  glass;  a 
peculiar  brown-yellow  shade  is  given  by  charcoal  in  a  fine  state  of  division, 
and  sesquioxide  of  uranium  produces  a  fine  greenish-yellow  glass.  Green 
glass  is  coloured  either  by  oxide  of  copper  or  sesquioxide  of  chromium, 
whilst  oxide  of  cobalt  gives  a  magnificent  blue  colour.  For  black  glass 
a  mixture  of  the  oxides  of  cobalt  and  manganese  is  employed.  The  white 
enamel  glass  is  a  flint  glass,  containing  about  10  per  cent,  of  binoxide  of 
tin.     Bone-ash  is  also  used  to  impart  this  appearance  to  glass. 

CHEMISTRY  OF  THK  :\rANUFAGTURE  OF  POTTERY 
AND  PORCELAIN. 

306.  The  manufacture  of  pottery  obviously  belongs  to  an  earlier  period 
of  civilisation  than  that  of  glass,  since  the  raw  material,  clay,  would  at 
once  suggest,  by  its  plastic  properties,  the  possibility  of  working  it  into 
useful  vessels,  and  the  application  of  heat  would  naturally  be  had  recourse 
to  in  order  to  dry  and  harden  it.  Indeed,  at  the  first  glance,  it  would 
appear  that  tliis  manufacture,  unlike  that  of  glass,  did  not  involve  the 
application  of  chemical  principles,  but  consisted  simply  in  fashioning  the 
clay  by  mere  mechanical  dexterity  into  the  required  form.  It  is  found, 
however,  at  the  outset,  that  the  name  of  daij  is  applied  to  a  large  class  of 
minerals,  diff'ering  very  considerably  in  composition,  and  possessing  in 
common  the  two  characteristic  features  of  plasticity  and  a  i)redorainance 
of  silicate  of  alumina. 

It  has  already  been  stated  (page  290)  that  kaolin  is  a  hydrated  silicate 
of  alumina,  and  it  is  from  this  material  that  the  best  variety  of  porcelain 
is  made.  This  clay  is  eminently  plastic,  and  can  therefore  be  readily 
moulded,  but  when  baked,  it  shrinks  very  much,  so  that  the  vessels  made 
from  it  lose  their  shape  and  often  crack  in  the  kiln.  In  order  to  prevent 
this,  the  clay  is  mixed  with  a  certain  proportion  of  sand,  chalk,  bone-ash, 
or  heavy-spar ;  but  another  difficulty  is  thus  introduced,  for  these  sub- 
stances diminish  the  tenacity  of  the  clay,  and  would  thus  render  the 
vessels  brittle.  A  further  addition  must  therefore  be  made  of  some  sub- 
stance which  fuses  at  the  temperature  employed  in  baking  the  ware,  and 
thus  serves  as  a  cement  to  bind  the  unfused  particles  of  clay,  &c.,  into 
a  compact  mass.  Felspar  (silicate  of  alumina  and  potash)  answers  this 
purpose  ;  or  carbonate  of  potash  or  of  soda  is  sometimes  added,  to  convert 
a  portion  of  the  silii;a  into  a  fu-ible  alkaline  silicate.  With  a  mixture  of 
clay  with  sand  and  felspar  (or  some  substitutes),  a  vessel  may  be  moulded 


410  SEVRES  AND  ENGLISH  POKCELAIN. 

which  will  preserve  its  shape  and  tenacity  when  baked,  but  it  will  be 
easily  peryious  to  water,  and  thus  quite  uuHt  for  ordinary  use.  It  has,  there- 
fore, to  be  waterproofed  by  the  application  of  some  easily  fusible  material, 
which  shall  either  form  a  glaze  over  the  surface,  or  shall  become  incor- 
porated with  the  body  of  the  ware,  and  the  vessel  is  then  fit  for  all  its 
uses.  Handles  and  ornaments  in  relief  are  moulded  separately,  and  fixed 
on  the  ware  before  baking,  and  coloured  designs  are  transferred  from  paper 
to  the  porous  ware  before  glazing. 

The  manufacture  of  Sem'es  porcelain  is  one  of  the  most  perfect  examples 
of  this  art.  The  purest  materials  are  selected  in  the  following  propor- 
tions:— Kaolin  (porcelain  clay),  62  parts;  chalk,  4  parts ;  sand,  17  parts; 
felspar,  17  parts.  These  niJiterials  are  ground  up  with  water  before 
being  mixed,  and  the  coarser  particles  allowed  to  subside ;  the  creamy 
fluids  containing  the  finer  particles  in  suspension  are  then  mixed  in 
the  proper  proportions,  and  allowed  to  settle ;  the  paste  deposited  at  the 
bottom  is  drained,  thoroughly  kneaded,  and  stored  away  for  some  months 
in  a  damp  place,  by  which  its  texture  is  considerably  improved,  and  any 
organic  matter  which  it  contains  becomes  oxidised  and  removed  ;  the 
oxidation  being  effected  partly  by  the  sulphates  present,  which  become 
reduced  to  sulphides.  It  is  then  moulded  into  the  required  tVjrms,  and 
dried  by  simple  exposure  to  the  air.  The  vessels  are  packed  in  cylindrical 
cases  of  a  very  refractory  clay,  which  are  arranged  in  a  furnace  or  kiln  of 
peculiar  construction,  apd  very  gradually  but  strongly  heated  by  the 
flame  of  a  wood  fire.  When  sufficiently  baked,  the  biscuit  poicelain  has 
to  be  glazed,  and  great  care  is  taken  that  the  glaze  may  possess  tlie  same 
expansibility  by  heat  as  the  ware  itself,  for  otherwise  it  would  crack  in  all 
directions  as  the  glazed  ware  cooled.  The  glaze  employed  at  Sevres  is  -a 
mixture  of  felspar  and  quartz  very  finely  ground,  and  susi)euded  in 
water,  to  which  a  little  vinegar  is  added  to  prevent  the  glaze  from  subsid- 
ing too  rapidly.  "When  the  porous  ware  is  dipped  into  this  mixture,  it 
absorbs  the  water,  and  retains  a  thin  coating  of  the  mixture  of  quartz  and 
felspar  upon  its  surface.  It  is  now  baked  a  second  time,  when  the  glaze 
fuses,  partly  penetrating  the  ware,  partly  remaining  as  a  varnish  upon  the 
surface. 

When  the  ware  is  required  to  have  some  uniform  colour,  a  mineral 
pigment  capable  of  resisting  very  high  temperatures  is  mixed  with  the 
glaze;  but  coloured  designs  are  painted  upon  the  ware  after  glazing,  the 
ware  being  then  baked  a  tiiird  time,  in  order  to  fix  the  colours.  These 
colours  are  glasses  colouied  with  metallic  oxides,  and  ground  up  with  oil 
of  turpentine,  so  that  they  may  be  painted  in  the  ordinary  way  upon  the 
surface  of  the  ware  ;  when  the  latter  is  again  heated  in  tlie  kiln,  the 
coloured  glass  fuses,  and  thus  contracts  a  firm  adhesion  with  the  «  are. 

Gold  is  applied  either  in  the  form  of  precipitated  metallic  gold,  or  of 
fulminating  gold,  being  ground  up  in  either  case  wiih  oil  of  turpentine,, 
burnt  in,  and  burnished. 

English  porcelain  is  made  from  Cornish  clay  mixed  with  ground  flints, 
burnt  bones,  and  sometimes  a  little  carbonate  of  soda,  borax,  and  binoxide 
of  tin,  the  last  improving  the  colour  of  the  ware.  It  is  glazed  with  a 
mixture  of  Cornish  s-tone  (coii>isting  of  quartz  and  felspar),  flint,  chalk, 
borax,  and  .-ometimes  white  lead  to  incrca-se  it>  fusibility. 

Sf one-ware  is  made  from  less  jmre  materials,  and  is  covered  with  a  glaze 
of  silicate  of  soda,  in  a  very  simple  manner,  by  a  process  known  as  salt- 


BUILDING  MATERIALS.  411 

glazing.  The  ware  is  coated  with  a  thin  film  of  sand  by  dipping  it  in  a 
mixture  of  fine  sand  and  water,  and  is  then  intensely  heated  in  a  kiln  into 
which  a  quantit}"^  of  damp  salt  is  presently  thrown.  The  water  is  decom- 
posed, its  hydrogen  taking  the  chlorine  of  the  salt  to  form  hydrochloric 
acid,  and  its  oxygen  converting  the  sodium  into  soda,  which  combines  with 
the  Scind  to  form  silicate  of  soda ;  this  fuses  into  a  glass  upon  the  surface 
of  the  ware, 

Pipkius,  and  similar  earthenware  vessels,  are  made  of  common  clay 
mixed  with  a  certain  proportion  of  marl  and  of  sand.  They  are  glazed 
with  a  mixture  of  4  or  5  parts  of  clay  with  6  or  7  parts  of  litharge.  The 
colour  of  this  ware  is  due  to  the  presence  of  peroxide  of  iron. 

Bricks  and  tiles  are  also  made  from  common  clay  mixed,  if  necessary, 
with  sand.  These  are  very  often  grey,  or  blue,  or  yellow,  before  baking, 
and  become  red  under  the  action  of  heat,  since  the  iron,  which  is  originally 
present  as  carbonate  (FeCO.^),  becomes  converted  into  the  red  peroxide 
(Fe.,(>3)  by  the  atmospheric  oxygen. 

The  impure  varieties  of  clay  fuse  much  more  easily  than  pure  clay, 
80  that,  for  the  m  xnufacture  of  the  refractory  bricks  for  lining  furnaces, 
of  glass- pots,  crucibles  for  making  cast-steel,  &c.,  a  pure  clay  is  employed, 
to  which  a  certain  quantity  of  broken  pots  of  the  same  material  is  added, 
to  prevent  the  articles  from  shrinking  whilst  being  dried. 

Dinas  firebricks  are  made  from  a  peculiar  siliceous  material  found  in 
the  Vale  of  Neath,  and  containing  alumina  with  about  98  per  cent,  of 
silica.  The  ground  rock  is  mixed  with  1  per  cent,  of  lime  and  a  little 
water  before  moulding.  These  bricks  are  expanded  by  heat,  whilst 
ordinary  firebricks  contract. 

Blue  bricks  are  glazed  by  sprinkling  with  iron  scurf,  a  mixture  of  par- 
ticles of  stone  and  iron  produced  by  the  wear  of  the  siliceous  grindstones 
employed  in  grinding  gun-barrel:*,  &c.  When  the  bricks  are  fired,  a  glaze 
of  silicate  of  iron  is  formed  upon  them. 

CHEMISTRY  OF  BUILDING  MATERIALS. 

307.  Chemical  principles  would  lead  to  the  selection  of  pure  silica 
(quartz,  rock-crystal)  as  the  most  durable  of  building  materials,  since  it  is 
not  acted  on  by  any  of  the  substances  likely  to  be  present  in  the  atmo- 
sphere ;  but  even  if  it  could  be  obtained  in  sufiiciently  large  masses  for 
the  purpose,  its  great  hanlness  presents  an  obstacle  to  its  being  hewn  into 
the  required  forms.  Of  the  building  stones  actually  employed,  granite, 
basalt,  and  porphyry  are  the  most  lasting,  on  account  of  their  capability 
of  resisting  for  a  great  length  of  time  the  action  of  water  and  of  atmo- 
spheric carbonic  acid;  but  their  hardness  makes  them  so  difficult  to  work, 
as  to  prevent  their  employment  except  for  the  construction  of  pavements, 
bridges,  &c.,  where  the  work  is  massive  and  straightforward,  and  much 
resistance  to  wear  and  tear  is  required.  The  millstone  yrit  is  also  a  very 
durable  stone,  consisting  chiefly  of  silica,  and  employed  for  the  founda- 
tions of  houses.  Freestone,  is  a  term  applied  to  any  stone  which  is  soft 
enough  to  be  wrought  with  hammer  and  chisel,  or  cut  with  a  saw ;  it 
juidutles  the  different  varieties  of  sandstone  and  limestone.  The  sand- 
stones consist  of  grains  of  sand  cemented  together  by  clay  or  limestone. 
The  Yorkshire  fiags  employed  for  paving  are  siliceous  stones  of  this 
description.     The  Craigleith  sandstone,  which  is  one  of  the  freestones 


412  MORTAK. 

usejl  ill  London,  contains  about  98  per  cent,  of  silica,  together  with  sonie 
carbonate  of  lime. 

The  building  stones  in  most  general  use  are  the  different  varieties  of 
carbonate  of  lime.  The  durabiUty  of  these  is  in  proportion  to  their  com- 
pact structure ;  thus  marble,  being  the  most  compact,  has  been  found  to 
resist  for  many  centuries  the  action  of  the  atmosphere,  whilst  the  more 
jiorous  limestones  are  corroded  at  the  surface  in  a  very  short  time.  Port- 
land stone,  of  which  St.  Paul's  and  Somerset  House  are  built,  and  Bath 
stont;  are  among  the  most  durable  of  these ;  but  they  are  all  slowly  cor- 
roded by  exposure  to  the  atmosphere.  The  chief  cause  of  this  corrosion 
apjteai-s  to  be  the  mechanical  disintegration  caused  by  the  expansion,  in 
freezing,  of  the  water  absorbed  in  the  pores  of  the  stone.  In  order  to 
determine  the  relative  extent  to  which  different  stones  are  liable  to  be 
<lisintegrated  by  frost,  a  test  has  been  devised,  which  consists  in  soaking 
the  stone  repeatedly  in  a  satunited  solution  of  sulphate  of  soda  and  allow- 
ing it  to  dry,  when  the  crystallisation  of  the  salt  disintegrates  the  stone, 
as  freezing  water  would,  so  that  if  the  particles  detached  from  the  surface 
b(;  collected  and  weighed,  a  numerical  expression  for  the  resistance  of  the 
material  will  be  obtained.  Magnesian  limestones  (carbonate  of  lime  with 
<;arbonixte  of  magnesia)  are  much  valued  for  ornamental  architecture,  on 
account  of  the  ease  with  which  they  may  be  carved,  and  are  said  to  be 
more  durable  in  proportion  as  they  approach  the  composition  expressed  by 
the  formula  CaCOg.MgCOg.*  The  niagnesian  limestone  from  Bolsover 
Moor,  of  which  the  Houses  of  Parliament  are  built,  contains  50  per 
<;ent.  of  calcium  carbonate,  40  of  magnesium  carbonate,  with  some  silica 
and  alumina. 

It  is  probable  that  a  slow  corrosion  of  the  surface  of  limestone  is  effected 
by  the  carbonic  acid  continually  deposited  in  aqueous  solution  from  the 
air ;  and  it  is  certain  that  in  the  atmosphere  of  towns  the  limestone  is 
attacked  by  the  sulphuric  acid  which  results  from  the  combustion  of  coal 
and  the  operations  of  chemical  works.  The  Houses  of  Parliament  have 
suffered  severely,  probably  from  this  cause.  Many  processes  have  been 
recommended  for  the  preservation  of  building  stones,  such  as  waterproof- 
ing them  by  the  application  of  oily  and  resinous  substances,  and  coating  or 
impregnating  them  with  solution  of  soluble  glass  and  similar  matters  ;  but 
none  seems  yet  to  have  been  thoroughly  tested  by  practical  experience. 

Purherlf,  Ancmter,  and  Caen  stones  are  well-known  limestones  employed 
for  building. 

The  mortar  employed  for  building  is  composed  of  1  part  of  freshly- 
slaked  lime  and  2  or  3  parts  of  sand  intimately  mixed  with  enough  water 
to  form  an  uniform  paste.  The  hardening  of  such  a  composition  appears 
to  be  due,  in  the  first  instance,  to  the  absorption  of  carbonic  acid  from 
the  air,  by  which  a  portion  of  the  lime  is  converted  into  carbonate, 
and  this,  uniting  with  the  unaltered  hydrate  of  lime,  forms  a  solid  layer 
adhering  closely  to  the  two  surfaces  of  brick  or  stone,  which  it  cements 
together.  In  the  course  of  time  the  lime  would  act  upon  the  silica,  pro- 
ducing silicate  of  lime,  and  this  chemical  action  would  render  the  adhesioa 
more  perfect.  The  chief  use  of  the  sand  here,  as  in  the  manufacture  of 
pottery  (page  409),  is  to  prevent  excessive  shrinking  during  the  drying  of 
the  mortar. 

*  Any  excess  of  calcium  carbonate  above  that  required  by  this  fonnula  may  be  dissolved 
out  by  treating  the  powdered  niagnesian  limestone  with  weak  acetic  acid. 


NITRE  OR  SALTPETRE.  418 

In  constructions  which  are  exposed  to  the  action  of  water,  mortars  of 
peculiar  composition  are  employed.  These  hydranUc  mortars,  or  cements, 
as  they  are  termed,  are  prepared  by  calcining  mixtures  of  carbonate  of 
lime  with  from  10  to  30  per  cent,  of  clay,  when  carbonic  acid  gas  is  expelled, 
and  the  lime  combines  with  a  portion  of  the  silica  from  the  clay,  producing 
a  silicate  of  lime,  and  probably  also,  with  the  alumina,  to  form  aluminate 
of  lime.  When  the  calcined  mass  is  ground  to  powder  and  mixed  with 
water,  the  silicates  of  alumina  and  lime,  and  the  aluminate  of  lime,  unite 
to  form  hydrated  double  silicates  and  aluminates,  upon  which  water  has 
no  action.  Roman  cement  is  prepared  by  calcining  a  limestone  containing 
about  20  per  cent,  of  daj',  and  hardens  in  a  very  sliort  time  after  mixing 
with  water. 

For  Portland  cement  (so-called  from 'its  resembling  Portland  stone)  a 
mixture  of  river  mud  (chiefly  clay)  and  limestone  is  calcined  at  a  very 
high  temperature. 

Concrete  is  a  mixture  of  hydraulic  cement  with  small  gravel.  A  speci- 
men of  this  material  from  a  very  ancient  Phoenician  temple  was  as  hard 
«s  rock,  and  contained  nearly  30  per  cent,  of  pebbles. 

Sf'offff  ceitu'iit  was  prepared  b}'  passing  air  containing  a  small  quantity 
of  sulphurous  acid  gas,  evolved  from  burning  sulphur,  over  quicklime 
heated  to  dull  redness.  The  setting  of  this  cement  appears  due  to  the 
presence  of  a  small  proportion  of  sulphate  of  lime  very  intimately  mixed 
with  the  quicklime.  The  mixture  of  these  substances  yields  the  cement 
by  a  less  circuitous  process. 

GUNPOWDER. 

308.  Gunpowder  is  a  very  intimate  mixture  of  saltpetre  (nitre  or 
nitrate  of  potassium),  sulphur,  and  charcoal,  which  do  not  act  upon  each 
other  at  the  ordinary  temperature,  but  when  heated  together,  arrange 
themselves  into  new  forms,  evolving  a  very  large  amount  of  gas. 

In  order  to  manufacture  gunpowder  capable  of  producing  the  greatest 
possible  effect,  great  attention  is  requisite  to  the  purity  of  the  ingredients, 
the  process  of  mixing,  and  the  form  ultimately  given  to  the  finislied 
})0wder. 

Chemistry  of  the  Ingkedients  of  Gunpowder — Saltpetre. — Nitrate 
■1}/ pota.^mirn  (KXO3),  nitre  or  mltpetre,  is  found  in  some  parts  of  India, 
especially  in  Bengal  and  Oude,  where  it  sometimes  appears  as  a  white 
incrustation  on  the  surface  of  the  soil,  and  is  sometimes  mixed  with 
it  to  some  depth.  The  nitre  is  extracted  from  the  earth  by  treating  it 
with  Avator,  and  the  solution  is  evaporated,  at  first  by  the  heat  of  the  sun, 
and  afterwards  by  artificial  heat,  Avlien  the  impure  crystals  are  obtained, 
which  are  packed  in  bags  and  sent  to  this  country  as  finniyh  (or  imj)ure) 
saltpetre.  It  contains  a  quantity  of  extraneous  matter  varying  from  1  to 
10  per  cent.,  and  consisting  of  the  chlorides  of  potassium  and  sodium, 
sulphates  of  potassium,  sodium,  and  calcium,  vegetable  matter  from  the 
soil,  sand,  and  moisture.  The  number  representing  the  Aveight  of  impurity 
present  is  usually  termed  the  refradwn  of  the  nitre,  in  allusion  to  the  old 
method  of  estimating  it  by  casting  the  melted  nitre  into  a  cake  and 
^!xamining  its  fracture,  the  appearance  of  which  varies  according  to  the 
Ainount  of  foreign  matter  present. 


414  ARTIFICIAL  PRODUCTION  OF  NITRE. 

Perwnan  or  Chili  saltpetre  is  the  nitrate  of  sodium  (NaNOg)  found 
in  Peru  and  Chili  in  beds  beneath  the  surface  soil.  It  is  often  spoken 
of  as  cubical  saltpetre,  since  it  crystallises  in  rhombohedra,  easily  mis- 
taken for  cubes,  whilst ^^mma^tc  saltpetre,  nitrate  of  potassium,  crystallises 
in  six-sided  prisms.  Nitrate  of  sodium  cannot  be  substituted  for 
nitrate  of  potassium  as  an  ingredient  of  gunpowder,  since  it  attracts 
moisture  from  the  air,  becoming  damp,  and  appears  to  be  less  powerful 
in  its  oxidising  action  upon  combustible  bodies  at  a  high  temperature. 
The  Peruvian  saltpetre,  however,  forms  a  very  important  source 
from  which  to  prepare  the  nitrate  of  potassium  for  gunpowder,  since 
it  is  easily  converted  into  this  salt  by  double  decomposition  with 
chloride  of  potassium.  The  latter  salt  is  now  imported  in  so  largo  a 
quantity  from  the  salt  mines  of  Stassfurth  (page  260)  that  it  enables 
nitrate  of  sodium  to  be  very  cheaply  converted  into  nitrate  of  jiotassium, 
and  renders  Indian  saltpetre  of  less  importance  to  the  manufacturer  of 
gunpowder. 

In  order  to  understand  the  production  of  saltpetre  by  the  decomposi- 
tion of  nitrate  ot  sodium  with  chloride  of  potassium,  it  is  necessary  to  be 
acquainted  with  the  solubility  of  those  salts  and  of  the  salts  produced 
by  their  mutual  decomposition. 

100  parts  of  boiling  water  dissolve  .  100  parts  of  cold  water  dissolve 

218  parts  of  nitrate  of  sodium,  50  parts  of  nitrate  of  sodium, 

53      ,,         chloride  of  potassium,  I         33      ,,         chloride  of  potassium, 

*200      ,,         nitrate  of  potassium,  |         30      ,,         nitrate  of  potassium, 

37      ,,        chloride  of  sodium.  36      ,,         chloride  of  sodium. 

It  is  a  general  rule  that  when  two  salts  in  solution  are  mixed,  which 
are  capable  of  forming,  by  exchange  of  their  metals,  a  salt  which  is  less 
soluble  in  the  liquid,  that  salt  will  be  produced  and  separated. 

Thus,  when  nitrate  of  sodium  and  chloride  of  potassium  are  mixed,  and 
the  solution  boiled  down,  chloride  of  sodium  is  deposited,  and  nitrate  of 
potassium  remains  in  the  boiling  liquid,  NaNOg  +  K(yl  =  KNO3  +  NaCl. 
When  this  is  allowed  to  cool,  the  greater  part  of  the  nitrate  of  potas- 
sium crystallises  out,  leaving  the  remainder  of  the  chloride  of  sodium  m 
solution. 

The  method  usually  adopted  is  to  add  the  chloride  of  potassium  by 
degrees  to  the  boiling  solution  of  nitrate  of  sodium,  to  remove  the 
chloride  of  sodium  with  a  perforated  ladle  in  proportion  as  it  is  deposited, 
and  after  allowing  the  liquid  to  rest  for  some  time  to  deposit  suspended 
impurities,  to  run  it  out  into  the  crystallising  pans. 

The  potassium-salt  required  for  the  conversion  of  nitrate  of  sodium 
into  nitrate  of  potassium  is  sometimes  obtained  from  the  refuse  of  th& 
beet-root  employed  in  the  the  manufacture  of  sugar. 

Chili  saltpetre  sometimes  contains  a  considerable  proportion  of  iodate. 
Yellow  samples  containing  chromate  are  occasionally  found. 

titrate  of  potassium  is  sometimes  prepared  from  the  nitrates  obtained 
in  the  nitre-heaps,  which  consist  of  accumulations  of  vegetable  and  animal 
refuse  with  limestone,  old  mortar,  ashes,  &c.  These  heaps  are  constructed 
upon  an  impermeable  clay  floor  under  a  shed  to  protect  them  from  rain. 
One  side  of  the  heap  is  usually  vertical  and  exposed  to  the  prevailing 
wind,  the  other  side  being  cut  into  steps  or  terraces.  They  are 
occasionally  moistened  with  stable  drainings,  which  are  allowed  to  run 
into  grooves  cut  in  the  steps  at  the  back  of  the  heap.     In  such  a  mass,. 


SALTPETRE  REFINING. 


415 


at  an  atmospheric  temperature  between  60''  and  70°  F.,  nitrates  of  the 
various  metals  present  in  the  heap  are  slowly  formed,  and  being  dissolved 
by  the  moisture,  are  left  by  it,  as  it  evaporates  on  the  vertical  side,  in 
the  form  of  an  efflorescence.  When  this  has  accumulated  in  sufficient 
quantity,  it  is  scraped  off,  together  with  a  few  inches  of  tlie  nitrified 
earth,  and  extracted  with  water,  which  dissolves  the  nitrates,  whilst  the 
undissolved  earth  is  built  up  again  on  the  terraced  back  of  the  heap. 
After  two  or  three  years  tlie  heap  is  entirely  broken  up  and  reconstructed. 
The  principal  nitrates  which  are  found  dissolved  in  water  are  those  of 
potassium,  calcium,  magnesium,  and  ammonium,  the  three  last  of  w^hich 
may  be  converted  into  nitrate  of  potassiuia  by  decomposing  them  with 
carbonate  of  potassium. 

The  formation  of  nitrates  in  these  heaps  probably  results  from  chemical 
changes  similar  to  those  which  occur  in  the  soils  in  which  nitre  is 
naturally  formed,  but,  at  present,  these  changes  are  not  thoroughly 
explained.  Some  chemists  are  of  opinion  that  nitrates  are  formed 
from  atmospheric  nitrogen  and  oxygen,  encouraged  by  the  presence  of 
porous  solids,  and  of  matters  undergoing  oxidation.  The  explanation 
which  is  best  supported  by  experimental  evidence  is  that  which  refers 
their  formation  to  tlie  oxidation  of  ammonia  (page  132),  evolved  by  the 
putrefaction  of  the  nitrogenised  matters  which  the  heaps  contain,  this 
oxidation  also  being  much  promoted  by  the  presence  of  the  strongly 
alkaline  lime,  of  the  porous  materials  capable  of  absorbing  ammonia  and 
presenting  it  under  circumstances  favourable  to  oxidation,  and  of  a 
peculiar  mycoderni  or  minute  fungus  (page  134). 

In  refininij  saltpetre  for  the  manufacture  of  gunpowder,  the  impure 
(r/rongh)  salt  is  dissolved  in  about  an  equal  weight  of  boiling  water  in  a 
copper  boiler,  the  solution  run  through  cloth  filters  to  remove  insoluble 
matter,  and  allowed  to  crystallise  in  a  shallow  wooden  trough  lined  with 
copper,  the  bottom  of  which  is  formed  of  two  inclined  planes  (fig.  275). 
Whilst  cooling,  the  solution  is  kept  in  continual  agitation  with  wooden 
stirrers,  in  order  that  the  saltpetre  may  be  deposited  in  the  minute  crj^stals 
known  as  saltpetre  floirr,  and  not  in  the  large  prisms 
which  are  formed  Avheu  the  solution  is  allowed  to 
crystallise  tranquilly,  and  which  contain  within  them 
cavities  enclosing  some  of  the  impure  liquor  from 
which  the  saltpetre  has  been  crystallised.  The  salt- 
petre, being  so  much  less  soluble  in  cold  than  in  hot 
water,  is,  in  great  part,  deposited  as  the  liquid  cools, 
whilst  the  clilorides  and  other  impurities  being  present 
in  small  proportion,  and  not  presenting  the  same 
disparity  in  their  solubility  at  different  temperatures, 
are  retained  in  the  liquid.  The  saltpetre  flour  is 
drained  in  a  wooden  trough  with  a  perforated  bottom, 
and  transferred  to  a  washing-cistern,  where  it  is 
allowed  to  remain  for  half  an  hour  in  contact  with 
two  or  three  successive  small  quantities  of  water,  to 
wash  away  the  adhering  impure  liquor ;  it  is  then  allowed  to  drain 
thoroughly,  and  in  that  state,  containing  from  3  to  6  per  cent,  of  water, 
according  to  the  season,  is  ready  to  be  transferred  to  the  incorporating  miU 
or  to  a  hot-air  oven,  where  it  is  dried  if  not  required  for  immediate  use. 

The  mother  liquor,  from  which  the  saltpetre  flour  has  been  deposited,, 


Ficr.  275. 


416  '     PROrEUTIES  OF  SALTPETRE. 

is  boiled  down  and  crystallised,  the  crystals  being  worked  u]>  with  the 
next  batch  of  grough  nitre.  The  final  washings  of  the  Hour  are  returned 
to  the  boiler  in  which  the  grough  nitre  is  originally  dissolved.  When 
the  saltpetre  contains  very  much  colouring  matter,  a  little  glue  or  animal 
diarcoal  is  employed  by  the  refiner  to  assist  in  its  removal. 

The  impurities  most  objectionable  in  the  saltpetre  employed  for  gun- 
powder would  be  the  chlorides  of  i^otassium  and  sodium,  which  cause  it 
to  absorb  jiioisture  easily  from  the  air ;  the  chief  test,  therefore,  to  which 
the  refiner  subjects  it,  is  the  addition,  to  its  solution  in  distilled  water, 
of  a  few  drops  of  solution  of  nitrate  of  silver,  which  causes  a  milkiness, 
due  to  the  separation  of  a  precipitate  of  chloride  of  silver,  if  the 
chlorides  have  not  been  entirely  removed.  Moreover,  the  sample  should 
dissolve  entirely  in  water,  to  a  perfectly  clear  colourless  solution,  which 
.should  have  no  effect  on  blue  or  red  litmus  paper,  and  should  give  no 
cloudiness  with  chloride  of  barium  (indicating  the  presence  of  sulphates), 
or  with  oxalate  of  ammonia  (indicating  lime),  when  these  are  added  to 
sei)arate  portions  of  it.  Very  minute  quantities  of  sulphates  and  of  lime, 
.such  as  may  have  been  derived  from  the  wse  of  river  water  in  washing 
the  flour,  are  generally  disregarded. 

/'roperfidfi  of  Holtpetre. — Nitrate  of  ])ota.ssium  is  usually  distinguishable 
by  the  long  striated  or  grooved  six-sided  prismatic  form  in  which  it 
crystallises  (though  it  may  also  be  obtained  in  rhombohedral  crystals  like 
those  of  nitrate  of  sodium),  and  by  the  deflagration  which  it  j)roduces  when 
thrown  on  red  hot  coals.  It  fuses  at  about  635°  F,  to  a  colourless  liquid, 
which  solidifies  on  cooling  to  a  translucent  brittle  crystalline  mass.  The 
ml  xiftindh'  of  the  shops  consists  of  nitre  which  has  been  fused  and  cast 
into  balls.  At  a  red  heat  it  effervesces  from  the  escai)e  of  bubbles  of 
oxygen,  and  is  converted  into  nitrite  of  potassium  (KNO.,),  which  is 
itself  decom])osed  by  a  higher  tem])erature,  evolving  nitrogen  and  oxygen, 
and  leaving  a  mixture  of  potash  (K.^O)  and  peroxide  of  potassium 
(K2O.2).  In  contact  with  any  combustible  body,  it  undergoes  decom- 
position with  great  rajjidity,  five-sixths  of  its  oxygen  being  available  for 
the  oxidation  of  the  combustible  substance,  and  the  nitrogen  being 
evolved  in  the  free  state;  thus,  in  contact  w-ith  carbon,  tlie  decom])osition 
of  the  nitre  may  be  i-e])resented  by  the  equation — 

2KN0..  -I-  C..  =  K^CO;,  +  C0._,  -j-  CO  -f  Ng. 

Since  the  combustion  of  a  large  quantity  of  material  may  be  thus 
effected  in  a  very  small  space  and  in  a  short  time,  the  temperature  pro- 
duced is  much  higher  than  that  obtained  by  burning  the  combustible 
in  the  ordinary  way.  The  si)ecific  gravity  of  salti)etre  is  2-07,  so  that 
1  cubic  inch  weighs  523  grains  (obtained  by  multiplying  the  weight  of 
a  i:ubic  inch  of  water,  252-5  grains,  by  2-07).  Since  202  grains  (2  mole- 
cules) of  nitre  contain  80  grains  (5  atoms)  of  oxygen  available  for  the 
o.xidation  of  combustible  bodies,  523  grains,  or  1  cubic  inch,  of  nitre, 
w(jul(l  contain  207  grains  or  605  cubic  inches  of  available  oxygen,  a 
volume  Avhich  would  be  contained  in  about  ^3000  cubic  inches  of  air ; 
hence,  1  volume  of  saltpetre  represents,  in  its'  power  of  sujiporting  com- 
bustion, 3000  volumes  of  atmospheric  air.  It  also  enables  .some  com- 
bustible substances  to  burn  without  actual  flame,  as  is  exemplified  by  its 
ust'.  in  towJipap'r  or  sloic  port-fire,  which  consists  of  )jai)er  soaked  in  a 
Aveak  solution  of  saltpetre  and  dried. 


COMPOSITION  OF  CHARCOAL. 


41Y 


If  a  continuous  design  be  traced  on  foolscap  paper  with  a  brush  dipped  in  a  solu- 
tion of  30  grains  of  saltpetre  in  100  grains  of  water,  and  allowed  to  dry,  it  will  be 
found  that  when  one  part  of  the  pattern  is  touched  with  a  red  hot  iron,  it  will 
gradually  burn  its  way  out,  the  other  portion  of  the  paper  remaining  unaffected. 

A  mixture  of  90  grains  of  saltpetre,  30  of  sulphur,  and  30  of  moderately  fine 
sawdust  {Bauitie's  flux)  will  deflagrate  with  sufficient  intensity  to  fuse  a  small  silver 
coin  into  a  globule ;  the  mixture  may  be  pressed  down  in  a  walnut  shell  or  a  small 
porcelain  crucible,  and  the  coin  buried  in  it,  the  flame  of  a  lamp  being  applied  out- 
side until  deflagration  commences. 

Piilvis  fulminans  is  a  mixture  of  3  parts  of  saltpetre,  1  part  of  sulphur,  and  2  of 
carbonate  of  potash,  all  carefully  dried  ;  when  it  is  heated  on  an  iron  ]ilate,  no  action 
takes  place  till  it  melts,  when  it  explodes  very  violently. 

Charcoal  for  Guxpowder. — Charcoal  has  been  already  described  as 
the  residue  of  the  destructive  distillation  of  wood,  in  which  process  the 
hydrogen  and  oxygen  of  the  wood  are  for  the  most  part  expelled  in  the 
forms  of  wood  naphtha  (CH^O),  pyroligneous  acid  (CgH^Og),  carbonic 
acid  gas,  carbonic  oxide,  water,  &c.,  leaving  a  residue  containing  a  much 
larger  proportion  of  carbon  than  the  original  wood,  and  therefore  capable 
of  producing  a  much  higher  temperature  (page  69)  by  its  combustion  with 
the  saltpetre.  The  higher  the  temperature  to  which  the  charcoal  is 
exposed  in  its  preparation,  the  larger  the  proportion  of  hydrogen  and 
oxygen  expelled,  and  the  more  nearly  does  the  charcoal  approach  in  com- 
position to  pure  carbon ;  but  it  is  not  found  advantageous  in  practice  to 
employ  so  high  a  temperature,  since  it  yields  a  dense  charcoal  of  difficult 
combustibility,  and  therefore  less  fitted  for  the  manufacture  of  powder. 
The  average  composition  of  wood,  exclusive  of  ash,  is,  in  100  parts — 


Carbon. 
50 


Hydrogen. 


Oxygen. 
44 


The  composition  of  the  charcoal  prepared  at  different  temperatures  is 
given  in  the  following  table  : — 


Temperature            Carbon. 
of  Charring,     i 

Hydrogen. 

Oxygen.                    Ash. 

270°  C. 
363° 
476° 
519° 

71 
80-1 

85-8 
86-2 

4-6 
3-71 
313 
3-11 

23 

14-55 
9-47 
9-11 

1-4 
1-64 
1-60 
1-58 

The  charcoal  employed  for  gunpowder  in  this  country  is  prepared  at 
temperatures  between  360°  C.  and  520°  C.  It  will  be  seen  that  the 
proportion  of  carbon,  upon  which  the  heating  value  of  the  charcoal 
depends,  increases  with  the  final  temperature  of  carbonisation;  but  it  has 
been  found  that  the  rapidity  with  which  the  temperature  is  raised  has 
also  a  great  effect  in  increasing  the  proportion  of  carbon,  as  shown  in  the 
following  table  : — 


Final 
Temperature. 

Time  of 
Heating. 

Percentage 
of  Caibon. 

Final 
Temperature. 

Time  of 
Heating. 

Percentage 
of  Caibon. 

410°  C. 

414° 

490° 

5    hours. 

n   „ 

81-65 
83  14 
84-19 

490  °C. 

555° 

558°, 

2f  hours 

H    „ 

3       „ 

86-34 
83-32 
86-52 

The  charcoal  prepared  between  260°  and  320°  C.  has  a  brown  colour 

(cliarhon  roux),  and  although  it  is  more  easily  inflamed  than  the  black 
charcoal  obtained  at  higher  temperatures,  the  presence  of  a  large  pro- 

2  D 


418 


CHARCOAL  FOR  GUNPOWDER. 


portion  of  oxygen  so  much  diminishes  its  calorific  value,  that  its  employ- 
ment in  gunpowder  is  not  advantageous.  It  is  used  on  the  Continent  in 
the  manufacture  of  sporting-powder,  and  is  prepared  by  exposing  the 
wood,  in  an  iron  cylinder,  to  the  action  of  high-pressure  steam  heated  to 
about  280°  C.  Charcoal  prepared  at  low  temperatures  gives  somewhat 
higher  velocities,  but  absorbs  much  more  moisture  than  that  prepared  at 
high  temperatures. 

Light  woods,  such  as  alder,  willow,  and  dogwood,*  are  selected  for  the 
preparation  of  charcoal  for  gunpowder,  because  they  yield  a  lighter  and 
more  easily  combustible  charcoal,  dogwood  being  employed  for  the  best 
quality  of  powder  for  small  arms.  This  wood  is  chiefly  imported,  since  it 
has  not  been  successfully  grown  in  this  country.  The  wood  is  stripped 
of  its  bark,  and  either  exposed  for  a  length  of  time  to  the  air  or  dried  in 
a  hot  chamber.  Considerable  loss  of  charcoal  takes  place  if  damp  wood 
be  charred,  a  portion  of  the  carbon  being  oxidised  by  the  steam  at  a  high 
temperature. 

In  order  to  convert  the  wood  into  charcoal,  1|  cwt.  of  wood  is  packed 
into  a  sheet-iron  cylinder  or  slip  (fig.  276),  one  end  of  which  is  closed 

by  a  tightly-fitting  cover,  and  the 
other  by  a  perforated  plate,  to 
allow  of  the  escape  of  the  gases 
and  vapours  expelled  during  the 
carbonisation.  This  cylinder  is 
then  introduced  into  a  cylindrical 
cast-iron  retort,  built  into  a  brick 
furnace,  and  provided  with  a  pipe 
(L)  for  the  escape  of  the  products, 
which  are  usually  carried  back 
into  the  furnace  (B)  to  be  con- 
sumed. The  process  of  charring 
occupies  from  2|  to  3|  hours,  and 
as  soon  as  it  is  completed,  which 
is  known  by  the  violet  tint  of  the 
(carbonic  oxide)  flame  from  the 
pipe  leading  into  the  fire,  the  slip  is  transferred  to  an  iron  box  or 
extinguisher,  where  the  charcoal  is  allowed  to  cooL  About  40  lbs.  of 
charcoal  are  obtained  from  the  above  quantity  of  wood.  Charcoal 
prepared  by  this  process  is  spoken  of  as  cylinder  charcoal,  to  distinguish 
it  from  pit  charcoal,  prepared  by  the  ordinary  process  of  charcoal- 
burning  described  at  page  65,  and  which  is  employed  for  fuze  com- 
positions, &c.,  but  not  for  the  best  gunpowder.  The  fitness  of  the 
charcoal  for  the  manufacture  of  powder  is  generally  judged  of  by  its 
physical  characters.  It  is  of  course  desirable  that  the  charcoal  should 
be  as  free  from  incombustible  matter  as  possible.  The  proportion  of  the 
ash  left  by  different  charcoals  varies  considerably,  but  it  seldom  exceeds 
2  per  cent.  This  ash  consists  chiefly  of  the  carbonates  of  potassium  and 
calcium ;  it  also  contains  calcium  phosphate,  magnesium  carbonate, 
silicate  and  sulphate  of  potassium,  chloride  of  sodium,  and  the  oxides  of 
iron  and  manganese.  • 

The  charcoal  is  kept  for  about  a  fortnight  before  being  ground,  for  if 

*  Dogwood  cliarcoal  is  not  made  from  the  true  dogwood  (cw?m«\  but  from  the  alder 
buclcthorn  {Rhamnus  frangiUa),  commonly  called  black  dogwood. 


Fig.  276. — Charcoal  retort. 


SULPHUR  FOR  GUNPOWDER.  419- 

ground  when  fresh,  before  it  has  absorbed  moisture  and  oxygen  from  the 
air,  it  is  liable  to  spontaneous  combustion.  The  grinding  is  effected  in  a 
mill  resembling  a  cotfee-mill,  and  the  charcoal  is  afterwards  sifted. 

The  properties  of  charcoal  have  been  already  described ;  its  great  ten- 
dency to  absorb  moisture  from  the  air  is  of  some  importance  in  the  manu- 
facture of  gunpowder,  from  its  causing  a  false  estimate  to  be  made  of  the 
proportion  employed,  unless  the  actual  amount  of  water  present  in  the 
charcoal  is  known. 

Tar  charcoal  is  the  name  given  to  sticks  of  charcoal  which  have  acci- 
dentally become  coated  with  a  shining  film  of  carbon  left  behind  by  tar 
which  has  condensed  upon  it  in  the  retorts ;  it  is  sometimes  rejected  by 
the  powder  manufacturer. 

Sulphur  for  Gunpowder. — Distilled  sulphur  (page  188)  is  the  variety 
always  employed  for  the  manufacture  of  gunpowder,  the  siiblimed  sulphur 
being  employed  for  fuze  compositions,  &c.  The  alleged  reason  for  the 
preference  is  that  the  sublimed  sulphur,  having  been  deposited  in  a 
chamber  containing  much  sulphurous  and  sulphuric  acid  vapours,*  its 
pores  have  become  charged  with  acid  which  would  be  injurious  in  the 
powder;  but  it  has  been  pointed  out  (page  191)  that  distilled  sulphur 
consists  entirely  of  the  soluble  or  electro-negative  variety  of  sulphur, 
whilst  sublimed  sulphur  contains  a  large  proportion  of  the  insoluble  or 
positive  sulphur,  which  would  probably  influence  its  action  in  gunpowder. 
The  sulphur  should  leave  scarcely  a  trace  of  incombustible  matter  when 
burnt,  and  after  stirring  the  powdered  sulphur  for  some  time  with  warm 
distilled  water,  the  latter  should  only  very  feebly  redden  blue  litmus. 
As  an  ingredient  of  gunpowder,  sulphur  is  valuable  on  account  of  the 
low  temperature  (500"  F.)  at  which  it  inflames,  thus  facilitating  the 
ignition  of  the  powder.  Its  oxidation  by  saltpetre  appears  also  to  be 
attended  with  the  production  of  a  higher  temperature  than  is  obtained 
with  charcoal,  which  would  have  the  efl'ect  of  accelerating  the  combustion 
and  of  increasing,  by  expansion,  the  volume  of  gas  evolved.  The  sulphur 
is  ground  under  edge-runners  (fig.  277)  and  sifted. 

The  difference  in  the  inflammability  of  sulphur  and  charcoal  is  strikingly  shown 
by  heating  a  square  of  coarse  wire-gauze  over  a  flame  till  it  is  red  hot  in  the  centre, 
placing  it  over  a  jar  of  oxygen,  allowing  it  to  cool  till  it  no  longer  kindles  charcoal- 
powder  sprinkled  through  it  from  a  pepper-box,  and  whilst  the  cloud  of  charcoal  is 
still  floating  in  the  gas,  throwing  in  sulphur  from  a  second  box  ;  the  hot  gauze  will 
inflame  the  sulphur,  and  this  will  kindle  the  charcoal. 

An  iron  rod  allowed  to  cool  V)elow  redness  may  be  used  to  stir  a  mixture  of  charcoal 
with  (3  parts  of)  nitre  ;  but  if  dipped  into  powdered  sulphur,  at  once  inflames  it, 
and  the  flame  of  the  sulphur  will  kindle  the  mixture.  The  efl'ect  of  the  same  rod 
upon  mixtures  of  nitre  with  charcoal  alone,  and  with  charcoal  and  sulphur,  is 
iustrnctive. 

The  acceleration  of  the  combustion  of  gunpowder  by  the  sulphur  is  well  shown  by 
laying  a  train,  of  which  one-half  consists  of  a  mixture  of  75  nitre  and  25  charcoal, 
and  the  other  of  75  nitre,  15  charcoal,  and  10  sulphur,  a  red  hot  iron  being  applied 
at  the  junction  of  the  two  trains  to  start  them  together. 

Manufacture  of  Gunpowder. — The  proportions  of  the  ingredients  of 
gunpowder  have  been  varied  somewhat  in  different  countries,  the  saltpetre 
ranging  from  74  to  77  per  cent.,  the  charcoal  from  12  to  16  per  cent.,  and 
the  sulphur  from  9  to  12  "5  per  cent.  English  Government  powder  contains 
7o  per  cent,  of  nitre,  15  per  cent,  of  charcoal,  and  10  per  cent,  of  sulphur. 

.  *  For  certain  compositions  in  which  sublimed  sulphur  is  used,  it  is  well  washed  with 
water  in  order  to  remove  the  acid  from  its  pores. 


420 


MANUFACTURE  OF  GUNPOWDER. 


Fig.  277.— Incorporating  mill. 


An  extra  pound  of  saltpetre  is  generally  added  at  Waltham,  to  compen- 
sate for  loss  in  manufacture. 

The  powdered  ingredients*  are  first  roughly  mixed  in  a  revolving  gun- 
metal  drum,  with  mixing  arms  .turning  in  an  opposite  direction,  and  the 
mixture  is  subjected,  in  quantities  of  about  50  lbs.  at  a  time,  to  the  action 
of  the  incorporating  mill  (fig.  277),  where  it  is  sprinkled  with  water, 

poured  through  the  funnel  (F),  or 
from  a  can  with  a  fine  rose,  and 
exposed  to  trituration  and  pressure 
under  two  cast-iron  edge-runners  (B), 
rolling  round  in  different  paths  upon 
a  cast-iron  bed,  a  very  intimate 
mixture  being  thus  effected  by  the 
same  kind  of  movement  as  in  a 
common  pestle  and  mortar,  the  distri- 
bution of  the  nitre  through  the  mass 
being  also  assisted  by  its  solubility  in 
water.  A  wooden  scraper  (C)  tipped 
with  copper  prevents  the  roller  from 
getting  clogged,  and  a  plough  (D) 
keeps  the  mixture  in  the  path.  Of 
course,  the  water  employed  to  moisten 
the  powder  must  be  as  free  from  deliquescent  salts  (especially  chlorides,  see 
page  416)  as  possible;  at  "Waltham  condensed  steam  is  employed  :  the 
quantity  required  varies  with  the  state  of  the  atmosphere.  The  duration 
of  the  incorporating  process  is  varied  according  to  the  kind  of  powder 
required,  the  slow-burning  powder  employed  for  cannon  being  sufficiently 
incorporated  in  about  three  hours,  whilst  rifle-powder  requires  five  hours. 

The  dark  grey  mass  of  mill-cake  which  is  thus  produced,  contains  2  or 
3  per  cent,  of  water.  It  is  broken  up  by  passing  between  grooved  rollers 
of  gun  metal,  and  is  then  placed,  in  layers  of  about  half  an  inch  thick, 
between  copper  plates  packed  in  a  stout  gun-metal  box  lined  inside  and 
outside  with  wood,  in  which  it  is  subjected  for  a  quarter  of  an  hour  to  a 
pressure  of  about  70  tons  on  the  square  foot,  in  a  hydraulic  press,  which 
Ims  the  effect  of  condensing  a  larger  quantity  of  explosive  material  into  a 
given  volume,  and  of  diminishing  the  tendency  of  the  powder  to  absorb 
moisture  from  the  air  and  to  disintegrate  or  dust  after  granulation.  The 
press-cake  thus  obtained  is  very  hard  and  compact,  resembling  slate  in 
ai)pearaiice.  As  far  as  its  chemical  nature  is  concerned,  it  is  finished 
gunpowder,  but  if  it  be  reduced  to, powder  and  a  gun  loaded  with  it,  the 
comlnis^tion  of  the  charge  is  found  to  take  place  too  slowly  to  produce  its 
full  effect,  since  the  pulverulent  form  offers  so  great  an  obstacle  to  the 
passage  of  the  flame  by  which  the  combustion  is  communicated  from  one 
end  of  the  charge  to  the  other.  The  press-cake  must,  therefore,  be 
(jraimlated  [corned)  or  broken  up  into  grains  of  sufficient  size  to  allow  the 
rapid  passage  of  the  flame  between  them,  and  the  consequent  immediate 
firing  of  the  whole  charge.  The  granulation  is  effected  by  crushing  the 
prnss-cake  between  successive  pairs  of  toothed  guti-metal  rollers,  from 
which  it  falls  on  to  sieves,  which  separate  it  into  grains  of  different  sizes, 
the  dust,  or  meal  poioder,  passing  through  the  last  sieve.     At  Waltham, 

•  The  amount  of  water  in  the  moist  saltpetre  (page  415)  is  ascertained  by  drying  and 
melting  a  weighed  sample  before  the  proportions  are  weighed  out. 


PROPERTIES  OF  GUNPOWDER.  421 

the  R.L.G.  (rifle  large  grain)  passes  through  a  sieve  of  4  meshes  to  the 
inch,  and  is  retained  on  one  of  8  meshes,  whilst  R.F.G.  (rifle  fine  grain) 
passes  through  a  12-mesh,  and  is  retained  on  a  20-mesh  sieve.  The 
granulated  powders  are  freed  from  dust  by  passing  them  through  revolv- 
ing cylinders  of  wooden  framework  covered  with  canvas  or  wire  cloth, 
and  the  fine  grain  powder  is  glazed  by  the  friction  of  its  own  grains 
against  each  other  in  revolving  barrels.  The  large-grain  powders  are 
sometimes  glazed  or  faced  with  graphite,  by  introducing  a  little  of  that 
substance  into  the  glazing-barrels  with  the  powder.  The  powder  is 
dried  in  a  chamber  heated  by  steam,  very  gradually,  so  as  not  to  injure 
the  grain,  and  is  once  more  dusted  in  canvas  cylinders  before  being  packed. 

For  very  large  charges,  the  grains  having  a  diameter  of  :|  to  |^  inch 
(R.L.G.)  are  found  to  burn  too  rapidly,  exerting  too  great  a  strain  upon 
the  gun.  In  such  cases,  pebble  powder,  the  grains  of  which  vary  from 
f  to  1|^  inch  or  more  in  diameter,  is  employed. 

Prismatic  powder  consists  of  large  grains  made  of  a  regular  six-sided 
prismatic  form  by  compressing  the  powder-meal  (without  previously 
making  it  into  press-cake)  in  moulds,  with  metal  punches,  whereas  the 
pebble  powder  is  irregular  iu  form.  The  prismatic  powder  is  made  with 
perforations  in  the  direction  of  its  length  to  facilitate  the  passage  of  flame 
through  the  charga 

Pellet  powder  is  moulded  in  a  similar  manner  into  cylindrical  pellets 
about  I  inch  long  and  f  inch  in  diameter,  perforated  at  one  end  to  about 
the  centre. 

309.  Properties  of  Gunpowder. — Good  gunpowder  is  composed  of 
hard  angular  grains,  which  do  not  soil  the  fingers,  and  have  a  perfectly 
uniform  dark  grey  colour.  Its  specific  gravity  (absolute  density)  as  deter- 
mined by  the  densimeter*  varies  between  1*67  and  1*84,  and  its  apparent 
density  (obtained  by  weighing  a  given  measure  of  the  grain  against  an 
equal  measure  of  water)  varies  from  0*89  to  0"94,  so  that  a  cubic  foot 
Avill  weigh  from  55  to  58  lbs,  "When  exposed  to  air  of  average  dryness, 
gunpowder  absorbs  from  0*5  to  1  "0  per  cent,  of  water.  In  damp  air  it 
absorbs  a  much  larger  proportion,  and  becomes  deteriorated  in  conse- 
quence of  the  saltpetre  being  dissolved,  and  crystallising  upon  the  surface 
of  the  grains.  Actual  contact  with  water  dissolves  the  saltpetre  and 
disintegrates  the  grains.  When  very  gradually  heated  in  air,  gunpowder 
begins  to  lose  sulphur,  even  at  212°  F.,  this  ingredient  passing  off"  rapidly 
as  the  temperature  rises,  so  that  the  greater  part  of  it  may  be  expelled 
without  inflaming  the  powder,  especially  if  the  powder  is  heated  in 
carbonic  acid  gas  or  hydrogen,  to  prevent  contact  with  air.  If  gunpowder 
be  suddenly  heated  to  600°  F.  in  air,  it  explodes,  the  sulphur  probably 
inflaming  first  ;  but  out  of  contact  Avith  air  a  higher  temperature  is 
required  to  inflame  it.  The  ignition  of  gunpowder  by  flame  is  not 
ensured  unless  the  flame  be  flashed  among  the  grains  of  powder  ;  it  often 
takes  some  time  to  ignite  powder  with  the  flame  of  a  piece  of  burning 
paper  or  stick,  but  contact  with  a  red  hot  solid  body  inflames  it  at  once. 
A  heap  of  good  powder,  when  fired  on  a  sheet  of  white  paper,  burns  with- 
out sparks  and  without  scorching  or  kindling  the  paper,  which  should 
exhibit  only  scanty  black  marks  of  charcoal  after  the  explosion.     If  the 

*  This  is  a  simple  apparatus  for  determining  the  weight  of  mercury  displaced  by  a  given 
weight  of  gunpowder,  from  which  all  the  air  has  been  exhausted. 


422  PRODUCTS  OF  EXPLOSION  OF  GUNPOWDER. 

powder  has  not  been  thoroughly  incorporated,  it  will  leave  minute 
globules  of  fused  nitre  upon  the  paper.  Two  ounces  of  the  powder  should 
be  capable  of  throwing  a  68-ib.  shot  to  a  distance  of  260  to  300  feet  from 
an  8-inch  mortar  at  45°  elevation. 

This  mode  of  testing  power  by  the  eprouvette  mortar  is  not  now 
applied  to  Government  powders.  Far  more  accurate  results  are  obtained 
by  measuring  the  velocity  imparted  to  a  projectile  of  known  weight  by  a 
given  charge  of  the  powder.  The  velocity  is  measured  by  means  of  a 
chronoscope  which  registers  the  distance  travelled  by  the  shot  in  a  given 
time  by  causing  it  to  cut  the  wire  of  one  electrical  circuit  at  the  com- 
mencement of  its  flight,  and  that  of  another  at  the  conclusion,  thus 
telegraphing  its  velocity  to  the  instrument  room  at  a  distance. 

Cannon  powder  (R.L.G.)  is  tested  by  firing  a  charge  of  1  lb.  from  a 
muzzle-loader  rifled  gun,  with  a  12-lb  shot.  Small  arm  powder  (R.F.G.) 
is  fired  from  a  Snider-Enfield  or  Martini-Henry  rifle.  The  mean  velocity 
at  a  distance  of  105  feet  from  the  muzzle  is  determined.  For  R.L.G. 
it  amounts  to  about  1000  feet  per  second.  A  charge  of  70  grs.  of  R.F.G. 
in  the  Snider-Enfield  rifle  gives  a  velocity  somewhat  greater  than  this. 

Very  fortunately,  it  is  difficult  to  explode  gunpower  by  concussion, 
though  it  has  been  found  possible  to  do  so,  especially  on  iron,  and  acci- 
dents appear  to  have  been  caused  in  this  way  by  the  iron  edge-runners  in 
the  incorporating  mill,  when  the  workmen  have  neglected  the  special 
precautions  which  are  laid  down  for  them.  The  use  of  stone  upon  iron 
in  the  incorporation  is  avoided,  because  of  the  great  risk  of  producing 
sparks,  and  copper  is  employed  in  the  various  fittings  of  a  powder  mill 
wherever  it  is  possible. 

The  electric  spark  is,  of  course,  capable  of  firing  gunpowder,  though 
it  is  not  easy  to  ensure  the  inflammation  of  a  charge  by  a  spark  unless  its 
conducting  powder  is  slightly  improved  by  keeping  it  a  little  moist,  which 
may  be  effected  by  introducing  a  minute  quantity  of  chloride  of  calcium. 

310.  Products  of  Explosion  of  Gunpowder. — In  the  explosion  of 
gunpowder,  the  oxygen  of  the  nitre  converts  the  carbon  of  the  charcoal 
chiefly  into  carbonic  acid  gas  (COo),  part  of  which  assumes  the  gaseous 
state,  whilst  the  remainder  is  converted  into  potassium  carbonate  (K2CO3). 
The  greater  part  of  the  sulphur  is  converted  into  potassium  sulphate 
(KgSO^).  The  chief  part  of  the  nitrogen  contained  in  the  nitre  is 
evolved  in  the  uncombined  state.  The  rough  chemical  account  of  the 
explosion  of  gunpowder,  therefore,  is  that  the  mixture  of  nitre,  sulphur, 
and  charcoal  is  resolved  into  a  mixture  of  potassium  carbonate,  potassium 
sulphate,  carbonic  acid  gas,  and  nitrogen,  the  two  last  being  gases,  the 
elastic  force  of  which,  when  expanded  by  the  heat  of  the  combustion, 
accounts  for  the  mechanical  effect  of  the  explosion. 

But  in  addition  to  these,  several  other  substances  are  found  among  the 
products  of  the  explosion.  Thus,  the  presence  of  potassium  sulphide 
(K2S)  may  be  recognised  by  the  smell  of  hydric  sulphide  produced 
on  moistening  the  solid  residue  in  the  barrel  of  a  gun,  and  hydric  sulphide 
(HgS)  itself  may  often  be  perceived  in  the  gases  produced  by  the  explosion, 
the  hydrogen  being  derived  from  the  charcoal.  A  little  marsh  gas 
(CH^)  is  also  found  among  the  gases,  being  produced  by  the  decomposition 
of  the  charcoal,  a  portion  of  the  hydrogen  of  which  is  also  disengaged 
iu  the   free  state.     Carbonic  oxide  (CO)  is  always  detected  among  the 


PKODUCTS  OF  EXPLOSION  OF  GUNPOWDER, 


423 


products.  It  is  evident  that  the  collection  for  analysis  of  the  products  of 
explosion  must  be  attended  with  some  trouble,  and  that  considerable 
ditferences  are  to  be  expected  between  the  results  obtained  by  different 
operators,  from  the  variation  of  the  circumstances  under  which  the  powder 
is  tired  and  the  products  collected.  When  the  powder  is  slowly  fired, 
a  considerable  proportion  of  the  nitrogen  in  the  saltpetre  is  evolved  in 
the  form  of  nitric  oxide  gas  (NO),  which  is  not  found  among  the 
products  of  the  rapid  explosion  of  powder. 

Some  of  the  most  recent  experiments  upon  the  explosion  of  gunpowder 
have  been  made  by  Noble  and  Abel  under  conditions  very  similar  to 
those  which  occur  in  practice,  the  powder  having  been  confined  in  a  strong 
vessel  of  mild  steel,  in  Avhich  the  powder  was  tired  by  electricity,  so  that 
the  gaseous  and  solid  products  of  the  explosion  remained  within  the 
vessel,  and  could  be  submitted  to  analysis. 

Three  samples  of  powder  manufactured  at  Waltham  Abbey  were  thus 
examined.     Their  composition  is  stated  in  the  following  table  : — 


Pebble 
Powder. 

Kifle 
Large  Grain. 

Fine  Grain. 

Nitre              .... 

Sulphur,        .... 

Cliai'coal,  viz.,  Carbon,  . 
Hydrogen, 
Oxygen, 
Ash, 

Water,            .... 

Sulphate  of  potassium,   . 

74-67 
10  07 
12-12 
0-42 
1-45 
0-23 
0-95 
0-09 

74-95 
10-27 
10-86 
0-42 
1-99 
0-25 
1-11 
0-15 

73-55 
10-02 
11-36 
0-49 
2-57 
0-17 
1-48 
0-36 

100-00 

100-00 

100-00 

The  quantities  of  gunpowder  exploded  in  different  experiments  varied 
from  3|  oz.  to  1  lb.  10  oz.,  and  the  pressures  observed  varied  from  1  ton 
to  over  36  tons  on  the  square  inch. 

The  solid  products  Avere  found  almost  entirely  collected  at  the  bottom 
of  the  vessel,  forming  an  exceedingly  hard  mass  of  a  dark  olive-green 
colour,  exceedingly  deliquescent,  smelling  strongly  of  hydric  sulphide, 
and  frequently  also  of  ammonia.  In  some  instances  the  solid  residue 
was  observed  to  become  heated  by  exposure  to  air,  from  the  rapid  absorp- 
tion of  oxygen. 

The  following  table  shows  the  proportions  of  solid  and  gaseous  products 
furnished  by  each  powder,  when  the  ratio  between  the  volume  of  the 
charge  and  that  of  the  containing  space  was  varied  so  that  the  maximum 
pressures  attained  were  those  stated  at  the  head  of  each  column : — 


Pebble  Powder. 

Rifle  Large  Grain. 

Fine  Grain. 

Pressure,  in  tons  per.  sq.  inch, 

Weight  of  solid  products  I'roni  | 

100  parts  powder,        .          .  \ 

W^eight   of  gaseous   products  ) 

from  100  parts  powder,        .  \ 

1-4 
56-12 

43-88 

12-5 
55-17 

44-83 

1-6 
57-22 

42-78 

35-6 
57-14 

42-86 

3-7 
58-17 

41-83 

18-2 
68-09 

41-92 

The  permanent  gases  generated  by  the  explosion  were  found  to  occupy. 


424 


CALCULATION  OF  THE  FORCE  OF  FIRED  GUNPOWDER. 


at  0°  C.  and  at  ordinary  atmospheric  pressure,  about  280  times  the  •volume 
of  the  original  powder. 

The  products  of  explosion  furnished  by  1  gramme  of   each  powder, 
were — 


Pebble 
Powder. 

Rifle  Large 
Grain. 

Fine  Grain. 

Potassium  carbonate  (KjCOs),    . 

,,         sulphate  (K2SO4), 
sulphide  (K.,S),  ■ 

,,         sulphocyauide  (KCNS), 

„         uitrate  (KNO3). 
Ammonium  carbonate, 

Sulphur, 

Chiircoal, 

Total  solid  products,  . 

Carbonic  acid  gas  (COj),    . 
Carbonic  oxide  (CO), 

Nitrogen, 

Suljihuretted  hydrogen  (HgS),    . 
Marsh  gas  (CH4),       .... 

Hydrogen, 

Oxygen, 

Total  gaseous  products, 

•3258 
•0710 
•1042 
•0014 
•0013 
•0005 
•0445 
•0008 

•3415 
•0844 
•0807 
•0013 
•0015 
•0004 
•0490 
•0004 

•2861 
•1252 
•0999 
•0007 
•0009 
•0003 
•0381 

•5495 

•5592 

•5512 

•2685 
•0477 
•1123 
•0111 
•0006 
•0006 

•2630 
•0422 
•1117 
•0109 
'OOOS 
•0009 
•0002 

•2689 
•0355 
•1123 
•0101 
•0004 
•0007 
•0003 

•4282 

•4408             ^4297 

From  this  table  it  appears  that  the  solid  residue  of  fired  gunpowder 
consists  chiefly  of  carbonate  and  sulphate  of  potassium,  with  usually 
smaller  proportions  of  sulphide  of  potassium.  The  gases  evolved  are 
clii(;tiy  carbonic  acid  gas  and  nitrogen,  with  a  small  quantity  of  carbonic 
oxide. 

The  great  variation  iu  the  proportions  of  sulphate  and  sulphide  of 
potassium,  coupled  with  our  knowledge  of  the  mutual  relations  of  these 
bodies  at  high  temperatures,  would  support  the  belief  that  the  sulphate 
is  first  produced,  and  is  partially  converted  into  sulphide  by  secondary 
reactions. 


311.  Calculation  of  the  Force  op  Fired  Gunpowder. —  The  complex 
character  of  the  decomposition,  and  its  variation  under  dififerent  conditions, 
render  it  impossible  to  write  a  single  general  equation  representing  the 
explosion  of  gunpowder;  but  in  order  to  illustrate  the  method  of  calculat- 
ing the  force  of  tired  powder  in  any  given  case,  we  may  take  the  following 
equation  as  a  simple  expression  of  the  principal  reaction — 

4KNO3  +  C4  +  S  =  K2CO3  +  K2SO4  +  N4  +  2CO2  +  CO . 

The  mechanical  force  exerted  in  explosion  depends  upon  the  production 
of  a  large  volume  of  gas  from  a  small  volume  of  solid,  the  volume  of  the 
gas  being  increased  by  the  expansive  effect  of  the  heat  generated  in  the 
combustion  of  the  charcoal  and  sulphur.  To  calculate  the  amount  of  this 
mechanical  force,  it  is  necessary  to  ascertain  the  volume  of  gas  which 
v.duld  be  evolved  by  a  given  volume  of  powder,  and  the  extent  to  which 
the  gas  would  be  expanded  by  the  heat  at  the  instant  of  explosion. 


CALCULATION  OF  THE  FORCE  OF  FIRED  GUNPOWDER.  425 

It  is  calculated,  from  the  Table  of  Atomic  "Weights  that — 

4KN0j  =   101    X    4   =   404  grammes. 
C^  =     12   X    4   =     48         „ 
S  =     32         „ 

Guupovvder,     .         .     484        ,, 

Grammes.  Litres  at  0°  C.  and  7fi0°  mm.  Bar. 

]Sr4  =   14    X    4     =     56     =  11-2      X      4     =     44-8 

2C'02   =   44    X    2     =     88     =  22-4      x      2     =     44-8 

CO                            =28  =     22-4 


Gaseous  products,  172  112 

Hence  it  appears  that  484  grammes  of  gunpowder  would  yield  112  litres 
of  gas  measured  at  0°  C.  and  760  mm.  barometic  pressure. 

We  have  next  to  determine  the  volume  of  this  gas  at  the  moment  of 
the  explosion. 

The  total  heat  produced  in  the  explosion  of  1  part  by  weight  of  gun- 
powder was  found  by  Noble  and  Abel  to  raise  the  temperature  of  714*5 
parts  by  weight  of  water  from  0°  C.  to  1°  C,  or  to  raise  the  temperature 
of  1  part  by  weight  of  water  from  0°  C.  to  7 14° '5  C,  supposing  the  water 
to  be  capable  of  bearing  so  great  an  elevation  of  temperature  without 
change  of  state. 

This  result  is  generally  expressed  by  saying  that  the  combustion  of  the 
powder  evolves  714"5  units  of  heat  (the  unit  of  heat  being  the  quantity 
required  to  raise  1  part  by  weight  of  water  from  0°  C.  to  1°  C). 

But  the  products  of  the  explosion  of  powder  will  be  raised  to  a  higher 
temperature  than  714°*5  C,  because  their  specific  heat  is  lower  than  that 
of  water. 

For  the  purpose  of  this  calculation,  the  specific  heat  of  a  substance  may 
be  defined  as  the  quantity  of  heat  required  to  raise  1  gramme  of  the 
su-bstance  through  1°  of  the  thermometer,  water  being  taken  as  the  unit. 

It  is  evident  that  if  the  specific  heat  of  each  product  of  tbe  explosion 
be  multiplit'd  by  the  actual  weight  of  that  product,  the  result  will  be  the 
quantity  of  heat  required  to  raise  that  product  1°  in  temperature. 

The  specific  heats  of  the  products  have  been  ascertained  by  experiment, 
and  are  contained  in  the  third  column  in  the  following  table.  The 
actual  weight  of  each  product  from  the  explosion  of  1  gramme  of  powder 
is  contained  in  the  second  column,  and  the  fourth  column  shows  the 
quantity  of  heat  required  to  raise  each  product  1°  C.  (representing  as 
unity  the  quantity  of  heat  required  to  raise  1  gramme  of  water  from  0"  C. 

tore.):— 

Calculating  from  the  above  equation,  the  unit  weight  of  gunpowder  gives — 

Potassium  carbonate, 
,,         sulphate. 
Nitrogen,    . 
C'arliouic  acid  gas, 
Carbonic  oxide,    . 

•2118 

The  quantity  of  heat,  therefore,  which  is  required  to  raise,  through  1°  C.  the  joint 
produt'.ts  of  the  explosion  of  1  gramme  of  gunpowder  is  0-2118  of  the  above-mentioned 
unit  of  heat. 

Dividing  the  714-5  units  of  heat  generated  in  the  explosion  by  the  quantity  of  heat 


Specific  Heat. 

•28 

X       ^21 62      - 

•0605 

•36 

X       -1901      = 

-0684 

•12 

X      ^2438     = 

-0293 

•18 

X      -2163     = 

•0389 

•06 

X      -2450     = 

-0147 

426 


PRESSURE  OF  FIRED  GUNPOWDER. 


required  to  raise  the  joint  products  through  1°,  we  obtain  3373°  C.  for  the  nnmber 
of  degrees  through  which  the  products  will  be  raised  by  the  explosion. 

The  expansion  of  gases  when  heated  amounts  to  -^j^    of  their  volume  at  0°  for 

each  degree  of  temperature. 

3373 
Hence  3373°  would  expand  the  gas  by  -^fs   "^  ^^  times  its  volume  at  0°,  or  each 

volume  of  gas  at  0°  would  become  13  volumes  at  the  moment  of  explosion. 
The   112  litres   of  gas  from  484  grammes  of  powder  would  become  112x13,  or 

1456 
1456  litres  at  the  moment  of  explosion  ;  and  1  gramme  of  powder  would  give    .„ . 

or  3  "008  litres  =  3008  cubic  centimetres  of  gas. 

In  an  ordinary  charge  of  gunpowder,  1  gramme  occupies  a  space  of  one  cubic  centi- 
metre, but  since,  according  to  Noble  and  Abel,  the  fused  solid  produces  occupy  one- 

2 
third  of  the  volume  of  the  original  powder  charge,  there  would  be  ^  cubic  centimetre 

to  be  occupied  by  the  3008  c.  c.  of  gas. 

Since  the  elastic  force  or  pressure  of  gases  increases  in  proportion  as  their  volume  is 
diminished,  the  3008  c.c.  of  gas,  when  confined  in  a  space  which  would  contain  only 
2  3 

o  c.c.  at  the  normal  pressure  of  one  atmosphere,  must  exert  a  pressure  of  3008  x -n 

=  4512  atmospheres  or  4512  x  147  lbs.,  or  29"6  tons  per  square  inch. 

The  experiments  of  Noble  and  Abel  gave  280  volumes  of  gas  at  0°  from  one  volume 
of  powder,  instead  of  231 '4  volumes,  as  required  by  the  equation  ;  these  280  volumes 
would  become  3640  volumes  at  the  temperature  of  the  explosion,  and  would  exert  a 
pressure  of  5460  atmospheres  in  the  space  available  for  the  gas ;  this  amounts  to 
nearly  36  tons  per  square  inch. 

Variations  in  the  proportions  of  the  ingredients  of  gunpowder  have  less  effect  upon 
the  total  energy  of  the  powder  than  upon  its  rate  of  burning.  Thus,  a  slowly  burn- 
ing powder  containing  a  large  proportion  of  charcoal  will  exert  the  same  pressure 
in  a  closed  vessel  as  is  exerted  by  military  powder.  For,  when  the  proportion  of 
carbon  is  large,  more  of  the  oxygen  of  the  nitre  is  converted  into  carbonic  oxide  and 
less  into  carbon  dioxide  ;  and  a  given  quantity  of  oxygen,  when  converted  into  CO, 
gives  twice  as  large  a  volume  of  gas  as  when  converted  into  COg.  But  the  formation 
of  CO.,,  from  a  given  weight  of  oxygen,  developes  1  "6  times  as  much  heat  as  that  of 
CO,  so  that  the  thermal  value  of  a  powder  varies  inversely  as  the  voluine  of  gas 
measured  at  0°  ;  and  the  maximum  pressure  produced  by  the  explosion  is  nearly  the 
same  for  powders  differing  greatly  in  composition.  This  is  illustrated  by  the  results 
of  Noble  and  Abel. 


Powder. 

Composition. 

Theitnal 
Value. 

Gas  at  0°. 

Maxm.  Pressure 

in  tons  per  sq. 

incii. 

Nitre. 

Ch. 

s. 

Mining,       .     .     . 
Military,     .     .     . 

67 
75 

19 
15 

14 
10 

509 
714 

360 
280 

44 
43 

In  calculating  the  pressure,  it  is  supposed,  of  course,  that  the  whole  of 
the  gas  is  evolved  at  once,  and  is  immediately  raised  to  the  same  tempera- 
ture, conditions  never  fulfilled  in  the  use  of  gunpowder  in  small  arms  or 
in  cannon,  where  the  combustion  of  the  charge  is  not  instantaneous,  but 
rapidly  progressive,  where  the  confining  space  is  rapidly  enlarged  by  the 
movement  of  the  projectile  long  before  the  whole  of  the  charge  has 
exploded,  and  where  the  heated  gas  is  cooled  by  contact  with  the  metal 
of  the  piece. 

The  calculation  given  above  can  be  regarded  only  as  an  illustration  of  the  method, 
as  there  are  several  circumstances  which  vitiate  the  conclusion  arrived  at.  The 
chemical  equation  on  which  it  is  based  is  confessedly  imperfect. 

We  know  little  or  nothing  of  the  real  condition  of  the  products  at  the  moment 
of  tlie  explosion  ;  it  is  probably  very  different  from  that  after  cooling,  when  we 
examine  them.     From  what  is  known  of  the  effect  of  heat  upon  carbonic  acid  gas  and 


EXPLOSIOX  OF  POWDER  UNDER  VARIED  CONDITIONS.  427 

carbonic  oxide,  it  is  almost  certain  that  these  gases  are  at  least  partially  resolved  into 
their  elements  at  the  moment  of  explosion,  and  it  is  scarcely  likely  that  the  complex 
molecules  of  sulphate  and  carbonate  of  potassium  would  exist  at  so  high  a  tempera- 
ture. Any  breaking  up  of  the  molecules  of  carbonic  acid  gas,  sulphate  and  carbonate 
of  potassium,  would  increase  the  expansion,  and  render  the  above  estimate  of  the  force 
of  tired  powder  too  low. 

If  dissociation  or  temporary  decomposition  (see  page  91)  of  the  products  occurs  as 
a  result  of  the  high  temperature,  the  acts  of  combination  which  must  take  place 
during  the  expansion  and  consequent  cooling  must  be  attended  with  evolution  of 
heat,  rendering  the  decrease  of  pressure  more  gradual  than  it  would  be  otherwise. 

The  actual  rate  of  expansion  of  gases  at  so  high  a  temperature  is  inferred  from  our 
exj)erience  of  their  behaviour  at  comparatively  low  temperatures,  and  there  are  some 
indications  of  a  want  of  agreement  under  the  two  conditions. 

The  experiments  of  Andrews  have  shown  that,  even  at  a  pressure  of  100  atmo- 
spheres, carbonic  acid  gas  exhibits  striking  deviations  from  the  law  that  the  pressure 
exerted  by  a  gas  is  inversely  as  its  volume. 

The  period  over  whicli  the  combustion  of  a  given  weight  of  powder 
extends  will,  of  course,  depend  upon  the  extent  of  surface  over  which  it 
can  be  kindled ;  thus  a  single  fragment  of  powder  weighing  10  grains, 
even  if  it  were  instantaneously  kindled  over  its  entire  surface,  could  not 
evolve  so  much  gas  in  a  given  time  as  if  it  had  been  broken  into  10 
separate  grains,  each  of  which  was  kindled  at  the  same  instant,  since  the 
inside  of  the  large  fragment  can  only  be  kindled  from  the  outside.  Upon 
this  principle  a  given  weight  of  powder  in  large  grains  will  occupy  a 
longer  period  in  its  explosion  than  the  same  weight  in  small  grains,  so 
that  the  large  grain  powder  is  best  fitted  for  ordnance,  where  the  ball  is 
very  heavy,  and  the  time  occupied  in  moving  it  will  permit  the  whole  of 
the  charge  to  be  fired  before  the  ball  has  left  the  muzzle,  whilst  in  small 
arms  with  light  projectiles,  a  finer  grained  and  more  quickly  burning 
charge  is  required.  If  the  fine  grain  powder  were  used  in  cannon,  the 
whole  of  the  gas  might  be  evolved  before  the  containing  space  had  been 
sensibly  enlarged  by  the  movement  of  the  heavy  projectile,  and  the  gun 
Avould  be  subjected  to  an  unnecessary  strain;  on  the  other  hand,  a  large 
grain  powder  in  a  musket,  would  evolve  its  gas  so  slowly  that  the  ball 
might  be  expelled  with  little  velocity  by  the  first  half  of  it,  and  the 
remainder  would  be  wasted.  There  is  good  reason  to  believe  that  even 
under  the  most  favourable  circumstances  a  large  proportion  of  every 
charge  of  powder  is  discharged  unexploded  from  the  muzzle  of  the  gun, 
and  is  therefore  wasted.  In  blasting  rocks  and  other  mining  operations, 
the  space  within  which  the  powder  is  confined  is  absolutely  incapable  of 
enlargement  until  the  gas  evolved  by  the  combustion  has  attained 
sufficient  pressure  to  do  the  whole  work,  that  is,  to  rend  the  rock,  for 
example,  asunder.  Accordingly,  a  slowly  burning  charge  will  produce  the 
efiect,  since  the  rock  must  give  way  when  the  gas  attains  a  certain  pres- 
sure, whether  that  happens  in  one  second  or  in  ten.  Indeed,  a  slowly 
burning  charge  is  advantageous,  as  being  less  liable  to  shatter  the  rock  or 
coal,  and  bringing  it  away  in  larger  masses  with  less  danger.  Nitrate  of 
baryta  and  nitrate  of  soda  are  sometimes  substituted  for  a  part  of  the 
nitrate  of  potash  in  mining  powder,  its  combustion  being  thus  retarded. 

Espir's  blasting  powder  contains  60  per  cent,  of  sodium  nitrate,  14  of 
sulphur,  and  26  of  hard  wood  sawdust. 

The  same  charge  of  the  same  powder  produces  very  different  results  when  heated 
in  different  ways.  If  5  grains  of  gunpowder  be  placed  in  a  wide  test-tube,  and  fired 
by  passing  a  heated  wire  into  the  tube,  a  slight  puff  only  is  perceived  ;  but  if  the  same 
amount  of  powder  be  heated  in  the  tube  by  a  spirit-lamp,  it  will  explode  with  a  loud 


428     EFFECT  OF  ATMQSPHERIC  PRESSURE  ON  FIRED  GUNPOWDER. 

report,  and  perhajis  shatter  the  tube  (a  cnpper  or  brass  tube  is  safer).  In  the  first 
case  the  combustion  is  propaga*^e(l  slowly  from  the  particle  first  touched  by  the  wire  ; 
in  the  second,  all  the  particles  are  luised  at  once  to  pretty  nearly  the  same  tempera- 
ture, and  as  soon  as  one  explodes,  all  the  rest  follow  instantaneously. 

When  <?unpo\vder  is  slowly  fired,  the  products  of  its  decomposition  are 
different  jFrom  those  mentioned  above  ;  thus,  nitric  oxide  (NO),  arising 
from  incomplete  decomposition  of  the  nitre,  is  perceived  in  considerable 
quantity,  and  may  be  recognised  by  the  red  colour  produced  when  it  is 
brought  in  contact  with  air. 

Tlie  white  smoke  resulting  from  the  explosion  of  gunpowder  consists 
chiefly  of  the  sulphate  and  carbonate  of  potassium  in  a  very  finely-divided 
state ;  it  seems  probable  that  at  the  instant  of  explosion  they  are  con- 
verted into  vapour,  and  are  afterwards  deposited  in  a  state  of  minute 
division  as  the  temperature  falls.  The  fouling  or  actual  solid  residue  in 
the  gun  is  very  trifling  when  the  powder  is  dry  and  has  been  well  incor- 
porated ;  a  damp  or  slowly  burning  powder  leaves,  as  might  be  expected, 
a  larger  residue.  The  residue  always  becomes  wet  on  exposure  to  air, 
from  the  great  attraction  for  moisture  possessed  by  the  carbonate  and 
sulphide  of  potassium. 

When  10  grains  of  Waltham  Abbey  gunpowder  are  fired  in  a  strong  air-tight  cylin- 
der, with  a  cavity  about  hu  inch  high  and  half  an  inch  in  diameter,  by  the  galvanic 
battery,  the  inleiior  of  the  cavity  is  covered  with  a  snow-white  powder  composed  of 
sulphate  and  carbonate  of  jjotassium,  which  deliquesces  rapidly  in  a  damp  atmosphere. 
No  nitric  oxide  is  found  in  the  gas  formed  by  the  exjilosion. 

If  a  small  quantity  of  powder  be  slightly  damped  and  rammed  into  a  wooden 
tube,  in  the  mouth  of  whidi  a  piece  of  quick  match  is  inserted,  the  charge  may  be 
kindled,  and  the  tube  held  with  its  mouth  under  water,  so  that  the  gases  may  be 
collected  in  an  inverted  jar.  These  will  be  found  to  contain  NO  (giving  a  brown 
colour  in  contact  with  air)  H.^S  (giving  a  black  precipitate  with  lead  acetate)  beside 
the  CO.^  (giving  a  white  precipitate  with  lime  water),  CO  and  N. 

312.  Effect  of  variations  of  atmospheric  'pressure  on  the  combustion  of 
yunpoicder. — From  the  circumstance  that  the  combustion  of  gunpowder  is 
independent  of  any  supply  of  oxygen  from  the  air,  it  might  be  supposed 
that  it  would  be  as  easily  inflamed  in  vacuo  as  under  ordinary  atmo- 
spheric pressure.  This  is  not  found  to  be  the  case,  however,  for  a 
mechanical  reason,  viz.,  that  the  flame  from  the  particles  which  are  first 
ignited  escapes  so  rapidly  into  the  vacuous  space,  that  it  does  not  inflame 
the  more  remote  particles.  For  a  similar  reason,  charges  of  powder  in 
fuzes  are  found  to  burn  more  slowly  under  diminished  atmospheric 
pressure,  the  flame  (or  heated  gas)  escaping  more  rapidly  and  igniting  less 
of  the  remaining  charge  in  a  given  time.  It  has  been  determined  that  if 
a  fuze  be  charged  so  as  to  burn  for  thirty  seconds  under  ordinary  atmo- 
spheric pressure  (30  inches  barometer),  each  diminution  of  1  inch  in 
barometric  pressure  will  cause  a  delay  of  1  second  in  the  combustion  of 
the  charge,  so  that  the  fuze  will  burn  for  thirty-one  seconds  when  the " 
barometer  stands  at  29  inches. 

The  manufacture  of  ganpowder  may  be  illustrated  by  the  following  experiments  on 

a  small  scale  : — 

Preparation  of  the  ingredmits— Charcoal.— k  few  small  pieces  of  wood  are  placed 
in  a  clay  crucible,  which  is  then  filled  up  with  drv  sand  and  heated  in  a  moderate 
fire  as  long  as  any  vapoure  are  evolved,  when  it  may  be  ."^et  aside  to  cool. 

^M///A//r.— 500  grains  of  roll  suljihur  may  be  distilled  in  a  Florence  flask,  using 
anotiier  fiask,  the  neck  of  which  has  been  cut  off"  (fig.  278),  for  a  receiver  from  which 
the  sulphur  is  afterwards  poured,  in  a  melted  state,  upon  a  piece  of  tin-plate. 


CHEMISTRY  OF  FUEL. 


429. 


Nitre.— 10(^0  grains  of  impure  nitre  are  dissolved,  at  a  moderate  heat,  in  4 
measured  ounces  of  distilled  water,  in  an  evaporating  dish  (fig.  279)  ;  the  solution  is 
filtered  into  a  beaker  which  is  placed  in  cold  wat^r,  and  stirred  with  a  glass  rod 
until  it  is  quite  cold.  The  saltpetre  flour  thus  obtained  is  collected  upon  a  filter, 
thoroughly  drained,  the  filter  removed  from  the  funnel,  spread  out,  the  saltpetre 
transferred  to  another  piece  of  filter  pa[)er,  and  ]iressed  between  the  paper  to  remove 
as  much  of  the  licjuid  as  possible  ;  it  is  then  spread  out  on  paper  and  dried  on  a  hot 
brick.    (For  the  mode  of  testing  its  purity  see  page  416.) 


Fig.  278.— Distillation  of 
sulphur. 


Fig.  279. 


Mixture  of  the  ingredients. — Sixty  grains  of  the  charcoal,  reduced  to  a  very  fine 
powder,  40  grains  of  the  sulphur,  also  previously  powdered,  and  300  grains  of  the 
dried  nitre,  are  very  intimately  mixed  in  a  mortar  ;  50  grains  of  the  mixture  are  set 
aside  for  comparison.  To  the  remainder  enough  water  is  ailded  to  make  it  into  a 
stiff  cake,  which  is  well  incorporated  under  the  pestle  for  some  time.  It  is  then 
scraped  out  of  the  mortar  and  allowed  to  dry  slowly  at  a  very  gentle  heat.  When 
perfectly  dry  it  is  crumbled  to  a  coarse  powder,  and  the  dust  sifted  out  through  a 
piece  of  wire  gauze.  It  will  be  found  instructive  to  compare,  in  trains  and  other- 
wise, the  firing  of  the  powder  in  grains,  of  the  dust,  and  of  the  mixed  ingredients 
without  incorporation,  observing  especially  the  diff'erence  in  rapidity  of  burning  and 
in  the  amount  of  residue. 


CHEMISTRY  OF  FUEL. 

313,  Several  of  the  applications  of  chemical  principles  in  the  combus- 
tion of  fuel  have  been  already  explained  and  illustrated.  The  object  of 
this  chapter  is  to  compare  the  chemical  coinposition  of  the  most  important 
varieties  of  fuel,  and  to  exemplify  the  principles  upon  which  their  heating 
power  may  be  calculated  from  the  results  furnished  by  the  analysis  of  the 
fuel. 

All  the  varieties  of  ordinary  fuel,  of  course,  contain  a  large  proportion 
of  carbon,  always  accompanied  by  hydrogen  and  oxygen,  and  sometimes  by 
small  proportions  of  nitrogen  and  sulphur  Certain  mineral  substances  are 
also  contained  in  all  sulid  fuels,  and  compose  the  ash  when  the  fuel  is  burnt. 

For  all  practical  purposes,  it  may  be  stated  that  the  amount  of  heat 
generated  by  the  combustion  of  a  given  weight  of  fuel  depends  upon  the 
weights  of  carbon  and  hydrogen,  respectively,  which  enter  into  combina- 
tion with  the  oxygen  of  tlie  air  in  the  act  of  combustion  of  the  fuel. 

It  has  been  ascertained  by  experiment  tliat  1  lb.  of  carbon  (in  the 
form  in  which  it  exists  in  wood-charcoal),  when  combining  with  oxygen 
to  form  carbon  dioxide,  produces  a  quantity  of  heat  which  is  capable  of 
raising  8080  lbs.  of  water  from  0°  to  1°  of  the  centigrade  thermometer. 
This  is  usually  expressed  by  saying  that  the  calorific  value  of  carb'm  is 
8080,  or  that  carbon  produces  8080  units  of  heat  during  its  combustion  to 


430        CALCULATION  OF  CALORIFIC  VALUE  OF  FUEL. 

carbon  dioxide.  If  the  fuel,  therefore,  consisted  of  pure  carbon,  it  would 
merely  be  necessary  to  multiply  its  weight  by  8080  to  ascertain  its  calorific 
value. 

One  pound  of  hydrogen,  during  its  conversion  into  water  by  combustion, 
evolves  enough  heat  to  raise  34,400  lbs.  of  water  from  0°  C.  to  1°  C.^  so 
that  the  calorific  value  of  hydrogen  is  34,400. 

If  the  fuel  consisted  of  carbon  and  hydrogen  only,  its  calorific  value 
would  be  calculated  by  multiplying  the  weight  of  the  carbon  in  1  lb. 
of  the  fuel  by  8080,  and  that  of  the  hydrogen  by  34,400,  when  the  sum 
of  the  products  would  represent  the  calorific  value.  But  if  the  fuel 
contains  oxygen  already  combined  with  it,  the  calorific  value  will  be 
diminished,  since  this  oxygen  will  consume  a  part  of  the  combus- 
tible without  generating  heat,  because  it  already  exists  in  a  state  of 
combination  with  the  carbon  and  hydrogen  of  the  fuel.  For  example, 
1  lb.  of  wood  contains  0'5  lb.  of  carbon,  0"06  of  hydrogen,  and  0'44 
of  oxygen.  Now,  oxygen  combines  with  one-eighth  of  its  weight  of 
hydrogen  to  form  water,  so  that  the  0*44  lb.  of  oxygen  will  convert 
•44  4-  y  =  -055  of  the  hydrogen  into  water,  without  evolution  of  avail- 
able heat,  leaving  only  0*005  available  for  the  production  of  heat.  The 
calorific  value  of  the  wood,  therefore,  would  be  represented  by  the  sum  of 
0-005  X  34,400  (  =  172)  and  0-5  x  8080  (  =  4040),  which  would  amount 
to  4212;  or  1  lb,  of  wood  should  raise  4212  lbs.  of  water  from  0°C.  to 

rc. 

These  considerations  lead  to  the  following  general  formula  for  calculaU 
ing  the  calorific  value  of  a  fuel  containing  carbon,  hydrogen,  and  oxygen, 
where  c,  h,  and  o,  respectively  represent  the  carbon,  hydrogen,  and  oxygen 
in  1  grain  of  fueL 

The  calorific  value  (or  number  of  lbs.  of  water  which  might  be  heated 

by  the  fuel  from  0°   C.  to  1°   C.)   =   8080  c   +.  34,400  Ch  -  -|\or 

8080  c   +   34,000  h  -  4300  a. 

The  calorific  value  of  a  fuel,  as  determined  by  experiment,  is  generally 
less  than  would  be  calculated  from  its  chemical  composition,  in  consequence 
of  the  absorption  of  a  certain  amount  of  heat  attending  the  chemical 
decomposition  of  the  fuel  In  the  case  of  compounds  of  carbon  and  hydro- 
gen, it  has  been  observed  that  even  when  they  have  the  same  composition 
in  100  parts,  they  have  not  of  necessity  the  same  calorific  value,  the  latter 
being  affected  by  the  diff'erence  in  the  arrangement  of  the  component  par- 
ticles of  the  compound,  which  causes  a  diff'erence  in  the  quantity  of  heat 
absorbed  during  its  decomposition.  Thus  olefiant  gas  (C2H4)  and  cetylene 
(CjgHgg)  have  the  same  percentage  composition,  and  their  calculated  calorific 
values  would  be  identical,  but  the  former  is  found  to  produce  11,858  units 
of  heat,  and  the  latter  only  11,055.  As  a  general  rule,  however,  it  is  found 
that  the  calorific  values  of  the  hydrocarbons  which  contain  a  multiple  of 
CH.,,  agree  more  nearly  with  the  calculated  numbers  than  do  those  of 
hydrocarbons  which  belong  to  the  marsh  gas  series. 

It  must  be  remembered  that  the  calorific  value  of  a  fuel  represents  the 
actual  amount  of  heat  which  a  given  weight  of  it  is  capable  of  producing, 
and  is  quite  independent  of  the  manner  in  which  the  fuel  is  burnt.  Thus, 
a  hundredweight  of  coal  will  produce  precisely  the  same  amount  of  heat  in. 
an  ordinary  grate  as  in  a  wind-furnace,  though  in  the  former  case  the  fire 
will  scarcely  be  capable  of  melting  copper,  and  in  the  latter  it  will  melt 


CALCULATION  OF  CALOKIFIC  INTENSITY  OF  FUEL.  43t 

steeL  The  difference  resides  in  the  tempei'ature  or  caloHfic  intensity  of 
the  two  fires ;  in  the  wind-furnace  through  which  a  rapid  draught  of  air 
is  maintained  by  a  chimney,  a  much  greater  weight  of  atmospheric  oxygen 
is  brought  into  contact  with  the  fuel  in  a  given  time,  so  that,  in  that 
time,  a  greater  weight  of  fuel  will  be  consumed  and  more  heat  will  be 
produced  ;  hence  the  fire  will  have  a  higher  temperature,  for  the  tem- 
perature represents,  not  the  quantity  of  heat  present  in  a  given  mass  of 
matter,  but  the  intensity  or  extent  to  which  that  heat  is  accumulated  at 
any  particular  point.  In  the  case  of  the  wind-furnace  here  cited,  a  further 
advantage  is  gained  from  the  circumstance  that  the  rapid  draught  of  air 
allows  a  given  weight  of  fuel  to  be  consumed  in  a  smaller  space,  and,  of 
course,  the  smaller  the  area  over  which  a  given  quantity  of  heat  is  distri- 
buted, the  higher  the  temperature  within  that  area  (as  exemplified  in  the 
use  of  the  common  burning-glass).  In  some  of  the  practical  applications 
of  fuel,  such  as  heating  steam-boilers  and  warming  buildings,  it  is  the 
ealoi~ific  value  of  the  fuel  which  chiefly  concerns  us,  but  the  case  is  different 
where  metals  are  to  be  melted,  or  chemical  changes  to  be  brought  about 
by  the  application  of  a  very  high  temperature,  for  it  is  then  the  calorific 
intensity,  or  actual  temperature  of  the  burning  mass,  which  has  to  be  con- 
sidered. No  trustworthy  method  has  yet  been  devised  for  determining 
by  direct  experiment  the  calorific  intensity  of  fuel,  and  it  is  therefore 
ascertained  by  calculation  from  the  calorific  value. 

Let  it  be  required  to  calculate  the  calorific  intensity,  or  actual  tempera- 
ture, of  carbon  burning  in  pure  oxygen  gas. 

Twelve  lbs.  of  carbon  combine  with  32  lbs.  of  oxygen,  producing  44  lbs. 
of  CO2 ;  hence  1  lb.  of  carbon  combines  with  2"67  lbs.  of  oxygen,  pro- 
ducing 3  "6 7  lbs.  of  COg.  It  has  been  seen  above  that  1  lb.  of  carbon 
evolves  8080  units  of  heat,  or  is  capable  of  raising  8080  lbs.  of  water 
from  0°  to  1°  C,  or,  on  the  supposition  that  the  water  would  bear  such  an 
elevation  of  temperature,  the  1  lb.  of  carbon  would  raise  1  lb.  of  water, 
from  0°  to  8080°  C.  If  the  specific  heat  (or  heat  required  to  raise  1  lb. 
through  1°,  see  page  425)  of  COg  were  the  same  as  that  of  water,  8080° 
divided  by  3"67  would  represent  the  temperature  to  which  the  3*67  lbs. 
of  CO2  would  be  raised,  and  therefore  the  temperature  to  which  the  solid 
carbon  producing  it  would  be  raised  in  the  act  of  combustion.  But  the 
specific  heat  of  carbonic  acid  gas  is  only  0*2 163,  so  that  a  given  amount 
of  heat  would  raise  1  lb.  of  CO2  to  nearly  five  times  as  high  a  temperature 
as  that  to  which  it  would  raise  1  lb.  of  water. 

Dividing  the  8080  units  of  heat  (available  for  raising  the  temperature 
of  the  CO2)  by  0  2 163,  the  quantity  of  heat  required  to  raise  1  lb.  of  COg 
through  1°,  we  obtain  37,355  for  the  number  of  degrees  through  which 
1  lb.  of  CO,  might  be  raised  by  the  combustion  of  1  lb.  of  carbon.  But 
there  are  3 '67  dbs.  of  CO2  formed  in  the  combustion,  so  that  the  above 
number  of  degrees  must  be  divided  by  3 '67  in  order  to  obtain  the  actual 
temperature  of  the  CO2  at  the  instant  of  its  production,  that  is,  the 
temperature  of  the  burning  mass.  The  calorific  intensity  of  carbon  burn- 
ing in  pure  oxygen  is,  therefore  (37,355°  C. -=- 3-67  =  )  10,178°  C.  or 
18,352°  F.  But  if  the  carbon  be  burnt  in  air,  the  temperature  will  be  far 
lower,  because  the  nitrogen  of  the  air  will  absorb  a  part  of  the  heat,  to 
which  it  contributes  nothing.  The  2 '67  lbs.  of  oxygen  required  to  bum 
1  lb.  of  carbon  would  be  mixed,  in  air,  with  8-93  lbs.  of  nitrogen,  so  that 
the  8080  units  of  heat  would  be  distributed  over  3-67  lbs.  of  carbonic 


432  CALCULATION  OF  CALORIFIC  INTENSITY  OF  FUEL. 

acid  gas,  and  8 '9 3  Iba.  of  nitrogen.  Since  the  specific  heat  of  carbonic 
acid  gas  is  0'2163,  the  product  of  3"67  x  0'2163  (or  0*794)  represents  the 
quantity  of  heat  required  to  raise  the  3-67  lbs.  of  CO9  from  0°  to  V  C. 

The  specific  heat  of  nitrogen  is  0-2438,  hence  8-93"x  0-2438  (or  2-177) 
represents  the  quantity  of  heat  required  to  raise  the  8-93  lbs.  of  atmo- 
spheric nitrogen  from  0°  to  1°  C. 

Adding  together  these  products,  we  find  that  0-794  +  2-177  =  2-971 
represents  the  quantity  of  heat  required  to  raise  both  the  nitrogen  and 
carbonic  acid  gas  from  0°  to  1°  C. 

Dividing  the  8080°  by  2-971,  we  obtain  2720°  C.  (4928°  F.)  for  the 
number  of  degrees  through  which  these  gases  would  be  raised  in  the  com- 
bustion, i.e.,  for  the  calorific  intensity  of  carbon  burning  in  air.  By  heat- 
ing the  air  before  it  enters  the  furnace  (as  in  the  hot-blast  iron  furnace) 
of  course  the  calorific  intensity  would  be  increai^ed  ;  thus  if  the  air  be 
introduced  into  the  furnace  at  a  temperature  of  600°  F.,  it  might  be  stated, 
without  serious  error,  that  the  temperature  producible  in  the  furnace 
would  be  5.528°  F.  (4928° +  600°).  The  temperature  might  be  further 
increased  by  diminishing  the  area  of  combustion,  as  by  employing  very 
compact  fuel  and  increasing  the  pressure  of  the  blast. 

In  calculating  the  calorific  intensity  of  hydrogen  burning  in  air,  from 
its  calorific  value,  it  must  be  remembered  that  in  the  experimental  deter- 
mination of  the  latter  number,  the  steam  produced  in  the  combustion  was 
condensed  to  the  liquid  form,  so  that  its  latent  heat  was  added  to  the 
number  representing  the  calorific  value  of  the  hydrogen  ;  but  the  latent 
heat  of  the  steam  must  be  deducted  in  calculating  the  calorific  intensity, 
because  the  steam  goes  off  from  the  burning  mass  and  carries  its  latent 
heat  with  it. 

One  lb.  of  hydrogen,  burning  in  air,  combines  with  8  lbs.  of  oxygen, 
producing  9  lbs.  of  steam,  leaving  26-77  lbs.  of  atmospheric  nitrogen,  and 
evolving  34,400  units  of  heat. 

It  has  been  experimentally  determined  that  the  latent  heat  of  steam  is 
537°  C,  that  is,  1  lb.  of  water,  in  becoming  steam,  absorbs  537  units  of 
heat  (or  as  much  heat  as  would  raise  537  lbs.  of  water  from  0°  to  1°  C.) 
without  rising  in  temperature  as  indicated  by  the  thermometer.  The 
9  lbs.  of  water  produced  by  the  combustion  of  1  lb.  of  liydrogen  will 
absorb,  or  render  latent,  537  x  9  =  4833  units  of  heat.  Deducting  this 
quantity  from  the  34,400  units  evolved  in  the  combustion  of  1  lb.  of 
hydrogen,  there  remain  29,567  units  of  heat  available  for  raising  the  tem- 
perature of  the  9  lbs.  of  steam  and  26-77  lbs.  of  atmospheric  nitrogen. 
The  specific  heat  of  steam  being  0-480,  the  number  (0-480x9  =  )  4-3-J 
represents  the  quantity  of  heat  required  to  raise  the  9' lbs.  of  steam 
through  1°  C.  ;  and  the  specific  heat  of  nitrogen  (0-243S)  multiplied  by 
its  weight  (26-77  lbs.),  give  6-53  units  of  heat  required  to  raise  the 
26-77  lbs.  of  nitrogen  through  1°  C.  By  dividing  the  available  heat 
(29,567  units)  by  the  joint  quantities  required  to  raise  the  steam  and 
nitrogen  through  1°  C.  (4-32  +  6-53=  10-85),  we  obtain  the  number  2725° 
C.  (4937°  F.)  for  the  calorific  intensity  of  hydrogen  burning  in  air. 

The  method  of  calculating  the  calorific  intensity  of  a  fuel  composed  of  carbon, 
hydrogen,  and  oxygen  will  now  be  easily  followed. 

Let  c  and  h  respectively  represent  the  weights  of  carbon  and  hydrogen  in  ]  lb. 

of  fuel,  and  0  that  of  oxygen.     Then  —  =  weight  of  hydrogen  required  to  convert 


COMPOSITION  AND  VALUE  OF  FUELS. 


438 


the  oxygen  into  water,  and  h  — r-  represents  the  hydrogen  which  is  available  for  the 

production  of  heat.    8080  c  +  34,400  (h  — — )  represents  the  calorific  value  in  °C., 

=  8080  c  +  34,400  h  -  4300  o. 

2-67  c  =  atmospheric  oxygen  consumed  by  the  carbon;  S\h —)  or  8  A  -  o  = 

atmospheric  oxygen  consumed  by  the  hydrogen  available  as  fuel. 

3  34  (2-67  c  +  8  A  -  o)  =  atmospheric  nitrogen  =  8-92  c  +  26-72  A  -  3-34  o. 

Multiplying  this  by  the  specific  heat  of  nitrogen  0-2438,  we  obtain — 
2-17  c  +  6-51  h  -  0-81  o  for  the  heat  required  to  raise  the  nitrogen  through  1°  C. 

0  794  c  represents  the  quantity  of  heat  required  to  raise  the  COj  through  1"  C,  and 
4-32  h  is  the  heat  required  to  raise  the  steam  through  1°.  Accordingly,  the  available 
heat,  8080  c  +  34,400  h  -  4300  o,  must  be  divided  by  0-794  c  +  4-32  A  +  (2-17  c 
+  6*51  A -0*81  o),  or  2-96  c+  10-83  A  -  0 -81  o  in  order  to  obtain  the  calorific  intensity. 

Hence,  the  calorific  intensity,  in  centigrade  degrees,  of  a  fuel  composed  of  carbon, 
hydrogen,  and  oxygen,  is  represented  by  the  formula — 
8080  c  +  34,400  h  -  4300  o 
2-96  c  +  10-83    h  -   081  o. 
The  actual  calorific  intensity  of  the  fuel  is  not  so  high  as  it  should  be 
according  to  theory,  because  a  part  of  the  carbon  and  hydrogen  is  con- 
verted into  gas  by  destructive  distillation  of  the  fuel,  and  this  gas  is  not 
actually  burnt  in  the  fire,  so  that  its  calorific  intensity  is  not  added  to  that 
of  the  burning  solid  mass.     Again,  a  portion  of  the  carbon  is  converted 
into  carbonic  oxide  (CO),  especially  if  the  supply  of  air  be  imperfect, 
and  much  less  heat  is  produced  than  if  the  carbon  were  converted  into 
carbon  dioxide  ;  although  it  is  true  that  this  carbonic  oxide  may  be  con- 
sumed above  the  tire  by  supplying  air  to  it,  the  heat  thus  produced  does 
not  increase  the  calorific  intensity  or  temperature  of  the  tire  itself. 

One  lb.  of  carbon  furnishes  2*33  lbs.  of  carbonic  oxide.  These  2-33 
lbs.  of  carbonic  oxide  evolve,  in  their  combustion,  5599  units  of  heat. 
But  if  the  1  lb.  of  carbon  had  been  converted  at  once  into  carbon  dioxide, 
it  would  have  evolved  8080  units  of  heat,  so  that  8080  -  5599,  or  2481, 
represents  the  heat  evolved  during  the  conversion  of  1  lb.  of  carbon  into 
carbonic  oxide^  showing  that  a  considerable  loss  of  heat  in  the  fire  is  caused 
by  an  imperfect  supply  of  air.  It  has  been  already  pointed  out,  in  the 
section  relating  to  Coal,  that  the  formation  of  carbonic  oxide  is  sometimes 
encouraged  with  a  view  to  the  production  of  a  flame  from  non-flaming 
coal,  such  as  anthracite. 

The  following  table  exhibits  the  average  percentage  composition  of  the 
principal  varieties  of  fuel  (exclusive  of  ash),  together  with  their  calculated 
calorific  values  and  intensities  : — 


Carbon. 

Hydrogen. 

Oxygen. 

Nitrogen. 

Sulphur. 

Calorific 
Value.— Intensity. 

Wood  (Oak)     . 

Peat, 

Liguite  (Bovey), 

Bituminous  coal, 

Cliarcoal, 

Anthracite, 

Coke,       . 

50-18 
61-53 
67-86 
79-38 
90-44 
91-86 

97-32 

6-08 
5-64 
5-75 
5-34 
2-91 
3-33 

0-49 

43-74    1        ... 

32^82 

23-39          0-57 

13-01          1-85 

6-63 

3-02          0-84 

2'-41 
0-39 

0-92 

4212°  C. 

5654 

6569 

7544 

8003 

8337 

2380°  C. 

■2547 

2628 

•2694 

2760 

2779 

•2761 

2-17 

8009 

In  all  ordinary  fires  and  furnaces,  a  large  amount  of  heat  is  wa-t'  d  in 
the  current  of  heated  products  of  combustion  escaping  from  the  chimney. 

2  E 


434  REGENERATIVE  FURNACE. 

Of  course,  a  portion  of  this  heat  is  necessary  in  order  to  produce  the 
draught  of  the  chimney.  In  boiler  furnaces  it  is  found  that,  for  this  pur- 
pose, the  temperature  of  the  air  escaping  from  the  chimney  must  not  be 
lower  than  from  500°  to  600°  F.  If  the  fuel  could  be  consumed  by  sup- 
plying only  so  much  air  as  contains  the  requisite  quantity  of  oxygen,  a 
great  saving  might  be  effected,  but  in  practice  about  twice  the  calculated 
quantity  of  air  must  be  supplied  in  order  to  effect  the  removal  of  the 
products  of  combustion  with  sufficient  rapidity. 

^tuch  economy  of  fuel  results  from  the  use  of  furnaces  constructed  on 
the  principle  of  Siemens'  regenerative  furnace,  in  which  the  waste  heat  of 
the  products  of  combustion  is  absorbed  by  a  quantity  of  firebricks,  and 
employed  to  heat  the  air  before  it  enters  tlie  furnace,  two  chambers  of 
firebricks  doing  duty  alternately,  for  absorbing  the  heat  from  the  issuing 
gas,  and  for  imparting  heat  to  the  entering  air,  the  current  being  reversed 
by  a  valve  as  soon  as  the  firebricks  are  strongly  heated. 

(For  the  principles  of  smoke  prevention,  and  other  particulars  of  the 
chemistry  of  fuel,  see  Goal.) 


ORGANIC  CHEMISTRY. 


314.  Altliough  it  is  impossible  to  propose  a  definition  of  the  term 
organic  substance  which  shall  not  be  applicable  to  some  of  the  substances 
commonly  regarded  as  inorganic,  it  is  found  advantageous  for  the  purposes 
of  study  to  treat  organic  chemistry  as  a  separate  division  of  the  science, 
dealing  especially  with  those  substances  which  are  usually  obtained, 
either  directly  or  indirectly,  from  animals  and  vegetables. 

One  very  important  distinction  between  organic  and  inorganic  substances 
is,  that  the  former  are  for  the  most  part  composed  of  carbon,  hydrogen, 
nitrogen,  and  oxygen,  in  different  proportions  and  in  various  modes  of 
arrangement,  and  that  they  are,  therefore,  much  more  frequently  con- 
vertible into  each  other  by  metamorphosis,  without  extraneous  addition 
of  matter,  than  inorganic  substances  are. 

It  has  been  already  pointed  out  that  the  chemist  is  gradually  learning 
to  produce,  though  by  somewhat  clumsy  and  circuitous  processes,  many  of 
the  substances  which  were  formerly  believed  incapable  of  being  formed, 
except  through  the  intervention  of  life ;  but  no  substance  possessing  an 
organised  structur'e,  such  as  woody  fibre,  or  muscular  fibre,  and  no  ab- 
solutely indispensable  organic  constituent  of  animal  or  vegetable  frames, 
has  yet  been  artificially  procured. 

It  will  not  escape  notice  that  the  four  elements  which  compose  the 
greater  number  of  organic  substances,  viz.,  hydrogen,  oxygen,  nitrogen, 
and  carbon,  are,  respectively,  monatomic,  diatomic,  triatomic,  and  tetra- 
tomic  elements  (page  247),  and  are,  therefore,  capable  of  forming  a  greater 
variety  of  compounds  than  would  be  the  case  if  they  were  elements  of 
equal  atomicities. 

Classification  op  Organic  Compounds. 

In  order  to  classify  organic  bodies,  it  is  necessary  to  ascertain — 

(1)  Their  empirical  formula,  which  denotes  the  relative  numbers  of 
atoms  of  their  elements. 

(2)  Their  molecular  formula,  denoting  the  absolute  number  of  atoms 
in  one  molecule. 

(3)  Their  rational  or  structural  formula,  denoting  the  mode  of  arrange- 
ment of  the  atoms  in  the  molecule. 

The  empirical  formula  is  at  once  deduced  from  the  ultimate  analysis  of 
the  organic  substance,  as  described  at  pp.  84  and  132. 

The  molecular  formula  is  ascertained  by  determining  the  molecular 
weight  of  the  compound. 

When  the  compound  is  capable  of  conversion  into  vapour  without 
decomposition,  its  molecular  weight  is  determined  by  converting  a  definite 


486  CLASSIFICATION  OF  ORGANIC  COMPOUNDS. 

weight  of  the  compound  into  vapour,  and  measuring  it.  The  molecidar 
iceif/ht  is  that  weight  which  occupies  the  same  volume  as  two  unit  weights 
of  hydrogen,  at  the  same  temperature  and  pressure.        ' 

Thus,  46  grains  of  alcohol,  when  converted  into  vapour,  occupy  the 
same  volume  as  2  grains  of  hydrogen.  Hence,  the  molecular  weight  of 
alcohol  is  46. 

Now,  by  ultimate  analysis,  it  is  found  that  100  parts  of  alcohol  contain 
52*18  of  carbon,  13'04  hydrogen,  and  34'78  oxygen.  Hence,  1  molecule, 
or  46  parts,  contain  24  parts  or  2  atoms  of  carbon,  6  parts  or  6  atoms 
hydrogen,  and  16  parts  or  1  atom  oxygen,  and  the  molecular  formula  of 
alcohol  is  CgHgO. 

But  when  the  substance  cannot  be  vaporised  without  decomposition, 
its  molecular  weight  must  be  determined  by  other  methods,  as  exempli- 
fied in  the  case  of  oxalic  acid  at  p.  85,  and  in  that  of  urea  at  p.  132. 

In  order  to  deduce  the  rational  formula  of  a  compound,  all  its  reactions 
(or  decompositions  with  other  compounds)  must  be  carefuUy  studied,  and 
that  arrangement  of  its  atoms  must  be  adopted  which  best  explains  the 
greater  number  of  the  reactions. 

For  example,  it  is  found  that  when  alcohol  is  acted  on  by  other  bodies, 
its  decomposition  is  most  easUy  explained,  in  the  greater  number  of  cases, 
by  regarding  it  as  composed  after  the  model  of  the  water  molecule  HgO, 
in  which  1  atom  of  hydrogen  is  replaced  by  the  group  CgHg  (ethyle). 
Hence,  the  rational  or  structural  formula  of  alcohol  is  CgHj.OH. 

The  examination  of  the  optical  properties  of  organic  compounds, 
especially  as  to  their  power  of  refracting  light,  of  influencing  its  polarisa- 
tion, and  of  absorbing  certain  portions  of  the  spectrum,  is  found  of  great 
assistance  in  ascertaining  their  constitution. 

When  the  molecular  and  rational  formulae  of  a  compound  have  been 
ascertained,  it  may  generally  be  assigned  to  one  of  the  following  divisions 
of  organic  substances  : — 

Chief  Classes  of  Organic  Compounds. 


1.  Hydrocarbons. 

2.  Alcohols. 

3.  Aldehydes. 

4.  Acids. 

5.  Ketones. 


6.  Ethers. 

7.  Organo-metallic  bodies. 

8.  Ammonia  derivatives. 

9.  Cyanogen  compounds. 


1.  The  Hydrocarbons  are  all  composed  of  carbon  and  hydrogen  only, 
and  constitute  the  largest  class  of  organic  compounds.  The  simplest 
example  of  this  class  is  marsh  gas  or  methane  CH4,  to  which  it  is  usual 
to  assign  the  rational  formula  H3C.H  which  represents  it  as  methyle 
hydride,  the  group  H3C  representing  tetratomic  carbon  (p.  248),  of  which 
three  out  of  the  four  hands  of  chemical  attraction  (p.  249)  are  satisfied 
by  hydrogen,  so  that  the  fourth  bond  is  available  for  attachment  to  any 
other  element  or  group  of  elements  ;  hence  methyle  is  designated  a 
monatomic  radical,  and  will  be  found  to  play  a  most  important  part  in 
the  formation  of  organic  compounds. 

The  term  methyle  is  derived  from  fiiOv,  wine,  and  v\rj,  wood,  because 
its  principal  compound  is  a  spirituous  substance  resulting  from  the  dis- 
tillation of  wood.  The  ending  -yle  is  generally  bestowed  upon  compound 
radicals,  because  vX-q  also  means  the  matter  of  which  a  thing  is  made.* 

•  The  omission  of  the  final  e,  so  common  in  modern  chemical  writings,  obscures  the 
derivation. 


ALDEHYDES — ACIDS — KETONES.  437 

2.  The  Alcohols  are  compounds  of  carbon,  hydrogen,  and  oxygen,  con- 
structed upon  the  model  of  water  in  which  one  half  of  the  hydrogen  is 
replaced  by  a  compound  radical,  which  is  very  generally  composed  of 
carbon  and  hydrogen. 

Thus  methyle  alcohol  is  H3C.OH  or  methyle  hydrate,  i.e.,  water  in 
which  an  atom  of  hydrogen  is  replaced  by  methyle. 

The  group  or  radical  OH  is  termed  hydroxyle,  and  is  evidently  mon- 
atomic,  because  one  of  the  two  bonds  of  the  diatomic  oxygen  is  satisfied 
by  the  hydrogen  atom,  leaving  the  other  bond  available  for  the  attach- 
ment of  another  element  or  group. 

The  methyle  alcohol  H3C.OH  is  evidently  derived  from  the  methyle 
hydride  H3C.H  by  the  substitution  of  hydroxyle,  OH,  for  hydrogen,  and 
this  substitution  may  be  effected  in  two  operations,  which  are  very  gene- 
rally employed  in  similar  cases. 

(1)  H3C.H  {Methyle  hydride)  +  Cl2  =  H.C.Cl  {Methyle  chloride)  +  HCl. 

(2)  H3C.CI  +  K.OH  {Potassium  hydrate)  =  KCl  +  H3C.OH  {Methyle  alcohol). 

3.  The  Aldehydes,  or  de-hydrogenised  alcohols,  are  products  of  oxida- 
tion of  the  alcohols,  whereby  hydrogen  has  been  removed.     Thus — 

H3C.OH  {Methyle  alcohol)   -I-   0   =  HoO   -f-  HgCO  {Methyle  aldehyde). 
In  the  methyle  aldehyde,  two  bonds  of  the  carbon  atom  are  united  to  the 
diatomic  oxygen  atom,  and  the  other  two  bonds  to  the  two  hydrogen  atoms. 

4.  The  Acids  result  from  a  further  oxidation  of  the  alcohols,  by  which 

not  only  is  hydrogen  removed,  but  oxygen  fills  up  the  vacancy  thus  left. 

For  example — 

(  TTO 
U^C.OB.  {Methyle  alcohol)  -I-   O2  =   H2O    +    0^  <  -g      {Formic  acid). 

The  acids  contain  the  group  or  radical  termed  oxatyle  (ofos,  acid), 
OC.OH,  which  is  monatomic,  because  twoof  the  four  bonds  of  the  tetra- 
tomic  carbon  are  satisfied  by  the  diatomic  oxygen,  and  a  third  by  the 
monatomic  hydroxyle  (OH),  leaving  a  fourth  bond  available  for  the 
attachment  of  another  element  or  group. 

5.  The  Ketones  are  derived  from  the  acids  by  the  substitution  of  a 
hydrocarbon  radical  for  hydroxyle. 

A     f         J   r\n  f  OH  Acetic  ketone   ^^  f  CH» 

Acetic  acid,  OCJ(.jj^  (acetone),       ^^•tCH3 

Hence,  the  ketones  contain  the  diatomic  group  carhonyle,  OC,  combined 
witli  two  hydrocarbon  radicals. 

6.  The  ethers  are  derived  from  the  alcohols  by  the  substitution  of  a 
compound  radical  for  the  hydrogen  in  the  hydroxyle  group. 

Methyle  alcohol,  H3C.OH;  Methyle  ether,  H3C.O.CH3. 

One  method  of  converting  an  alcohol  into  an  ether  is  shown  in  the 
following  equations : — 

(1)  H fi. OB.  {Methyle  hydrate)  ■\-^a.-='B.^G.O^a.  {SodiiimmethylaU)  +  H. 

(2)  HgC.OXa-l-HgCI  {Methyle  iodide)  =  Xal -f  H3C.O.CH3  {Methyle  ether). 

7.  The  Organo-metalUc  bodies  are  derived  from  the  alcohols  by  the 
substitution  of  a  metal  for  the  hydroxyle. 

Methyle  alcohol,  H3C.OH ; 
Sodium-methyle,  H3C.l!^a  ;  Zinc-methyle,  H3C.Zn.CH3 


438 


HYDROCARBONS. 


8.  The  Ammonia  derivatives  are  formed  from  ammonia  by  the  substi- 
tution of  a  compound  radical  for  hydrogen. 

Ammonia,  NHgj  Methylamine,  HgC.NHg;  Dimethylamine,  (HgC)^.^!!; 
Trimethylamine,  ^"(0113)3. 

9.  The  Cyanogen  compounds  are  those  which  contain  the  radical  CN, 
which  is  monatomic,  because  only  three  of  the  bonds  of  the  tetratomic 
carbon  are  satisfied  by  the  triatomic  nitrogen. 

Hydrocarbons. 

The  hydrocarbons  are  divided  into  series,  in  each  of  which  a  definite 
ratio  exists  between  the  atoms  of  hydrogen  and  carbon.  The  most  im- 
portant of  these  series  are  shown  in  the  following  table,  in  which  n  repre- 
sents a  whole  number : — 


Table 

of  Hydrocarbons. 

Name  of  Series. 

General  Formulae. 

Examples. 

ParafEnes,  . 

C„H.»4-2 

CH4      Methane. 

Olefines, 

C„H.^  „ 

C2H4     Ethene. 

Acetylenes, 

C»H,„_2 

CgHj     Ethine. 

Terpenes,    . 

C„H^„_4 

CjoHig  Turpentine. 

Benzenes,    . 

C„H  „_g 

CgHj     Benzene. 

Cinnamenes, 

C„H^„_8 

CgHg     Cinnamene. 

Naphthalenes, 

C„H,„_,, 

CigHg   Naphthalene. 

Anthracenes, 

C„K»_i8 

C14H10  Anthracene. 

In  any  given  series  of  hydrocarbons,  the  successive  members  of  the 
series  will  be  seen  to  differ  by  CHg  or  by  some  multiple  of  CHg.  Thus, 
in  the  series  of  paraffines,  we  have 


CH4,     CaHg, 

Methane.    Ethane. 


CsHg, 


C4H10,  &c. 

Butane. 


Propane. 

This  is  due  to  the  successive  methylation  or  replacement  of  hydrogen  by 
methyle ;  thus — 

H3C.H,     H3C.CH3,     H3C.CH2(CH3),     H3C.CH2.CH2(CH3) 

Methane.  Ethane.  Propane.  Butane. 

A  series  of  compounds  of  which  the  members  differ  thus  by  CHg  is  said 
to  be  liomologons  (ofioLos,  like,  Xoyos,  proportion),  and  the  members  are 
homologties. 

Compounds  occupying  similar  positions  in  different  series  are  said  to 
be  isologous  (to-os,  equal). 

In  the  following  table,  A,  B,  and  C  are  three  homologous  series,  whilst 
1,  2,  3,  and  4  are  isologous  series : — 


1 

2 

3                       4 

A 
B 
C 

CH4 

CgHg 
C2H4 
^2X12 

C3H8 
^sHg 
C3H4 

C4H10 
C4Hg 
C4Hg 

The  number  of  the  hydrocarbons  is  very  great,  because  the  same 
number  of  atoms  of  C  and  H  may  form  different  compounds  according  to 
their  grouping. 


CYANOGEN  AND  ITS  COMPOUNDS.  439 

Thus,  there  are  three  hydrocarbons  which  have  the  same  molecular 
formula,  CsHjg,  hut  which  are  altogether  different  bodies.  This  may  be 
accounted  for  by  the  difference  in  their  rational  or  structural  formulae. 


Normal  pentane,  H3C(CH,)(CH2)(CH2)CH3. 

i  CH3 
tCH, 

HqC      )         /-,         f      CHq 


Isopentane,     .     H3C(CH2)(CH)  i  ^^3 


Neopentane,    .     ^^]  ^  [  chJ 


CH3 
i 
3 


Compounds  which  contain  the  same  elements  in  the  same  proportions, 
but  yet  have  different  properties,  are  said  to  be  isomeric  or  isomerides 
(to-o?,  equal,  />tepo9,  a  part). 

When  it  is  known  that  the  grouping  of  their  atoms  is  different,  they 
are  also  termed  metameric  or  metamerides. 

Compounds,  of  which  the  molecular  formulae  are  multiples  of  each 
otlier  by  some  whole  number,  are  polymeric  or  polymerides  {ttoXxxs,  many) ; 
thus  benzene,  CgHg,  is  a  polymeride  of  acetylene  CgH,. 

In  the  following  pages,  the  strictly  scientific  classification  of  organic 
substances  has  not  been  adhered  to,  since  it  would  often  render  it  neces- 
sary to  describe,  in  separate  sections,  substances  which  are,  in  nature, 
closely  connected  with  each  other,  but  an  empirical  arrangement  has  been 
followed,  so  that  the  reader  may  find  his  memory  assisted,  and  the  interest 
of  the  subject  sustained,  by  being  enabled  to  bring  the  facts  and  explana- 
tions into  immediate  connection  with  familiar  processes  of  ordinary  life.* 

One  of  the  most  conspicuous  substances  standing  upon  the  boundary 
between  organic  and  inorganic  chemistry  is  the  compound  of  carbon  and 
nitrogen  known  as  cyanogen,  which  is  intimately  connected  mth  inorganic 
substances  through  some  of  the  processes  for  its  production,  and  through 
its  similarity  to  the  chlorine  group  of  elements,  whilst  the  origin  and 
chemical  properties  of  a  large  number  of  its  compounds  give  them  a  claim 
to  be  ranked  among  organic  substances.  The  study  of  this  substance, 
therefore,  will  form  a  fit  introduction  to  organic  chemistry. 

CYANOGEN  AND  ITS  COMPOUNDS. 

315.  In  the  beginning  of  the  last  century,  a  manufacturer  of  colours  at 
Berlin  accidentally  obtained  a  blue  powder  when  precipitating  sulphate  of 
iron  with  potash.  This  substance  was  used  as  a  colour,  under  the  name 
of  Prnsdan  him,  for  several  years,  before  any  explanation  of  its  production 
was  attempted,  or  even  before  the  conditions  under  which  it  was  formed 
were  exactly  determined.  In  1724  it  was  shown  that  Prussian  blue  could 
be  prepared  by  calcining  dried  animal  matters  with  carbonate  of  potash, 
and  mixing  the  aqueous  solution  of  the  calcined  mass,  first  with  sulphate 
of  iron  and  afterwards  with  hydrochloric  acid ;  but  the  most  important  step 
towards  the  determination  of  its  composition  was  made  by  Macquer,  who 
found  that  by  boiling  it  with  an  alkali,  Prussian  blue  was  decomposed, 
yielding  a  residue  of  red  oxide  of  iron,  and  a  solution  which  reproduced 
the  blue  when  mixed  with  a  salt  of  iron,  from  which  he  inferred  that  the 

*  The  nunibert)f  organic  substances  known  to  the  chemist  is  so  great  that  a  mere  list  of 
them  would  occupy  a  volume.  In  the  present  work  a  selection  has  been  made  of  those 
which  are  interesting  for  their  practical  applications,  or  instructive  from  theoretical  con- 
siderations. 


440  YELLOW  PRUSSIATE  OF  POTASH. 

colour  was  a  compound  of  the  oxide  of  iron  with  an  acid  for  which  the 
alkali  had  a  more  powerful  attraction — a  belief  confirmed,  in  1782,  by 
Scheele's  observations,  that  when  an  alkaline  solution  prepared  for  making 
the  blue  was  exposed  to  the  air,  or  to  the  action  of  carbonic  acid,  it  lost 
the  power  of  furnishing  the  colour,  but  the  escaping  vapour  struck  a  blue 
on  paper  impregnated  with  oxide  of  iron.  Scheele  also  prepared  this  acid 
in  a  pure  state,  and  it  soon  after  obtained  the  name  oi  pncssic  acid. 

In  1787,  Berthollet  found  prussic  acid  to  be  composed  of  carbon, 
hydrogen,  and  nitrogen,  but  he  also  showed  that  the  power  of  the  alka- 
line liquor  to  produce  Prussian  blue  depended  upon  the  presence  of  a 
yellow  salt  crystallising  in  octahedra,  and  containing  prussic  acid,  potash, 
and  oxide  of  iron,  though  the  latter  was  so  intimately  bound  up  with  the 
other  constituents,  that  it  could  not  be  separated  by  those  substances 
which  are  usually  employed  to  precipitate  iron. 

Porrett,  in  1814,  applying  the  greatly  increased  resources  of  chemistry 
to  the  investigation  of  this  subject,  decomposed  Prussian  blue  with  baryta, 
and  subsequently  removed  the  baryta  from  the  salt  thus  obtained  by 
means  of  sulphuric  acid,  when  he  obtained  a  solution  of  the  acid,  which 
he  named  ferruretted  cliyazic  acid. 

In  1815  Gay-Lussac,  having  boiled  Prussian  blue  (or  prussiate  of  iron, 
as  it  was  then  called)  with  red  oxide  of  mercury  and  water,  and  crystal- 
lised the  so-called  prussiate  of  mercury,  exposed  it,  in  the  dry  state,  to  the 
action  of  heat,  and  obtained  a  gas  having  the  composition  CN,  which  was 
called  cyanogen*  in  allusion  to  its  connexion  with  Prussian  blue.  It 
was  then  seen  that  the  substance  which  had  been  called  ferruretted  chyazic 
acid  contained  iron  and  the  elements  of  cyanogen,  whence  it  was  called 
ferrocyanic  acid,  and  its  salts  were  spoken  of  as  ferrocyanates.  Eobiquet 
first  obtained  this  acid  in  the  crystallised  state,  having  the  composition 
CgH^NgPe ;  and  since  it  was  found  that,  when  brought  in  contact  with 
metallic  oxides,  it  exchanged  the  H^  for  an  equivalent  quantity  of  the 
metal,  according  to  the  equation — 

H^.CfiNeFe  +  2M"0  =  M^'.C^^^Ye  +  2H2O, 
it  was  concluded  that  the  CgNgFe  composed  a  distinct  group  or  radical, 
which  was  named  ferrocyanogm,  Fey,  the  acid  being  called  hydroferro- 
cyanic  acid,  and  the  aedts  fe7'rocyanides. 

316.  Pnissiate  of  potash.  — The  yellow  prussiate  of  potash  or  potassium 
fetrocyanide  (K^CgNgFe.SAq.)  is  manufactured  upon  a  large  scale  by 
a  process  which  is  the  more  interesting  because  it  turns  to  account  some 
of  the  commonest  kinds  of  refuse,  such  as  old  leather,  hoof-parings, 
blood,  and,  in  short,  any  animal  matter  rich  in  nitrogen,  and  not  appli- 
cable to  any  more  economical  purpose.  Sometimes  these  substances  are 
first  subjected  to  destructive  distillation  for  the  carbonate  of  ammonia 
which  they  are  capable  of  yielding,  and  the  residual  highly  nitrogenised 
charcoal  is  then  used  for  the  production  of  the  ferrocyanide  of  potassium. 
Such  matters  are  fused  in  an  iron  vessel  with  carbonate  of  potash  and  iron 
filings,  and  the  fused  mass  is  heated  with  water  in  open  boilers,  when  a 
yellow  solution  is  obtained,  which,  after  evaporation,  deposits  truncated 
pyramidal  crystals  of  ferrocyanide  of  potassium,  containing  three  molecules 
of  water. 

The  production  of  the  ferrocyanide  may  be  explained  in  the  following 

*  From  Kvaveoi,  blue. 


PRUSSIAN  BLUE.  441 

manner: — (1)  The  carbon  containing  nitrogen  decomposes  the  potassium 
carbonate  at  a  high  temperature,  producing  potassium  cyanide  and  car- 
bonic oxide  gas  ;  KgCOg  +  C^  +  Xg  =  2KCN  +  SCO.  (2)  Sulphur,  derived 
partly  from  the  animal  matters  and  partly  from  potassium  sulphate 
present  as  an  impurity  in  the  potashes,  combines  with  the  iron  to  form 
ferrous  sulphide.  (3)  On  treating  the  fused  mass  with  water,  the 
ferrous  sulphide  is  dissolved  by  the  potassium  cyanide,  yielding  potassium 
sulphide  and  ferrocyanide — 

FeS  +  6KCN  =  K4Fe(C:N")6  +  KgS . 

Since  the  presence  of  the  potassium  sulphide  in  the  liquor  somewhat 
hinders  the  crystallisation  of  the  ferrocyanide,  some  makers  simply  melt 
pure  potassium  carbonate  with  the  animal  charcoal,  extract  the  potassium 
cyanide  from  the  residue  by  treatment  with  water,  and  digest  the  solution 
with  finely-ground  spathic  iron  ore  (ferrous  carbonate) — 

FeCOg  -f  6KCN"  =  K^Fe(CX)e  +  K2CO3 . 

Pnissian  blue. — When  solution  of  ferric  sulphate  is  added  to  one  of 
potassium  ferrocyanide,  a  very  dark  blue  precipitate  is  obtained,  which, 
when  thoroughly  washed,  is  soluble  in  pure  water.  This  is  used  by  dyers 
under  the  name  of  soluble  Prusdan  blue,  and  is  formed  thus — 

2K^Fcy  -I-  Fe2(SO,)3  =  SK.^SO^  +  K2Fe2Fcy2; 

showing  that  the  soluble  blue  is  a  potassio-ferric  ferrocyanide.  If  potas- 
sium ferrocyanide  be  added  to  solution  of  ferric  sulphate,  the  precipitated 
Prussian  blue  is  not  soluble;  2Fe2(S04)3-l- 3K^Fcy  =  6K2S04-fFe4Fcy3. 
The  Prussian  blue  is  ferric  ferrocyanide,  the  4  atoms  of  triatomic  iron 
saturating  the  3  atoms  of  the  tetratomic  group  ferrocyanogen,  Fe"Cy'g. 
This  compound  radical  has  never  yet  been  obtained  in  the  separate  state, 
but  it  can  be  traced  through  a  complete  series  of  compounds,  in  which  it 
exactly  resembles  chlorine  in  its  chemical  relations ;  thus  the  hydroferro- 
cyanic  acid  (H^Fcy),  and  the  ferrocyanides  of  the  metals,  are  perfectly 
analogous  to  hydrochloric  acid  and  the  chlorides,  though  containing  a 
compound  radical  instead  of  a  simple  one ;  but  whereas  chlorine  is  a 
monatomic  radical  combining  only  with  1  atom  of  hydrogen,  ferrocyano- 
gen is  tetratomic.  Oxalic  acid  is  capable  of  dissolving  Prussian  blue,  and 
this  solution  forms  the  basis  of  ordinary  blue  ink. 

Prussian  blue  is  sometimes  prepared  with  the  green  sulphate  of  iron 
(FeSO^),  but  in  that  case  it  is  necessary  to  expose  the  precipitate  for 
some  time  to  the  air,  since  the  first  result  is  a  nearly  white  precipitate  * 
of  potassio-ferrous  ferrocyanide ;  K^Fcy  -f  FeSO^  =  KgSO^  -t-  Ys..^e"¥cy. 
When  this  precipitate  is  exposed  to  the  air,  it  gradually  acquires  a 
dark  blue  colour,  becoming  eventually  converted  into  Prussian  blue  by 
oxidation ;  6K2FeFcy  -t-  O3  =  SK^Fcy  -|-  Fe4Fcy3  -f  Fe203. 

Prussian  blue  is  easily  decomposed  by  alkalies,  a  brown  residue  of  ferric 
oxide  being  left,  Fe^Fcyj-f  12KH0  =  3K4Fcy-h  2Fe203-^6H20.  This 
decomposition  is  turned  to  account  by  the  calico-printer  for  producing  a 
buff  or  white  pattern  upon  a  blue  ground.  The  stuff  having  been  dyed 
blue  by  passing,  first  through  a  solution  of  per-salt  of  iron,  and  afterwards 
through  one  of  potassium  ferrocyanide,  the  pattern  is  discharged  by  an 
alkali,  which  leaves  the  brown  peroxide  of  iron  capable  of  being  removed 

*  Tliis  precipitate  may  be  obtained  perfectly  white  by  shaking  iron  filings  with  solution 
of  sulphurous  acid,  and  filtering  into  a  weak  solution  of  potassium  ferrocyanide. 


442  HYDROCYANIC  OR  PRUSSIC  ACID. 

by  a  dilute  acid,  when  the  stuff  has  been  rinsed,  so  as  to  leave  the  design 
white. 

H ydroferrocyanic  acid.— By  decomposing  a  cold  saturated  solution  of 
potassium  ferrocyanide  with  about  an  equal  volunje  of  hydrochloric  acid, 
colourless  crystals  of  hydroferrocyanic  acid  (H^Fcy)  are  obtained,  which 
are  insoluble  in  hydrochloric  acid,  but  readily  soluble  in  water.  When 
a  solution  of  this  acid  is  heated,  it  evolves  hydrocyanic  acid  (HCN),  and 
deposits  a  white  precipitate  of  ferrous  ferrocyanide,  FcgFcy,  which  becomes 
blue  on  exposure  to  the  air,  being  converted  into  Prussian  blue. 

The  decomposition  of  the  hydroferrocyanic  acid  by  heat  is  represented 
by  the  equation,  SH^CygFe  =   12HCy  +  FcaCFeCyJ, 

Hydroferro-  Hydrocyanic         Ferrous  ferro- 

cyanic  acid,  acid,  cyanide, 

and  the  formation  of  Prussian  blue  from  this  last  compound  on  exposure 
to  air  by  SFt-jFcy  +  63  =  Fe^Fcyg  +  FcgOg. 

Hydrocyanic  or  Prussic  acid. — Advantage  is  taken  of  the  decomposition 
of  potassium  ferrocyanide  by  acids,  in  the  preparation  of  solution  of 
hydrocyanic  acid  for  medicinal  use.  For  this  purpose,  2  parts  of  potassium 
ferrocyanide  in  powder  are  distilled  with  1|  parts  of  oil  of  vitriol  diluted 
with  2  parts  of  water,  the  vapour  of  hydrocyanic  acid  being  carefully 
condensed  {see  fig.  47).  The  decomposition  of  the  ferrocyanide  by  the 
sulphuric  acid  yields  hydroferrocyanic  acid,  which  is  then  decomposed  as 
in  the  equation  given  above.  There  is  left  in  the  retort  the  ferrous 
ferrocyanide  as  a  pale  greenish  salt,  which  rapidly  becomes  blue  when 
exposed  to  the  air. 

The  solution  of  hydrocyanic  acid  thus  obtained  is  colourless,  and 
exhales  the  remarkable  odour  of  the  acid ;  its  acid  characters  are 
very  feeble  indeed,  even  more  so  than  those  of  carbonic  acid,  but 
it  is  extremely  poisonous,  a  very  small  dose  destroying  life  almost 
immediately.  Hydrocyanic  acid  is  found  in  laurel  water,  and  in  water 
distilled  from  the  kernels  of  many  stone  fruits,  such  as  the  peach,  apricot, 
and  plum.  In  minute  doses  hydrocyanic  acid  is  a  very  valuable  remedy, 
and  is  employed  in  medicine  in  solutions  of  different  strengths.  One  of 
these,  which  is  known  as  the  acid  of  the  London  Pharmacopoeia,  contains 
2  per  cent,  of  hydrocyanic  acid,  and  is  prepared  by  the  process  mentioned 
above,  being  afterwards  diluted  with  water  to  the  proper  strength. 
Sckeele's  acid  varies  in  strength,  but  usually  contains  between  4  and  5  per 
cent,  of  hydrocyanic  acid.  This  acid  is  prepared  from  Prussian  blue 
by  the  process  originally  employed  by  Scheele  when  the  acid  was  dis- 
covered. It  consists  in  boiling  Prussian  blue  with  water  and  red  oxide 
of  mercui'y  until  the  blue  colour  disappears ;  ferric  oxide  is  separated,  and 
mercuric  cyanide  (HgCyg)  passes  into  solution ;  the  latter  is  filtered, 
mixed  with  diluted  sulphuric  acid,  and  shaken  with  iron  filings,  which 
precipitate  the  mercury  in  the  metallic  state,  leaving  free  hydrocyanic  acid 
in  the  liquid,  which  is  then  distilled — 

HgCy2  +  Fe  +  H2SO4  =  2HCy  +  FeSO^  +  Hg. 

In  order  clearly  to  understand  this  process,  it  must  be  known  that  the 
mercury  exhibits  a  special  tendency  to  combine  with  cyanogen,  which  is 
sufficiently  powerful,  in  this  instance,  to  bring  about  the  decomposition 
of  the  ferrocyanogen  existing  in  the  Prussian  blue,  a  part  of  the  cyanogen 
being  exchanged  for  the  oxygen  of  the  mercuric  oxide. 

It  is  from  the  cyanide  of  mercury  that  the  pure  anhydrous  hydrocyanic 


PEEPARATION  OF  CYANOGEN.  443 

acid  and  cyanogen  itself  are  prepared.  For  these  purposes,  it  may  be 
obtained  by  dissolving  the  red  oxide  of  mercury  in  hydrocyanic  acid, 
when  a  double  decomposition  takes  place,  exactly  as  with  hydrochloric 
acid,  HgO  +  2HCy  =  HgCyg  +  HgO,  and  the  mercuric  cyanide  is  obtained 
in  square  prismatic  crystals  on  evaporating  the  solution.  If  these  crystals 
be  dried  and  gently  warmed  with  strong  hydrochloric  acid,  mercuric 
chloride  will  be  formed,  and  hydrocyanic  acid  evolved,  HgCy2  +  2HCl 
=  HgCl2  +  2HCy.  The  mixed  vapours  of  hydrochloric  and  hydrocyanic 
acid  are  passed  over  fragments  of  marble  (CaCOg),  which  absorb  the 
hydrochloric  acid  (CaCOg  +  2HC1  =  CaCl^  +  H.^O  +  CO2),  but  not  the 
hydrocyanic,  since  the  latter  is  too  weak  an  acid  even  to  displace  carbonic 
acid.  The  mixture  of  hydrocyanic  acid  and  carbon  dioxide  is  passed  over 
calcium  chloride  to  remove  aqueous  vapour,  and  afterwards  through  a 
tube  cooled  in  a  mixture  of  ice  and  salt,  when  the  hydrocyanic  acid  is 
condensed  to  a  colourless  liquid,  which  evaporates  so  rapidly  when  exposed 
to  the  air  that  it  lowers  the  temperature  to  the  freezing-point  of  the  acid, 
which  is  about  0°  F. ;  at  a  little  above  the  ordinary  temperature  (79°  F.) 
it  boils,  and  emits  a  vapour  which  burns  with  a  blue  flame.  When  kept 
for  some  time  it  is  liable  to  undergo  spontaneous  decomposition,  evolving 
ammonia,  and  being  converted  into  a  brown  mass  of  uncertain  composition. 
The  aqueous  solution  of  the  acid  suffers  a  similar  change,  and  since 
exposure  to  light  favours  the  decomposition,  the  medicinal  acid  is  usually 
kept  in  bottles  covered  with  paper.  The  presence  of  a  very  small  quantity 
of  sulphuric  acid  prevents  this  change,  and  hence  the  acid  prepared  by 
distilling  ferrocyanide  of  potassium  with  sulphuric  acid,  Avliich  usually 
contains  traces  of  the  latter,  can  be  preserved  much  better  than  that 
prepared  by  other  methods. 

Among  tlie  products  of  decomposition  is  a  crystalline  solid  body  having  the  same 
percentage  composition  as  the  acid  itself,  and  believed  to  be  H3C3N3. 

By  passing  HCl  gas  into  HCN  mixed  with  acetic  ether  cooled  in  ice  and  salt,  a 
colourless  crystalline  compound,  2HCN.3PIC1,  is  obtained.  It  is  insoluble  in  ether 
and  in  acetic  ether,  and  is  decomposed  by  water,  yielding  formic  acid  and  ammonium 
chloride.  Alcohol  also  decomposes  it  with  productiou  of  hydric  chloride,  ethyle 
chloride,  ammonium  chloride,  formic  ether,  and  the  hydrochlorate  of  a  base  termed 
Jontmmidine  HC.NjHj,  which  might  evidently  be  formulated  as  formyldiaminc 
or  two  molecules  of  ammonia  with  triatomic  formyle  in  place  of  3  atoms  of  hydrogen. 

When  hydriodic  acid  gas  is  passed  into  anhydrous  hydrocyanic  acid  cooled  by  ice, 
a  crystalline  body  is  fonned,  which  has  the  composition  HCN.HI.  It  is  readily 
soluble  in  water  and  alcohol,  but  not  in  ether,  and  may  be  sublimed  with  little 
decomposition.  This  substance  is  not  acid,  and  does  not  answer  to  the  tests  for 
hydrocyanic  acid.  When  decomposed  by  potash,  it  gives  ainmonia,  potassium 
formiate,  and  potassium  iodide,  so  that  it  may  be  regarded  as  the  hydriodate  of  an 
ammonia  formed  by  the  substitution  of  1  molecule  of  the  triatomic  radical  formyle 
(CH)  for  the  3  atoms  of  hydrogen  ;  ov  formylamhie  hydriodate  N(CH)"'.HI. 

When  hydrocyanic  acid  is  acted  on  by  nascent  hydrogen  (zinc  and  sulphuric  acid) 
it  yields  methylamine,  HCN  +  H4  =  NH2CH3. 

317.  Cyanogen*  itself  (CN)2  can  be  prepared  by  the  mere  action  of 
heat  upon  the  cyanide  of  mercury  (in  a  test-tube  provided  with  a  glass 
jet  for  burning  the  gas,  fig.  280).  This  salt  resolves  itself  into  metallic 
mercury,  cyanogen,  and  a  brown  substance  which  has  been  called  para- 
ci/anogen  (C^N^),  and  appears  to  have  been  formed  by  the  union  of  four 
atoms  of  cyanogen.     Cyanogen  gas  is  easily  distinguished  from  all  others 

*  Cyanogen  appears  to  be  produced  by  direct  combination  of  carbon  with  nitrogen  at  the 
high  temperature  of  the  electric  light. 


444  CYANIDE  OF  POTASSIUM. 

by  its  peculiar  odour  and  its  property  of  burning  with  a  pink  flame  edged 
with  green.  Being  nearly  twice  as  heavy  as  air  (sp.  gr.  1  -8),  it  may  be 
collected  by  downward  displacement,  for  water  dissolves  about  four  times 
its  volume  of  the  gas,  yielding  a  solution  which 
is  prone  to  undergo  a  spontaneous  decomposition 
remarkable  for  the  comparatively  complex  pro- 
ducts which  it  furnishes,  amongst  which  we  trace 
the  oxalate  (NH4)2C204  and  formiate(NH4CH02) 
of  ammonium,  and  urea  (CH^NgO),  all  derived, 
be  it  remembered,  from  the  elements  of  cyanogen 
and  water.  In  its  chemical  relations,  cyanogen 
presents  a  striking  resemblance  to  chlorine. 
Thus,  at  a  slightly  elevated  temperature,  potas- 
sium and  sodium  take  fire  in  it,  forming  the 
cyanides  of  those  metals,  precisely  as  the  chlorides 
would  be  formed.  Again,  when  cyanogen  is 
absorbed  by  a  solution  of  potash,  the  cyanide  and  cyanate  of  potassium 
are  formed — 

2KH0   +  Cyg  =   KCyO  (Potassium  cyanate)    +   KCy  (Potassium  cyanide)    +  H,0, 

just  as  the  chloride  and  hypochlorite  of  potassium  result  from  the  action 
of  chlorine  upon  potash,  2KH0  +  Clg  =  KCIO  +  KCl  -1-  H2O.  A  pressure 
of  about  4  atmospheres  is  required  to  liquefy  cyanogen,  when  it  forms 
a  colourless  liquid  of  sp.  gr.  0"87,  freezing  to  a  crystalline  mass  at 
-  30°  F. 

Cyanide  of  potassium. — The  most  useful  of  the  cyanides  is  potassium 
cyanide,  which  is  extensively  employed  in  electro-plating  and  gilding. 

This  salt  may  be  formed  by  a  very  interesting  process,  which  is  one  of 
the  few  in  which  the  atmospheric  nitrogen  takes  part,  and  consists  in 
passing  air  over  red  hot  charcoal  which  has  been  previously  soaked  in  a 
strong  solution  of  potassium  carbonate  and  dried,  when  the  nitrogen 
requisite  for  the  formation  of  the  cyanide  is  absorbed  from  the  air,  and 
carbonic  oxide  is  disengaged ;  KgCOg  -1-04  +  ^2  =  2KCN  -|-  SCO. 

It  is  probably  by  a  similar  change  that  the  potassium  cyanide  is 
produced  in  blast-furnaces  (page  304)  in  which  iron  ores  are  reduced, 
the  potash  being  derived  from  the  ash  of  the  fuel.  The  cyanide  is  always 
prepared  for  use  from  the  ferrocyanide,  which  is  resolved  by  a  very  high 
temperature  into  potassium  cyanide  and  iron  carbide,  with  evolution 
of  nitrogen ;  K^CygFe  =  4KCy  +  YeO^  +  Ng. 

In  order  to  avoid  the  loss  of  the  2  atoms  of  cyanogen,  it  is  usual 
to  fuse  the  ferrocyanide  with  potassium  carbonate  in  the  proportion  of  3 
parts  of  the  dry  carbonate  to  7  parts  of  the  dried  ferrocyanide  ;  the 
mixture  is  fused  in  a  covered  earthen  crucible,  and  occasionally  stirred 
until  gas  ceases  to  be  evolved  ;  the  crucible  is  then  removed  from  the  fire, 
allowed  to  stand  for  a  minute  or  two  that  the  metallic  iron  may  subside, 
and  the  clear  fused  cyanide  poured  out  on  to  a  stone.  The  change  involved 
in  this  process  is  represented  by  the  following  equation — 

K.CygFe  -|-  KgCOg  =  5KCy  +  KCyO  -h  Fe  -i-  CO2, 

whence  it  will  be  seen  that  the  commercial  potassium  cyanide  is  contami- 
nated with  cyanate.  It  also  contains  a  considerable  quantity  of  carbonate, 
so  that  the  proportion  of  cyanide  is  often  only  60  per  cent.     The  white 


CYANIDE  OF  POTASSIUM.  445 

porcelaiu-like  masses  of  potassium  cyanide  deliquesce  when  exposed  to 
the  air,  and  emit  the  odour  of  hydrocyanic  acid  as  well  as  that  of 
ammonia ;  the  former  is  disengaged  from  the  cyanide  by  the  action  of 
the  atmospheric  carbonic  acid,  whilst  the  ammoniacal  odour  is  due  to  the 
ammonium  carbonate  produced  by  the  action  of  moisture  upon  the 
cyanate  ;  2KCX0  +  4H2O  =  K2CO3  +  (NH4)2C03. 

Pure  potassium  cyanide  is  deposited  in  colourless  cubical  crystals  when 
vapour  of  hydrocyanic  acid  is  passed  into  an  alcoholic  solution  of  potash, 
or  it  may  be  obtained  by  boiling  the  commercial  cyanide  with  alcohol 
and  filtering  while  hot,  when  the  cyanide  crystallises  out  as  the  solution 
cools. 

The  use  of  potassium  cyanide  in  electro-plating,  and  gilding  depends 
upon  the  power  of  a  solution  of  the  salt  to  dissolve  the  cyanides  of  gold 
and  silver,  forming  compounds  which  are  easily  decomposed  by  the 
galvanic  current,  with  deposition  of  metallic  gold  or  silver  upon  any 
object  capable  of  conducting  the  current,  which  may  be  attached  to  the 
negative  pole  (page  380).  Solution  of  potassium  cyanide  is  also  able 
to  dissolve  metallic  silver,  chloride,  iodide,  and  sulpliide  of  silver,  which 
is  taken  advantage  of  in  fixing  photographic  images,  and  in  cleaning 
silver  or  gold  lace. 

At  a  high  temperature,  potassium  cyanide  is  a  very  powerful  reducing 
agent,  abstracting  an  atom  of  oxygen  from  most  of  the  metallic  oxides, 
so  as  to  liberate  the  metals,  being  itself  converted  into  potassium  cyanate. 
Thus,  when  the  stannic  oxide  is  fused  with  potassium  cyanide  SnOg 
+  2KCy  =  Sn  4-  2KCyO.  This  property  of  the  cyanide  is  often  applied 
in  chemical  experiments.  The  cyanate  is  readily  distinguished  by  the 
peculiar  pungent  odour  of  cyanic  acid,  which  it  emits  when  treated  with 
dilute  sulphuric  acid,  though  the  greater  part  of  the  cyanic  acid  is 
decomposed  with  effervescence,  yielding  ammonium  sulphate  and  carbonic 
acid  gas — 

2KCN0  +  2H2SO4  +  2H2O  =  K2SO4  +  (NH4)2SO,  +  2CO2. 

The  following  process,  for  the  preparation  of  potassium  cyanate,  published  by  C.  A. 
Bell,  is  very  satisfactory :  4  parts  of  perfectly  dried  potassium  ferrocyanide  are  in- 
timately mixed  with  3  parts  of  potassium  bichromate  ;  the  mixture  is  thrown,  in  small 
portions,  into  a  porcelain  or  iron  dish  heated  sufficiently  to  kindle  it.  When  the 
whole  has  smouldered  and  blackened,  it  is  allowed  to  cool,  introduced  into  a  flask, 
boiled  with  strong  methylated  alcohol  and  filtered ;  the  potassium  cyanate  crystallises 
out  on  cooling. 

When  fused  potassium  cyanate  is  triturated  with  dried  oxalic  acid,  and 
the  mass  treated  with  water,  a  white  insoluble  substance  is  left,  which  has 
been  called  cyamelide,  and  has  the  composition  CHNO,  being  metameric 
with  cyanic  acid,  HCNO  ;  when  this  substance  is  distilled,  cyanic  acid 
passes  over  as  a  colourless  liquid,  which  can  only  be  preserved  at  a  very 
low  temperature,  for  if  the  receiver  containing  it  be  removed  from  the 
freezing  mixture  employed  to  condense  the  cyanic  acid,  the  latter  becomes 
hot  and  turbid,  soon  begins  to  boil  violently,  and  is  converted  into  a 
white  mass  of  cyamelide  resembling  porcelain. 

Potassium  cyanide,  when  fused  with  sulphur,  forms  a  compound  cor- 
responding to  potassium  cyanate,  but  containing  sulphur  in  place  of 
oxygen,  and  having  the  formula  KCyS,  which  is  commonly  spoken  of  as 
potassium  sulphocyanide,  being  represented  as  containing  a  compound 
radical,   sulphocyanogen   CyS  =  Scy.      The   potassium   sulphocyanide   is 


446  RED  PRUSSIATE  OF  POTASH. 

generally  prepared  by  fusing  3  parts  of  dried  potasanm  ferrocranide  and 
1  part  of  potassium  carbonate  (the  materials  for  making  potassium  cyanide) 
with  2  parts  of  sulphur  in  a  covered  crucible.  By  washing  the  cooled 
mass  with  boiling  water,  the  sulphocyanide  is  extracted,  and  may  be 
obtained,  by  evaporating  the  solution,  in  prismatic  crystals  resembling 
nitre.  By  decomposing  the  potassium  sulphocyanide  with  lead  acetate,  the 
lead  sulphocyanide  (Pb(CyS)2)  is  obtained,  and  this,  when  acted  upon  with 
sulphuretted  hydrogen,  yields  lead  sulphide  and  hydrosulphocyanic  acid, 
HCyS,  the  latter  being  a  colourless  oily  liquid  which  may  be  crystallised 
by  cold.  This  acid  is  remarkable  for  the  dark  red  colour  (due  to  ferric 
sulphocyanide)  which  it  gives  with  ferric  salts,  for  which  potassium 
sulphocyanide  is  frequently  employed  as  a  test.  A  very  delicate  test 
(Liebig's  test)  for  hydrocyanic  acid,  in  cases  of  poisoning,  is  also  founded 
upon  that  circumstance,  for  if  a  watch-glass  moistened  with  yellow 
ammonium  sulphide  (page  271)  be  exposed  to  the  action  of  vapour  of 
hydrocyanic  acid,  the  latter  is  absorbed  and  converted  into  ammonium 
sulphocyanide — 

(NH4)2S  +  S2  +  2HCy  =  2NH^CyS  +  H^S, 
by  applying  a  gentle  heat  to  the  watch-glass,  any  excess  of  ammonium 
sulphide  is  volatilised,  and  a  drop  of  ferric  chloride  will  then  give  the 
blood-red  colour  with  the  sulphocyanide. 

By  covering  potassium  cyanide  with  water  in  a  flask,  and  saturating  with  hydro- 
sulphuric  acid,  Wallace  obtained  a  yellow  substance,  sparingly  soluble  in  water,  which 
he  terms  chrysean.  It  appears  to  have  the  formula  C4H5N3Sg,  and  to  be  formed  by 
the  reaction  4KCN  +  5HjS  =  2 KgS  +  NH^HS  +  C4H5N'sSj.  Chrysean  crystallises  from 
boiling  water  in  golden  needles.  It  dissolves  in  alcohol,  ether,  acids,  and  alkalies, 
crystallising  out  unchanged.  Its  alcoholic  solution  has  a  tine  red  colour,  and  changes 
to  a  fugitive  green  on  adding  a  little  alkali. 

Solution  of  potassium  cyanide  dissolves  iodine  readily,  and  if  the  solution  be  gently 
warmed,  fine  needles  of  cyanogen  iodide,  CNI,  condense  on  the  cool  sides  of  the  vessel. 

318.  Ferricyanide  of  potassium. — When  chlorine  is  passed  into  a  solu- 
tion of  potassium  ferrocyanide,  the  liquid  assumes  a  brown  colour,  and, 
when  evaporated,  deposits  beautiful  red  rhombic  prisms,  which  are  found, 
on  analysis,  to  have  the  composition  KgCy^Fe,  having  been  formed  from 
the  ferrocyanide  according  to  the  equation — 

K^CygFe  {Ferrocyanide)  4-   CI  =   KgCygFe  (Ferricyanide)   -f-   KCl . 

This  salt  is  known  bs  red  prussiate  of  potash,  or  potassium  ferricyanide, 
and  is  used  in  dyeing ;  for  if  a  piece  of  stutf  be  heated  in  a  solution  of 
the  ferricyanide  acidulated  with  acetic  acid,  a  blue  compound  similar  to 
Prussian  blue  is  deposited  in  the  fibre. 

Potassium  ferricyanide  is  also  employed  for  the  preparation  of  TumJndVs 
hliie  (ferrous  ferricyanide),  which  is  precipitated  when  a  solution  of  that 
salt  is  mixed  with  one  of  ferrous  sulphate — 

SFeSO^  +  2K3(Cy6Fe)  =  3K2SO4  +  Fe3(Cy6Fe)2.* 

In  calico-printmg,  a  mixture  of  potassium  ferricyanide  with  potash  is 
employed  as  a  discharge  for  indigo,  such  a  mixture  acting  as  a  powerful 
bleaching  agent,  in  consequence  of  its  tendency  to  impart  oxygen  to  any 
substance  in  need  of  that  element,  the  ferricyanide  being  converted  into 
the  ferrocyanide  ;  thus — 

2K3(Cy6Fe)  (Ferricyanide)   +  2KH0   =  2K^{CyQYe)  (Ferroepanide)  +  0  +  RoO. 

'  It  has  been  stated  that  this  precipitate  is  really  the  ferroso-ferric  ferrocyanide 
Fe'Fe/'Fcyjj. 


CHLORIDES  OF  CYANOGEN.  447 

The  ferricyanide  is  assumed  to  contain  a  compound  radical  ferricyanogen 
(C.VgFe),  which  differs  from  ferrocyanogen  in  containing  triatomic  iron 
Fe'",  instead  of  diatomic  iron,  Fe".  The  formula  Cyg'Fe'"  shows  that 
this  radical  must  be  triatomic  and  not  tetratomic  like  Cyg'Fe".  The 
hydroferricyanic  acid  (HgCygFe)  can  be  obtained  in  a  crystallised  state, 
and  many  of  the  corresponding  ferricyanides  have  been  examined. 

Ferrocyanogen  and  ferricyanogen  are  not  the  only  compound  radicals 
of  this  description ;  there  are  cobcUticyanogeti  (CygCo),  manganicyanogen 
(CygMn),  chromo cyanogen  (CygCr)  and  chromicyanogen  (CygCr),  platino- 
cyanogen  (Cy^Pt),  palladiocyanogen  (Cy^Pd),  and  iridiocyanogen  (Cy^Ir), 
but  none  of  these  have  received  any  useful  applications.  The  platino- 
cyanides  are  remarkable  for  their  brilliant  colours. 

319.  GMorides  of  cyanogen. — When  moist  mercuric  cyanide  is  shaken 
up  in  a  bottle  of  chlorine  gas,  and  set  aside  for  some  time  in  a  dark  place, 
the  yellow  colour  of  the  chlorine  disappears,  and  the  bottle  is  filled  with 
a  colourless  gas  having  a  remarkably  pungent  and  tear-exciting  odour  ;  this 
is  the  gaseous  cyanogen  chloride  (CyCl) ;  HgCyg  +  Cl^  =  HgClg  4-  2CyCl. 
If  light  have  access  during  this  experiment,  an  oily  liquid  cJdoride, 
Cy2^^2»  ^^  produced. 

The  cyanogen  chloride  gas  may  by  liquefied  by  a  pressure  of  four 
atmospheres,  and  if  the  liquid  is  kept  for  some  days  in  a  sealed  tube,  it  is 
converted  into  a  white  mass  of  solid  cyanogen  chloride,  Cy^Clg.  When 
this  is  acted  on  by  water,  it  yields  cyanuric  acid,  H^CyaOg,  according 
to  the  equation  CygClg  +  SHgO  =  3HC1  +  HgCygOg.  This  acid  is  very 
interesting  on  account  of  its  polymeric  relation  to  cyanic  acid  (HCyO), 
which  may  be  obtained  from  it  by  distillation.  It  is  a  tribasic  acid,  and 
forms,  like  tribasic  pliosphoric  acid  (page  231),  three  series  of  salts,  having 
the  formulae,  respectively,  W^Cy.fi^,  WJlCj^O.^,  M'H.jCygOg. 

T\\Q  phosphorous  cyanide,  PCyj,  has  been  sublimed  in  tabular  crystals 
from  a  mixture  of  silver  cyanide  and  phosphorous  chloride  heated  in  a 
sealed  tube  to  280°  F.  for  some  hours,  and  afterwards  distilled  in  a 
current  of  dry  carboni  cacid  gas.  Phosphorous  cyanide  inflames  at  a  very  low 
temperature,  and  is  decomposed  by  water,  yielding  cyanic  and  phosphorous 
acids. 

320.  Nitroprusside^.—Wh&xv  potassium  ferrocyanide  is  boiled  with  dilute  nitric 
acid,  a  point  is  attained  at  which  the  solution  gives  a  slate- coloured  precipitate  with 
ferrous  sulphate  ;  if  it  be  then  boiled  with  an  excess  of  sodium  carbonate,  filtered, 
and  evaporated,  it  deposits  ruby-red  prismatic  crystals  of  sodium  nitroprusside 
(Na4CyioN203Fe.2.4A(i.),  from  which  the  nitroprussides  of  other  metals  may  be 
obtained. 

Tlie  hydronitroprussic  acid  (H4CyjoN'203Fe2.2Aq. )  has  also  been  prepared  and 
crystallised. 

The  nitroprussides  were  found  by  Hadow  to  be  formed  from  a  double  molecule 
of  the  ferricyanides  by  the  exchange  of  a  molecule  of  cyanogen  for  a  molecule  of 
nitrous  anhydride  (NjO^),  and  the  simultaneous  removal  of  2  atoms  of  the  metal  with 
which  the  ferricyanogen  was  combined.  Thus  the  double  molecule  of  potassium 
ferricyanide,  KgCyi^Feg,  becomes  nitroprusside  of  potassium,  K4Cyi(,N203Fejj,  when 
boiled  with  nitric  acid,  other  products  being  formed  at  the  same  time  by  the  oxidising 
action  of  the  nitric  acid. 

Based  upon  this  view  of  its  constitution,  a  more  certain  and  economical  process 
for  the  production  of  sodium  nitroprusside  was  devised  by  Hadow,  which  consists 
in  acting  upon  the  potassium  ferricyanide  with  sodium  nitrite,  acetic  acid,  and 
mercuric  chloride,  when  the  mercury  removes  a  molecule  of  cyanogen,  and  the  chlorine 
2  atoms  of  potassium,  the  nitrite  acting  on  the  residue  of  the  ferricyanide,  and  con- 
verting it  into  nitroprusside,  which,  by  double  decomposition  with  the  sodium  acetate. 


448         PREPARATION  OF  FULMINATE  OF  MERCURY. 

yields  potassium  acetate  and  sodium  nitroprasside.  The  mercuric  cyanide  crystallises 
out  first,  and  the  sodium  uitroprusside  may  be  obtained  in  crystals  from  the  evapo- 
rated solution. 

The  more  recent  researches  of  Stiideler  have  still  further  simplified  the  constitution 
of  the  nitroprussides.  By  the  action  of  potassium  cyanide  upon  ferrous  sulphate, 
he  obtained  an  oranf?e  precipitate  composed  of  KFe./'Cy,,  in  which  2  atoms  of 
diatomic  iron  have  replaced  4  atoms  of  monatomic  potassium  in  5  molecules  of  the 
cyanide ;  5KCy  +  2re"S04  =  KFc/Cys  +  2K,S04. 

When  this  precipitate  was  treated  with  potassium  nitrite,  it  furnished  the  nitro- 
prusside;  K'Fe/Cy5'  +  KN02  =  Kj'Fe"(NO)'Cy5  + FeO. 

According  to  this,  the  hypothetical  radical  of  the  nitropnissides  would  contain 
Cys(XO)'Fe",  representing  ferrocyanogen  Cyj,Fe"  in  which  (NO)'  has  replaced  Cy*. 
The  monatomic  character  of  the  NO  is  shown  in  potassium  nitrite  KNOj  or  K'(NO)'0". 
It  will  be  observed  that  Stadeler's  formula  for  the  nitroprussides  diflFers  from  Hadow's 
only  by  a  single  atom  of  oxygen  in  Hadow's  molecule,  thus — 

Double  molecule  of  potassium  nitroprusside  (Stiideler),  K4Fe2N202Cyio, 

Potassium  nitroprusside  (Hadow),  K4FejjNg03Cy,o 

so  that  whereas  Hadow  believed  in  the  substitution  of  nitrous  anhydride  (NjOg)  for  a 

part  of  the  cyanogen,  Stadeler  finds  that  it  is  really  NO,  the  radical  of  the  nitrous 

anhydride  ((NO)'(NO)'0")  which  replaces  the  cyanogen.* 

On  the  latter  view,  the  diatomic  character  of  the  assumed  radical  Cy5'(N0)'  Fe"  is 
at  once  explained,  for  it  evidently  requires  2  atoms  of  potassium  to  complete  the 
saturation  of  tlie  Cyj. 

The  sodium  nitroprusside  is  used  as  a  test  for  the  alkaline  sulphides,  with  a  very 
slight  trace  of  which  it  gives  a  magnificent  purple  colour.  Thus,  an  inch  or  two  of 
human  hair,  fused  with  sodium  carbonate  before  the  blowpipe,  will  yield  sufficient 
sodium  sulphide  to  strike  a  purple  tint  with  the  nitroprusside. 

321.  The  Fulminates. — The  violently  explosive  compound  known  as 
fulminate  of  mercury,  which  is  so  largely  employed  for  the  manufacture 
of  percussion  caps,  is  connected  with  the  series  of  cyanogen  compounds. 

Preparation  of  fidminate  of  mercury. — This  substance  is  prepared  by 
the  action  of  alcohol  upon  a  solution  of  mercury  in  excess  of  nitric  acid ; 
and  as  this  action  is  of  a  violent  character,  some  care  is  necessary  in  order 
to  avoid  an  explosion.  On  a  small  scale,  the  fulminate  may  be  obtained 
without  any  risk  by  strictly  attending  to  the  following  prescription  : — 

Weigh  out,  in  a  watch-glass,  25  grains  of  mercury,  transfer  it  to  a  half-pint  beaker, 
add  half  an  ounce  (measured)  of  ordinary  concentrated  nitric  acid  (sp.  gr.  1'42),  and 
apply  a  gentle  heat.  As  soon  as  the  last  particle  of  mercury  is  dissolved,  place  the 
beaker  ujwm  the  table,  away  from  any  flame,  and  pour  into  it,  pretty^  quickly,  at 
arm's  length,  5  measured  drachms  of  alcohol  (sp.  gr.  0  87).  Verj'  brisk  action  will 
ensue,  and  the  solution  will  become  turbid  from  the  separation  of  crystals  of  the 
fulminate,  at  the  same  time  evolving  very  dense  white  clouds,  which  have  an  agree- 
able odour,  due  to  the  presence  of  nitrous  ether,  aldehj'de,  and  other  products  of  the 
action  of  nitric  acid  upon  alcohol.  The  heavy  character  of  these  clouds  is  caused  by 
the  presence  of  mercury,  though  in  what  form  has  not  been  ascertained ;  much  nitrous 
oxide  and  hydrocyanic  acid  are  evolved  at  the  same  time.  Wlien  the  action  has 
subsided,  the  beaker  may  be  filled  with  water,  the  fulminate  allowed  to  settle,  and  the 
acid  liquid  poured  off".  The  fulminate  is  then  collected  on  a  filter,  washed  with  water 
as  long  as  the  washings  taste  acid,  and  dried  by  exposure  to  air. 

On  a  large  scale,  the  preparation  of  mercuric  fulminate  is  carried  out  in  the  open  air, 
under  sheds.  At  Montreuil,  300  grammes  of  mercury  are  dissolved  in  3  kilogrammes 
of  colourless  nitric  acid  of  sp.  gr.  1  "4,  in  the  cold.  The  solution  is  transferred  to  a 
retort,  and  2  litres  of  strong  alcohol  are  added.  In  summer  no  heat  is  applied,  and 
the  vapours  are  condensed  in  a  receiver  and  added  to  a  fresh  charge. 

When  the  action  has  ceased,  the  contents  of  the  retort  are  poured  into  a  shallow  pan, 
and  when  cold,  the  fulminate  is  collected  in  a  conical  earthen  ve.ssel  ])artially  plugged 
at  the  narrow  end.  It  is  washed  with  rain  water,  and  drained  until  it  contains  20  per 
cent,  of  water,  being  stored  in  that  state. 

*  Stadeler's  view  is  confirmed  by  the  recent  analyses  of  certain  nitroprussides  by 
Bernheimer. 


MANUFACTURE  OF  PERCUSSION  CAPS.  449 

Mermnic  fulminate  is  represented  by  the  fonnula  HgCgNgOg,  being 
derived  from  the  hypothetical /wZmmz'c  acid,  HgCgNgOg,  by  the  substitu- 
tion of  Hg"  for  Hg. 

Its  production  by  the  action  of  nitric  acid  upon  mercury  and  alcohol 
may  be  explained  by  the  following  reactions  : — • 

(1)  Mercury,  dissolved  in  nitric  acid,  yields  mercuric  nitrate  and 
nitrous  acid  ;  SHNOg  +  Hg  =  Hg(X03),  +  HNO2  +  HgO. 

(2)  Nitrous  acid,  acting  upon  alcohol  (ethyle  hydrate),  gives  nitrous 
ether  (ethyle  nitrite)  and  water  ;  C2H5.OH  +  HNO2  =  CgHg.NOg  +  HgO. 

(3)  Ethyle  nitrite,  acted  on  by  another  molecule  of  nitrous  acid,  gives 
f ulminic  acid  and  water ;  C2H.NO2  +  11X02  =  3200X202  +  2H2O . 

(4)  Mercuric  nitrate  (formed  in  the  first  reaction)  may  be  supposed  to 
act  upon  the  f ulminic  acid,  producing  mercuric  fulminate  and  nitric  acid ; 
Hg(N03)2  +  H2C2N2O2  =  HgC2N202  +  2HNO3. 

Properties  of  mercuric  fulminate. — This  substance  is  deposited  in 
the  above  process  in  fine  needle-like  crystals,  which  often  have  a  grey 
colour  from  the  accidental  presence  of  a  little  metallic  mercury.  It  may 
be  purified  by  boiling  it  with  water,  in  "which  it  is  sparingly  soluble,  and 
allowing  the  fulminate  to  crystallise  from  the  filtered  solution.  Very 
moderate  friction  or  percussion  will  cause  it  to  detonate  violently,  so  that 
it  must  be  kept  in  a  corked  bottle  lest  it  should  be  exploded  between  the 
neck  and  the  stopper.  It  is  usually  preserved  in  a  wet  state,  with  about 
one-fifth  its  weight  of  "water.  Its  explosion  is  attended  with  a  bright 
flash,  and  with  grey  fumes  of  metallic  mercury.  The  equation  which 
represents  the  decomposition  is  HgC2N202  =  Hg-<-2CO-}-!N"2 ;  and  its 
violence  must  be  attributed  to  the  sudden  evolution  of  a  large  volume  of 
gas  and  vapour  from  a  small  volume  of  solid,  for  the  fulminate,  being 
exceedingly  heavy  (sp.  gr,  4*4),  occupies  a  very  small  space  when  com- 
pared with  the  gaseous  products  of  its  decomposition,  especially  when  the 
latter  are  expanded  by  the  heat.  One  gramme  of  fulminate  evolves  403*5 
units  of  heat,  giving  an  estimated  maximum  pressure  of  48,000  atmo- 
spheres. The  evolution  of  heat  during  the  explosion,  apparently  in 
contradiction  to  the  rule  that  heat  is  absorbed  in  decomposition,  must  be 
ascribed  to  the  circumstance  that  the  heat  evolved  by  the  oxidation  of 
the  carbon  exceeds  that  absorbed  in  the  decomposition  of  the  fulminate. 
A  temperature  of  195°  C.  explodes  fulminate  of  mercury,  and  the  same 
result  is  brought  about  by  touching  it  with  a  glass  rod  dipped  in  concen- 
tiated  sulphuric  or  nitric  acid.     The  electric  spark,  of  course,  explodes  it. 

Gap  composition, — The  explosion  of  mercuric  fulminate  is  so  violent 
and  rapid  that  it  is  necessary  to  moderate  it  for  percussion  caps.  For 
this  purpose  it  is  mixed  with  potassium  nitrate  or  chlorate,  the  oxidising 
l^roperty  of  these  salts  possibly  causing  them  to  be  preferred  to  any  merely 
inactive  substances,  since  it  would  tend  to  increase  the  temperature  of  the 
flash  by  burning  the  carbonic  oxide  into  carbon  dioxide,  and  would  thus 
ensure  the  ignition  of  the  cartridge.  For  military  caps,  in  this  country, 
potassium  chlorate  is  always  mixed  with  the  fulminate,  and  powdered 
glass  is  sometimes  added  to  increase  the  sensibility  of  the  mixture  to 
explosion  by  percussion.  Antimony  sulphide  is  sometimes  substituted  for 
powdered  glass,  apparently  for  the  purpose  of  lengthening  the  flash  by 
taking  advantage  of  the  powerful  oxidising  action  of  potassium  chlorate 
upon  that  compound  (page  165).  Since  the  composition  is  very  liable  to 
explode  under  friction,  it  is  made  in  small  quantities  at  a  time,  and  with- 

2  F 


450  PEEPARATION  OF  FULMINATE  OF  SILVER. 

out  contact  with  any  hard  substance.  After  a  little  of  the  composition 
has  been  introduced  into  the  cap,  it  is  made  to  adhere  and  waterproofed 
by  a  drop  of  solution  of  shellac  in  spirit  of  wine. 

If  a  thin  train  of  mercuric  fulminate  be  laid  upon  a  plate,  and  covered,  except  a 
little  at  one  end,  with  gunpowder,  it  will  be  found  on  touching  the  fulminate  with  a 
hot  wire,  that  its  explosion  scatters  the  gunpowder,  but  does  not  inflame  it.  On 
repeating  the  experiment  with  a  mixture  of  10  grains  of  the  fulminate  and  15  grains 
of  potassium  chlorate,  made  upon  paper  with  a  card,  the  explosion  will  be  found  to 
inflame  the  gunpowder. 

By  sprinkling  a  thin  layer  of  the  fulminate  upon  a  glass  plate,  and  firing  it  with  a 
hot  wire,  the  separated  mercury  may  be  made  to  coat  the  glass,  so  as  to  give  it  all  the 
appearance  of  a  looking-glass. 

Although  the  effect  produced  by  the  explosion  of  mercuric  fulminate 
is  very  violent  in  its  immediate  neighbourhood,  it  is  very  slightly  felt  at 
a  distance,  and  the  sudden  expansion  of  the  gas  will  burst  fire-arms, 
because  it  does  not  allow  time  for  overcoming  the  inertia  of  the  ball, 
though,  if  the  barrel  escape  destruction,  the  projectile  effect  of  the  fulmi- 
nate is  found  inferior  to  that  of  powder.  It  has  been  proved  by  experi- 
ment, that  the  mean  pressure  exerted  by  the  explosion  of  mercuric 
fulminate  is  very  much  lower  than  that  produced  by  gun-cotton,  and 
only  |ths  of  that  produced  by  nitroglycerine.  Its  great  pressure  is  due 
to  its  instantaneous  decomposition  into  CO,  N  and  Hg  vapour  within  a 
space  not  sensibly  greater  than  the  volume  of  the  fulminate  itself,  which 
volume  being  very  small,  on  account  of  the  high  density  of  the  fulminate, 
the  escaping  gases  exert  an  enormous  pressure  at  the  moment  of  explosion. 
This  detonating  property  of  mercuric  fulminate  renders  it  exceedingly 
useful  for  effecting  the  detonation  of  gun-cotton  and  nitroglycerine. 
Berthelot  finds  that  even  such  stable  gases  as  acetylene,  cyanogen,  and 
nitric  oxide  are  decomposed'  into  their  elements  by  the  detonation  of 
mercuric  fulminate. 

Mercuric  fulminate  is  generally  contaminated  with  mercuric  oxalate 
(HgC204),  which  is  one  of  the  secondary  products  formed  during  its 
preparation. 

Fulminate  of  .vlver,  AggCgNgt)^,  is  prepared  by  a  process  very  similar 
to  that  for  fulminate  of  mercury ;  but  since  its  explosive  properties  are  far 
more  violent,  it  is  not  advisable  to  prepare  so  large  a  quantity.  Ten  grains 
of  pure  silver  are  dissolved,  at  a  gentle  heat,  in  70  minims  of  ordinary 
concentrated  nitric  acid  (sp.  gr.  1  -42)  and  .50  minims  of  water.  As  soon 
as  the  silver  is  dissolved,  the  lamp  is  removed,  and  200  minims  of  alcohol 
(sp.  gr.  0"87)  are  added.  If  the  action  does  not  commence  after  a  short 
time,  a  very  gentle  heat  may  be  applied  until  effervescence  begins,  when 
the  fulminate  of  silver  will  be  deposited  in  minute  needles,  and  may  be 
further  treated  as  in  the  case  of  fulminate  of  mercury.*  Silver  fulminate 
is  also  produced  Avhen  nitrous  anhydride  is  passed  into  an  alcoholic  solu- 
tion of  silver  nitrate.  When  dry,  the  fulminate  must  be  handled  mth 
the  greatest  caution,  since  it  is  exploded  far  more  easily  than  the  mercury 
salt ;  it  should  be  kept  in  small  quantities,  wrapped  up  separately  in  paper, 
and  placed  in  a  card-board  box.  Nothing  harder  than  paper  should  be 
employed  in  manipulating  it.     The  violence  of  its  explosion  renders  it 

"  If  the  nitric  acid  and  alcohol  are  not  of  the  exact  strength  here  prescribed,  it  may  be 
somewliat  difficult  to  start  the  action  unless  two  or  three  drops  of  red  nitric  acid  (contain- 
I  n  g  n  i  trous  acid )  are  added.  Standard  silver  (containing  copper)  may  be  used  for  preparing 
the  fulminate. 


CHEMICAL  CONSTITUTION  OF  THE  FULMINATES.        451 

useless  for  percussion  caps,  but  it  is  employed  in  detonating  crackers. 
Silver  fidminate  is  sparingly  soluble  in  cold  water,  but  dissolves  in  36 
parts  of  boiling  water. 

If  a  minute  particle  of  the  fulminate  be  placed  upon  a  piece  of  quartz,  and  gently 
pressed  with  the  angle  of  another  piece,  it  will  explode  with  a  flash  and  smart  report. 

A  throic-dmcn  detonating  cracker  may  be  made  by  scrcAving  up  a  particle  of  silver 
fulminate  in  a  piece  of  thin  paper,  with  some  fragments  obtained  by  crushing  a 
common  quartz  pebble. 

The  explosion  of  silver  fulminate  may  be  compared  with  that  of  the  mercury  salt, 
by  heating  small  equal  quantities  upon  thin  copper  or  platinum  foil,  when  the  fulminate 
of  mercury  will  explode  with  a  slight  puff,  and  will  not  injure  the  foil,  but  that  of 
silver  will  give  a  loud  crack  and  rend  a  hole  in  the  metal. 

If  a  particle  of  silver  fulminate  be  placed  upou  a  glass  plate  and  touched  with  a 
glass  rod  dipped  in  oil  of  vitriol,  it  will  detonate  and  leave  a  deposit  of  silver  upon  the 
glass. 

When  silver  fulminate  (AggCgNgOg)  is  dissolved  in  warm  ammonia, 
the  solution  deposits,  on  cooling,  crystals  of  a  douhle  fidminate  of  silver 
and  ammonium^  Ag{lS^^G2^cf).2,  wbicli  is  even  more  violently  explosive, 
and  is  dangerous  while  still  moist.  A  similar  compound  is  formed  with 
merciu'ic  fulminate. 

On  adding  potassium  chloride  in  excess  to  silver  fulminate,  only  half 
the  silver  is  removed  as  chloride,  and  the  douhle  fulminate  of  silver  and 
potassium,  AgKC2N202'  ^^J  ^^  crystallised  from  the  solution.  By 
the  careful  addition  of  nitric  acid,  the  K  may  be  replaced  by  H,  and  the 
acid  silver  fulminate,  AgHC2N"20.,,  obtained,  which  is  easily  soluble  in 
boiling  water,  and  crystallises  out  on  cooling  ;  by  boiling  with  silver  oxide, 
it  is  converted  into  the  normal  fulminate. 

Various  other  fulminates  and  double  fulminates  have  been  obtained. 
They  are  all  explosive. 

Chemical  constitution  of  the  fulminates. — The  fact  of  the  existence  of 
double  fulminates  and  acid  fiUminates  renders  it  necessary  to  \vrite  the 
formula  of  silver  fulminate,  for  example,  Ag2C2N2^2'  ii^stead  of  AgCXO, 
in  order  to  shoAv  that  half  of  the  silver  is  capable  of  being  exchanged  for 
another  metal  or  for  hydrogen.  It  will  be  seen  that  this  formula  would 
also  represent  2  molecules  of  silver  cyanate  (AgCNO),  but  the  properties 
of  this  salt  are  entirely  different  from  those  of  the  fulminate.  That  a 
strong  connexion  exists,  however,  between  the  fulminates  and  the 
cyanogen  compounds,  is  shown  by  several  reactions.  Thus,  if  mercuric 
fulminate  be  heated  with  hydrochloric  acid,  it  is  dissolved  with  evolu- 
tion of  a  powerful  odour  of  hydrocyanic  acid,  whilst  mercuric  chloride 
and  oxalate,  with  ammonium  chloride,  remain  in  the  solution.  Again,  if 
an  excess  of  silver  fuliuinate  be  acted  on  by  hydrosulphuric  acid,  cyanic 
acid  may  be  obtained  in  solution,  and  becomes  converted  into  hydrosulpho- 
cyanic  acid,  when  the  hydrosulphuric  acid  is  in  excess.  By  decomposing 
the  double  fulminate  of  copper  and  ammonium  (Cu(NH4)2(C2N202)2) 
with  hydrosulphuric  acid,  there  are  produced,  hydrosulphocyanic  acid  and 
urea,  the  latter  having  the  same  composition  as  ammonium  cyanate — 

Cu(XH,)2(CoN.30,)o  +  3HoS  =  CuS  +  2H,0  +  2HCNS  +  2CH,N20 

Ilydrosulpho-  Urea. 

cyanic  acid. 

These  reactions  have  induced  many  chemists  to  regard  the  fulminates 
as  compounds  derived  from  an  acid  having  the  composition  H2Cy202, 
intermediate  in  composition  between  cyanic  acid  (HCyO)  and  cyanuric 


452  PRODUCTS  FROM  COAL. 

acid  (11307303),  but  the  fulminic  acid  has  not  yet  been  obtained  in  a 
separate  form.  The  formula  C''Hg"Cy'(N02)'  agrees  better  with  modern 
researches. 

Mercuric  fulminate  dissolves  when  boiled  with  solution  of  potassium  chloride,  and 
the  solution,  when  evaporated,  yields  crystals  of  potassium fuhninuratc  ox  isocyanurate, 
KC.,N.,H203,  which  has  the  same  percentage  composition  as  acid  potassium  cyanurate 
KHjCysOg,  but  the  acid  contained  in  the  fulminurate  forms  only  one  series  of 
salts,  and  is  therefore  monobasic.  The  fulminnrates  are  feebly  exjdosive.  The 
production  of  fulminuric  acid  from  the  hypothetical  fulminic  acid  may  be  represented 
by  the  equation  2(H2CjNs02)  +  H20r:C02  +  NH3  +  HC3N3Hj03. 

PRODUCTS  OF  THE  DESTRUCTIVE  DISTILLATION 
OF  COAL. 

322.  Much  of  the  extraordinary  progress  made  by  chemistry  during 
the  last  half  century  must  be  attributed  to  the  introduction  and  great 
extension  of  the  manufacture  of  coal  gas.  N'o  other  branch  of  manufac- 
ture has  brought  into  notice  so  many  compounds  not  previously  obtained 
from  any  other  source,  and,  above  all,  oflFering,  at  first  sight,  so  very 
little  promise  of  utility,  as  to  press  urgently  upon  the  chemist  the  necessity 
for  submitting  them  to  investigation. 

Although  many  important  additions  to  chemical  knowledge  have  re- 
sulted from  the  labours  of  those  who  have  engaged  in  devising  the  best 
methods  of  obtaining  the  coal  gas  itself  in  the  state  best  fitted  for  con- 
sumption, far  more  benefit  has  accrued  to  the  science  from  investigations 
into  the  nature  of  the  secondary  products  of  the  manufacture,  the  removal 
of  which  was  the  object  to  be  attained  in  the  purification  of  the  gas. 

Of  the  compounds  of  carbon  and  hydrogen,  very  little  was  known  pre- 
viously to  the  introduction  of  coal  gas  ;  and  although  the  liquid  hydro- 
carbons composing  coal-naphtha  were  originally  obtained  from  other 
sources,  the  investigation  of  their  chemical  properties  has  been  greatly 
promoted  by  the  facility  with  which  they  may  be  obtained  in  large  quan- 
tities from  that  liquid.  The  most  important  of  these  hydrocarbons, 
benzole  or  benzene,  was  originally  procured  from  benzoic  acid;  but  it  would 
have  been  impossible  for  it  to  have  fulfilled  its  present  useful  purposes, 
unless  it  had  been  obtained  in  abundance  as  a  secondary  product  in  the 
manufacture  of  coal  gas  ;  for,  leaving  out  of  consideration  the  various  uses 
to  which  benzene  itself  is  devoted,  it  yields  the  nitrobenzene,  so  much 
used  in  perfumery,  and  from  this  we  obtain  aniline,  from  which  many 
of  the  most  beautiful  dyes  are  now  prepared. 

The  na2)hthalene  found  so  abundantly  in  coal-tar  possesses  a  peculiar 
interest,  as  having  formed  the  subject  of  the  beautiful  researches  by  which 
Laurent  was  led  to  propose  the  doctrine  of  substitution,  which  has  since 
thrown  so  much  light  upon  the  constitution  of  organic  substances. 

We  are  also  especially  indebted  to  coal-tar  for  our  acquaintance  with  the 
very  interesting  and  rapidly  extending  class  of  volatile  alkalies,  of  which 
the  above-mentioned  aniline  is  the  chief  representative,  and  for  phenic  or 
carbolic  acid,  from  which  are  derived  the  large  number  of  substances  com- 
posing the  phenyle-series. 

The  retorts  in  which  the  distillation  of  coal  is  effected  are  made  either 
of  cast-iron  or  of  stoneware,  generally  having  the  form  of  a  flattened 
cylinder,  and  arranged  in  sets  of  three  or  five,  heated  by  the  same  coal  fire 
fig.  281),     The  charge  for  each  retort  is  about  two  bushels,  and  is  thrown 


MANUFACTURE  OF  COAL  GAS. 


453 


on  to  the  red  hot  floor  of  the  retort,  as  soon  as  the  coke  from  the  previous 
distillation  has  been  raked  out ;  the  mouth  of  the  retort  is  then  closed 
witli  an  iron  plate  luted  with  clay.  An  iron  pipe  rises  from  the  upper 
side  of  the  front  of  the  retort  projecting  from  the  furnace,  and  is  curved 
round  at  the  upper  extremity,  Avhich  passes  into  the  side  of  a  much  wider 
tube,  called  the  liydrauUc  main,  running  above  the  furnaces,  at  right 
angles  to  the  retorts,  and  receiving  the  tubes  from  all  of  them.  This  tube 
is  always  kept  half  full  of  the  tar  and  water  which  condense  from  the  gas, 
and  below  the  surface  of  this  liquid  the  delivery  tubes  from  the  retorts 
are  allowed  to  dip,  so  that  although  the  gas  can  bubble  freely  through  the 
liquid  as  it  issues  from  the  retort,  none  can  return  through  the  tube  whilst 
the  retort  is  open  for  the  introduction  of  a  fresh  charge. 


Fig.  281. — Manufacture  ofjcoal  gas. 

The  aqueous  portion  of  the  liquid  deposited  in  the  hydraulic  main  is 
known  as  the  ammoniacal  liquo7\  from  its  consisting  chiefly  of  a  solution 
of  various  salts  of  ammonium,  the  chief  of  which  is  the  carbonate ; 
sulphide,  cyanide,  and  sulphocyanide  of  ammonium  are  also  found  in  it. 

From  the  hydraulic  main  the  gas  passes  into  the  condenser,  which  is 
composed  of  a  series  of  bent  iron  tubes  kept  cool  either  by  the  large  sur- 
face which  they  expose  to  the  air,  or  sometimes  by  a  stream  of  cold 
"Water.  In  these  are  deposited,  in  addition  to  water,  any  of  the  volatile 
hydrocarbons  and  ammonium  salts  which  may  have  escaped  condensation 
in  the  hydraulic  main.  Even  in  the  condenser  the  removal  of  the 
ammoniacal  salts  is  not  complete,  so  that  it  is  usually  necessary  to  pass  the 
gas  through  a  scrubber  or  case  containing  fragments  of  coke,  over  which 
a  stream  of  water  is  allowed  to  trickle,  in  order  to  absorb  the  remaining 
ammoniacal  vapours. 

The  tar  which  condenses  in  the  hydraulic  main  is  a  very  complex 
mixture,  of  which  the  following  are  some  of  the  leading  components  : — 


454 


PURIFICATION  OF  COAL  GAS. 


Boiling-point. 

Fonnula. 

Sp.  Gr. 

Neftbal  Hydrocarbons. 

Liquid. 

Benzene, 

176'  F.' 

C«H, 

0-88 

Toluene, 

230° 

CrH. 

0-87 

Xylene,           ... 

284° 

CsHio 

0-87 

Isocumene,*  . 

338° 

C9H12 

0-85 

Solid. 

Naphthalene, 

428° 

CioHg 

Anthracene,    . 

680° 

Chrysene, 

Cu,H,2 

Pyrene 

CigUjo 

Alkaline  Products. 

Ammonia, 

NH3 

Aniline, 

360° 

CgHyN 

1-02 

Picoline, 

271° 

C.HyN 

0-96 

Quinoliue, 

462° 

CnHyN 

1-08 

Pyridine, 

240° 

CfiHsN 

Acids. 

Carbolic  acid, 

370° 

CeHgO 

1-07 

Kresylic    ,,    . 

397° 

C^HsO 

Rosolic      ,,    . 

C19H14OS 

Brunolic   ,,    . 

Acetic       „    . 

243° 

C2H4O2 

106 

The  gas  is  now  passed  through,  the  lime-pwrijier,  which  is  an  iron  box 
with  shelves,  on  which  dryslaked  lime  is  placed  in  order  to  absorb  the 
carbonic  acid  gas  and  sulphuretted  hydrogen,  and  the  last  portions  of 
ammonia  are  removed  by  passing  the  gas  through  dilute  sulphuric  acid. 

A  great  many  other  methods  have  been  devised  for  the  purification  of 
the  gas  from  sulphuretted  hydrogen,  but  none  appears  to  be  so  efficacious 
and  economical  as  that  which  consists  in  passing  the  gas  over  a  mixture 
of  ferrous  sulphate  (green  vitriol  or  copperas),  slaked  lime,  and  sawdust 
(which  is  employed  to  prevent  the  other  materials  from  caking  together). 
The  lime  decomposes  the  ferrous  sulphate,  forming  calcium  sulphate  and 
ferrous  hydrate  ;  FeS04  +  Ca(H0)2  =  Fe(H0)2  +  CaSO^. 

The  action  of  air  upon  the  mixture  soon  converts  the  ferrous  into 
ferric  hydrate,  which  absorbs  the  sulphuretted  hydrogen  and  the  hydro- 
cyanic acid,  producing  with  the  former  ferrous  sulphide,  and  with  the 
latter  Prussian  blue  or  some  similar  compound.  The  calcium  sulphate 
existing  in  this  purifying  mixture  is  useful  in  absorbing  any  vapour  of 
ammonium  carbonate  from  the  gas,  forming  ammonium  sulphate  and 
calcium  carbonate.! 

The  action  of  the  sulphuretted  hydrogen  on  the  ferric  oxide  may  be 
tluis  represented,  Fe203  +  SHgS  =  2FeS  +  S  +  SHgO  ;  and  the  circumstance 
which  especially  conduces  to  the  economy  of  the  process,  is  the  facility 
with  which  the  ferrous  sulphide  may  be  reconverted  into  the  ferric  oxide 
by  mere  exposure  to  the  action  of  atmospheric  oxygen,  for  2FeS  +  03 
=  Fe^Og  4-  S2,  thus  reviving  the  power  of  the  mixture  to  absorb  sulphuret- 
ted hydrogen.     Accordingly,  if  a  small  quantity  of  air  be  admitted  into  the 

*  Benzene,  originally  derived  from  benzoic  acid  ;  toluene,  from  balsam  of  tolu  ;  xylene, 
found  among  the  products  from  wood  (^uXoi/) ;  isocumene,  isomeric  with  cumene,  obtained 
from  oil  of  cummin. 

t  Ferric  oxide,  derived  from  various  natural  and  artificial  sources,  is  also  employed  for 
the  purification  of  coal  gas. 


PURIFICATION  OF  COAL  GAS. 


455 


purifier  together  with  the  gas,  it  reconverts  the  ferrous  sulphide  into  ferric 
oxide,  and  the  oxidation  is  attended  with  enough  heat  to  convert  into 
vapour  any  benzene  which  may  have  condensed  in  the  purifying  mixture, 
and  of  which  the  illuminating  value  would  otherwise  be  lost.  The  same 
purifying  mixture  may  thus  be  employed  to  purify  a  very  large  quantity 
of  gas,  until  the  separated  sulphur  has  increased  its  bulk  to  an  incon- 
venient extent,  when  it  is  distilled  off  in  iron  retorts.  The  various 
processes  which  have  been  devised  for  the  removal  of  the  carbon  disulphide 
vapour  are  mentioned  at  page  218. 

The  purified  gas  is  passed  into  the  gasometers,  from  which  it  is  sup- 
plied for  consumption. 

In  the  manufacture  of  coal  gas,  attention  is  requisite  to  the  temperature 
at  which  the  distillation  is  effected,  for  if  it  be  too  low,  the  solid  and 
liquid  hydrocarbons  will  be  formed  in  too  great  abundance,  not  only 
diminishing  the  volume  of  the  gas,  but  causing  much  inconvenience  by 
obstructing  the  pipes.  On  the  other  hand,  if  the  retort  be  too  strongly 
heated,  the  vapours  of  volatile  hydrocarbons,  as  well  as  the  olefiant  gas 
and  marsh  gas,  may  undergo  decomposition,  depositing  their  carbon 
upon  the  sides  of  the  retort,  in  the  form  of  gas-carbon,  and  leaving  their 
hydrogen  to  increase  the  volume  and  dilute  the  illuminating  power  of  the 
gas. 

These  efi"ects  are  well  exemplified  in  the  following  analysis  of  the  gas 
collected  from  Wigan  cannel  coal  at  different  periods  of  the  distillation  : — 


In  100  volumes.                                |     1st  hour. 

5th  hour. 

lOth  hour. 

Oiefiant  gas  and  volatile  hydrocarbons, 

Marsh  gas, 

Carbonic  oxide, 

Hydrogen, 

Nitrogen, 

13-0 

82-5 

3-2 

0-0 

1-3 

7-0 
56-0 
11-0 
21-3 

47 

0-0 
20-0 
10-0 
600 
10-0 

The  increase  of  the  carbonic  oxide  after  the  first  hour  must  be  attri- 
buted to  the  decomposition  of  the  aqueous  vapour  by  the  carbon  as  the 
temperature  rises,  and  the  increase  of  the  nitrogen  may  probably  be 
ascribed  to  the  decomposition  of  the  ammonia  into  its  elements  at  a  high 
temperature. 

•323.  One  of  the  most  useful  of  the  secondary  products  of  the  coal  gas 
manufacture  is  the  ammonia,  and  this  process  has  been  already  noticed  as 
a  principal  source  of  the  ammoniacal  salts  found  in  commerce. 

Next  in  the  order  of  usefulness  stands  the  coal-tar,  wliich  deserves 
attentive  consideration,  not  only  on  that  account,  but  because  the  extrac- 
tion of  the  various  useful  substances  from  this  complex  mixture  affords  an 
excellent  example  of  x>i'oximate  orrjanic  analijtns,  that  is,  of  the  separation 
of  an  organic  mixture  into  its  immediate  components. 

For  the  separation  of  the  numerous  volatile  substances  contained  in 
coal-tar,  advantage  is  taken  of  the  difference  in  their  boiling-points,  which 
will  be  observed  on  examining  the  table  at  page  454. 

A  large  quantity  of  the  tar  is  distilled  in  an  iron  retort,  when  water 
passes  over,  holding  salts  of  ammonia  in  solution,  and  accompanied  by  a 
brown  oily  off'ensive  liquid  which  collects  upon  the  surface  of  the  water. 
This  is  a  mixture  of  the  hydrocarbons  wliich  are  lighter  than  water,  viz., 
benzene,  toluene,  xylene,  and  isocumene,  all  having,  as  represented  in  the 


456  COAL-NAPHTHA. 

table  at  page  454,  a  specific  gravity  of  about  0'85.  100  parts  of  the  tar 
yield,  at  most,  10  parts  of  this  light  oil. 

As  the  distillation  proceeds,  and  the  temperature  rises,  a  yellow  oil 
distils  over,  which  is  heavier  than  water,  and  sinks  in  the  receiver.  This 
oil,  commonly  called  dead  oil,  is  much  more  abundant  than  the  light  oil, 
amounting  to  about  one-fourth  of  the  weight  of  the  tar,  and  contains  those 
constituents  of  the  tar  which  have  a  high  specific  gravity  and  boiling- 
point,  particularly  naphthalene,  aniline,  quinoline,  and  carbolic  acid.  The 
proportion  of  naphthalene  in  this  oil  augments  with  the  progress  of  the 
distillation,  as  would  be  expected  from  its  high  boiling-point,  so  that  the 
last  portions  of  the  oil  which  distil  over  become  nearly  solid  on  cooling. 
When  this  is  the  case,  the  distillation  is  generally  stopped,  and  a  black 
viscous  residue  is  found  in  the  retort,  which  constitutes  pitch,  and  is 
employed  for  the  preparation  of  Brunswick  black  and  of  asphalt  for 
paving. 

The  light  oil  which  first  passed  over  is  rectified  by  a  second  distillation, 
and  is  then  sent  into  commerce  under  the  name  of  coal-naphtha,  a  quan- 
tity of  the  heavy  oil  being  left  in  the  retort,  the  lighter  oils  having  lower 
boiling-points. 

This  coal-naphtha  may  be  further  purified  by  shaking  it  with  sulphuric 
acid,  which  removes  several  of  the  impurities,  whilst  the  pure  naphtha 
collects  on  the  surface  when  the  mixture  is  allowed  to  stand.  When  this 
is  again  distilled  it  yields  the  rectified  coal-iiaphtha. 

This  light  oil,  especially  when  distilled  from  cannel  coal  at  a  low  temperature, 
contains,  in  addition  to  the  hydrocarbons  above  enumerated,  some  belonging  to  the 
marsh  gas  series  (C«H2,+2),  and  others  more  recently  brought  to  light,  belonging  to  a 
series  tlie  general  formula  of  which  is  C"H2«-2  ;  but  these  last  appear  to  be  acted  ou 
by  the  sulphuric  acid,  employed  to  remove  the  basic  substances  from  the  light  oil,  in 
such  a  manner  that  they  are  converted  into  polymeric  hydrocarbons,  having  the 
general    formula  CsnHi^.i,  of  which  the  three  following  have   been  particularly 


\ 


examined  : — 


Formula. 
C14H24 


Boilinjr-point. 
410°  F. 
464° 
536° 


The  hydrocarbons  CgHjo,  CyHjo,  and  C8H14,  from  which  these  appear  to  have  been 
formed  by  the  action  of  sulphuric  acid,  would  evidently  be  the  higher  homologues 
of  acetylene,  C^H.,. 

The  distillation  of  cannel  coal,  and  of  various  minerals  nearly  allied  to  coal,  at  low 
temperatures,  is  now  extensively  carried  on  for  the  manufacture  of  paraffin  and 
paraffin  oil  (see  Paraffin). 

The  separation  of  the  hydrocarbons  composing  this  naphtha  is  efiected 
by  a  process  in  constant  use  for  similar  purposes,  and  known  asfractioTial 
distillation. 

This  consists  in  distilling  the  liquid  in  a  retort  (A,  fig.  282)  through 
the  tubulure  of  which  a  thermometer  (T)  passes,  to  indicate  the  tempera- 
ture at  which  it  boils.  The  first  portion  wliich  distils  over  will,  of  course, 
consist  chiefly  of  that  liquid  which  has  the  lowest  boiling-point;  and  if 
the  receiver  (R)  be  changed  at  stated  intervals  corresponding  to  a  certain 
rise  ill  the  temperature,  a  series  of  liquids  will  be  obtained,  containing 
substances  the  boiling-points  of  which  lie  within  the  Hmits  of  temperature 
between  which  such  liquids  were  collected. 

When  these  liquids  are  again  distilled  separately  in  the  same  way,  a 
,L,'reat  part  of  each  is  generally  found  to  distil  over  within  a  few  degrees 


SEPARATION  OF  THE  HYDROCARBONS  IN  COAL-NAPHTHA. 


457 


on  either  side  of  some  particular  temperature,  which  represents  the  "boil- 
ing-point of  the  substance  of  which  that  liquid  chiefly  consists  ;  and  if  the 
receivers  be  again  changed  at  stated  intervals,  a  second  series  of  distillates 
will  be  obtained,  the  boiling-points  of  which  are  comprised  within  a 
narrower  range  of  temperature.  It  will  be  evident  that,  by  repeated  dis- 
tillations of  this  description,  the  mixture  will  eventually  be  resolved  into 
a  number  of  liquids,  each  distilling  over  entirely  at  or  about  one  par- 
ticular degree,  viz.,  the  boiling-point  of  its  chief  constituent. 

To  apply  this  to  the  separation  of  the  constituents  of  light  coal-naphtha. 

The  crude  light  oil  is  first  agitated  with  dilute  sulphuric  acid,  which  removes  any 
basic  substances  present  in  it,  and  afterwards  with  a  dilute  solution  of  potash,  to 
separate  carbolic  acid.  The  adhering  jiotash  is  removed  by  shaking  with  water,  and 
the  naphtha  is  allowed  to  remain  at  rest,  so  that  all  the  water  may  settle  down,  and 
the  naphtha  may  be  drawn  off  for  distillation. 


Fractional  distillation. 


The  naphtha  begins  to  boil  at  about  160°  F. ,  but  only  a  small  quantity  distils  over 
before  the  temperature  has  risen  to  180",  when  the  receiver  may  be  changed;  between 
180°  and  200°  a  considerable  quantity  of  the  naphtha  distils  over,  and  at  the  latter 
degree  the  receiver  is  changed  a  second  time.  The  receiver  is  changed  at  every  20° 
throughout  the  distillation,  until  nearly  the  whole  of  the  naphtha  has  passed  over, 
which  will  be  the  case  at  about  360°.  * 

Ten  unequal  quantities  of  liquid  will  have  been  thus  obtained,  diminishing  as  the 
temperature  rises. 

Each  of  these  must  then  be  distilled  in  a  smaller  retort  than  the  first,  also  provided 
with  a  thermometer. 

The  first  portion  (160°  to  180°)  will  probably  begin  to  boil  at  150°,  and  will  distil 
in  great  part  before  160°,  when  the  receiver  may  be  changed.  When  the  temperatui'c 
reaches  170°  it  will  probably  be  found  that  nothing  remains  worth  distilling.  The 
liquid  passing  over  in  this  distillation  between  160°  and  170°  may  be  added  to  that 
which  is  next  to  be  distilled  (180°  to  200°). 

Tiie  second  portion  (180°  to  200°)  will  begin  to  boil  at  about  175°,  and  will  distil 
over  chiefly  between  that  temperature  and  185°,  when  the  receiver  may  be  changed. 
Nearly  the  whole  will  have  passed  over  before  195°,  and  this  last  fraction  may  be 
added  to  that  previously  obtained  from  200°  to  220°. 

When  all  the  first  series  of  liquids  have  been  thus  distilled,  it  will  be  found  that 
the  second  series  consists  chiefly  of  six  portions  distilling  between  the  following 
degrees  of  temperature,  viz.,  150°-160°,  175°-185°,  180°-190°,  240°-250°,  300°-310°, 
340°-350°. 

*  On  the  large  scale,  that  portion  of  the  naphtha  which  is  distilled  over  between  180° 
and  250°  F.  is  sold  as  benzene,  and  employed  for  the  preparation  of  aniline. 


458 


BENZOLE  OR  BENZENE. 


By  another  distillation  of  each  of  these  portions,  a  third  series  of  liquids  will  be 
formed,  consisting  chiefly  of  five  portions  distilling  between  the  following  points, 
viz.,  US'-lbO",  175°-180%  230°-235°,  288''-293°,  336°-342''. 

The  portion  distilling  between  145°  and  150°  is  comparatively  small  in  quantity, 
and  has  not  yet  been  fully  examined. 

That  obtained  between  175*  and  180°  is  more  abundant  than  either  of  the  othefs, 
and  is  nearly  pure  benzene  (CgHg), 

The  portion  boiling  between  230°  and  235°  is  chiefly  toluene  (CyHg),  whilst  288°  to 
293"  gives  xylene  {CgHjo),  and  336°  to  342°  isocumene  (CgHu). 

In  order  to  separate  the  benzene  completely  from  the  hydrocarbons  which  still 
adhere  to  it,  the  portion  boiling  between  175°  and  180°  is  exposed  to  a  temperature 
of  32°  F.,  when  the  benzene  alone  freezes,  the  other  hydrocarbons  remaining  liquid, 
and  being  easily  extracted  by  pressure. 

A  simple  method  of  separating  liquids  which  have  difierent  boiling-points  consists 
Lu  distilling  them  in  a  flask  (F,  fig.  283)  connected  with  a  spiral  worm  (W)  of  pewter 
or  copper,  surrounded  by  water,  or  some  other  liquid,  maintained  at  a  temperature 
just  above  the  boiling-point  of  the  particular  liquid  which  is  required  to  distil  over. 
The  greater  part  of  the  less  volatile  liquids  will  condense  in  the  worm  and  run  back 


Fig.  283.— Refluxing  Condenser. 

into  the  flask.  Thus,  in  extracting  benzene  from  the  light  oil,  the  liquid  in  A  might 
be  kept  at  180°  F.,  when  the  toluene,  &c.,  would  be  partly  condensed  in  the  worm, 
and  the  portion  which  passed  into  the  receiver  would  consist  chiefly  of  benzene. 
When  little  more  distilled  over,  the  temperature  of  A  might  be  raised  to  230°,  and 
the  receiver  changed,  when  the  distillate  would  contain  toluene  as  its  predominant 
constituent,  and  so  on. 

324.  Benzole  or  Benzene,  CgHg.* — The  pure  benzene  is  a  brilliant  colour- 
leas  liquid,  exhaling  a  powerful  odour  of  coal  gas;  it  boils  at  176°  F.,  and 
is  very  inflammable,  bximing  with  a  smoky  flame.  It  mixes  readily  ^vith 
alcohol  and  wood-spirit,  but  not  with  water.  Its  property  of  dissolving 
caoutchouc  and  gutta-percha  renders  it  very  useful  in  the  arts,  and  it  is  an 
excellent  solvent  for  the  removal  of  grease,  paint,  &c.,  from  clothes  and 
furniture. 

When  benzene  is  treated  with  hydric  peroxide,  it  is  slowly  converted  into  phenol 
(carbolic  acid)  C^HgO. 

Benzene  combines  directly  with  chlorine  to  form  a  solid  bensene  cMoride,  CgHgCl^ 
wliich  is  decomposed  by  an  alcoholic  solution  of  potash,  yielding  chlorobenzene, 

•  In  commerce,  the  term  benzole  is  usually  applied  to  the  lighter  portions  (of  low 
boiling-point)  distilled  from  coal-naphtha,  whilst  benzene  is  that  distilled  from  petroleum. 


ANILINE  OK  PHENYLAMINE.  459 

By  the  action  of  an  aqueous  solution  of  hypochlorous  acid  upon  benzene,  a  crys- 
talline body  has  been  obtained,  having  the  composition  CgHgOLjO;,,  and  called  tri- 
chlorhyclrine  of  phenose.  When  acted  on  by  alkalies,  this  substance  yields  a  sweet 
substance  called  phenose,  isomeric  with  dry  grape  sugar — 

CgHgClaOg  +  3KH0  =  CgHi^O,.  {Phenose)  +  3KC1 . 

This  substance  has  not  been  crystallised ;  it  forms  a  deliquescent  amorphous  mass, 
which  is  easily  soluble  in  water  and  alcohol,  but  insoluble  in  ether.  It  reduces  the 
oxides  of  copper  and  silver  like  grape-sugar,  and  when  acted  on  by  nitric  acid  is  con- 
verted into  oxalic  acid.     Phenose  has  not  been  found  capable  of  fermentation  by  yeast. 

The  benzene  or  aromatic  series  of  hydrocarbons  is  generally 
represented  as  containing  a  double  chain  of  six  carbon  atoms  1 

linked  together  by  one  and  two  bonds  alternately,  forming  Q 

what  is  called  the  aromatic  nucletis  or  KekuMs  chain,     it  /        *N. 

will  be  seen  that  each  of  the  tetratomie  carbon  atoms  has  one  ^  n^ 

free  bond.     If  all  these  be  attached  to  hydrogen  atoms,       "  C  C  2 

benzene  CgHg  is  produced.     By  the  successive  replacement  of  1 1  I 

these  hydrogen  atoms  by  CHj,  the  other  aromatic  hydro-  1 1  I 

carbons  are  formed.     But  the  position   of  the  particular       c  f  p  » 

hydrogen  atoms  which  are  thus  replaced  influences  the  nature 
of  the  product.     Thus,  if  the  group  CH3  be  attached  to  each  >^         y^ 

of  the  carbon  atoms  marked  1  and  2  or  1  and  6,  the  resulting  /\     ^ 

compound,  CgHm,  is  orthorylcne,  boiling  at  140°  to  Hl°  C.  ;  . 

whilst  if  CH3  be  attached  to  the  carbon  atoms  marked  1  and  ^ 

3  or  1  and  5,  vietaxylcnc,  CgHj^,  boiling  at  137°  C,  is  obtained,  and  if  the  CHg  be  at- 
tached to  the  carbon  atoms  marked  1  and  4,  paraxylcne  or  7nethyle-toluene,  CgHjo, 
is  obtained. 

325.  Aniline. — The  chief  purpose  to  which  benzene  is  devoted  is  the 
preparation  of  aniline,  Avhich  is  subsequently  converted  into  the  brilliant 
dyes  now  so  extensively  used.  It  has  been  already  noticed  at  page  139, 
that  when  benzene  is  dissolved  in  fuming  nitric  acid,  violent  action  takes 
place,  and  a  dark  red  liquid  is  formed,  from  which  water  precipitates  a 
heavy  yellow  oily  liquid,  smelling  of  bitter  almonds,  and  known  as  nitro- 
henzole  or  nitrobenzene,  which  has  the  composition  C^H5(N02),  and  may  be 
regarded  as  derived  from  benzene  by  the  substitution  of  a  molecule  of  nitric 
peroxide  for  an  atom  of  hydrogen ;  CgHg  +  HNO3  =  CgH5(N0.2)  +  HgO. 

When  nitrobenzene  is  placed  in  contact  with  diluted  sulphuric  acid  and 
metallic  zinc,  the  (nascent)  hydrogen  removes  the  whole  of  the  oxygen, 
and  2  atoms  of  hydrogen  are  acquired  instead,  producing  CgHjNHg,  or 
CgH^N,  aniline  ;  Q>^4^^(d.^  -f  Hg  =  CgH.X  +  2H2O. 

That  aniline  has  been  produced  may  be  shown  by  neutralising  the 
excess  of  sulphuric  acid  with  potash,  and  adding  chloride  of  lime  (hypo- 
chlorite of  lime),  which  gives  a  fine  purple  colour  with  aniline. 

The  conversion  of  nitrobenzene  into  aniline  on  a  large  scale  is  more 
conveniently  effected  by  gently  heating  it,  in  a  retort,  with  iron  borings 
and  acetic  acid,  when  the  deoxidising  action  of  the  ferrous  acetate 
Fe(C2H302)25  first  produced,  materially  assists  the  change,  this  salt  being 
converted  into  a  basic  ferric  acetate  2[Fe2(C2H302)6]Fe203,  which  is  left 
in  the  retort,  and  the  aniline  may  be  distilled  over,  accompanied  l)y  water. 
At  the  close  of  the  distillation  a  red  oil  passes  over,  which  solidities  to  a 
crystalline  mass.  This  is  azohenzide,  CpH^N,  originally  obtained  by  dis- 
tilling nitrobenzene  with  an  alcoholic  solution  of  potash. 

(When  nitrobenzene,  in  alcoholic  solution,  is  reduced  by  zinc  in  the 
presence  of  hydrochloric  acid,  the  solution  neutralised  by  sodium  car- 
bonate and  boiled  with  alcohol,  a  crystalline  compound  of  aniline  with 
zinc  chloride  (ZnCl2.2CgHK-N)  is  obtained.) 

Since  aniline  is  only  slightly  soluble  in  water,  and  has  the  sp.  gr.  1  '02, 


460  DYES  FROM  COAL-TAR. 

the  larger  portion  of  it  collects  at  the  bottom  of  the  liquid  in  the  receiver, 
which  is  milky  from  the  presence  of  minute  drops  of  aniline  in  suspension. 
By  pouring  the  contents  of  the  receiver  into  a  tall  vessel,  the  greater  part 
of  the  aqueous  fluid  may  be  separated,  and  the  aniline  may  be  purified  by 
a  second  distillation,  when  the  remaining  water  will  pass  over  first,  the 
boiling-point  of  aniline  being  360°  F. 

Aniline  *  presents  many  striking  features ;  though  colourless  when  per- 
fectly pure,  it  soon  becomes  brown  if  exposed  to  the  air :  its  odour  is 
verypeculiar,  and  somewhat  amraoniacal,  and  its  taste  is  very  acrid.  A 
drop  falling  upon  a  deal  table  stains  it  intensely  yellow.  But  the  charac- 
ter by  which  aniline  is  most  easily  recognised,  and  that  which  leads  to 
its  useful  applications,  is  the  production  of  a  violet  colour  with  solution 
of  chloride  of  lime,  by  which  a  very  minute  quantity  of  aniline  may  be 
detected.  The  change  of  colour  is  due  to  oxidation,  and  a  gi-eat  number 
of  processes  have  been  patented  from  time  to  time  for  the  production  of 
crimson,  purple,  and  violet  dyes  by  the  action  of  various  oxidising  agents 
upon  aniline. 

326.  Coal-tar  dyes. — The  first  dye  ever  manufactured  from  aniline  on  a  large  scale 
was  that  known  as  mauiv,\  or  aniline  purple,  which  is  obtained  by  dissolving  aniline 
in  diluted  sulphuric  acid,  and  adding  solution  of  bichromate  of  potash,  when  the 
liquid  gradually  becomes  dark-coloured,  and  deposits  a  black  precipitate,  which  is 
filtered  oH",  washed,  boiled  with  coal-naphtha  to  extract  a  brown  substance,  and  after- 
wards treated  with  hot  alcohol,  which  dissolves  the  mauve.  The  chemical  change 
by  which  the  aniline  has  been  converted  into  this  colouring-matter  cannot  at  present 
be  clearly  traced,  but  the  basis  of  the  colour  has  been  found  to  be  a  substance  which 
has  the  composition  C27H24N4,  and  has  been  termed  mauv6ine.  It  forms  black 
shining  crystals,  resembling  specular  iron  ore,  which  dissolve  in  alcohol,  forming  a 
violet  solution,  and  in  acids,  with  production  of  the  purple  colour.  Mauviiine  com ' 
bines  with  the  acids  to  form  salts  ;  its  alcoholic  solution  even  absorbs  carbonic  acid 
gas.  The  hydrochlorate  of  inauvanc,  C27H24N4,2HC1,  forms  prismatic  needles  with 
a  green  metallic  lustre. 

Very  brilliant  red  dyes  are  obtained  from  commercial  aniline  by  the  action  of 
carbon  tetrachloride,  stannic  chloride,  ferric  chloride,  cupric  chloride,  mercuric 
nitrate,  corrosive  sublimate,  and  arsenic  acid.  It  \vill  be  noticed  that  all  these  agents 
are  capable  of  undergoing  reduction  to  a  lower  state  of  oxidation  or  chlorination, 
indicating  that  the  chemical  change  concerned  in  the  transformation  of  aniline  into 
aniline-red  is  one  in  which  the  aniline  is  acted  on  by  oxygen  or  chlorine. 

The  easiest  method  of  illustrating  the  production  of  aniline-red,  on  the  small  scale, 
consists  in  heating  a  few  drops  of  aniline  in  a  test-tube  with  a  fragment  of  corrosive 
sublimate  (mercuric  chloride),  which  soon  fuses  and  acts  upon  the  aniline  to 
form  an  intensely  red  mass  composed  of  aniline-red,  calomel,  and  various  secondary 
])roducts.  By  heating  this  mixture  with  alcohol  the  red  dye  is  dissolved,  and  a  skein 
of  silk  or  wool  dipped  into  the  liquid  becomes  dyed  of  a  fine  red,  which  is  not  removed 
by  washing. 

On  the  large  scale,  magenta  (as  aniline-red  is  commonly  termed)  is  generally  pre- 
pared by  heating  aniline  to  about  320°  F.  with  arsenic  acid,  when  a  dark  semi-solid 
mass  is  obtained,  which  becomes  hard  and  brittle  on  cooling,  and  exhibits  a  green 
metallic  reflection.  This  mass  contains,  in  addition  to  aniline-red,  several  secondary 
products  of  the  action,  and  arsenious  acid.  On  boiling  it  with  water,  a  splendid 
ri'd  solution  is  obtained,  and  a  dark  resinous  or  pitchy  mass  is  left.  If  common  salt 
be  added  to  the  red  solution  as  long  as  it  is  dissolved,  the  bulk  of  the  colouring 
matter  is  precipitated  as  a  resinous  mass,  which  may  be  purified  from  certain 
adhering  matters  by  drying  and  boiling  with  coal-naphtha.  The  red  colouring 
matter  is  the  arseniate  of  a  colourless  organic  base,  which  has  been  called  rosaniline, 
and  has  the  composition  CjoHjgNj.HjO.  If  the  red  solution  of  arseniate  of  rosaniline 
be  decomposed  with  calcium  hydrate  suspended  in  water,  a  pinkish  precipitate  is 

*  Aniline  derives  its  name  from  anil,  the  Portuguese  for  indigo,  from  which  it  may  be 
obtained  by  distillation  with  potash, 
t   French  for  marsh-mallow,  in  allusion  to  tlie  colour  of  the  flower. 


CHRYSAITILINE — ANILINE-BLUE.  461 

obtained,  which  consists  of  rosaniline  mixed  with  calcium  arseniate,  and  the  solution 
entirely  loses  its  red  colour. 

By  treating  the  precipitate  with  a  small  quantity  of  acetic  acid,  the  rosaniline  is 
converted  into  rosaniline  acetate  (C2oH|9N3,C2H40.2),  forming  a  red  solution,  which 
may  be  filtered  off  from  the  undissolved  calcium  arseniate.  On  evaporating  the 
solution  to  a  small  bulk,  and  allowing  it  to  stand,  the  acetate  is  obtained  in  crystals 
which  exhibit  the  peculiar  green  metallic  lustre  of  the  wing  of  the  rose-beetle, 
characteristic  of  the  salts  of  rosaniline.  This  salt  is  the  commonest  commercial  form 
of  magenta  ;  its  colouring  power  is  extraordinary,  a  very  minute  particle  imparting 
a  red  tint  to  a  large  volume  of  water.  Silk  and  wool  easily  extract  the  whole  of  the 
colouring  matter  from  the  aqueous  solution,  becoming  dyed  a  fast  and  brilliant  crim- 
son ;  cotton  and  linen,  however,  have  not  so  strong  an  attraction  for  it,  so  that  if  a 
pattern  be  worked  in  silk  upon  a  piece  of  cambric,  which  is  then  immersed  in  a 
solution  of  magenta  and  afterwards  washed  in  hot  water,  the  colour  will  be  washed 
out  of  the  cambric,  but  the  red  silk  pattern  will  be  left. 

If  a  boiling  solution  of  rosaniline  acetate  be  mixed  with  excess  of  ammonia,  the 
bulk  of  the  rosaniline  will  be  precipitated,  but  if  the  solution  be  filtered  while  hot, 
it  deposits  colourless  needles  of  rosaniline,  which  become  red  when  exposed  to  the 
air,  from  absorption  of  carbonic  acid,  and  formation  of  the  red  rosaniline  carbonate. 

Water  dissolves  but  little  rosaniline;  alcohol  dissolves  it  abundantly,  forming  a 
deep  red  solution.  Rosaniline  forms  two  classes  of  salts  with  acids,  those  with 
1  molecule  of  acid  {monacid  salts)  being  crimson,  and  those  Avith  3  molecules 
{triacid  salts)  having  a  brown  colour.  Thus,  if  colourless  Rosaniline  be  dissolved  in 
a  little  dilute  hydrochloric  acid,  a  red  solution  is  obtained,  which  contains  the 
monacid  rosaniline  hydrochlorate,  CooHjgNj.HCl  ;  but  if  an  excess  of  hydrochloric 
acid  be  added,  the  red  colour  disappears,  and  a  brown  solution  is  obtained,  from  which 
the  triacid  hydrochlorate,  C^oHjgNj.SHCl,  may  be  crystallised  in  brown-red  needles. 

For  experimental  illustration  of  the  properties  of  rosaniline,  the  liquid  obtained  by 
boiling  a  solution  of  the  acetate  with  a  slight  excess  of  lime  diffused  in  water,  and 
filtering  while  hot,  is  very  well  adapted.  The  solution  has  a  yellow  colour,  and  may 
be  preserved  in  a  stoppered  bottle  without  alteration.  If  air  be  breathed  into  it 
through  a  tube,  the  liquid  becomes  red  from  production  of  rosaniline  carbonate. 
Characters  painted  on  paper  with  a  brush  dipped  in  the  solution  are  invisible  at  first, 
but  gradually  acquire  a  beautiful  rose  colour. 

When  the  red  solution  of  rosaniline  hydrochlorate  is  slightly  acidified  with  hydro- 
chloric acid  and  placed  in  contact  with  zinc,  the  solution  becomes  colourless,  the 
rosaniline  acquiring  2  atoms  of  hydrogen,  and  becoming  leucaniline  (from  X^vKhs, 
white)  C.,oH.2iN3,  the  hydrochlorate  of  which  (C2QH21N3..3HCI)  forms  a  colourless 
solution.  Oxidising  agents  reconvert  the  leucaniline  into  rosaniline.  It  has  been 
observed  that  pure  aniline  does  not  yield  aniline-red  when  heated  with  con'osive 
sublimate  or  arsenic  acid,  it  being  necessary  that  it  should  contain  another  organic 
base,  toluidinc  (C7H9N),  which  is  derived  from  toluene  (C7Hg)  in  the  same  way  in  which 
aniline  is  derived  from  benzene.  Since  the  benzene  obtained  from  coal-naphtha  almost 
invariably  contains  toluene,  the  aniline  obtained  from  it  is  very  seldom  free  from 
toluidine.  If  the  aniline  be  pi'epared  with  benzene  derived  from  benzoic  acid,  and 
therefore  free  from  toluene,  no  red  is  obtained.  A  mixture  of  70  parts  of  toluidine 
with  30  of  aniline  is  said  to  answer  best  for  the  preparation  of  the  red  and  violet 
colouring  matters.  Such  a  mixture  would  contain  2  molecules  of  toluidine  (C-H<)N) 
and  1  of  aniline  (CgHjN),  or  CooHjgN.j,  only  requiring  the  removal  of  Hg  by  an  oxidis- 
ing agent  to  yield  rosaniline  CjoHigN.;. 

Aniline-yelloxo  or  chrysa7iil ine  (from  xp^fffos,  golden)  is  found  among  the  secondary 
products  obtained  in  the  preparation  of  aniline-red.  It  forms  a  bright  yellow 
powder,  resembling  chrome-yellow,  and  having  the  composition  C.^oHi^Ng.  It  is 
nearly  insoluble  in  water,  but  dissolves  in  alcohol.  Chrysaniline  has  basic  properties 
and  dissolves  in  acids,  forming  salts.  On  dissolving  it  in  diluted  hydrochloric  acid, 
and  mixing  the  solution  with  the  concentrated  acid,  a  scarlet  crystalline  precipitate 
of  ehrysaniline  hydrochlorate  (C.2oHi-X.j.2HCl)  is  obtained,  which  is  insoluble  in 
strong  hydrochloric  acid,  but  very  soluble  in  water.  A  characteristic  feature  of 
chrysaniline  is  the  sparing  solubility  of  its  nitrate.  Even  from  a  dilute  .solution  pf 
the  hydrochlorate,  nitric  acid  precipitates  chrysaniline  nitrate  (C20H17N3.HNO3)  in 
ruby-red  needles. 

Anilinc-bluc  is  produced  when  a  salt  of  rosaniline  (the  commercial  acetate,  for 
example)  is  boiled  with  an  excess  of  aniline,  which  converts  the  rosaniline  (C.^oHjgN'a) 
into  triphenylic  rosaniline  (C.,oHi6(CfiH5)3]Sr3),  which  may  be  regarded  as  having  been 
formed  by  the  introduction  of  3  atoms  of  the  hypothetical  radical  phenyle  (CgHj) 


462  HYDROCrAN-ROSANILIXE — PHENYLAMINE. 

in  place  of  3  atoms  of  hydrogen,  the  latter  having  been  evolved  in  the  form  of 
ammonia — 

CaoHisNgHCl  +  S[(C,H,)H2N]  =  C2,H,«(C,H3)3N3.HC1  +  3NH3. 

Rosanlllne  AnninP  Trtplienylic  rosaniUne 

hjdrochlorate.  fluuiuc.  hydrochlorate. 

The  hydrochlorate  is  an  ordinary  commercial  form  of  aniline-blue  ;  it  has  a  brown 
colour,  refuses  to  dissolve  in  water,  but  yields  a  fine  blue  solution  in  alcohol.  If  it 
be  dissolved  in  an  alcoholic  solution  of  ammonia,  the  addition  of  water  causes  a  white 
precipitate  of  the  hydrated  base,  triphenylic  rosaniline,  CgoHi5(CgH5)jN3.HjO,  which 
becomes  bluish  when  washed  and  dried. 

Just  as  rosaniline  yields  leneaniline  when  acted  on  with  nascent  hydrogen,  so  tri- 
phenylic rosaniline  yields  triphenylic  leucaniline  (C2oH,s(C6H5)3N3  ;  this  is  not  basic 
like  leucaniline,  but  a  neutral  colourless  substance,  which  is  reconverted  into  blue  by 
oxidising  agents.  Compounds  corresponding  to  triphenylic  rosaniline,  but  containing 
niethyle,  ethyle,  or  amyle  in  place  of  phenyle,  are  obtained  by  digesting  rosaniline 
with  the  iodides  of  these  radicals,  at  a  high  temperature,  in  sealed  tubes.  Thus,  by 
the  action  of  ethyle  iodide  (CiHgl)  upon  rosaniline,  a  blue  crystalline  body  insoluble 
in  water,  but  soluble  in  alcohol,  is  obtained,  which  is  a  compound  of  ethyle  iodide 
with  triethylic  rosaniline  ;  C2oHie(C.2H5)3N3. 

CaoHiaNs  +  \QM,l  =  C,oH,6(C,H5)3N3.C,H5l  +  SHI . 
„        ,,,  Tri-ethyl-rosanlUne 

KosanlUne.  eth/l-lodate. 

Anilinc-violct  is  formed  in  a  similar  manner  with  methyle  iodide.  Other  com- 
pounds have  been  obtained  from  aniline,  presenting  almost  every  variety  of  colour. 
A  green  dye  is  prepared  by  the  action  of  a  mixture  of  hydrochloric  acid  and  potassium 
chlorate  upon  aniline,  and  under  particular  conditions  a  black  may  be  obtained  with 
the  same  agents.  Another  green  has  been  made  by  acting  upon  magenta  with 
;ildehyde. 

When  a  solution  of  rosaniline  acetate  is  treated  with  potassium  cyanide,  it  gi-adually 
loses  its  red  colour,  and  deposits  a  white  crystalline  precipitate  of  a  base  which  has 
been  termed  Jiydroq/an-rosaHiline,  having  the  formula  Cj,]H.2oN4,  and  containing  the 
elements  of  rosaniline  and  hydrocyanic  acid ;  but  this  acid  cannot  be  detected  in  it 
by  the  ordinary  tests,  leading  to  the  belief  that  the  new  base  should  be  regarded  as 
leucaniline  (C._;(,H2iN3),  in  which  one  atom  of  hydrogen  is  replaced  by  cyanogen 
(C2oH.,o(CN)N3).  The  hydrocyan-rosaniline  is  almost  insoluble  in  water,  and 
sparingly  soluble  in  boiling  alcohol.  When  precipitated  from  its  salts  bj'  adding  an 
alkali,  it  becomes  pink  on  exposure  to  sunshine. 

The  present  extensive  application  of  aniline  to  the  manufacture  of  these 
(lyes  affords  a  niost  striking  example  of  the  direct  utility  of  pure  chemistry 
to  the  arts  ;  for,  twenty-five  years  ago,  the  name  of  this  substance  was 
not  knowTi  to  any  but  scientific  chemists,  whilst  at  present  many  tons  are 
annually  consumed  to  supply  the  wants  of  the  dyers  of  silk  and  woollen 
goods. 

327.  Aniline  ranks  as  a  powerful  organic  base,  combining  readily  with 
acids  to  form  salts  which  are,  generally  speaking,  easily  crystallised.  Like 
ammonia,  it  unites  directly  with  the  acids,  without  any  separation  of 
water ;  thus,  the  formula  of  aniline  sulphate  is  2CgH;N.H,S0^,  hydro- 
chlorate of  aniline  is  CjjH-X.HCl,  and  exactly  as  the  addition  of  potash 
to  the  salts  of  ammonia  causes  the  separation  of  ammoniacal  gas,  so  when 
added  to  the  salts  of  aniline,  it  precipitates  that  base  in  the  form  of  oily 
ilrops,  which  render  the  liquid  milky.  This  resemblance  in  disposition 
lietween  aniline  and  ammonia  leads  to  the  impi-ession  that  they  must  be 
moulded  after  a  common  type,  and,  accordingly,  aniline  is  often  represented 
as  formed  from  ammonia  (NH3)  by  the  substitution  of  the  compound 
radical  phenyle  {C,.H.)  for  an  atom  of  hydrogen,  and  upon  this  supposition 
i^  termed  pheHi/lmiiine,  NH2(CgH5)  =  C^H^N. 

This  view  of  the  constitution  of  aniline  is  supported  by  the  circum- 
stance  of  its   formation   when   phenic  or  carbolic  acid   i.s  heated  with 


HOMOLOGUES  OF  BENZENE.  463 

ammonia  in  a  tube  hermetically  sealed;  for  there  is  reason  to  believe  that 
this  acid,  mentioned  above  as  one  of  the  chief  acid  products  of  the 
destructive  distillation  of  coal,  is  phenylic  hydrate  (CgH5)H0,  and  its 
action  upon  ammonia  would  then  be  clearly  explained  by  the  equation — 

(C6H5)HO   +  NHg  =   H.O   +  NH2(C6H5) 

Phenic  acid.  Aniline  or  phenylamine. 

When  aniline  is  dissolved  in  alcohol  and  acted  on  by  nitrous  anhydride,  2  mole- 
cules of  it  lose  3  atoms  of  (monatomic)  hydrogen,  and  acquire,  in  their  stead,  1  atom 
of  (triatomic)  nitrogen,  depositing  a  yellow  compound,  which  has  been  called  dia- 
zoamidobenzenc- — 

4C6H7N   +   N2O3  =   2Ci2HjiNs  +   3H,0. 
Aniline.  Diazoamidobenzene. 

When  N2O3  acts  upon  a  hot  solution,  a  base  is  formed  isomeric  with  the  above,  and 
called  amido-dipJienylimidc,  which  is  identical  with  a  yellow  colouring  matter  obtained 
by  the  action  of  sodium  staunate  upon  a  salt  of  aniline.  Its  slightly  acid  solutions 
impart  an  intensely  yellow  colour  to  silk  or  wool,  which  is  removed  by  heat,  tlie 
base  being  volatile.  The  action  of  nitrous  anhydride  on  aniline  affords  an  example 
of  a  general  method  of  producing  compounds  in  which  nitrogen  is  substituted  for 
hydrogen. 

By  acting  upon  one  of  the  salts  of  aniline  with  N.^Oa,  a  salt  of  diazohenzenc  0^^.^ 
is  obtained.  This  may  be  represented  as  being  derived  from  aniline  CpHyN,  by  the 
substitution  of  one  atom  of  triatomic  nitrogen  for  three  atoms  of  hydrogen.  The 
salts  of  diazobeuzene  are  very  explosive. 

Diazobenzene  nitrate  C^'H.J^.yli'NO^  is  prepared  by  passing  K^O^  gas  into  a  strong 
aqueous  solution  of  aniline  nitrate  until  a  little  of  the  solution  no  longer  gives  a 
turbidity  with  potash.  Alcohol  then  precipitates  the  diazobenzene  nitrate  in  colour- 
less prisms;  2(CHH7N.HN03)  +  N203=2(CfiH4No.HN03)  +  3H20.  This  salt  is  said 
to  be  as  sensitive  to  a  shock  as  mercuric  fulminate,  and  has  been  proposed  for  use  in 
detonating  primers.  When  heated  it  detonates  with  extreme  violence  at  90°  C, 
whilst  mercuric  fulminate  requires  195°  C. 

Accompanying  the  aniline  in  coal-tar,  there  are  found  three  other  bases, 
viz.,  pi/ridine,  picoUne,  and  quinoUne.  It  will  be  seen  that  picoline 
(CqHyN)  is  isomeric  with  aniline,  from  which,  however,  it  differs  in  a 
very  striking  manner,  for  its  salts  are  by  no  means  easily  crystallisable, 
and  it  furnishes  no  violet  colour  Avith  oxidising  agents,  such  as  chloride 
of  lime.  Picoline  occurs  among  the  products  of  the  distillation  of  bones. 
Quinoline  is  also  formed  when  some  of  the  vegetable  alkaloids  are  distilled 
with  potash. 

Quinoline  has  been  obtained  by  the  action  of  strong  sulphuric  acid  upon 
a  mixture  of  nitrobenzene,  aniline,  and  glycerine;  CgH^NO,-}- 2C6H-K' 
+  SCgHgOg  =11 H2O  +  SC^HkN  {Quinoline). 

328.  The  other  constituents  of  the  light  coal-naphtha,  viz.,  toluene, 
xylene,  and  isocumene,  belong  to  the  benzene  series  of  hydrocarbons 
(page  438). 

On  reference  to  the  table  at  page  454,  it  will  be  seen  that  the  boiling- 
points  of  the  members  of  this  series  are  raised  54°  F.  for  each  addition  of 
CHg.  Thus  xylene  (Cj^H-iq)  boils  at  284°,  or  54°  higher  than  toluene 
(C-Hg),  which  boils  at  230° ;  whilst  benzene  (C,;Hp,)  boils  at  54°  beloAv 
this,  or  176°. 

The  members  of  this  group  are  also  intimately  connected  mth  those 
of  another  homologous  series,  known  as  aromatic  acids,  including — 

Benzoic  acid,  .  .  C-H^O., 
Tohuc  acid,  .  .  CgHgOg 
Cuminic  acid,    .         .     C,„Hi._>Oo. 

By  distilling  each  of  these  acids  with  barium  hydrate,  the  correspond- 


464  PHENOLE  OK  CARBOLIC  ACID. 

ing  hydrocarbon  is  obtained,  a  molecule  of  COg  being  removed  by  the 
barium  hydrate  ;  thus,  C^H^Og  (Benzoic  acid)  -  COg  -  CgHg  {Benzene). 

The  similarity  between  this  decomposition  and  that  by  which  marsh 
gas  (CH^)  is  derived  from  acetic  acid  (C2H4O2)  will  be  at  once  apparent 
(see  page  98). 

Each  member  of  the  benzene  series  of  hydrocarbons,  when  acted  upon 
by  nitric  acid,  yields  a  nitro-compound  corresponding  in  composition  to 
nitrobenzene,  and  this,  under  the  influence  of  reducing  agents  (such  as 
ferrous  acetate,  or  an  alkaline  hydrosulphate,  or  stannous  chloride)  yields 
a  base  homologous  with  aniline. 

Thus  we  have  the  three  following  homologous  series : — 

Hydrocarbon.  Nitro-compound.  Base. 

"  "  ""  Aniline,  CgHyN 

Toluidine,  C^HjN" 

Xylidine,  CgHuN. 


Benzene,  C^Hg 
Toluene,  CjHg 
Xylene,      CgHi, 


Nitrobenzene,  CpHgNOj 
Nitrotoluene,  C7H7NO2 
Nitroxylene,       CgH^NOa 

When  benzene  is  dissolved  in  concentrated  sulphuric  acid,  the  solution  diluted,  and 
neutralised  with  chalk,  the  liquid  filtered  from  the  calcium  sulphate  contains  the 
calcium  salt  of  mlphohcnzolic  or  henzcnc-sidphonic  add  (acid  phenyls  sulphite) — 

CgHg  +  H2SO4  =   HjO  +   CgHjSOaH  (Sulphobenzolic  add). 

The  acid  itself  may  be  obtained  in  crystals. 

Toluenc-sulphonic  add,  C^HgSO;,,  is  formed  in  a  similar  way.  By  fusing  the  potash 
salts  of  these  acids  with  caustic  potash,  the  corresponding  j^AcreoZcs  are  obtained;  thus — 

CgHsSO.K   +   KHO  =   K2SO3  +   CfiHsOH 
Potassium  benzene  Potassium         Phenole 

sulphonate,  sulphite. 

Each  hydrocarbon  of  this  series  furnishes  a  sulpho-acid  and  a  phenole  ;  thus — 

Hydrocarbon.  Sulpho-acld.  Phenole. 


Benzene,  CgHj 
Toluene,  CyHg 
Xylene,      CgHj, 


Benzeue-sulphonic,  CgHgSO;, 
Toluene-sulphonic,  CyHgSOj 
Xylene-sulphonic,      CgHjoSOg 


CgHjO 

CyHgO 

0,H,„0. 


329.  Carbolic  or  phenic  acid,  or  phenole  (CgHgO),  derives  its  interest 
chiefly  from  its  constituting  a  great  part  of  the  ordinary  commercial 
kreasote  (from  xpeas,  flesh,  and  o-w^o),  to  preserve).  It  is  also  present  in 
cow's  urine  and  in  that  of  some  other  animals.  It  is  found  chiefly  in 
the  heavy  or  dead  oil  of  coal-tar  (page  456),  particularly  in  that  portion 
Avhich  distils  over  between  300°  and  400°  F.,  when  the  oil  is  submitted 
to  fractional  distillation,  and  it  appears  to  be  the  carbolic  acid  which 
confers  upon  this  heavy  oil  its  valuable  antiseptic  properties,  leading  to 
its  employment  for  the  preservation  of  wood  from  decay. 

In  order  to  extract  the  acid  from  that  portion  of  the  dead  oil  which  distils  between 
.300°  and  400°  it  is  treated  with  caustic  soda.  A  crystalline  mass  is  deposited  which 
is  separated  from  the  liquid  portion  and  heated  with  a  little  water,  when  a  solution 
of  sodium  carbolate  is  obtained.  This  is  separated  from  a  quantity  of  oil  which  floats 
above  it,  and  decomposed  with  sulphuric  acid,  when  the  carbolic  acid  separates  as 
an  oily  layer  upon  the  surface.  This  is  drawn  off,  digested  with  a  little  fused  calcium 
chloride  to  remove  the  water,  and  distilled.  The  distilled  liquid,  when  exposed  to 
a  low  temperature,  solidifies  to  a  mass  of  long  colourless  needles,  which  are  easilj' 
liquefied  by  heat. 

Carbolic  acid  has  the  peculiar  taste  and  smell  of  kreasote.  It  dissolves 
sparingly  in  water,  but  readily  in  alcohol.  When  a  piece  of  deal  is  wetted 
with  solution  of  carbolic  acid,  and  afterwards  with  hydrochloric  acid,  it 
becomes  blue  on  drying. 

The  genuineness  of  a  commercial  sample  of  carbolic  acid  may  be  tested  by  shaking 
about  a  drachm  of  it  with  half  a  pint  of  warm  water,  which  will  dissolve  the  pure 


PTCRIC  OR  CARBAZQTIC  ACID.  465 

acid  entirely,  but  will  leave  any  "dead  oil"  undissolved.  A  solution  of  1  part  of 
caustic  soda  in  10  parts  of  water  should  dissolve  5  parts  of  pure  carbolic  acid. 

When  carbolic  acid  is  shaken  with  one-fourth  of  its  weight  of  water,  and  exposed 
to  a  temperature  of  39°  F.,  it  deposits  six-sided  prismatic  crystals  of  a  hydrate, 
2C^HgO.H.20,  which  is  soluble  in  water,  alcohol,  and  ether,  and  fuses  at  61°  F. 

'I'he  acid  properties  of  carbolic  acid  are  of  a  very  feeble  and  doubtful  character. 
It  is  the  representative  of  the  class  of  phenoles  which  resemble  the  alcohols  in  com- 
position, but  are  distinguished  from  them  by  their  tendency  to  combine  with  alkalies. 
Carbolic  acid,  or  phenole,  or  phenyle  hydrate,  CgH5(0H). 

When  distilled  with  chloride  of  zinc  or  of  aluminium,  phenole  yields  2}hevyle  ether  or 
diphenyle  oxide  (C6H5)20,  and  a  compound  0(CgH4)jCH2.  When  this  is  acted  on  by 
oxidising  agents,  it  yields  a  ketone  containing  OJ^CgHJvjCO.  On  fusing  this  with 
potash  it  yields  potassium  salicylate  HO(CgH4)C02K,  and  potassium  phenate 
CgH^OK. 

The  aqueous  solution  of  phenole  gives  a  purple  blue  colour  with  ferric  chloride,  and 
a  pale  yellow  precipitate  with  bromine  water  {trihromophenole  Cfi.^v.Jd) ;  this  is  an 
exceedingly  delicate  test  for  phenole. 

By  the  action  of  zinc  chloride  on  mixtures  of  alcohols  with  phenole,  the  elements  of 
water  are  abstracted,  and  phenoles  are  obtained  in  which  alcohol  radicals  replace 
hydrogen ;  thus  phenole  and  amylic  alcohol  yield  amylephenole,  CgH4C5Hu.  OH. 

Carbolic  acid  is  very  largely  used  as  an  antiseptic  agent.  In  medicine 
it  is  found  very  valuable,  especially  for  the  treatment  of  putrid  sores ; 
and,  in  admixture  with  sulphite  of  lime,  it  forms  the  substance  known  as 
MacDougaU's  dmnfectant.  Calvert's  disinfecting  powder  consists  of  clay 
with  12  or  15  per  cent,  of  carbolic  acid. 

330.  Picric  add. — "When  carbolic  acid  is  boiled  with  fuming  nitric 
acid,  the  solution,  on  cooling,  deposits  beautiful  yellow  crystals  of  carha- 
zotic  or  2iici'ic  acid,  also  called  trinitrophenic  or  nitrophenis-ic  acid,  because 
it  appears  to  be  formed  from  phenic  acid  by  the  substitution  of  3XO2  ^°^ 
H3,  just  as  nitrobenzene  is  formed  from  benzene  by  the  substitution  of 
X'Oj  for  H. 

The  composition  of  picric  acid,  upon  this  view,  would  be  expressed  by 
the  formula  HCgH2(X02)30,  the  atom  of  hydrogen  being  capable  of  dis- 
placement by  a  metal,  forming  a  picrate  or  carbazotate  ;  thus  if  the  acid 
be  added  to  a  solution  of  potash,  a  yellow  precipitate  of  potassium 
carbazotate  or  picrate,  KCgH2(N02)30,  is  obtained,  which  has  led  to  the 
employment  of  this  acid  as  a  test  for  potassium. 

Picric  acid  is  not  easily  soluble  in  water,  but  dissolves  readily  in  alcohol. 
Its  solutions  have  the  property  of  staining  the  skin  and  other  organic 
matters  yellow,  which  is  turned  to  advantage  by  the  sUk-dyer.  The 
intensely  bitter  taste  of  the  acid  has  also  led  to  its  employment  for  the 
adulteration  of  beer,  to  simulate  the  bitter  of  the  hop. 

Picric  acid  is  a  very  common  product  of  the  action  of  nitric  acid  upon 
organic  substances  ;  indigo,  silk,  and  many  resins  furnish  it  in  consider- 
able quantity.  It  is  economically  obtained  in  a  pure  state  by  the  action 
of  nitric  acid  upon  Botany  Bay  gum,  but  considerable  quantities  are 
manufactured  for  the  dyer  by  treating  the  crude  carbolic  acid  from  coal- 
tar  with  nitric  acid.  Picric  acid,  as  might  be  anticipated  from  its  com- 
position, explodes  when  sharply  heated,  its  carbon  and  hydrogen  being 
oxidised  by  the  nitric  peroxide. 

The  picrates  of  potassium  and  ammonium  are  far  more  explosive  than 
the  acid  itself,  particularly  when  mixed  with  nitre.  Such  mixtures  have 
been  employed  instead  of  gunpowder  for  blasting,  and  as  bursting  charges 
for  shells. 

2g 


466  PICRIC  OR  CARBAZOTIC  ACID. 

If  1  part  of  picric  acid  be  dissolved  in  9  parts  of  hot  water,  and  the  solution  added 
gradually  to  2  parts  of  potassium  cyanide  dissolved  in  4  of  water  at  60°  C,  the  solu- 
tion becomes  deep  red,  and  deposits  brown  crystalline  scales  with  a  green  lustre. 
Tliese  consist  of  potassium  isopurpirrate  or  picroajamate,  KC8H4N,,0„,  a  salt  which 
explodes  violently  when  heated.  When  decomposed  with  ammonium  chloride,  it 
gives  the  ammonium  isopurpurato  which  resembles  murexide,  and  is  used  in  dyeing. 

When  picric  acid  is  distilled  with  chloride  of  lime,  it  yields  a  heavy 
colourless  oil  having  a  very  pungent  odour  of  mustard,  and  boiling  at 
235°  F.  This  substance  has  been  called  cMoropicrine  or  nitrockloroform, 
and  has  the  remarkable  formula  CCl3(X02),  which  may  be  represented  as 
formed  upon  the  type  of  marsh  gas,  CH^,  in  which  3  atoms  of  the 
hydrogen  are  replaced  by  chlorine,  and  the  fourth  by  nitric  peroxide. 
Mills  has  obtained  it  by  the  action  of  red  nitric  acid  upon  chloroform 
(CHCI3).  Chloropicrine  is  frequently  met  with  among  the  products  of 
the  action  of  chlorinating  agents  upon  organic  substances.  It  is  almost 
insoluble  in  water,  but  dissolves  easily  in  alcohol  and  ether. 

When  an  alcoholic  solution  of  chloropicrine  is  acted  on  by  sodium,  it 
yields  the  ethyle  subcarbonate,  and  when  treated  with  potassium  cyanide, 
it  exchanges  2  atoms  of  chlorine  for  cyanogen,  forming  an  unstable  dark 
red  semi-fluid  substance,  having  the  composition  CClCy2(N02),  which 
may  be  regarded  as  derived  from  marsh  gas  (CH^)  by  the  substitution  of 
2  atoms  of  cj'anogen,  1  atom  of  chlorine,  and  1  atom  of  nitric  peroxide, 
for  the  4  atoms  of  hydrogen. 

By  the  action  of  nascent  hydrogen  (distillation  with  acetic  acid  and 
iron  filings),  chloropicrine  is  converted  into  methylamine — 

CCI3NO2  +  H12  =  NH2.CH3  +  2H2O  +  3HC1. 

Chloropicrine.  Methylamine. 

It  will  be  instructive  to  compare  the  composition  of  the  most  impor- 
tant members  of  the  phenyle  sei-ies,  as  that  group  of  organic  compounds  is 
termed,  which  contain  the  radical  phenyle  (CgH^). 

Benzole  or  phenyle  hydride,         .         .         .  (CjHg)!! 

Aniline  or  phenylamine,     ....  (CgHg)NH2 

Phenic  acid  or  phenyle  hydrate,  .         .         .  (CgHjjOH 

Trinitrophenic  or  picric  acid,        .         .         .  [CgH2(N02)3]OH. 

It  is  evident  that  whilst  aniline  may  be  regarded  as  ammonia  in  which 
phenyle  is  substituted  for  an  atom  of  hydrogen,  phenic  acid  can  be 
represented  as  formed  from  a  molecule  of  water  by  the  substitution  of 
phenyle  for  half  the  hydrogen,  and  benzene  may  be  represented  as  a 
molecule  of  hydrogen,  HH,  in  which  one  of  the  atoms  is  replaced  by 
phenyle. 

Some  specimens  of  the  kreasote  found  in  commerce  boil  at  a  higher 
temperature  than  carbolic  acid ;  this  is  due  to  the  presence  of  Jtvpsylic 
arid  or  kresole  (C^HgO),  corresponding  to  carbolic  acid,  but  regarded  as 
containing  the  radical  krcsyle  (C7H-)  in  place  of  phenyle.  The  analogy 
in  composition  is  attended  with  a  resemblance  in  properties,  for  kresylic 
acid  has  the  same  antiseptic  property  as  carbolic  acid,  and  is  applicable 
to  similar  purposes.  When  acted  on  by  nitric  acid,  it  yields  trinitro- 
Jiroiylic  acid  (iiCjU^C^O^^O),  just  as  carbolic  acid  gives  trinitrophenic 
acid  (HC,H2(N02)30). 

Aurine,  Cj^H^^Og,  is  a  yellow  crystalline  body  obtained  in  the  prepara- 
tion of  coraUin  by  the  action  of  a  mixture  of  sulphuric  and  oxalic  acids 
upon  phenole — 


NAPHTILVLINE  OR  NAPHTHALENE.  467 

306^,(011)  +  H,CA  =  SHgO  +  CO  +  CigHi.Og. 
It  is  dissolved  by  alkalies  and  reprecipitated  by  hydrochloric  acid. 

331.  Naphthaline  or  naphthalene. — The  most  prominent  constituent 
of  the  heavy  oil  of  coal-tar  is  the  naphthalene,  which  is  easily  procured  in 
a  pure  state  from  the  portions  obtained  at  the  close  of  the  distillation,  by 
simply  pressing  the  semi-solid  mass  to  remove  any  liquid  hydrocarbon?, 
and  boiling  with  alcohol,  from  which  the  naphthalene  crystallises  on 
cooling  in  brilliant  pearly  flakes,  which  may  be  still  further  purified  by 
the  process  of  sublimation. 

In  itself  naphthalene  is  not  very  interesting,  being  a  remarkably  in- 
different substance,*  but  it  has  been  made  the  subject  of  several  beauti- 
ful investigations  which  have  thrown  much  light  upon  the  action  of 
chemical  agents  on  organic  compounds  in  general. 

The  most  important  of  these  researches  is  that  upon  the  action  of 
chlorine  and  bromine  on  naphthalene,  which  originated  the  now  almost 
universally  accepted  doctrine  of  substitution,  and  f  uUy  established  the  fact, 
that  an  element  may  be  replaced  in  a  given  compound  by  an  equivalent 
quantity  of  another  element  of  a  totally  diff'erent  chemical  character. 

Thus,  by  the  action  of  chlorine  upon  naphthalene,  the  hydrogen  is 
removed  in  the  form  of  hydrochloric  acid,  and  there  are  obtained  six  new 
compounds  by  the  progressive  substitution  of  chlorine  for  the  hydrogen, 
which  Laurent  distinguished  by  names  indicating  the  number  of  atoms 
of  chlorine  present  by  means  of  the  different  vowels  in  the  last  syllable, 
introducing  a  new  penultimate  syllable  when  the  vowels  were  exhausted, 
as  will  be  seen  in  the  following  list : — 

Chlonaphtuse,  .  .  Wanting 

Chlonaphthalase,  .  CjoHoCl^ 

Chlonaphthalese,  .  Wanting 

Chlonaphthalise,  .  CjoClg 

It  will  be  observed  that  the  original  naphthalene  type  is  here  preserved 
throughout,  the  sum  of  the  atoms  being  always  18,  and  the  number  of 
carbon  atoms  10. 

One  of  the  most  unexpected  results  of  Laurent's  investigation  was  the 
discovery  that  some  of  these  compounds  may  be  obtained  in  several 
distinct  forms  or  modifications,  which  are  isomeric,  or  have  the  same 
composition,  but  exhibit  very  difierent  properties.  Thus  there  are  seven 
varieties  of  chlonaphtese,  aU  containing  CjoHgClg,  and  yet  differing  from 
each  other  as  much  as  substances  not  having  the  same  composition. 
Two  of  them  are  liquids,  and  the  five  solid  forms  all  fuse  at  different 
temperatures,  ranging  between  88°  and  214°  F.  Seven  different  forms  of 
chlonaphtise  likewise  exist,  and  four  of  chlonaphtose. 

To  account  for  this,  Laurent  supposed  it  to  be  by  no  means  indifferent 
which  atom  of  hydrogen  has  been  removed  from  the  compound,  believing 
each  to  have  its  assigned  place  and  specific  function.  Thus  it  may  easily 
be  conceived  that  the  replacement  of  different  atoms  of  hydrogen  by 
chlorine  should  give  the  seven  modifications  of  chlonaphtese — 
[N^aphthaline,  C^qH  H  H  H  H  H  H  H 

Chlonaphtese  a,        C^oCl  CI  H  H  H  H  H  H 
Clilonaphtese  (i,       C^^K  H  CI  CI  H  H  H  H , 

*  A  crimson  dye,  ??^««7t?aZa,  containing  the  base  azo-dinaphthy lamina,  C30H21N3,  has  been 
prepared  from  naphthalene. 


Naphthalene,     . 

•     CjflHg 

Chlonaphtase,    . 

.     C10H7CI 

Chlonaphtese,    . 

•     CioHgClj 

Chlonaphtise,     . 

•    C10H5C13 

Chlonaphtose,    . 

•     CjoH^Cl^ 

468  SUBSTITUTION  PRODUCTS  FROM  NAPHTHALENE. 

and  80  on.     Other  more  recent  investigations  have  given  greater  prob- 
ability to  this  hypothesis. 

Bromine,  as  might  be  anticipated,  yields  results  similar  to  those  with 
chlorine;  but  it  could  not  have  been  predicted  that  substitution  com- 
pounds might  be  obtained  in  which  one  part  of  the  hydrogen  is  replaced 
by  chlorine  and  the  other  by  bromine.  Thus,  by  acting  upon  a  chlorine 
substitution  compound  with  bromine,  or  vice  versd,  the  following  sub- 
stances were  produced  :* — 

Chlorebronaphtise,        CioHgCljBr 

Chlorebronaphtose,        CioH4Cl2Br2 

Chloribronaphtose,        CioH4Cl3Br 

Bromechlonaphtuse,      CioHsBfjCI;, 

Bromachlonaphtose,      CioH4BrCl3 

It  will  be  observed  that  chloribronaphtose  and  bromachlonaphtose 
have  the  same  composition,  though  they  possess  different  properties,  and 
are  obtained  in  very  different  ways,  the  former  being  procured  by  the 
action  of  bromine  on  chlonaphtise  (CjoHjClg),  and  the  latter  by  the 
action  of  chlorine  upon  bronaphtese  (CjoHgBrg).  Another  confirmation 
is  thus  obtained  of  the  belief,  that  upon  the  position  of  the  hydrogen 
which  is  replaced,  depends  the  character  of  the  resulting  compound. 

According  to  modem  chemical  views,  the  carbon- 

l'             I  atoms  in  naphthalene  are  regarded  as  being  linked 

P             £  together  to  form  two  "rings."     The  tetratomic  atoms 

/y      \    /      <S.  being  linked  together  by  single  and  double   bonds 

'z           ^  •'           V^  p  alternately,  there  are  eight  free  bonds  for  the  attach- 

2'  C                C  ment  of  atoms  of  hydrogen  or  of  any  radical  replacing 

I                 11  liydrogen.     The  isomeric  substitution  derivatives  are 

^  '                 ' '                 '  ,7  then  distinguished  by  indicating  the  numbers  of  the 

3  C                C                C  >5  carbon-atoms  to  which  the  radical  is  attached.     Thus 


n\  /  \  y^  the  different  varieties  of  chlonaphtese,  CioHgCl„,  are 

V  r    '  C  distinguished  as  1  :  1' dichloronaphthalene,  1 :  2,1:3 

.1  I  aud  1  :  3',  according  to  the  position  of  the  carbon- 

atoms  to  which  the  chlorine-atoms  are  attached. 

Naphthalene  is  capable  of  direct  union  with  chlorine  to  form  two 
naphthalene  chlorides,  having  the  formulae  C^oHgCl,  and  CjoHgCl^,  which 
may  obviously  be  regarded  as  composed  of  substitution  products  combined 
witli  hydrochloric  acid. 

AYlien  acted  upon  by  nitric  acid,  naphthalene  furnishes  three  substitu- 
tion products,  in  which  I,  2,  and  3  atoms  of  hydrogen  are  replaced 
by  XOo ;  and  each  of  these  compounds,  under  the  influence  of  reducing 
agents,  yields  a  base,  just  as  nitrobenzene,  under  similar  treatment,  yields 
aniline. 

By  prolonging  the  action  of  boiling  nitric  acid  upon  naphthalene, 
and  evaporating  the  solution,  crystals  of  napMhalic  or  phthalic  acid, 
\\.fl^^O^,  are  obtained.  Through  this  acid,  naphthalene  is  connected 
with  the  phenyle  series;  for  when  phthalic  acid  is  heated  with  lime,  it 
yields  calcium carbonateand benzene ;  HgCgH^O^  +  2CaO  =  C^Hg  +  2CaC03. 

^loreover,  by  digesting  calcium  phthalate  with  calcium  hydrate  at  an 
elevated  temperature  for  several  hours,  it  is  converted  into  benzoate  and 
carbonate  of  calcium ;  2CQ.C^B.S)i  +  Ca(H0)2  =  O^iC^'Rff.^ct  +  2CaC03. 

Calcium  phthalate.  Calcium  benzoate. 

*  In  naming  these  compounds,  Laurent  proceeded  upon  the  same  principle.  The  vowel 
iiuniediately  after  the  syllable  cMor-  or  hrom-,  indicating  the  number  of  atoms  of  that 
element,  whilst  the  vowel  in  the  last  syllable  shows  how  many  atoms  of  hydrogen  have 
been  replaced.  The  name  begins  with  chlor-  when  the  compound  has  been  obtained  by 
the  action  of  bromine  upon  a  chlorine  substitution  product,  and  vice  versd,. 


ANTHRACENE.  469 

.  By  the  action  of'  heat  upon  phthalie  acid,  the  anhydride,  CgH^Og,  is 
obtained  in  needle-like  crystals.  This,  when  heated  with  resorcine  to 
200°  C,  yields  Jiuoresceine,  CgoH^gOg,  as  a  brown  crystalline  body  dis- 
solved by  ammonia  to  a  red  solution  having  a  green  fluorescence.  Acetic 
acid  also  dissolves  it,  and  on  adding  bromine  to  the  solution,  a  feebly 
acid  body  crystallises  out  which  is  called  eosine,  CgoHg^r^Oj ;  the  potas- 
sium salt,  CgoHgKoBr^Oj,  is  known  in  commerce  as  soluble  eosine,  and 
forms  a  fine  red  dye.     Muoresceine  is  employed  as  a  yellow  dye  on  silk. 

Resorcine,  C^^^iOWj^,  is  a  very  soluble  crystalline  phenole  obtained 
by  distilling  the  extract  of  Brazil-wood,  or  by  the  action  of  sodium 
hydrate  upon  benzene-disulphonic  acid  obtained  by  the  action  of  sulphuric 
acid  on  benzene. 

Anthracene  or  paranaphthalene,  Cj^Hj^q,  which  is  found  among  the' 
last  products  of  the  distillation  of  coal-tar,  differs  from  naphthalene  in 
being  almost  insoluble  in  alcohol,  and  fusing  only  at  415°  F.,  whilst 
naphthalene  fuses  at  176°  F.* 

Anthracene  has  been  obtained  by  heating  benzyle  chloride  with 
water  ;  4C-H;C1  {benzyle  chloride)  =  C^^iq  {anthracene)  +  Ci^H^^)  diben- 
zyle)  +  4Ha. 

Phenanthrene,  Cj^H^o,  isomeric  with  anthracene,  is  contained  in  the 
portion  of  coal-tar  which  boils  between  590°  and  660°  F.  It'  is  soluble 
in  alcohol,  and  crystallises  in  colourless  plates  with  a  blue  fluorescence. 
If  it  be  dissolved  in  glacial  acetic  acid,  and  acted  on  by  chromic  acid,  it 
yields  phenanthraquitione  Cj^HgOg. 

Chrysene,  C^gH^^?  ^^^  pyrene,  CiqHjq,  are  obtained  at  the  close  of  the 
distillation  of  coal-tar ;  they  are  crystalline  solids  not  possessing  any 
special  importance,  and  have  also  been  observed  among  the  products  of 
the  destructive  distillation  of  fatty  and  resinous  bodies. 

Idrialene,  C22H14,  has  been  obtained  from  Idrialite,  a  mineral  found  in  the  mercury- 
mines  of  Idria. 

It  is  worthy  of  remark  that  pyrene  CjgHjQ  contains  more  carbon  than  any  other 
hydrocarbon  (95  per  cent. ),  and  even  more  than  is  to  be  foixnd  in  coal  itself. 

Acridi'iic,  CjgHgN,  is  a  crystallisable  base  found  in  crude  anthracene  and  anthra- 
cene oils,  which  has  a  very  irritating  action  on  the  skin. 

DESTRUCTIVE  DISTILLATION  OF  WOOD. 

3S2.  The  destructive  distillation  of  wood  may  be  advantageously 
studied  in  order  to  gain  an  insight  into  the  effects  of  heat  upon  organic 
substances  comparatively  free  from  nitrogen,  just  as  that  of  coal  may 
serve  as  a  general  illustration  of  the  behaviour  of  nitrogenised  bodies 
under  similar  treatment. 

The  principal  distinction  between  the  two  cases  will  be  found  to  con- 
sist in  the  absence  of  basic  substances  from  the  products  of  the  distilla- 
tion of  non-nitrogenised  bodies. 

"Wood  (freed  from  sap)  consists  of  cellulose,  vascvlose  (or  lignine),  and 
mineral  substances  or  ash.  The  cellulose  composes  the  wood  cells  and 
fibres,  whilst  the  vasculose  is  the  chief  constituent  of  the  vessels  which 
bind  them  together.  They  may  be  separated  by  the  action  of  solution  of 
cupric  oxide  in  ammonia,  which  dissolves  the  cellulose  only.  Vasculose 
is  dissolved  w^hen  heated  with  caustic  alkalies  under  pressure,  Avhich  is 

*  Tlie  tar  from  Newcastle  coal  yields  most  anthracene,  and  that  from  cannel  coal  gives 
most  paraffin.     Much  anthracene  is  now  employed  for  the  manufacture  of  alizarine. 


470 


PRODUCTS  FROM  WOOD. 


turned  to  advantage  in  preparing  wood  and  straw  for  the  manufacture 
of  paper.  It  is  also  acted  on  by  oxidising  agents,  such  as  chlorine-water 
and  chloride  of  lime,  which  do  not  attack  cellulose,  but  convert  vasculose 
into  resinous  substances  soluble  in  alkalies.  The  proportion  of  vasculose 
increases  with  the  hardness  and  density  of  the  wood.  Poplar  contains 
only  18  per  cent,  of  vasculose,  whilst  iron- wood  contains  40  per  cent. 
The  shells  of  nuts  contain  more  vasculose  in  proportion  to  their  hardness  ; 
walnut  shells  contain  44  per  cent,  and  cocoa-nut  shells  58  per  cent. 
Vasculose  is  always  accompanied  in  the  wood  by  resinous  matters,  giving 
rise  to  the  differences  of  colour  in  woods,  and  by  a  small  quantity  of 
nitrogenised  matter,  and  of  ash  deposited  with  it  from  the  sap. 

The  following  results  of  the  analysis   of  several   woods  will  exhibit 
their  general  correspondence  in  composition  : — 

Wood  dried  in  vacuo  at  284°  F. 


' 

Beech. 

Oak. 

Birch. 

Aspen. 

Willow. 

Carbon,  

49-46 

49-58 

50-29 

49-26 

49-98 

Hydrogen,       .... 

5-96 

5-78 

6-23 

6-18 

6  07 

Oxygen, 

42-36 

41-38 

41-02 

41-74 

89 -38 

Nitrogen,         .         .         .         .  | 
Sulphur,          .         .         .         .\ 

1-22 

1-23 

1-43 

0-96 

0-95 

Ash, 

1-00 
100-00 

2  03 

1-03 

1-86 

3-67 

100-00 

100-00 

100-00 

100-00 

Cellulose  in  a  nearly  pure  condition  constitutes  cotton,  linen,  and  the 
best  kinds  of  (unsized)  paper,  since  the  processes  to  which  the  woody 
fibre  is  subjected  in  the  preparation  of  these  materials  destroy  and 
sejiarate  the  less  resistant  lignine  and  the  matters  which  accompany  it. 

On  comparing  the  composition  of  wood  with  that  of  coal,  it  will  be 
obvious  that  the  large  proportion  of  oxygen  in  the  former  must  give  rise 
to  a  great  difference  in  the  products  of  destructive  distillation.  Accord- 
ingly, it  is  found  that  water,  carbonic  oxide,  carbonic  acid,  and  acetic 
acid,  all  highly  oxidised  bodies,  are  produced  in  large  quantity,  and  that 
the  gaseous  products  of  the  distillation  of  wood  burn  with  far  less  light 
than  those  from  coal,  in  consequence  of  the  smaller  proportion  of  the 
heavier  hydrocarbons. 

The  principal  products  of  the  action  of  heat  upon  wood  are — 


Wood-Tar. 

Solids. 

Paraffin, 

CxH2*+2 

Pyrene,  . 

^16"l0 

Naphthalene, 

C'loHg 

Chrysene, 

CjgHia 

Cedriret, 

CjgHjjOg 

Besin, 

Pittacal, 

CasHjgOg 

Liquids. 

Toluene, 

CyHg 

Pyroligneous  or    ) 

.     C.,H,0, 

Xylene, 

^'sHio 

acetic  acid,         \ 

Cymene, 

C,oHi4 

Wood-naphtha, 

.     CH4O 

Kreasote, 

.         C^HgO 

Methyle  acetate. 

.     CH3.C.I 

Picaniar, 

Methyle  formiate, 

.     CH.,.CH 

Kapnomor,    . 

•         C,oH„0 

Acetone, 

.     CjHeO 

Eupione, 

•         C,H,2 

Water, 

WOOD-NAPHTHA.  471 

Gases. 

Marsh  gas, CH4 

Carbonic  oxide, CO 

Carbon  dioxide, COg 

Of  these  products,  by  far  the  most  important  are  the  pyroligneous  acid, 
the  wood-naphtha,  and  acetone. 

The  distillation  of  wood  with  a  view  to  the  preparation  of  these  sub- 
stances, is  conducted  in  the  manner  described  in  the  section  on  wood- 
charcoal  (page  65),  when  the  distillate  separates  into  two  portions,  the 
heavier  insoluble  part  constituting  the  wood-tar,  whilst  the  light  aqueous 
layer  contains  the  pyroligneous  acid,  naphtha,  and  acetone. 

On  distilling  this,  the  two  last,  boiling  respectively  at  150°  and  133° 
F.,  first  distil  over,  and  then  the  acetic  acid,  which  boils  at  243°  F.  The 
acid  so  obtained,  however,  is  contaminated  with  tarry  matters,  which 
communicate  the  peculiar  odour  of  wood  smoke,  and  adapt  it  especially 
for  the  preservation  of  meat.  In  order  to  obtain  pure  acetic  acid,  this 
crude  acid  is  neutralised  with  sodium  carbonate,  and  the  sodium  acetate 
thus  obtained  is  moderately  heated  to  expel  the  foreign  substances.  It 
is  then  further  purified  by  solution  in  water  and  crystallisation,  and  is 
distilled  with  sulphuric  acid,  which  converts  the  sodium  into  sulphate, 
leaving  the  acetic  acid  to  distil  over.* 

333.  Wood-naphtha, — Methylic  alcohol,  H3C.OH. — In  order  to  obtain 
the  wood-naphtha  (or  pyroligneous  ether,  or  v:ood-epirit,  or  pyroxylic 
spirit),  the  portion  which  distils  over  below  212°  F.  is  rectified,  in  a  still 
containing  chalk,  which  retains  the  acetic  acid  as  calcium  acetate. 

The  wood-naphtha  so  obtained  generally  consists  chiefly  of  methylic 
alcohol  (CH^O),  but  contains  also  acetone,  methyle  acetate,  and  certain 
oily  substances  which  impart  to  it  a  peculiar  odour,  and  cause  it  to 
become  milky  when  mixed  Avith  water.  Wood  generally  yields  about 
1  part  of  naphtha  to  20  of  acetic  acid.  In  order  to  obtain  the  pure 
methylic  alcohol,  calcium  chloride  is  dissolved  to  saturation  in  the  crude 
wood-spirit,  when  a  definite  crystaUisable  compound  is  formed,  of  4 
molecules  of  methylic  alcohol  and  1  of  calcium  chloride,  CaCl9.4CH40. 
This  is  heated  in  a  retort  placed  in  a  vessel  of  boiling  Avater,  as  long  as 
any  acetone  and  methyle  acetate  pass  over,  the  above  compound  not 
being  decomposed  at  212°  F.  An  equal  weight  of  water  is  then  added 
to  the  residue  in  the  retort,  and  the  distillation  continued,  when  the 
methylic  alcohol  distils  over,  accompanied  by  water,  and  the  calcium 
chloride  remains  in  the  retort.  The  diluted  methylic  alcohol  is  digested 
for  some  time  Avith  powdered  quicklime,  and  again  distilled,  when  it  is 
obtained  in  a  state  of  purity. 

The  useful  applications  of  crude  wood-naphtha  depend  upon  its 
burning  with  a  nearly  smokeless  flame  in  lamps  (though  as  a  source 
of  heat  only,  not  of  light),  and  upon  its  power  of  dissolving  most 
resinous  substances  employed  in  the  preparation  of  varnishes,  stififening 
for  hat:^,  &c. 

Methylic  alcohol  is  the  first  member  of  the  very  important  homologous 
series  of  alcohols  of  which  ordinary  alcohol  or  spirit  of  wine  is  the  type 
(see  page  437),  and  the  consideration  of  which  may  be  postponed  until 
the  chemical  history  of  that  alcohol  shall  have  been  studied. 

*  In  Condj-'s  patent,  advantage  is  taken  of  the  formation  of  an  easily  crystaUisable 
compound  ot  calcium  acetate  with  calcium  chloride  CaCl2.Ca(C2H3O2)2.10Aq. 


472  .      PARAFFIN.      ' 

One  of  the  most  interesting  compounds  derived  from  wood-spirit  is 
the  methyle  salicylate  or  oil  of  winter  green  (GHg.C^HjOy),  which  is 
extracted  from  the  flowers  of  the  Gattltkei-ia  procumheiis,  and  was  one 
of  the  first  vegetable  products  to  be  prepared  artificially  by  the  chemist. 
It  is  obtained  by  distilling  wood-spirit  with  sulphuric  acid  and  salicylic 
acid  (HC7H5O3),  the  latter  acid  being  formed  by  the  action  of  fused 
potash  upon  the  salicine  (C^gHigOy)  extracted  from  willow  bark. 

334.  Paraffin  ifi^^^  is  a  semi-transparent,  waxy  substance,  which 
distils  over  with  the  last  portions  of  the  tar  from  wood,  and  may  be 
obtained  in  larger  quantity  by  distilling  peat,  as  well  as  from  the  mineral 
known  as  Boghead  cannel*  and  from  bituminous  shale.  It  is  also  found 
abundantly  in  the  petroleum  or  mineral  naphtha  imported  from  Rangoon, 
and  has  lately  been  observed  in  small  cavities  in  lava  near  Etna. 

In  order  to  extract  the  paraffin  from  wood-tar,  advantage  is  taken  of 
its  great  resistance  to  the  action  of  most  chemical  agents,t  for  which  pur- 
pose the  later  portions  of  the  distillate  are  moderately  heated  with  con- 
centrated sulphuric  acid,  which  decomposes  and  chars  most  of  the  sub- 
stances mixed  with  the  paraffin,  and  allows  the  latter  to  collect  as  au 
oily  layer  upon  the  surface ;  this  is  allowed  to  cool  and  solidify,  when  it 
may  be  purified  by  pressure  between  blotting-paper,  and  solution  in  a  hot 
mixture  of  alcohol  and  ether,  from  which  it  is  deposited,  on  cooling,  in 
brilliant  plates. 

When  the  oil  f4'om  shale  is  re-distilled,  the  last  portions  of  the  distillate 
(heavy  oil)  contain  much  paraffin,  which  crystallises  in  scales  as  the  oil 
cools.  This  is  run  into  bags,  which  are  squeezed  by  hydraulic  pressure 
to  remove  the  liquid  portion,  which  is  then  artificially  cooled  to  20°  F., 
when  more  paraffin  crystallises  out,  and  is  purified  by  recrystallisation 
from  naphtha,  deodorised  by  blowing  steam  through  it,  and  decolorised 
by  animal  charcoal,  which  is  removed  by  filtration. 

Paraffin  fuses  at  about  110°  F.,  and  may  be  distilled  at  a  higher 
temperature;  it  burns,  like  wax,  with  a  very  luminous  flame,  and  is 
employed  as  a  substitute  for  wax  in  the  manufacture  of  candles.  It  is 
insoluble  in  water,  and  dissolves  sparingly  in  alcohol,  ether  being  the  best 
solvent  for  it. 

It  has  been  shown  by  Thorpe  and  Young  that  when  solid  paraffin  is 
strongly  heated,  under  pressure,  it  is  almost  completely  resolved  into 
liquid  hydrocarbons  :  from  a  specimen  of  paraffin  fusing  at  115°  F., 
they  obtained  the  following  liquid  members  of  the  marsh-gas  series ; 
CjHjo,  C^Hj^,  CyHjg,  CgHjg,  C9H20,  as  well  as  several  olefines  (page  438). 

The  substance  known  as  parajfin  oil,  which  is  used  for  lubricating 
machinery,  is  the  less  volatile  portion  of  the  hydrocarbons  formerly 
obtained  by  the  destructive  distillation  of  Boghead  cannel  (found  at 
Bathgate,  near  Edinburgh),  and  since  that  was  worked  out,  from  the 
bituminous  shales  of  Linlithgow  and  Mid-Lothian.  It  is  composed  chiefly 
of  heptylene,  C-H^^,  and  other  hydrocarbons  of  the  olefine  series.  The 
more  volatile  portion  of  the  hydrocarbons  so  obtained  is  employed  for 
illuminating  purposes. 

Acetone  will  be  described  hereafter. 

Ut  the  other  products  of  the  destructive  distillation  of  wood  enumerated  at  page  470 

*  The  kerosene  shale  of  New  South  Wales  resembles  Boghead  cannel  in  composition. 
t  To  which  it  owes  its  name,  from  xxiruvi,  little ;  affinis,  allied. 


PETROLEUM.  4:'7Z 

gofnehave  been  described  amongst  the  products  obtained  from  coal,  and  the  remainder 
have  been  but  little  studied,  and  have  not  received  any  nseful  application. 

Eupione  {fv-iriui',  very  fat)  or  pentane  (CjHij)  is  a  liquid  lighter  than  water,  and 
boiliug  at  102°  F. 

Kapuomor  (icairvhs,  smoke,  fio7pa,  a  part)  is  an  oily  liquid,  which  boils  at  360°  F. 
.    Picamar  (pix,  pitch,  amarus,  bitter)  is  another  oily  liquid,  heavier  than  water. 

Cedriret  [cedria,  pitch,  rete,  a  net,  in  allusion  to  its  interlaced  crystals)  or  ca'vidig- 
none.,  CigHigOg,  is  insoluble  in  ordinary  solvents,  but  crystallises  from  phenole  in  blue 
needles. 

Pittacal  {irirra,  pilch,  Ka\hs,  beautiful)  is  a  blue  solid. 

Hofmann  lias  shown  pittacal  to  be  an  acid  {eupittonic  acid  H2C25H24O9),  and  has 
prepared  it  from  the  crude  dimethyl-ether  of  pyrogallol  extracted  from  beech-wood 
tar.  This  ether  is  a  mixture  of  dimethyle-pyrogallate  C6(CH3)2H(OH)3  and  di- 
methyle-methyle-pyrogallate  C6(CH3)H.2{OCH3)20H.  When  these  are  heated  with 
excess  of  soda,  in  contact  with  air,  the  latter  removes  hydrogen  by  oxidation,  and- 
pittacal  is  produced^ 

2CgHjj03   -f-  C9H12O3  =   3H2  -I-   CgsHjgOg. 

The  sodium  eupittonate  thus  formed  is  dissolved  in  water,  and  the  indigo-blue 
solution  mixed  with  HCl,  when  it  becomes  carmine-red,  and  deposits  a  resinous  body 
which  yields  crystals  of  eupittonic  acid  when  purified. 

Stockholm  tar  is  collected  during  the  carbonisation  of  pine  wood,  con- 
taining a  large  quantity  of  resin,  the  tar  running  oflf  through  an  aperture 
at  the  lower  part  of  the  pit,  in  which  the  imperfect  combustion  of  the 
wood  is  carried  on.  It  differs  from  ordinary  tar  in  containing  large 
quantities  of  resin  and  turpentine,  the  latter  being  separated  from  it  by 
distillation,  and  the  residue  constituting  the  pitch  of  commerce. 

Petroleum. — There  are  found,  in  different  parts  of  the  earth,  generally 
in  or  near  the  coal-formations,  several  solid  or  liquid  hydrocarbons,  pro- 
bably formed  during  the  conversion  of  vegetable  remains  into  coal,  some 
of  which  have  received  useful  applications. 

Bitumen  is  the  name  given  to  a  number  of  these  compounds  of  carbon 
and  hydrogen.  The  chief  solid  variety  is  asplialtum  or  mineral  pitch, 
which  resembles  coal,  but  is  easily  fusible  and  dissolves  in  turpentine. 
It  is  abundant  on  the  shores  of  the  Dead  Sea  and  in  the  island  of  Trini- 
dad. It  is  used  for  making  the  black  varnish  known  as  japan,  and  is 
mixed  with  limestone,  &c.,  and  cast  into  blocks  for  paving.  Asphaltum 
contains  oxygen  as  well  as  carbon  and  hydrogen. 

The  Rangoon  tar  has  already  been  noticed  as  containing  a  considerable 
quantity  of  paraffin ;  the  liquid  part  of  this  tar,  after  distillation  and 
treatment  with  oil  of  vitriol  to  remove  hydrocarbons  of  the  benzene  series,* 
is  the  liquid  in  which  potassium  and  sodium  are  preserved;  it  is  com- 
monly called  jjetroleum  or  rocJi-oil,  and  appears  to  be  a  mixture  of  several 
hydrocarbons.  Petroleum  is  also  employed  occasionally  as  a  solvent  for 
caoutchouc  and  resinous  substances.  In  the  neighbourhood  of  the  Caspian 
Sea  there  are  several  springs  from  which  rock-oil  flows,  together  with  water, 
from  the  surface  of  which  it  is  skimmed  and  sent  into  commerce. 

The  petroleum  from  the  Caucasus  contains  hydrocarbons  isomeric  with 
the  olefines  (C,H..„),  but  more  nearly  resembling  the  paraffins  in  their 
chemical  characters. 

American  petroleum. — Within  the  last  few  years  abundant  supplies  of 
petroleum  have  been  obtained  from  wells  and  springs  in  Pennsylvania 
and  Canada,  and  the  demand  for  it  to  serve  as  an  illuminating  agent,  and 
for  the  lubrication  of  machinery,  has  created  a  new  branch  of  commerce, 

*  These  hydrocarbons,  when  treated  with  oil  of  vitriol,  form  acids  wliich  are  soluble  in 
water.     Thus  benzene  is  converted  into  sid^jhobenzoUc  acid,  HCgHj.SOa. 


474  OIL  OF  TURPENTINE. 

giving  rise  to  the  rapid  growth  of  "  oil  cities  "  in  the  neighbourhood  of  the 
wells.  These  rock-oils  have  a  very  peculiar  unpleasant  odour,  and  appear 
to  consist  chiefly  of  hydrocarbons  belonging  to  the  homologous  series  of 
•which  marsh  gas  (CH^)  is  a  member.  Thus,  the  Pennsylvanian  petroleum 
has  furnished  the  hydrocarbons,  C4Hj„,  C5H12,  CgHj^,  Cyll^g,  CgHjg,*  CgHgQ. 
Ethane  C2Hg  has  been  found,  together  with  marsh  gas,  among  the  gases 
contained  in  coaL  In  addition  to  these,  the  hydrocarbons,  CipHgo,  CiiHgg, 
C12H04,  homologous  with  olefiant  gas  (CgH^),  have  been  obtained  from  it. 
Some'  of  the  members  of  the  benzene  series  appear  also  to  be  present  in 
the  Canadian  petroleum. 

Those  hydrocarbons  which  contain  fewer  than  6  atoms  of  carbon,  boil 
at  or  below  100°  ¥.,  and  are  separated  from  the  petroleum  (or  kerosene  or 
paraffin  oil)  intended  for  burning  in  lamps,  as  being  dangerous  on  account 
of  their  volatility.  Since  each  molecule  of  these  hydrocarbons  contains  a 
large  amount  of  combustible  matter,  a  small  volume  of  the  vapour  will 
render  a  large  volume  of  air  dangerously  explosive.  Thus,  2  vols,  of 
pentane  CgHjg  would  confer  explosive  properties  on  more  than  80  vols,  of 
air,  which  would  be  required  to  supply  the  16  atoms  of  oxygen  for  con- 
verting the  C  into  CO2  and  the  H  into  HOg.  The  more  volatile  napfithas 
have  a  specific  gravity  between  0*67  and  0"69;  the  burning  oils  between 
0"8  and  0"81  ;  the  lubricating  oils  between  0-86  and  0'9.  The  more 
volatile  hydrocarbons  are  sold  under  the  name  of  petroleum  spirit,  which 
is  much  used  as  a  solvent,  and  is  sometimes  called  kerosoline,  or  ligroine. 

Bituminous  shale,  when  distilled,  furnishes  products  which,  as  far  as 
they  are  known,  are  closely  allied  to  those  obtained  from  wood  and  coaL 

Ozokerite,  or  mineral  wax,  is  imported  from  Galicia,  Hungary,  and 
Kussia,  for  the  manufacture  of  candles.  It  contains  85  per  cent,  of  carbon 
and  1 5  of  hydrogen,  and,  when  purified  from  an  oil  useful  for  illuminating 
purposes,  consists  of  a  group  of  solid  hydrocarbons  of  the  marsh  gas  series, 
melting  at  140°  F. 

Bog-butter,  found  in  the  Irish  peat-mosses,  is  a  similar  body.  Another 
mineral  resembling  this,  found  in  New  South  Wales,  contained  80 '6  per 
cent.  C,  5-6  H,  5-5  N,  1-6  0,  and  67  of  ash. 

Vaseline  is  a  soft  substance  belonging  to  the  paraffin  series,  useful  for 
lubricating  purposes. 

Oil  of  Turpentine  and  Substances  allied  to  it. 

335.  Turpentine  is  the  generic  name  given  to  the  viscous  exudation 
obtained  by  incising  the  bark  of  various  species  of  pine.  Several  varieties 
of  turpentine  are  met  with  in  commerce,  of  which  the  two  best  known 
are  the  common  turpentine  which  is  obtained  from  the  Scotch  fir,  and 
Venice  turpentine  from  the  larch. 

These  are  both  solutions  of  colophony  or  common  resin  {C^^^O^  in 
the  essential  oil  of  turpentine  (Cj^H^g),  and  when  distilled,  yield  from  75 
to  90  per  cent,  of  resin,  which  remains  in  the  retort,  and  from  25  to  10 
per  cent,  of  the  essential  oil,  commonly  sold  as  spirits  of  turpentine. 

This  essence  of  turpentine  boils  at  320°  F.,  and  floats  upon  water  (sp. 
gr.  0-864:),  in  which  it  is  very  sparingly  soluble,  its  proper  solvents  being 
alcohol  and  ether.     Its  great  inflammability  renders  it  useful  as  a  fuel  for 

*  lli'ptane,  CyHj,,  obtained  by  distilling  the  exudation  of  the  Firms  sahiana  or  nut  pine 
of  California,  is  a  remarkable  example  of  a  paraffin  from  the  vegetable  kingdom.  It  is 
usfil,  under  the  nttwitoi  Ahietene,  as  a  substitute  for  benzene  in  removing  grease-spots,  &c. 


OIL  OF  TURPENTINE.  '  475 

lamps,  but  the  large  proportion  of  carbon  which  it  contains  causes  it  to 
bum  with  a  smoky  flame,  rendering  it  necessary  either  to  employ  lamps 
constructed  especially  to  afford  an  extra  supply  of  air  to  the  flame,  or  to 
mix  it  with  a  certain  proportion  of  alcohol.  Camphine  is  distilled  fron^ 
the  turpentine  of  the  Boston  pine. 

The  property  of  turpentine  to  dissolve  resinous  and  fatty  substances 
renders  it  exceedingly  useful  in  the  preparation  of  paints  and  varnishes, 
and  for  the  removal  of  such  substances  from  fabrics.  It  is  also  an  excel- 
lent solvent  for  caoutchouc. 

One  of  the  most  remarkable  features  of  this  essential  oil  is  the  facility  with  which 
it  changes  into  isomeric  or  metameric  modifications,  exhibiting  great  difl'erences  in 
their  pliysical  and  chemical  properties. 

When  heated  in  a  closed  vessel  to  about  480°  F.  for  some  hours,  oil  of  turpentine 
is  converted  into  two  isomeric  modifications  dinering  greatly  from  the  original  oil  in 
the  temperature  at  which  they  boil  ;  for  whilst  oil  of  turpentine  distils  over  entirely 
at  320°  F.,  one  of  these  modifications,  known  as  isoterebenthene,  boils  at  350°  F.,  and 
the  other,  metatcrebenthaie,  at  660°. 

When  digested,  in  the  cold,  with  a  small  proportion  of  oil  of  vitriol,  oil  of  turpen- 
tine yields  <crc5e«c  (CioHig)  and  colopJiene,  the  former  boiling  at  320°  F.,  but  dittering 
from  oil  of  turpentine  in  its  odour,  which  resembles  thyme,  and  in  its  want  of  action 
upon  polarised  light. 

Colophene  has  a  far  higher  boiling-point  (600°),  and  is  much  heavier  than  tui-pentine 
(sp.  gr.  0-940),  from  which  it  is  also  distinguished  by  its  indigo-blue  colour  when  seen 
obliquely,  though  it  is  colourless  by  directly  transmitted  light.  Moreover,  the  specific 
gravity  of  the  vapour  of  colophene  is  9  "52,  whilst  that  of  turpentine  is  476,  or  one- 
lialf  that  of  colophene,  rendering  it  probable  that  if  the  composition  of  turpentine  be 
CijHjg  (  =  2  volumes)  ;  that  of  colophene  is  f'2oH?2  (  =  2  volumes),  a  relation  expressed 
by  saying  that  colophene  is  polymeric  with  turpentine.  Colophene  is  also  obtained 
by  the  distillation  of  colophony. 

The  ordinary  oil  of  turpentine  appears  to  be  really  itself  a  compound  of  two  isomeric 
hydrocarbons,  for  when  hydrochloric  acid  gas  is  passed  into  it,  two  distinct  isomeric 
compounds  are  formed,  both  expressed  by  the  formula  CjqHij.HCI,  but  one  being  a 
solid,  and  the  other  a  liquid  even  at  0°  F. 

The  solid  compound,  which  is  known  as  artificial  camphor  or  hydrochlorate  ofdadyle, 
forms  white  prismatic  crystals  very  similar  to  camphor,  and  when  its  vapour  is  passed 
over  heated  quicklime,  the  latter  removes  the  hydrochloric  acid,  and  the  hydrocarbon 
known  as  camphilcnc  or  dadylc  (S^s,  a  piiic-torch)  is  obtained,  which  is  isomeric  with 
oil  of  turpentine,  but  boils  at  273°  instead  of  320°  F.,  and  is  without  any  action  upon 
polarised  light. 

The  liquid  compound  formed  by  the  action  of  hydrochloric  acid  upon  oil  of  tur- 
pentine is  called  hydrochlorate  of  peucyle  ;  arid  when  distilled  with  quicklime  yields 
terehilene  ov peucyle  {wevKri,  the  pine),  also  isomeric  with  oil  of  turpentine,  but  without 
action  on  polarised  light. 

Although  oil  of  turpentine  is  not  miscible  with  water,  it  is  capable  of  forming 
three  compounds  with  it  in  different  proportions.  When  the  oil  is  long  kept  in 
contact  with  water,  crystals  are  deposited  which  have  the  composition  CioHjg.SHjO  ; 
boiling  water  dissolves  these,  and  deposits  them  in  a  prismatic  form  on  cooling. 
The  crj'stals  fuse  at  about  217°  F.,  and  when  further  heated,  lose  a  molecule  of 
water,  yielding  another  crystalline  hydrate,  which  sublimes  without  alteration  at 
about  480°  F.  When  exposed  to  the  air,  this  hydrate  again  absorbs  a  molecule  of 
water. 

By  distilling  the  aqueous  solution  of  either  of  the  preceding  hydrates  with  a 
little  sul])huric  acid,  a  liquid  hydrate  smelling  of  hyacinths  is  obtained  ;  it  contains 
(Cj(,Hjg)oHoO,  and  is  called  terpinole. 

When  oil  of  turpentine  is  exposed  to  the  air,  it  slowly  becomes  solid, 
absorbing  oxygen,  and  becoming  converted  into  resinous  bodies.  Among 
these  bodifes  there  is  found  a  small  quantity  of  camphoi'ic  'peroxide, 
C^Hj^O^,  Avhich  undergoes  decomposition  in  contact  with  water,  yielding 
camphoric  acid  and  hydric  peroxide  j  CjqHj^O^  +  2HoO  =  Ci^HjijO^  -F  HgO,. 
This  explains  the  observation  that  old  oil  of  turpentine  exhibits  many  of 


476  '  .    ESSENTIAL  OILS.    •■ 

the  reactions  of  hydric  peroxide.  By  passing  air  and  steam  through  oil 
of  turpentine,  a  powerfully  oxidising  solution  containing  hydric  peroxide 
has  been  prepared  by  Kingzett,  and.  proposed,  under  the  name  of  Sanitas, 
for  disinfecting  purposes.  It  is  worthy  of  remark  that  the  leaves  of  the 
Eucalyptus  glohalus  (gum-tree  of  Australia),  so  much  esteemed  for  its 
sanitary  influence,  also  yield  an  oil  siiuilar  to  oil  of  turpentine,  which 
becomes  brown  and  resinous  when  exposed  to  air. 

Common  resin  or  colophony.* — This  substance  is  composed  of  two 
isomeric  acids  known  as  sylvic  and  piriic.  When  common  resin  is  treated 
with  cold  alcohol,  the  greater  portion  of  it  is  dissolved;  and  if  the  alcohol 
be  evaporated,  it  leaves  an  amorphous  substance,  which  is  pi7iic  acid; 
The  residue,  left  undissolved  by  cold  alcoholy  is  dissolved  by  hot  alcohol, 
and  deposited  in  colourless  prisms,  which  are  sylvic  acid.  These  acids 
have  the  composition  HC20H29O2.  The  pinate  and  sylvate  of  sodium 
obtained  by  dissolving  resin  in  solution  of  soda  or  sodium  carbonate,  are 
largely  used  in  the  manufacture  of  yellow  soap,  and  of  the  size  for  paper- 
makers.  By  distilUng  common  resin  with  the  aid  of  superheated  steam, 
it  is  obtained  nearly  free  from  colour. 

336.  The  terpenes  or  turpentine  series  of  hydrocarhons,  Q^^^_^. — Oil 
of  turpentine  is  the  representative  of  a  large  class  of  hydrocarbons,  derived 
like  itself  from  the  vegetable  kingdom.  All  the  individuals  of  this  group 
resemble  turpentine  in  their  liability  to  suffer  conversion  into  isomeric 
modifications,  in  their  solidification  by  absorption  of  oxygen  when  exposed 
to  the  air,  in  their  combination  with  water  to  form  crystalline  hydrate?, 
and,  above  all,  in  their  tendency  to  form  artificial  camphors  by  combining 
with  hydrochloric  acid. 

The  oils  of  bergamotte,  birch,  camomile,  cari'away,  cloves,  hops,  juniper, 
lemons,  orange,  parsley,  pepper,  savin,  tolu,  ihym.e,  and  valerian,  contain 
the  same  hydrocarbon  CjoH^g,  generally  accompanied,  in  the  natural  oil, 
by  the  product  of  its  oxidation,  bearing  a  relation  to  the  hydrocarbon 
similar  to  that  which  colophony  bears  to  turpentine.  Essential  oil  of 
poplar  is  a  di-terpene  CooHgg  • 

'J'liese  essential  oils  are  generally  extracted  from  the  flowers,  fruit, 
leaves,  or  seeds,  by  distillation  with  water,  the  portion  of  the  plant 
selected  being  suspended  in  the  still  by  means  of  a  bag  or  perforated 
vessel,  so  that  there  may  be  no  danger  of  its  being  scorched  by  contact 
with  the  hot  sides  of  the  still,  and  so  contaminating  the  distillate  with 
empyrcumatic  matters  (e/ATrvpcuw,  to  scorch).  The  water  which  distils  over 
always  holds  a  little  of  the  essential  oil  in  solution,  and  it  is  in  this  way 
that  the  fragrant  distilled  waters  of  the  druggist  are  obtained.  When  the 
essential  oil  is  present  in  large  proportion,  it  collects  as  a  separate  layer 
upon  the  surface  of  the  water,  from  which  it  is  easily  decanted.  The  oil 
which  is  dissolved  in  the  water  may  be  separated  from  it  by  saturating 
the  liquid  with  common  salt,  when  the  oil  rises  to  the  surface,  or  by 
shaking  it  with  ether,  which  dissolves  the  oil  and  separates  from  the 
water,  the  ethereal  solution  floating  upon  its  surface,  and  leaving  the  oil 
when  the  ether  is  evaporated. 

In  cases  like  that  of  jasmine,  where  the  delicate  perfume  of  the  flower 
would  be  injured  by  the  heat,  the  flowers  are  pressed  between  woollen 

•  Colophon,  a  city  of  Ionia,  whence  resin  was  obtained  by  the  Greeks. 


BALSAJkIS — RESINS.  477 

cloths  saturated  with  oil  of  poppy  seeds,  which  thus  acquires  a  powerful 
odour  of  the  flower. 

Carbon  disulphide  is  also  sometimes  employed  as  a  solvent  for  extract- 
ing the  essential  oils. 

Oil  of  peppermint  contains  menthene  (CjoHjg),  and  menthole  (CjoHgoO); 
essence  of  cedar-toood  contains  cedrene  (CigHg^). 

337.  CampJwrs. — Closely  allied  to  the  essential  oils  are  the  different 
varieties  of  camphor,  which  appear  to  be  formed  by  the  oxidation  of 
hydrocarbons  corresponding  to  the  essential  oils. 

Common  camphor  (CjoH^gO)  is  found  deposited  in  minute  crystals  in 
the  wood  of  the  Laurus  camphora  or  camphor  laurel,  from  which  it  is 
obtained  by  chopping  up  the  branches  and  distilling  them  with  water  in 
a  still,  the  head  of  which  is  filled  with  straw,  upon  which  the  camphor 
condenses.  It  is  purified  by  subliming  it  in  large  glass  vessels  containing 
a  little  lime. 

Camphor  passes  into  vapour  easily  at  the  ordinary  temperature  of  the 
air,  and  is  deposited  in  brilliant  octahedral  crystals  upon  the  sides  of  the 
bottles  in  which  it  is  preserved.  It  fuses  at  347°  F.,  and  boils  at  399°  F., 
and  is  very  inflammable,  burning  with  a  bright  smoky  flame.  It  is  some- 
times dissolved  in  the  oil  used  for  the  lamps  of  magic  lanterns,  to  increase 
its  illuminating  power.  Camphor  is  lighter  than  water  (sp.  gr.  0'996), 
and  whirls  about  upon  its  surface  in  a  remarkable  w\ay,  dissolving  mean- 
while ver}"-  sparingly  (1  part  in  1000),  alcohol  and  ether  being  its  appro- 
priate solvents. 

When  distilled  with  phosphoric  anhydride,  camphor  loses  a  molecule  of  water,  and 
yields  the  hydrocarbon  cyniene  (CiqHj^)  homologoiis  with  benzene.  Cymene  is  found 
in  the  oil  of  wild  thyme. 

Bor')i4;o  camphor  (Cj(,HjgO)  is  obtained  from  the  exudation  of  the  Dryobalanops 
camphora*  When  this  exiidation  is  distilled,  a  hydrocarbon  called  bornceiie  (Ci(,Hjg), 
isomeric  with  oil  of  turpentine,  first  passes  over,  and  afterwards  the  camphor,  which 
is  neither  so  fusible  nor  so  volatile  as  ordinary  camphor,  and  emits  quite  a  different 
odour  ;  it  also  crystallises  in  prisms  instead  of  octahedra,  and  may  be  converted 
into  ordinary  camphor. by  the  action  of  nitric  acid,  which  oxidises  2  atoms  of 
hydrogen,  CjoHigO  {Borneo  camjyhor)  -^.2  =  Ci^iqO  [Common  caviphor). 

The  Borneo  camphor  appeai-s  to  have  been  formed  by  the  combination  of  borneeue 
with  water,  for  if  this  hydrocarbon  be  distilled  with  solution  of  potash,  it  combines 
with  a  molecule  of  water,  and  is  converted  into  the  camphor.  On  the  other  hand, 
when  Borneo  camphor  is  distilled  with  phosphoric  anhydride,  it  loses  a  molecule 
of  water,  and  yields  borneene.  It  is  interesting  to  remark  that  this  hydrocarbon  is 
also  found  in  the  essential  oil  of  valerian. 

The  oil  of  campJwr,  which  accompanies  the  camphor  distilled  from  the  camohor 
laurel,  contains  an  atom  of  oxj-gen  less  than  common  camphor,  its  formula  being 

(CioHi6).20. 

338.  Balsams. — The  vegetable  exudations  known  as  balsams  are  mix- 
tures of  essential  oils  with  resins  and  acids  probably  produced  by  the 
oxidation  of  the  oils. 

Balsam  of  Peru  contains  an  oily  substance  termed  cinnameine 
(C27H06O4).  ^  crystalline  body,  styracine  (Cj^HgO),  a  crystalline  volatQe  acid, 
the  cinnamic  (CgHgO.,),  and  a  peculiar  resin. 

Balsam  of  tolu  also  contains  cinnamic  acid  and  styracine,  together 
with  certain  resins,  which  appear  to  have  been  formed  by  the  oxidation 
of  styracine. 

Storax,  also  a  balsamic  exudation,  contains  the  same  substances,  accom- 

*  The  fragrant  essence  of  lign-aloes  has  the  same  composition  as  Borneo  camphor. 


478  RESINS. 

panied  by  a  peculiar  hydrocarbon,  which  has  been  named  sty  role,  stijrolenf., 
or  cinnamene,  and  has  the  composition  CgHy.  This  liquid  is  characterised 
by  a  remarkable  change  which  it  undergoes  when  heated  to  about  400°  F. , 
being  converted  into  a  colourless  solid,  metastyrole,  which  is  polymeric 
with  styrole,  into  which  it  is  reconverted  by  distillation.  Styrole  is  also 
obtained  by  distilling  dragon's  blood  with  zinc-dust. 

339.  Fesitis. — Colophony  is  the  best  known  member  of  the  class  of 
resins,  which  are  generally  distinguished  by  their  resinous  appearance, 
fusibility,  inflammability,  burning  with  a  smoky  flame,  insolubility  in 
water,  and  solubility  in  alcohol. 

As  to  their  chemical  composition,  fchey  are  all  rich  in  carbon  and  hydro- 
gen, containing  generally  a  small  proportion  of  oxygen,  and  appear  to 
have  been  formed,  like  colophony  (page  474),  by  the  oxidation  of  a  hydro- 
carbon analogous  to  turpentine. 

Most  of  the  resins  also  resemble  colophony  in  their  acid  characters, 
their  alcoholic  solutions  reddening  blue  litmus  paper,  and  the  resins 
themselves  being  soluble  in  the  alkalies.  This  is  the  case  with  sandarach 
and  guaiacum  resin,  the  former  of  which  contains  three,  and  the  latter 
two,  resinous  acids. 

Copal  appears  to  contain  several  resins,  some  neutral  and  some  acid, 
and  is  distinguished  by  its  difficult  solubility  in  alcohol,  in  which  it  can 
be  dissolved  only  after  long  exposure  to  the  vapour  of  the  solvent ;  but 
if  it  be  exposed  to  the  air  for  some  time,  at  a  moderately  high  tempera- 
ture, it  absorbs  oxygen,  and  becomes  far  more  easily  soluble.  Copal  is 
readily  dissolved  by  acetone.  Animi  and  elemi  resins  are  somewhat 
similar  in  properties  to  copal.  AW.  these  resins  are  used  in  the  manu- 
facture of  varnishes. 

Guaiacum  resin  is  distinguished  by  its  tendency  to  become  blue  under 
the  influence  of  the  more  refrangible  and  chemically  active  (violet)  rays 
of  the  solar  spectrum,  as  well  as  under  that  of  certain  oxidising  agents, 
such  as  chlorine  and  ozone. 

Lac,  so  much  used  in  the  arts,  belongs  to  the  class  of  resins,  being  the 
exudation  of  certain  tropical  trees  punctured  by  an  insect.  In  its  crude 
natural  state,  encrusting  the  small  branches,  it  is  known  as  stick-la/;,  and 
has  a  deep  red  colour;  when  broken  ofi"  the  branches  and  boiled  with 
water  containing  sodium  carbonate,  it  furnishes  a  red  colouring  matter  very 
largely  used  in  dyeing,  leaving  a  resinous  residue  termed  seed-lac,  by  fusing 
which  the  shell-lac  is  obtained.  This  resin  is  very  complex,  containing 
several  distinct  resinous  bodies.  It  is  largely  used  in  the  manufacture  of 
hats,  of  sealing-wax,  and  of  varnishes.  The  lacquer  applied  to  brass  derives 
its  name  from  this  resin,  being  an  alcoholic  solution  of  shell-lac,  sandarach, 
and  Venice  turpentine.  Indian  ink  is  made  by  mixing  lamp-black  with 
a  solution  of  100  grains  of  lac  in  20  grains  of  borax  and  4  ounces  of  water. 

Drar/on's  hlood  is  a  resin  from  a  plant  of  the  Lily  tribe  {Dracosna 
draco)  ;  it  gives  a  red  solution  in  alcohol^  which  is  used  in  lacquering. 

Amber,  a  fossil  resinous  substance,  more  nearly  resembles  this  class  of 
l»odies  than  any  other,  and  contains  several  resinous  bodies.  It  is  distin- 
guished by  its  insolubility,  for  alcohol  dissolves  only  about  one-eighth, 
and  ether  about  one- tenth  of  it.  After  fusion,  however,  it  becomes  soluble 
in  alcohol,  and  is  used  in  this  state  for  the  preparation  of  varnishes. 

The  distinguishing  peculiarity  of  amber  is,  that  it  yields  succinic  acid, 
H./'^H^O^  {succinutn,  amber),  when  digested  with  alkalies,  distilled,  or 


BENZOIC  ACID. 


479 


oxidised  by  nitric  acid  ;  in  the  latter  case  ordinary  camphor  is  formed  at 
the  same  time. 

Succinic  acid  is  also  found  in  some  of  the  resins  of  coniferous  trees,  and 
in  the  leaves  of  the  wormwood.  As  calcium  succinate,  it  occurs  as  an 
exudation  from  the  stems  of  mulberry-trees.  It  is  among  the  products 
of  the  action  of  nitric  acid  upon  most  fatty  and  waxy  substances,  and  is 
present  in  wines  and  other  fermented  liquors,  being  produced  during  the 
fermentation  of  sugar.  The  acid  is  characterised  by  the  cough-provoking 
vapour  which  it  emits  when  heated.* 

Varnishes  are  prepared  by  dissolving  resins  in  alcohol,  or  wood-spirit, 
or  acetone,!  a  little  turpentine  or  some  fixed  oil  being  added  to  prevent  the 
resin  from  cracking  when  the  solvent  has  evaporated.  In  order  to  promote 
the  solution  of  the  resin,  it  is  usually  powdered  before  being  treated  with 
the  solvent,  and  mixed  with  coarsely-powdered  glass  to  prevent  it  from 
becoming  lumpy.  Methylated  spirit  is  now  very  generally  used  for  the 
preparation  of  varnishes  ;  it  is  simply 
si^irit  of  wine,  to  which  a  little  wood 
naphtha  has  been  added,  to  deter 
persons  from  drinking  it,  and  to  pre- 
vent other  frauds  upon  the  Excise. 

Benzoin,  or  gum  benzoin,  as  it  is 
erroneously  called,  is  also  a  vegetable 
resinous  product,  and  is  distinguished 
by  the  presence  of  benzoic  acid 
(HC-HgOg),  which  may  be  obtained 
from  it  by  heating  the  resin  in  an 
iron  or  earthen  vessel  (fig.  281:) 
covered  with  a  perforated  sheet  of 
stout  paper,  over  which  a  drum  or  cone 
of  paper  is  tied.  "When  the  heat  of  a 
sand-bath  is  applied,  benzoic  acid  rises  in  vapour,  and  is  condensed  in 
beautiful  feathery  crystals  in  the  paper  drum.  It  may  also  be  extracted 
by  boiling  the  resin  with  water  and  lime,  when  the  benzoic  acid  is  dis- 
solved in  the  form  of  calcium  benzoate  Ca(C7H.0.2).2.  and  being  but 
sparingly  soluble  in  water,  may  be  precipitated  by  addmg  hydrochloric 
acid  to  the  filtered  solution. 

Benzoic  acid  is  generally  recognised  by  its  feathery  appearance  and 
peculiar  agreeable  odour,  though  this  does  not  really  belong  to  the  acid, 
but  to  a  little  essential  oil  which  is  not  easily  separated ;  the  vapour  of 
the  acid  itself  is  very  irritating,  and  produces  coughing.  It  fuses  when 
moderately  heated,  and  burns  with  a  smoky  flame.  Benzoic  acid  dissolves 
in  about  200  parts  of  cold  and  25  parts  of  boiling  water.  Alcohol  and 
ether  dissolve  it  easily. 

The  salts  of  benzoic  acid,  or  henzoates,  have  no  practical  importance, 
but  the  behaviour  of  benzoic  acid  when  distilled  with  an  excess  of  lime 
or  baryta  has  already  been  referred  to  as  furnishing  the  important  hydro- 
carbon, benzene  (see  page  468). 

*  Succinic  acid  has  been  obtained  artificially  by  the  action  of  potassium  cyanide  upon  a 
solution  of  chloropropionic  acid — 

CsHgCIO.,  +  KCN  +  2H2O  =  C4Hfi04  +  KCl  -H  NH3 
Chloropropionic.  Succinic. 

"t*  Acetone  readily  dissolves  copal,  mastic,  and  sandarach. 


Fig.  284. 


480  OIL  OF  BITTER  ALMONDS. 

Oil  op  Bitter  Almonds  and  irs  Derivatives. — Benzoyle  Series, 

340.  Benzoic  acid  results  from  the  oxidation  of  the  essential  oil  of 
hitter  almonds  (C^HgO),  which  slowly  absorbs  an  atom  of  oxygen  from 
the  air,  and  is  converted  into  benzoic  acid  (C-HgOg). 

The  formiition  of  the  essential  oil  of  bitter  almonds  is  one  of  the  most 
interesting  processes  of  vegetable  chemistry. 

Both  the  bitter  and  the  sweet  almond  contain  a  large  quantity  of  a 
fixed  oil,  which  may  be  extracted  from  them  by  pressure,  but  which  has 
no  particular  taste  or  odour,  and  differs  entirely  from  the  essential  oil  of 
bitter  almonds,  being,  in  fact,  very  similar  to  ordinary  olive  oil.  The 
residue,  or  almond-cake,  which  is  left  after  expressing  the  oil,  contains,  in 
the  case  of  the  bitter  almond  only,  a  bitter  principle,  amounting  to  about 
^^^th  of  the  weight  of  the  almond,  which  may  be  extracted  from  the  cake 
by  hot  alcohol,  and  may  be  crystallised  from  the  solution;  this  substance 
is  called  amygdaline,  and  is  represented  by  the  formula  CjoHgyiS'Oji,  the 
crystals  containing,  in  addition,  3  molecules  of  water. 

Now,  if  the  residue  left  after  extracting  the  amygdaline  with  alcohol 
be  mixed  with  water  and  distilled,  it  does  not  yield  any  essential  oil, 
although  this  may  be  obtained  in  abundance  from  the  original  cake  after 
maceration  in  water,  particularly  if  it  be  digested  with  water  for  several 
hours  before  distillation. 

The  sweet  almond,  which  contains  no  amygdaline,  does  not  afford  any 
essential  oil  when  distilled  with  water,  showing  that  the  amygdaline  is 
really  the  source  of  the  essence.  Again,  if  boiling  water  be  poured  over 
the  bitter  almond  cake,  no  essential  oil  is  produced,  even  when  the  mix- 
ture is  allowed  to  stand  for  some  time,  but  if  to  this  mixture  there  be 
added  an  emulsion  of  sweet  almonds  prepared  with  cold  water,  the  bitter 
almond  oil  is  at  once  formed,  which  is  not  the  case,  however,  if  the  emul- 
sion be  prepared  with  boiling  water. 

From  this  it  is  evident  that  a  substance  exists  in  both  sweet  and  bitter^ 
almonds  which  is  capable  of  developing  the  essence  from  the  amygdaline 
contained  in  the  latter,  but  which  loses  its  power  when  acted  upon  by 
hot  water.  This  may  be  still  further  proved  by  dissolving  pure  amygda- 
line in  water,  and  adding  an  emulsion  of  sweet  almonds,  when  the  essence 
is  at  once  produced. 

When  the  emulsion  of  sweet  almonds  is  filtered  and  mixed  with  alcohol, 
a  white  substance  resembling  albumen  is  precipitated,  which  contains 
carbon,  hydrogen,  nitrogen,  and  oxygen,  and  very  easily  putrefies  when 
exposed  to  the  air  in  a  moist  state.  If  this  substance,  which  is  called 
emulsine  or  synaptase  (trwarrTO),  to  bring  into  action),  be  dissolved  in  cold 
water,  and  mixed  with  a  solution  of  amygdaline,  the  oil  of  bitter  almonds 
is  soon  formed  in  abundance,  but  if  the  solution  of  emulsine  be  boiled,  it 
is  no  longer  capable  of  developing  the  essence.  On  examining  the  solu- 
tion of  amygdaline  in  which  the  essential  oil  has  been  produced  by  the 
action  of  enndsine,  it  is  found  to  contain,  in  addition,  hydrocyanic  acid 
(CHN),  grape-sugar  (CgHj^O-),  and  formic  acid  (CH2O2),  so  that  the 
decomposition  may  be  thus  represented — 

2C2oH.,.XOii  =  iC^Yi^O  +  2CHN  +  CgHi^O.  -i-  4CH2O2  +  3H2O. 

Aa,yKdaline.         Bltter^alraond      Hydrocyanic      o^ape  sugar.        Formic  add. 

The  formation  of  the  essential  oil  of  bitter  almonds  must  be  regarded, 
therefore,  as  dependent  upon  a  species  of  fermentation  or  metamorphosis 


BENZOYLE  SERIES.  481 

of  the  bitter  prindple  amygdaline,  induced  by  contact  with  an  albuminous 
substance,  eraulsine,  itself  very  prone  to  undergo  decomposition  when 
exposed  to  air  in  the  presence  of  moisture. 

This  essential  oil  may  also  be  obtained  from  laurel  leaves,  and  from  the 
kernels  of  most  stone  fruit. 

When  the  oil  of  bitter  almonds  is  distilled  over,  it  is  accompanied  by 
the  hydrocyanic  acid  formed  at  the  same  time,  and  it  is  this  which 
renders  the  ordinary  commercial  oil  so  powerful  a  poison,  for  if  it  be 
purified  by  distillation  with  a  mixture  of  lime  and  ferrous  chloride  (see 
Prussian  hhie),  which  retains  the  hydrocyanic  acid,  it  becomes  compara- 
tively harmless.  A  better  process  for  obtaining  the  pure  oil  of  bitter 
almonds  consists  in  shaking  the  crude  oil  with  an  equal  volume  of  a 
strong  solution  of  hydrosodic  sulphite  (NaHSOj),  with  which  it  forms  a 
white  crystalline  compound.  If  this  be  distilled  with  solution  of  sodium 
carbonate,  the  pure  oil  passes  over. 

The  poisonous  properties  of  laurel-water,  and  similar  preparations,  are 
also  due  to  the  presence  of  hydrocyanic  acid. 

The  crude  essential  oil  of  bitter  almonds  also  contains  a  crystalline  substance  called 
hcnzoinc  {C\^ifi.^,  whicli  is  interesting  as  being  polymeric  with  the  essence,  into 
which  it  ma}'  be  converted  by  passing  its  vapour  through  a  red  hot  tube.  The  crude 
oil  may  be  entirely  converted  into  this  substance  by  shaking  it  with  an  alcoholic 
solution  of  potash. 

When  tlie  pure  essential  oil  of  bitter  almonds  (C^HgO)  is  acted  upon  by  dry 
chlorine,  it  evolves  hydrochloric  acid,  and  becomes  converted  into  a  colourless  liquid, 
having  an  odour  of  horse-radish,  and  containing  C^HjClO,  an  atom  of  hydrogen 
having  been  removed,  and  its  place  filled  by  an  atom  of  chlorine.  If  this  liquid  be 
acted  upon  by  the  bromides,  iodides,  cyanides,  or  sulphides  of  the  metals,  the 
chlorine  is  removed  in  its  turn,  the  vacancy  being  filled  up  by  bromine,  iodine, 
cyanogen  or  sulphur,  compounds  being  obtained  which  have  the  formulse — 

C-HjBrO,  C-HjIO,  C^HgCyO,  (C7H50).,S . 

When  boiled  with  water,  this  chlorine  compound  is  converted  into  benzoic  acid — 

CyHgClO  +  H,0  =  C7H5O2.H  +  HCl. 

On  comparing  the  composition  of  these  compounds  with  that  of  the  essential  oil 
from  which  they  are  derived,  our  attention  is  called  to  the  existence  of  C7H5O  in 
all  of  them — 

Oil  of  bitter  almonds,         .         {C^\{fi)R 

Benzoic  acid,     .         .         .         (C-H50)H0 

Chlorine  compound,  .         (CyHgOiCl 

Bromine        „  .         .         (C7H50)Br,  &c. 

This  circumstance  led  many  chemists  to  assume  the  existence  in  these  compounds 
of  the  radical  bcnzoyla  (CVHgO),  capable  of  playing  the  part  of  an  elementary  sub- 
stance in  uniting  with  oxygen,  chlorine,  &c. ,  and  therefore  resembling  the  elements 
iu  its  chemical  tendencies,  from  which  resemblance  it  is  spoken  of  as  a  quasi-element 
or  compound  radical. 

The  radical  benzoyle  itself  has  been  recently  obtained  in  a  separate  state  by  the 
action  of  sodium  on  benzoyle  chloride.  It  forms  prismatic  crystals,  which  fuse 
easily,  and  may  be  sublimed  without  decomposition.  They  are  sparingly  soluble  in 
alcohol  and  ether.  The  formula  C^HgO  should  be  doubled  to  express  correctly  a 
molecule  of  this  radieal  (see  Alcohol  radicals). 

It  will  be  noticed  that  benzoic  anhydride  is  not  included  in  the  above  enumeration 
of  the  benzoyle  series.  This  compound,  which  may  be  represented  as  Bz^O,  or 
(CVHgO).^©,  is  obtained  by  heating  sodium  benzoate  with  benzoyle  chloride — 

NaBzO  +  BzCl  =  XaCl  +  Bz,0 . 
This  substance  has  no  acid  properties  whatever.     It  does  not  dissolve  in  cold  water, 
but  if  boiled  with  water,  is  slowly  converted  into  benzoic  acid. 

When  oil  of  bitter  almonds  is  decomposed  by  potassium  hydrate  dissolved  in 
alcohol,  it  yields  benzoic  alcohol  (CyHgO),  which  will  be  more  particularly  noticed 

2  H 


482  GLUCOSIDES. 

hereafter.     When  heated  with  strong  hydriodic  acid,  bitter  almond  oil  ia  converted 
into  toluene  C^Hg. 

341.  Very  closely  connected  with  the  essential  oil  of  bitter  almonds  are  the  essences 
of  cinnamon  and  cassia,  which  consists  chieHy  of  an  oxidised  essence,  represented 
by  the  formula  CjjHgO,  and  convertible  by  boiling  with  nitric  acid  into  the  essence 
of  almonds.  By  heating  the  essence  of  cinnamon  with  caustic  potash,  it  is  oxidised 
and  converted  into  jwtassium  cinnaniate — 

CgHgO  (Oil  of  ciniMtnctn)  +  KHO  =  KCgH^O.^  (Potassium  cinnaiyiate)  +  Hj. 

On  dissolving  this  salt  in  water,  and  adding  an  acid,  the  cinnamic  acid  is  precipi- 
tated in  feathery  flakes,  closely  resembling  benzoic  acid,  both  in  appearance  and 
themical  characters.* 

The  same  reasons  exist  as  in  the  case  of  the  benzoyle  series,  for  assuming  the 
existence,  in  the  compounds  derived  from  oil  of  cinnamon,  of  the  radical  einnamyle, 
CjjHyO,  so  tliat  the  oil  of  cinnamon  would  be  einnamyle  hydride  (CgH^O)}!,  and 
cinnamic  acid  the  einnamyle  hydrate  (C9H70)HO. 

Essential  oil  of  cuviin  is  a  mixture  of  the  hydrocarbon  cymene  (CiftHi4),  which  has 
been  already  noticed,  with  an  oxidised  essence,  C^oHjoO,  which  is  closely  analogous 
to  those  of  almonds  and  cinnamon,  and  is  called  cumyle  hydride  (CioHuOjH  ;  when 
acted  upon  by  oxidising  agents  it  yields  cuminic  acid  (HCjoHjiOj,),  which  resembles 
benzoic  acid,  but  is  cliaracterised  by  an  odour  similar  to  that  of  the  bug.  From 
cumyle  hydride  an  oily  compound  has  been  obtained,  which  is  polymeric  with  the 
supposed  radical  cumyle,  having  the  composition  C20H22O2,  and  that  it  is  re^illy  com- 
posed of  a  double  molecule  of  that  radical  is  rendered  very  probable  by  its  behaviour 
when  fused  with  potash,  its  hydrogen  converting  one  molecule  of  cumyle  into  cumyle 
hydride,  whilst  its  oxygen  converts  the  other  into  cuminic  acid;  C3oH220«  +  KHO 
=  (C,„H„0)H  +  K(C,oHnO)0. 

The  essential  oils  oi  aniseed,  fennel,  and  tarragon  contain,  in  addition  to  a  hydro- 
carbon isomeric  with  turpentine,  a  solid  crystalline  oxidised  essence  (CioHiaO) 
isomeric  with  cumyle  hydride.  That  this  substance  is  not  cumyle  hydride,  however, 
is  at  once  proved  by  the  action  of  oxidising  agents,  which  convert  it  into  anisyle 
hydride  (CgHyO.j)!!,  and  anisic  acid  HC^H703,  the  latter  being  isomeric  with  winter- 
green  oil  (see  page  472). 

342.  Salicinb  and  its  Derivatives — Glucosides. — Oil  of  spircea,  <k 
meadow  siceet,  consists  chiefly  of  the  compound  (C^HgOg)  isomeric  with 
benzoic  acid;  this  compound  is  easily  obtained  artificially  by  the  oxida- 
tion of  salidne,  a  bitter  substance  extracted  from  willow  bark,  by  boiling 
it  in  water,  removing  the  colouring  matter  and  tannin  from  the  solution 
by  boiling  with  lead  hydrate,  precipitating  the  excess  of  lead  by  hydro- 
sulphuric  acid,  and  evaporating  the  filtered  liquid,  when  the  salicine 
crystallises  out,  and  may  be  obtained,  by  recrystallising  from  alcohol,  in 
beautiful  white  needles  having  the  composition  CjgH^gO-.. 

Salicine  is  sparingly  soluble  in  cold  water  and  insoluble  in  ether,  but 
dissolves  readily  in  boiling  water  and  in  alcohol.  It  is  readily  distin- 
guished by  the  red  colour  which  it  gives  with  concentrated  sulphuric  acid, 
which  manifests  its  presence  when  applied  to  the  inner  bark  of  the  willow. 
When  distilled  with  dilute  sulphuric  acid  and  potassium  dichromate,  it 
yields  the  oil  of  spiraea. 

The  changes  suffered  by  salicine  when  boiled  with  a  dilute  mineral  acid  (as  snl- 
phuric)  are  very  remarkable,  for  after  the  boiliug  has  been  continued  for  a  few 
minutes,  the  solution  is  found  to  contain  grape-sugar,  together  with  a  crystalline 
substance  called  saligenine,  which  is  distinguished  by  the  intense  blue  colour  which 
it  ijives  with  ferric  chloride.  The  change  is  easily  explained,  for  the  addition 
of  2  molecules  of  water  to  salicine  would  provide  the  elements  of  grape-sugar  and 
Kiiligenine  ;  OisHigOy  -t-  2H2O  -  C^HsOj  +  G^\{^^0^. 
Salicine.  Salij^enine.      Grape -supar. 

Emulsine  or  synaptase  is  capable  of  effecting  this  change  in  salicine,  and  it  will 
be  remembered  that  grape-sugar  is  one  of  the  products  of  the  action  of  that  ferment 

*  Oil  of  bitter  almonds  ha-s  been  converted  into  cinnamic  acid  by  heating  it  with  acetic 
oxychloride  ;  C7H60-f-(C.^H50)Cl  =  C7H,(CaH30)0-t-HCL 


SALICYLE  SERIES.  483 

upon  amygdaline.  If  the  ebullition  of  the  diluted  acid  be  continued  for  a  length 
of  time,  the  liquid  deposits  a  resinous  substance,  salirctine,  which  is  isomeric  with 
oil  of  bitter  almonds  (CyHgO). 

A  very  striking  example  of  the  stability  of  types,  notwithstanding  the  substitution 
of  one  element  for  another,  is  found  in  the  circumstance  that  salicine,  under  the 
influence  of  chlorine,  yields  three  different  products  containing  chlorine  in  place 
of  hydrogen,  and  that  when  these  are  boiled  with  dilute  acids,  they  yield  other 
products  containing  chlorine,  and  bearing  the  same  relation  to  their  chlorinated 
primitive  wliich  saligenine  and  saliretine  respectively  bear  to  salicine. 

Thus  we  have — 


Salicine,    ....  Cj^Hig    q? 

Chlorosaliciue,    .     .  C^^^^  \  0^ 

Dichlorosalicine,      .  C^^p,^^  i  Oj 

Trichlorosalicine,    .  Cijp.i'  [  O7 


Saligenine C-Hg    O2 

Chlorosaligenine,      .     .     .  Cyp/  [  O2 

Dichlorosaligenine,        .     .  C;.^^  |  0.^ 

Trichlorosalagenine,      .     .  C^Tr,"  [  O2 


When  salicine  is  fused  with  potassium  hydrate,  the  mass  dissolved  in  water,  and 
hydrochloric  acid  added,  beautiful  needles  of  salicylic  acid  (HC7H5O3),  are  separated. 
This  acid  may  also  be  obtained  from  the  oil  of  spiraea  by  a  similar  process,  and  it 
will  be  seen  that  salicylic  acid  bears  the  same  relation  to  this  oil  as  benzoic  acid  bears 
to  oil  of  bitter  almonds — 

Oil  of  bitter  almonds,         C7H5O  |         Oil  of  spiraea,    .  .         CvHgO., 

Benzoic  acid,     .         .         C-HgOo        |        Salicylic  acid,  .         .         C-HgOs. 

Salicylic  acid  has  been  found  in  the  leaves,  stems,  and  rhizomes  of  some  of  the 
Violacea;. 

Salicylic  acid  is  now  prepared  from  phenole  (carbolic  acid) ;  one  molecular  weight  of 
crystallised  phenole  is  dissolved  in  a  strong  solution  of  one  molecular  weight  of  sodium 
hydrate;  CgHgOH  +  NaOH  =  CgH50Xa  +  HOH.  The  resulting  solution  of  sodium- 
phenole  is  evaporated  to  complete  dryness,  the  solid  transferred  to  a  retort,  heated  to 
100°  C,  and  a  slow  stream  of  CO2  passed  over  it,  the  temperature  being  raised,  after 
many  hours,  to  1 80°  C.  Phenole  then  distils  over,  and  continues  to  do  so  till  the 
temperature  has  risen  to  250°  C. ,  when  di-sodium  salicylate  remains  in  the  retort  ; 
2CfiHgONa  +  CO2  =  C7H4Na203  +  CgHgOH. 

The  sodium  salt  is  dissolved  in  water  and  decomposed  by  hydrochloric  acid,  when 
the  salicylic  acid  is  precipitated. 

On  account  of  its  easy  decomposition  into  CO.,  and  phenole,  salicylic  acid  has  been 
recommended  as  an  antiseptic,  since  it  is  inodorous,  nearly  tasteless,  and  not  poison- 
ous in  moderate  doses.* 

Salicylic  acid  is  an  example  of  a  vwnobasic  diatomic  acid.  It  forms  two  sodium 
salts,  Na.2C7H403  and  NaC^HjOa.  But  the  constitution  of  salicylic  acid  is  CgH4.0H. 
COOH,  showing  that  it  contains  only  one  oxatyle  group  (COOH)  upon  Avhich  the 
basicity  of  an  acid  depends.  Hence  the  nonnal  sodium  salicylate  is  Cgll^.  OH.  COONa, 
and  the  salt  containing  Na,  is  a  basic  salt,  CgH4.  ONa.  COONa. 

Lactic  acid,  CJl^.  OH.  COOH,  is  another  example  of  the  same  kind,  the  normal  sodium 
lactate  being  C2H4. OH. COONa,  and  the  di-sodium  salt  C2H4. ONa. COONa. 

Exactly  as  chemists  have  been  led  to  consider  the  bitter  almond  oil  as  benzoyle 
hydride,  so  they  have  regarded  oil  of  spiraia  as  salicyle  hydride  (C7H5O.2.H),  assum- 
ing the  existence  of  the  radical  salicyle  (C7Hg02),  of  which  salicylic  acid  would  be 
the  hydrate.  We  find  this  view  of  the  constitution  of  these  compounds  supported  by 
the  circumstance,  that  when  the  oil  of  spiraea  is  heated  with  benzoyle  chloride,  a  sub- 
stance is  obtained  which  may  be  regarded  as  composed  of  the  two  radicals  salicyle 
and  benzoyle  ;  C7H502H  +  C7H,O.Cl  =  C7HgO.C7Hg02  +  HCl. 
Oil  of  spirsea.       pfjoride*       Benzoyle-salicyle. 

From  a  careful  study  of  the  behaviour  of  salicine  under  the  action  of  various  re- 
agents, the  inference  has  been  drawn  that  it  is  a  compound  of  saligenine  (C7H8O.2) 
with  a  substance  (CgHioO,)  which  becomes  converted  into  grape-sugar,  by  assimila- 
tion of  water,  as  soon  as  it  is  separated  from  the  saligenine. 

Salicine  is  occasionally  employed  in  medicine  as  a  febrifuge,  and  is  a 
common  adulteration  of  quinine. 

*  Much  of  the  commercial  salicylic  acid  consists  of  sodium  salicylate. 


484  CONIFERINE — VANILLINE. 

Salicine  is  the  chief  member  of  the  class  of  substances  termed  gluco- 
aides,  from  the  presence  of  grape-sugar  (glucose)  among  their  products  of 
decomposition.  To  this  class  belong  several  other  substances  ranch  re- 
sembling salicine,  and,  like  it,  extracted  from  the  barks  of  different  trees. 

Conifcrine,  Ci8Hj,08.2Aq.,  is  a  crystalline  glucoside  contained  in  the  glutinous 
liquid  {cambium)  found  in  spring  between  the  inner  and  outer  barks  of  coniferous 
trees.  With  strong  sulphuric  acid  it  gives  a  violet  colour  changing  to  red,  the  red 
solution  depositing  a  blue  resin  on  addition  of  '.vater.  When  heated  with  diluted 
acids,  it  yields  glucose  and  a  resinous  substance.  If  coniferine  be  kept  in  contact 
with  water  and  a  little  emulsine  (p.  480)  at  a  temperature  of  170"  to  190°  F.,  it  splits 
up  into  glucose'  and  a  white  crystalline  precipitate  which  dissolves  on  shaking  with 
ether,  and  may  be  obtained  b}'  evaporating  the  ethereal  solution.  This  substance  has 
the  formula  Ci„Hi203,  and  its  formation  from  coniferine  is  expressed  by  the  equation — 

C,fiH.^.jOg  -I-   HjO   =  C^Hj^Og   +   C10TI12O3. 
Coniferine.  Glucose. 

When  the  crystalline  body  is  exposed  to  the  air  it  exhales  the  odour  of  vanilla. 
On  distilling  it  with  potassium  dichromate  and  sulphuric  acid,  aldehyde  pas.ses  over, 
followed  by  an  aqueous  liquid  from  which  ether  extracts  a  crystalline  body  having  the 
composition  CgHgOs,  and  identical  with  vanilline,  which  constitutes  the  aroma  of 
vanilla,  and  is  often  seen  covering  the  surface  of  vanilla-pods  with  small  crystals. 

The  conversion  of  the  product  of  the  fermentation  of  coniferine  into  vanilline  is 
represented  thus  ;  CjoHi-^Oa -f  0  =  C2H4O  {aldehyde) +  QgHg03  {vanilline). 

Vanilline  fuses  at  ITd""  F.,  and  sublimes  unchanged.  It  was  formerly  mistaken  for 
benzoic  acid,  for  it  is  sparingl}'  soluble  in  water,  but  readily  soluble  in  alcohol  and 
ether.     It  is  also  strongly  acid,  and  forms  well-defined  salts.* 

The  artificial  production  of  vanilline  from  so  abundant  a  source  is  of  considerable 
importance,  since  vanilla-pods  are  imported  into  this  country  at  a  high  price  from 
Mexico,  being  the  seed-vessel  of  an  orchidaceous  plant  ( Vanilla  planifolia). 

Coumarinc,  CgHsCj,  is  the  substance  which  causes  the  smell  of  hay  and  of  the 
Tonka  bean  (Coumaroma  odorata),  from  which  it  may  be  extracted  by  boiling  with 
alcohol,  when  crystals  of  coumarine  are  deposited  on  cooling.  It  has  been  obtained 
artificially  from  the  oil  of  meadow  sweet,  salicyle  hydride,  by  treating  it  with  sodium, 
and  decomposing  the  sodium-salicylide  with  acetic  anhydride — 

NaCyHjOj     +     (C.,H30).p     =     NaC^HaOj.      -t-     C^HjO.  C7HA ; 
Sodium  gaiicylide.      Acetic  anliydride.      Sodium  acetate.  Acetyle-salicylide. 

and  CaHjO.C^HjOa  =  H^O   +  CgHfiOj 
Coumarine. 

343.  Populine  {C^H^fig)  is  a  sweet  crystalline  substance  obtained  from  the  bark 
and  leaves  of  the  aspen,  and  especially  interesting  from  its  close  connexion  with  the 
benzoyle  and  salicyle  series  ;  for  when  boiled  with  solution  of  baryta,  it  is  decom- 
posed into  benzoic  acid  and  salicine — 

2C,,Uofig  +   Ba(H0)2  =   Ba(C7H502).,  -h2C,3H,807 
Populine.  Barium  benzoate.        Salicine. 

Xor  is  this  the  only  connecting  link,  for  populine  yields  oil  of  spirsea  when  distilled 
with  sulphuric  acid  and  potassium  dichromate,  and  when  boiled  with  dilute  acids  it 
furnishes  benzoic  acid,  saliretine,  and  grape-sugar — 

CaoH-vjOg   -I-   2H2O  =   HC^HjO.,   -f-,   C^HsO   +   ChHj^O, 
Populine.  Benzoic  acid.      Saliretine.       Grape-sugar. 

In  order  to  explain  this  production  of  benzoyle  and  salicyle  compounds  from  populine, 
it  is  usual  to  regard  this  substance  as  formed  from  salicine  (C13HJ8O7)  by  the  introduc- 
tion of  benzoyle  (C^HjO),  in  the  place  of  an  atom  of  hydrogen — 

C^H^Og  =  C„H,,(C7H50)0, 
Populine.  Benzoyle-salicine. 

Phloridzine  {C^^^O^^)  is  extracted  from  the  bark  of  the  apple,  pear,  plum,  and 
cherry  tree  ;  it  crystallises  readily,  is  slightly  bitter,  and  when  boiled  with  dilute 
acids,  yields  grape-sugar  and  a  resinous  substance  called  phloretine  (C15H14O5).     Its 

*  For  further  information  respecting  the  constitution  and  structural  fornmlaof  vanilline, 
see  Proceedings  of  the  Royal  Society,  xxii.  p.  398. 


ALLYLE  SERIES.  485 

most  interesting  property  is  that  of  forming  a  red  cojnpound  {■pMoridzeinc)  when 
exposed  to  the  joint  influences  of  air  and  ammonia — 

C01H24O10  (Phloridzine)   +   O3   +   2NH3  =   CaiHaoNjOia  {Phloridzeine). 

This  red  compound  combines  with  ammonia  to  form  a  purple  mass  with  a  coppery- 
lustre,  which  dissolves  in  water  with  a  fine  blue  colour.  The  production  of  this 
colouring  matter  from  phloridzine  is  an  excellent  example  of  that  conjoined  action  of 
air  and  ammonia  by  which  certain  natural  coloiiring  matters,  such  as  litmus,  are 
formed  from  substances  w'hich  are  themselves  destitute  of  colour. 

Quercitrine  (C3;,H3q07)  is  the  yellow  colouring  matter  extracted  by  alcohol  from 
the  bark  of  the  quercitron.  It  is  a  crystallisable  substance,  and  is  decomposed  by 
boiling  with  acids  into  grape-sugar  and  a  yellow  crystalline  body  called  quercetine 
(CorHisOio). 

Esculine  (C.21H24O13)  is  extracted  from  the  bark  of  the  horse-chestnut  bj'  boiling 
water.  If  the  tanniu  and  colouring  matter  be  precipitated  from  the  infusion  by 
lead  acetate,  the  filtered  liquid  treated  with  hydric  sulphide  to  remove  the  excess  of 
lead,  and  the  solution,  after  a  second  filtration,  evaporated,  the  esculine  is  obtained 
in  colourless  needles.  It  is  remarkable  for  its  fluorescence  ;  although  its  solution  is 
colourless  by  transmitted  light,  it  appears  of  a  beautiful  deep  blue  colour  when 
viewed  at  certain  angles.  This  substance  is  also  a  glucoside,  for  when  boiled  with 
dilute  acids,  it  yields  grape-sugar  and  a  crystalline  substance  known  as  esculetine  ; 
C.,iH.,,0i3  +  5H2O  =  CgHfiOj  +  2CsR,fiT 
Jisculine.  Esculetine.        Grape-sugar. 

Paviine  also  occurs  in  the  horse-chestnut  bark,  but  in  a  far  larger  quantity  in  the 
bark  of  the  ash.     It  is  distinguished  from  esculine  by  exhibiting  a  green  fluorescence. 

Hesperidine,  Cj-jHaeOja,  is  contained  in  the  fruit,leaves,  and  stalks  of  the  orange-tree 
and  other  members  of  the  same  family  ;  it  is  resolved  by  acids  into  glucose  and 
Jicsperctinc,  Ci5Hi40g. 

Saponine  is  a  substance  closely  allied  to  the  glucosides,  and  is  found  in  the  soap- 
wort,  the  fruit  of  the  horse-chestnut,  the  pimpernel,  the  root  of  the  pink,  and  in 
many  other  plants.  It  may  be  extracted  by  boiling  alcohol,  which  deposits  it  in  an 
amorphous  state  on  cooling.  Saponine  is  soluble  in  water,  and  its  solution  is  char- 
acterised by  the  readiness  with  which  it  lathers,  like  soap  and  water,  although  it 
may  contain  a  very  small  quantity  of  saponine.  This  property  leads  to  the  use  of 
decoctions  containing  it,  such  as  those  of  the  soap-wort  and  of  the  soap-nut  of  India, 
for  the  purpose  of  cleansing  certain  delicate  fabrics. 

Picrotoxine  (CsgH^oOig)  is  a  crystalline  substance,  to  which  the  poisonous  properties 
of  Cocculus  indicus  are  due.  It  appears  to  have  feeble  acid  tendencies,  and  is  ex- 
tracted from  an  acidified  solution  by  shaking  with  ether.  On  evaporating  the  ethereal 
solution  it  leaves  prismatic  needles  of  an  intensely  bitter  taste. 

344.  Essential  Oils  containing  Sulphur — Alltle  Series. — The 
essential  oils  of  asafoetida,  of  garlic,  Jiorse-radish,  JeeJcs,  mustard,  onions, 
and  radishes,  differ  from  those  which  have  been  already  described  by 
containing  sulphnr. 

Those  of  asafoetida,  garlic,  leeks,  onions,  and  radishes  are  composed 
essentially  of  the  same  substance,  represented  by  the  formula  CgH^QS. 
The  essence  of  mustard  and  that  of  horse-radish  are  composed  of  C^H^NS. 

The  chemistry  of  the  origin  of  essential  oil  of  mustard  is  analogous  to 
that  of  essence  of  almonds.  The  oil  is  obtained  from  the  seeds  of  the 
black  mustard  after  removing  the  fixed  oil  (which  has  no  pungency 
whatever)  by  pressure  ;  on  moistening  the  crushed  seed  with  water,  the 
production  of  the  essential  oil  is  indicated  by  its  peculiar  odour,  and  it 
may  be  separated  from  the  seeds  by  distillation.  The  mustard  seeds 
contain  a  salt  of  potash  with  a  peculiar  acid  called  myronic  acid* 
(HCiQHjgNS.20,Q),  together  with  a  substance  similar  to  the  emulsine  of 
almonds,  which  has  been  termed  myrosinp,  and  is  capable  of  inducing  the 
decomposition  of  the  mj'ronic  acid,  and  the  consequent  production  of 
essence  of  mustard,  just  as  the  emulsine  of  almonds  develops  the  essential 
*  From  nvpov,  an  unguent. 


486  ALLYLE  SEKIES. 

oil  by  the  decomposition  of  the  amygdaline ;  in  the  case  of  mustard,  how- 
ever, the  nature  of  the  decomposition  has  not  been  so  clearly  made  out, 
but  is  probably  represented  by  the  equation — 

KCjoHigNSaOio  =  C^H.NS  +  CgHj^O,  +  KHSO^. 

Potassium  myronate.  '^nms'ta^d"^  Glucose. 

The  essence  of  mustard  has  been  produced  artificially  in  a  very  inter- 
esting and  remarkable  manner. 

When  glycerine  (the  sweet  principle  of  the  fats  and  fixed  oils)  is  dis- 
tilled with  iodine  and  phosphorus,  a  colourless  ethereal  liquid  is  obtained, 
wliich  has  the  composition  C3H5I,  and  is  called  allyle  iodide,  because, 
when  distilled  with  sodium,  it  yields  sodium  iodide  and  a  volatile 
liquid  composed  of  (03115)2  and  called  di-cdlyle,  in  allusion  to  its  peculiar 
odour  {allium,  garlic).  The  formation  of  allyle  iodide  is  explained  by 
the  following  equation;  2C3H8O3  +  2PI2  =  2C3H5T  -1-  2H3PO3  +  l^. 

Glycerine,  Allyle  iodide. 

When  allyle  iodide  is  distilled  with  potassium  sulphocyanide,  an  oily 
liquid  is  obtained,  identical  in  properties  and  composition  with  oil  of 
mustard  or  allyle  sidphoearhimide,*  its  ai'tificial  production  being  thus 
explained ;  C3H5I   +   K(CNS)   =   KC3H5.CS    +    KI. 

.,,  ,    i   ,•  I  Potassium        Allyle  siilphocarbimide, 

Aijyie  loawe.  suipliocyanirte.  or  oil  of  mustard. 

Additional  interest  is  created  in  this  artificial  formation  of  oil  of  mus- 
tard when  it  is  found  to  be  convertible  into  oil  of  garlic,  by  being  heated 
with  potassium  sulphide,  when  potassium  sulphocyanide  is  formed  at  the 
same  time,  thus ;  2(N.C3Hg.CS)    +   K^S    =   (03X15)08   +   2K(0NS) 

Essence  of  mustard.  Essence  of  garlic.        J^-l^^^yaZde. 

Hence  it  is  inferred  that  the  essence  of  garlic  is  allyle  sidphide. 

The  oil  of  Cochlearia  officinalis  (scurvy-grass)  is  sometimes  sold  as 
essential  oil  of  mustard,  which  it  much  resembles ;  but  the  former  is 
butyle  sulphocyanide  O^Hg.CNS,  and  boils  at  160°  C,  whilst  the  latter 
boils  at  147°  0. 

A  considerable  number  of  compounds  are  included  in  the  allyle  series,  but  are  not 
at  present  possessed  of  any  practical  importance. 

The  allylic  alcohol  (CjHgHO)  is  interesting  as  the  prototype  of  a  new  class  of 
alcohols,  parallel  with  that  represented  by  common  alcohol  (C.2H5HO).  In  order  to 
obtain  it,  allyle  iodide  is  decomposed  by  silver  oxalate,  when  allyle  oxalate  is  obtained ; 
2C,H5l  +  AgsC20,= (C3H,)A04  +  2AgI. 

1?V  treating  allyle  oxalate  with  ammonia,  allylic  alcohol  and  oxamide  are  obtained ; 
(C3H5)oC,,04  +  2NH3  =  2C3HSHO  +  C.,H4N202. 
Allyle  oxalate.  Aliyiic  alcohol.    Oxamide. 

*  A  sidphocarhimide  is  metameric  with  a  sulphocyanide  ;  but  in  the  latter,  the  alcohol 
radical  is  combined  with  the  sulphur,  whilst,  in  the  former,  it  is  combined  with  the 
nitrogen.  Thus,  ethyle  sulphocyanide,  decomposed  by  potassium  hydrate,  yields  potassium 
sulphocyanide  and  ethyle  hydrate  (alcohol)  — 


«{g5?'  +  o|g=  Hex +  «{&''■ 


But  ethyle  sulphocarbimide  yields  ethylamine,  potassium  carbonate  and  potassium 
sulphide — 

n{  gf »  +  40|  g    =  N  I  ^^^  +  K,C03  +  K,S  +  H,0. 

The  name  sulphocarbimide  alludes  to  the  hypothetical  body  HNCS  (metameric  with 
hydric  sulphocyanide) ;  the  termination  iinide  being  often  applied  to  bodies  in  which  a 
.siuL'le  atom  of  H  is  united  to  N. 


GUM-RESINS.  487 

Allyle-alcohol  is  also  found  among  the  products  of  the  distillation  of  glycerine  with 
oxalic  acid. 

Allyleue  (C3H4),  the  olefiaut  gas  of  the  allyle  series,  is  homologous  with  acetylene, 
(CjHo),  and  much  resembles  it  in  its  chemical  relations.  It  has  been  prepared  by 
heating  chlorinated  propylene  in  a  sealed  tube  with  sodium-alcohol.  The  chlorin- 
ated propylene  is  a  product  of  the  action  of  phosphoric  chloride  upon  acetone  ; 
CsHfiO  {Acetone)  +  PCI5  =  CsHgCl  {Chlorinated propylene)  +  PCI3O  +  HCl ; 

CaHgCl  +  CiHsNaO  {Sodium-alcohol)  =031!^  (Allylene)  +  l<iaCl  + 0^0.^0  {Alcohol). 

By  its  action  on  ammoniacal  silver  nitrate,  it  yields  argentallylene,  CgHgAg. 
"When  sodium  is  heated  in  allylene,  carbon  and  hydrogen  are  liberated,  and  sodic 
acetylide  is  formed,  C3H4-l-Na.,=C,Na.,  +  0  +  H4,  a  little  propylene  (CaHg)  is  formed 
at  the  same  tin^e. 

By  heating  diallyle  tetrabromide  (CgHioBrj)  with  alcoholic  potash,  dipropargyle 
(CgHg)  is  obtained,  a  liquid  having  the  same  composition  as  benzene,  but  boiling  at 
85°  C. ,  whilst  benzene  boils  at  80°, 

345.  Gum-resins. — The  gum-resins  consist  of  a  mixture  of  gum  with 
resin,  and  occasionally  with  essential  oil,  and  are  distinguished  by  their 
behaviour  when  triturated  with  water,  which  dissolves  the  gum  and  leaves 
the  oil  and  resin  suspended,  giving  the  liquid  a  milky  appearance.  They 
also  difler  from  most  resins  in  being  only  partially  soluble  in  alcohol  The 
gum-resins  exude  from  the  plants  producing  them  in  a  milky  state, 
gradually  solidifying  by  exposure  to  the  air. 

Asafoftida  contains  a  resin  of  the  composition  Cg^H.^gOj,  and  owes  its 
powerful  odour  to  an  essential  oil  containing  sulphur,  which  has  been 
already  noticed.  Galbanum,  ammoniacum,  aloe^,  oUbanum  or  frankincense, 
scamrnony,  gamboge,  myrrh,  and  euph&rbium,  also  belong  to  the  class  of 
gumresins. 

Caoutchotic  (CjHg)  is  so  far  allied  to  the  gum-resins,  that  it  is  procured 
from  a  milky  exudation  furnished  by  several  tropical  plants,  particularly 
by  the  Hcevcea  guianensis  and  Jatropha  elastica.  Incisions  are  made  in 
these  trees,  and  the  milky  liquid  thus  obtained  is  spread  upon  a  clay 
bottle-shaped  mould,  which  is  then  suspended  over  a  fire ;  a  layer  of 
caoutchouc  is  thus  deposited  upon  the  mould,  and  its  thickness  is  after- 
wards increased  by  repeated  applications  of  the  milky  liquid,  the  mould 
being  eventually  broken  out  of  the  caoutchouc  bottle  thus  formed.  The 
dark  colour  of  the  caoutchouc  found  in  commerce  is  believed  to  be  due 
to  the  smoke  from  the  fire  over  which  it  is  dried,  for  pure  caoutchouc  is 
Avhite,  and  may  be  obtained  in  this  state  by  dissolving  in  washed  ether 
and  precipitating  it  by  the  addition  of  alcohol,  in  which  it  is  insoluble. 
The  caoutchouc  of  commerce  contains  a  small  quantity  of  albumen,  derived 
from  the  original  milky  liquid,  this  being  really  a  solution  of  albumen 
holding  in  suspension  about  30  per  cent,  of  caoutchouc,  which  rises  to  the 
surface  like  cream,  when  the  juice  is  diluted  with  water  and  allowed  to 
stand,  becoming  coherent  and  elastic  when  exposed  to  air.  It  will  be 
remembered  that  many  of  the  chief  uses  of  caoutchouc  depend  upon  its 
physical  rather  than  its  chemical  properties,  its  lightness  (sp.  gr.  0"93) 
and  impermeability  to  water,  adapting  it  for  the  fabrication  of  waterproof 
articles  of  clothing,  of  life-buoys,  &c.,  while  its  remarkable  elasticity  gives 
rise  to  a  still  greater  variety  of  applications. 

For  the  manufacture  of  waterproof  cloth,  caoutchouc  is  dissolved  in 
rectified  turpentine,  and  the  solution  is  spread,  in  a  viscid  state,  over  the 
surfaces  of  two  pieces  of  cloth  of  the  same  size,  Avhich  are  then  laid  face 
to  face  and  passed  between  rollers,  the  pressure  of  which  causes  perfect 


488  INDIA-RUBBER. 

adhesion  between  the  two  surfaces.  Carbon  disulphide,  benzene,  and  coal 
naphtha,  petroleum,  the  oils,  both  fixed  and  volatile,  are  also  capable  of 
dissolving  caoutchouc. 

Marine  glue  is  a  solution  of  caoutchouc  with  a  little  shell-lac  in  coal-tar 
naphtlia. 

Waterjyroof  felt  is  made  by  matting  together  fibres  of  cotton  im- 
])rcgnated  with  a  solution  of  caoutchouc  in  naphtha,  and  passing  the  felt 
between  rollers.  When  kept  for  a  length  of  time  its  strength  and  water- 
proof qualities  are  deteriorated,  in  consequence  of  the  oxidation  of  the 
caoutchouc,  which  is  thus  converted  into  a  resinous  substance  resembling 
shell-lac,  and  easily  dissolved  by  alcohol. 

The  alkalies  and  diluted  acids  are  without  effect  upon  caoutchouc,  "When 
gently  warmed  it  becomes  far  more  soft  and  pliable ;  it  fuses  at  about 
250°  F.,  and  is  converted  into  an  oily  liquid  which  becomes  viscid  on 
cooling,  but  will  not  again  solidify,  and  is  useful  for  lubricating  stop- 
cocks. When  further  heated  in  air  it  burns  with  a  bright  smoky  flame. 
Heated  in  a  retort,  caoutchouc  is  decomposed  into  several  hydrocarbons, 
one  of  which,  called  isoprene,  boils  at  about  100°  F.,  and  has  the  com- 
position CjHg,  while  caoutcMne  has  the  same  composition  as  oil  of 
turpentine,  and  boils  at  340°  F. ;  they  are  well  adapted  for  dissolving 
caoutchouc. 

Vxdcanisd  caoutchouc  is  produced  by  incorporating  this  substance 
with  2  or  3  per  cent,  of  sulphur,  which  not  only  increases  in  a  remark- 
able manner  its  elasticity,  but  prevents  it  from  cohering  under  pressure, 
and  from  adhering  to  other  surfaces  unless  strongly  heated.  The 
vulcanised  caoutchouc  is  also  insoluble  in  turpentine  and  naphtha. 
Ordinary  vulcanised  caoutchouc  generally  contains  more  sulphur  than  is 
stated  above,  which  causes  it  to  become  inelastic  and  brittle  after  it  has 
been  sometime  in  use ;  and  for  some  purposes,  such  as  the  manufacture 
of  overshoes,  it  is  found  advantageous  to  add  some  lead  carbonate  as  well 
as  sulphur. 

When  a  sheet  of  caoutchouc  is  allowed  to  remain  for  some  time  in 
fused  sulphur  at  250°  F.,  it  absorbs  12  or  15  per  cent,  of  that  element 
without  suffering  any  material  alteration  ;  but  if  it  be  heated  for  a  short 
time  to  300°  F,,  it  becomes  vulcanised;  and  when  still  further  heated,  is 
converted  into  the  black  horny  substance  called  vukanite  or  ebonite,  and 
used  for  the  manufacture  of  combs,  &c.  By  treating  the  vulcanised 
caoutchouc  with'sodium  sulphite,  the  excess  of  sulphur  above  2  or  3  per  cent, 
may  be  dissolved  out.  The  Avhole  of  the  sulphur  may  be  removed,  and 
the  caoutchouc  devulcanised,  by  boiling  it  with  a  10  per  cent,  solution  of 
caustic  soda. 

There  are  several  processes  employed  for  the  manufacture  of  vulcanised 
caoutchouc;  sometimes  the  sulphur  is  simply  incorporated  with  it  by 
mechanical  means.  Another  process  consists  in  immersing  the  caoutchouc 
in  a  mixture  of  100  parts  of  carbon  disulphide,  and  2-5  parts  of  chloride  of 
sulphur  (SgClg),*  or  in  dissolving  the  sulphur  in  oil  of  turpentine,  which 
is  afterwards  used  to  dissolve  the  caoutchouc;  when  the  turpentine  has 
evaporated,  a  mixture  of  caoutchouc  and  sulphur  is  left,  which  may  easily 
be  moulded  into  any  desired  form,  and  afterwards  vulcanised  by  exposure 
to  high  pressure  steam  having  a  temperature  of  about  280°  F, 

The  true  chemical  constitution  of  vulcanised  caoutchouc  is  not  yet 
*  A  mixture  of  sulphur  and  chloride  of  lime  is  said  to  be  sometimes  employed. 


GUTTA  PERCHA — GOBK.  489 

understood:  it  has  been  suggested  that  the  sulphur  has  been  substituted 
for  a  portion  of  the  hydrogen  in  the  original  caoutchouc,  but  it  does  not 
seem  improbable  that  this  hydrocarbon  may  combine  directly  with  sulphur. 

Caoutchouc  is  by  no  means  rare  in  the  vegetable  world,  being  found  in 
the  milky  juices  of  the  poppy  (and  thence  in  opium),  of  the  lettuce,  and 
of  the  euphorbium  and  asclepia  families. 

Gutta  peirha,  like  caoutchouc,  is  originally  a  milky  juice,  which  exudes 
from  incisions  made  into  the  wood  of  the  Isonandra  percha,  a  native  of 
the  Eastern  archipelago.  This  juice  soon  solidifies,  when  exposed  to  air, 
to  a  brownish  mass  heavier  than  caoutchouc  (sp.  gr.  0"98),  and  differing 
widely  from  it  by  being  tough  and  inelastic  at  the  ordinary  temperature, 
becoming  quite  soft  and  plastic  when  heated  nearly  to  the  boiling-point 
of  water.  Being  impervious  to  water,  it  is  employed  as  a  waterproof 
material  and  for  water-pipes,  whilst  its  want  of  conducting  power  for 
electricity  is  turned  to  account  in  the  coating  of  wires  for  the  electric 
telegraph. 

Gutta  percha  is  dissolved  by  the  same  substances  which  dissolve 
caoutchouc.  It  dissolves  very  slowly  in  ether,  but  is  not  affected  by 
diluted  acids  and  alkalies,  and  is  employed  for  the  manufacture  of  bottles 
in  Avhich  hydrofluoric  acid  is  kept.  It  liquefies  at  a  moderately  high 
temperature,  and  is  afterwards  decomposed,  yielding  products  similar  to 
those  obtained  from  caoutchouc. 

Tlie  gutta  percha  of  commerce  appears  to  contain  only  about  80  per 
cent,  of  pure  gutta  percha  (C.20H32),  Avhich  is  soluble  in  ether,  the  re- 
mainder consisting  of  two  resins,  Avhich  may  be  dissolved  out  by  boiling 
with  alcohol,  when  a  white  crystalline  resin  (C20II32O2)  is  deposited  on 
cooling,  leaving  an  amorphous  resin  (CgoHg^O)  in  solution. 

Pure  gutta  percha,  exposed  to  air,  is  gradually  converted  into  these 
resinous  bodies,  unless  light  be  excluded. 

Cork  is  the  bark  of  a  species  of  oak  (Que)-cus  suher)  growing  chiefly  in 
France  and  Spain.  It  consists  chiefly  of  a  cellular  substance,  insoluble 
in  water,  alcohol,  and  ether,  termed  suherine,  which  is  richer  in  carbon  than 
cellulose,  and  yields  suberic  acid  when  oxidised  by  nitric  acid.  It  is  much 
lighter  than  cellulose  (sp.  gr.  014).  The  waterproof  nature  of  cork  is 
due  to  the  presence  of  c,enne,  which  forms  about  2  or  3  per  cent,  of  the 
cork,  and  may  be  extracted  from  it  by  boiling  with  alcohol ;  it  is  de- 
posited ill  needles  on  cooling. 

346.  Gums. — Connected  with  the  substances  just  described  as  being 
immediate  products  of  vegetable  life,  are  the  gvms,  which,  though  resem- 
bling the  resins  in  transparency  and  lustre,  are  at  once  distinguished  from 
them  by  their  solubUity  or  softening  in  water,  and  by  their  insolubility  in 
alcohol. 

Gum  urahic,  which  may  be  studied  as  the  representative  of  this  class, 
is  an  exudation  from  certain  species  of  acacia,  and  consists  essentially  of 
araUne,  which  has  the  composition  C-^^^^O-^^  It  dissolves  readily,  even 
in  cold  water,  in  large  proportion,  forming  a  viscid  liquid,  from  which  the 
arabine  is  precipitated  in  white  flakes  on  adding  alcohol. 

When  arabine  is  boiled  with  diluted  sulphuric  acid,  it  is  slowly  converted 
into  grape-sugar  (C6HJ4O7)  by  assimilating  the  elements  of  water,  a  pro- 
perty connecting  it  closely  with  starch,  which  is  susceptible  of  a  similar 
conversion. 


490  GUM — STARCH. 

15 ut  a  chemical  property  distinguisliing  the  gums  is  their  behaviour 
•with  nitric  acid,  which  furnishes  mucic  acid  (H^CgHgOg)  and  oxalic  acid 
{M.JC.^O^.  The  latter  acid  is  also  formed  by  the  action  of  nitric  acid  upon 
starch  and  sugar,  whilst  mucic  acid  may  be  obtained  by  a  similar  process 
from  sugar  of  milk  and  from  manna  sugar  (mannite). 

Gum  Senegal  is  often  used  in  place  of  gum  arable,  especially  by  calico- 
printers  to  thicken  their  colours.  It  is  darker  in  colour  than  gum  arable, 
but  also  consists  essentially  of  arabine. 

Gum  tragacanth  iS^i^ifPio),  which  exudes  from  the  Astragalus  traga- 
cantha,  is  far  less  transparent  than  gum  arable,  from  which  it  also  differs 
by  not  dissolving  in  water,  but  merely  swelling  up  to  a  soft  gelatinous 
mass.  This  variety  of  gum,  which  is  also  called  mucilage,  cei-asine,  or 
bassorine,  is  found,  together  with  arabine,  in  the  gum  which  exudes 
from  the  cherry,  plum,  almond,  and  apricot  trees,  and  gives  the  mucila- 
ginous character  to  the  watery  decoctions  prepared  from  certain  seeds,  such 
as  linseed  and  quince-seed,  and  from  the  root  of  the  marsh-mallow. 

Gelose  or  C7«>«a-?noss  resembles  the  gums,  and  is  remarkable  for  forming 
a  jelly  with  500  parts  of  water.     Its  formula  is  said  to  be  CgHjoOj. 

Starch. 

347.  Starch  (CgH^^Og)  differs  widely  from  the  vegetable  products  just 
noticed,  in  being  an  indispensable  constituent  of  certain  parts  of  plants, 
in  possessing  an  organised  structure,  and  playing  a  very  important  part  in 
the  nutrition  of  the  plant. 

In  composition,  it  is  seen  to  correspond  with  cellulose,  which  has  also, 
it  will  be  remembered,  an  organised  structure ;  but  the  function  of  cellu- 
lose in  the  plant  appears  to  be  chiefly,  if  not  entirely,  a  mechanical  one, 
since  it  forms  the  skeleton  or  framework  of  the  plant,  for  which  its  resist- 
ance to  chemical  change  especially  adapts  it ;  whilst  it  will  be  seen  that 
si  arch  suffers  chemical  changes  in  the  vegetable,  which  may  be  compared 
in  some  measure  to  the  digestion  of  the  food  in  the  animal  body. 

Starch  is  manufactured  chiefly  from  potatoes,  wheat,  and  rice,  the  solid 
portion  of  which  consists  chiefly  of  starch,  as  appears  in  the  following 
result  of  analysis  : — 


Potatoes. 

Wheat. 

Rice. 

Starch, 

.     20-2 

60-8 

83-0 

Water, 

.     75-9 

121 

5-0 

Gluten, 

10-5 

6  0 

Albumen, 

'.       2-3 

2-0 

Dextrine  and  sugar, 

10-5 

io 

Woody  fibre. 

'.       0-4 

1-5 

4-8 

Oily  matter, 

.       0-2 

11 

0-1 

Mineral  matter,     . 

.       1-0 

1-5 

0-1 

100-0  100-0  100-0 

In  order  to  extract  the  starch,  the  potatoes  are  rasped  to  a  pulp,  which 
is  washed  upon  a  sieve,  under  a  stream  of  water,  as  long  as  the  latter  is 
icmlered  milky  by  the  starch  suspended  in  it,  the  woody  fibre  being  left 
b(dun(l  upon  the  sieve.  The  milky  liquid  is  allowed  to  settle,  and  the 
clear  water  drawn  off ;  the  deposited  starch  is  then  stirred  up  with  fresh 
water,  and  again  allowed  to  subside,  this  process  being  repeated  as  long 
as  the  water  is  coloured,  after  which  the  starch  is  mixed  up  with  a  small 
quantity  of  water,  and  passed  through  a  fine  sieve  to  separate  mechani- 


MANUFACTURE  OF  STARCH. 


491 


cally  mixed  impurities ;  it  is  finally  drained  and  dried,  first  in  a  current 
of  air,  and  afterwards  by  a  gentle  heat. 

Starch  cannot  be  extracted  from  wheat  so  easily  as  from  potatoes,  on 
account  of  the  much  larger  proportion  of  other  solid  matters  from  which 
it  must  be  separated. 

To  extract  the  starch,  the  coarsely-ground  wheat  is  moistened  with 
water,  and  allowed  to  putrefy,  as  it  easily  does,  in  consequence  of  the  alter- 
able character  of  the  gluten  (which  contains  carbon,  hydrogen,  nitrogen, 
oxygen,  and  sulphur)  ;  the  putrefying  gluten  excites  fermentation  in  the 
sugar  and  part  of  the  starch,  producing  acetic  and  lactic  acids.  These 
acids  are  capable  of  dissolving  the  remainder  of  the  gluten,  which  may 
then  be  washed  away  by  water,  the  subsequent  processes  being  similar  to 
those  employed  in  the  extraction  of  potato  starch. 

A  far  more  economical  and  scientific  method  of  extracting  the  starch 
consists  in  dissolving  the  gluten  by  means  of  a  weak  alkaline  solution, 
which  leaves  the  starch  untouched.  This  process  is  especially  applied  in 
the  manufacture  of  starch  from  rice. 

The  whole  rice  is  allowed  to  soak  for  twenty-four  hours  in  water  con- 
taining g^th  of  its  weight  of  caustic  soda ;  it  is  then  washed  and  ground 
into  flour,  which  is  again  soaked  for  two  or  three  days  in  a  fresh  alkaline 
solution  ;  the  starch  is  allowed  to  settle,  and  the  alkaline  liquor  holding 
the  gluten  in  solution  is  drawn  off.  To  complete  the  purification  of  the 
starch,  it  is  stirred  up  with  water,  the  heavier  woody  fibre  allowed  to  sub- 
side, and  the  milky  liquid  is  run  off"  into  another  vessel,  where  it  deposits 
the  starch. 

Starch  is  usually  sent  into  commerce  in  the  rough  prismatic  fragments 
into  which  it  splits  during  the  process  of  drying,  and  is  generally  coloured 
blue  by  the  addition  of  a  little  artificial  ultramarine  or  smalt,  in  order  to 
correct  the  yellow  tint  of  linen.  Commercial  starch  generally  contains 
about  18  per  cent,  of  water. 

Starch  being  possessed  of  an  organised  structure,  might  be  expected  to 
vary  in  external  characters  with  the  source  from  which  it  was  derived ; 
and,  accoidingly,  we  find  that,  with  the  help  of  the  microscope,  it  may  be 
ascertained  from  what  plant  any  particular  specimen  of  starch  Avas  pro- 
cured, a  result  which  could  not  be  arrived  at  by  a  chemical  examination. 

Thus,  powdered  starch  from  the  potato  (P,  fig.  285)  appears  under  the 
microscope  in  very  irregular  ovoid  granules,  marked  with  concentric  rings, 


Fior.  285, 


and  of  larger  size  than  those  from  most  other  vegetables,  the  long  diameter 
of  the  grains  being  usually  about  g^  inch.  Wheat  starch  (W)  exhibits 
grains  which  are  nearly  circular,  and  are  not  marked  with  rings  ;  they  are 
much  smaller  than  those  of  potato  starch,  having  a  diameter  of  about 
__i^  of  an  inch.     The  grains  of  rice  starch  (E)  are  angular,  and  still 


492  PROPERTIES  OF  STARCH. 

smaller,  measuring  only  about  -^j^^  of  an  inch  in  diameter.  A  represents 
the  starch  granules  of  arrow- root. 

Starch  is  quite  unaffected  by  cold  water ;  but  if  it  be  heated  with  water 
to  a  temperature  above  140°  F.,  the  granules  swell  up,  burst,  and  yield 
the  well-known  viscid  liquid  used  by  laundresses.  If  this  be  mixed  with 
a  large  quantity  of  water,  and  allowed  to  stand,  some  of  the  imperfectly 
bur-st  granules  subside,  but  the  greater  part  of  the  starch  remains  so  inti- 
mately mixed  with  the  water,  that  it  is  not  separated  by  filtration  through 
paper,  though  it  has  been  shown  that  when  the  rootlets  of  a  hyacinth  are 
immersed  in  the  diluted  magma  of  starch,  the  water  alone  is  taken  up  by 
the  capillary  vessels,  affording  a  strong  presumption  that  the  starch  was 
simply  in  a  state  of  su.spension  in  the  water.  If  the  boiled  starch  be  eva- 
porated to  dryness,  a  brittle  mass  remains,  which  may  again  be  taken  up 
without  difficulty  by  Avater. 

This  peculiar  behaviour  of  starch  with  water  is  closely  connected  with 
its  use  as  food.  Raw  starch  is  digested  with  difficulty,  and  often  passes 
unaltered  through  the  bowels ;  but  the  ease  with  which  the  starch  gela- 
tinised by  heat  is  digested,  is  shown  by  the  wholesomeness  of  sago, 
tapioca,  and  arrow-root,  which  consist  simply  of  starch,  and  are  prepared 
for  food  by  heating  them  with  water  to  the  point  at  which  the  granules 
burst. 

Airoic-root  is  the  starch  extracted  from  the  root  of  the  Maranta  at'un- 
dinacea,  and  of  some  other  tropical  plants. 

In  the  preparation  of  tapioca  and  sago,  the  starch  is  dried  at  a  tem- 
perature above  140°  F.,  so  that  it  loses  its  ordinary  farinaceous  appearance 
and  becomes  semi-transparent. 

Saffo  is  manufactured  from  the  pith  of  certain  species  of  palm,  natives 
of  tlie  East  Indian  islands.  The  tree  is  split  so  as  to  expose  the  pitb, 
which  is  mixed  with  water,  and  the  starch  having  been  separated  from 
the  woody  fibre  in  the  usual  manner,  is  pressed  through  a  perforated 
metallic  plate,  which  moulds  it  into  small  cylinders ;  these  are  placed  in  a 
revolving  vessel  and  broken  into  rough  spherical  grains,  which  are  steamed 
upon  a  sieve,  and  dried. 

Tapioca  is  obtained  from  the  roots  of  the  Jatropha  maniliot,  a  native 
of  America.  The  roots  are  peeled  and  subjected  to  pressure,  which 
squeezes  out  a  juice  employed  by  the  Indians  to  poison  their  arrows,  and 
containing  a  deleterious  substance  which  has  been  named  jatrophine. 
When  the  juice  is  allowed  to  stand,  it  deposits  starch,  which  is  well 
washed,  pressed  through  a  colander,  and  dried  at  212°  F. 

O.m'cf/o,  or  corn-tlour,  is  the  flour  of  Indian  corn  deprived  of  gluten  by 
treatment  with  a  weak  solution  of  soda. 

348.  Dextrine. — When  starch  is  heated  in  an  oven  to  about  400°  F. 
for  an  hour  or  two,  it  becomes  easily  soluble  in  cold  water,  yielding  a 
solution  having  all  the  properties  of  gum ;  the  starch  has  indeed  been 
converted  into  a  new  substance  known  as  dextrine  or  British  gum,  which 
is  largely  used  by  calico-printers  for  thickening  their  colours,  and  is  sub- 
stituted for  ordinary  gum  in  many  other  applications.  There  is  a  current 
anecdote  which  attributes  tht  discovery  of  dextrine  to  a  conflagration  at 
a  starch-factory,  where  the  work-people,  who  assisted  in  quenching  the 
fire,  observed  the  gummy  properties  of  the  water  which  had  been  thrown 
over  the  torrefied  starch.     In  toasting  bread,  a  portion  of  the  starch  is 


CONVERSION  OF  STARCH  INTO  DEXTRINE.  493 

converted  into  dextrine,  which  is  dissolved  by  the  water  in  the  prepara- 
tion of  toast  and  water.  Farinaceous  foods  for  infants  are-  made  by  baking 
flour,  in  order  to  convert  the  starch  into  dextrine. 

It  is  very  remarkable  that  the  composition  of  dextrine  (CgH^QO.)  is 
precisely  that  of  starch  ;  they  are  isomenc  bodies,  so  that  the  difference  in 
their  properties  must  be  ascribed  to  a  difference  in  the  arrangement  of 
their  component  particles;  the  name  of  dextrine  was  conferred  upon  this 
gummy  substance  on  account  of  the  power  possessed  by  its  solution  of 
causing  a  right-handed  rotation  in  a  ray  of  polarised  light.  When  oxidised 
by  nitric  acid,  dextrine,  like  starch,  is  converted  into  oxalic  acid,  a  cir- 
cumstance distinguishing  it  from  the  ordinary  gum,  which  furnishes  mucic 
acid  when  acted  upon  by  nitric  acid. 

Dextrine  is  usually  prepared  on  the  large  scale  by  moistening  10  parts 
of  starch  with  3  parts  of  water  acidulated  with  yt'o^^  ^^  nitric  acid ;  the 
mixture  is  allowed  to  dry,  and  spread  upon  trays  in  an  oven,  where  it  is 
heated  for  an  hour  or  so  to  240°  F.  The  nitric  acid  thus  allows  the 
starch  to  be  converted  into  dextrine  at  a  temperature  which  would  be 
quite  inadequate  to  efiect  the  transformation  of  starch  alone. 

This  power  of  accelerating  the  conversion  of  starch  into  dextrine  is 
shared  by  all  acids.  Hence  if  starch  be  boiled  with  water,  and  the  viscid 
liquid  so  obtained  be  mixed  with  an  acid,  and  again  boiled,  it  gradually 
becomes  thinner,  and  is  eventually  converted  into  dextrine.  The  change 
is  very  readily  effected  by  boiling  the  starch  solution  with  a  few  drops  of 
sulphuric  acid,  and  the  gradual  conversion  of  the  starch  may  be  traced  by 
means  of  an  aqueous  solution  of  iodine.  On  adding  this  solution  to  a 
portion  of  the  (cold)  solution  of  starch,  it  produces  the  usual  dark  blue 
colour ;  but  on  adding  it,  at  intervals,  to  portions  of  the  acidulated  and 
boiled  liquid,  taken  away  and  cooled  for  the  purpose,  the  blue  colour  will 
be  replaced  by  a  peculiar  vinous  purple  tint  Avhicli  iodine  imparts  to  solu- 
tions of  dextrine  containing  a  little  unchanged  starch. 

The  solution  of  iodine  is  much  used  in  proximate  organic  analysis  as  a 
test  for  starch,  and  it  is  necessary  to  bear  in  mind  that  the  blue  colour  is 
bleached  by  alkalies  (which  take  up  the  iodine)  and  by  heat,  though,  in 
the  latter  case,  it  may  be  restored  by  cooling  the  liquid.  The  blue  colour 
does  not  appear  to  be  due  to  the  formation  of  any  definite  chemical  com- 
pound with  the  starch,  but  rather  to  a  mechanical  adhesion  of  very  finely 
divided  iodine  to  the  particles  of  starch.  The  sensitiveness  of  starch  lo 
the  action  oifree  iodine  has  given  rise  to  its  application  in  the  preparation 
of  paper  for  the  prevention  of  forgery  in  bankers'  cheques,  &c.  If  paper 
be  impregnated  with  a  mixture  of  potassium  iodide  and  starch,  which 
is  perfectly  white,  it  will  acquire  an  intense  blue  colour  on  the  application 
of  any  of  the  bleaching  agents  (chlorine,-  hypochlorous  acid,  chlorides  of 
lime  and  soda)  generally  used  for  removing  ink,  as  thesa  liberate  the 
iodine,  which  immediately  blues  the  starch. 

If  the  ebullition  of  the  dextrine  in  contact  with  the  sulphuric  acid  be 
continued,  the  solution  entirely  loses  its  property  of  being  coloured  by 
iodine,  and  acquires  a  sweet  taste,  the  dextrine  having  been  converted 
into  glucose  {C^y2^d^  by  assimilating  the  elements  of  a  molecule  of 
■water ;  *  Cq^-J)-^  (Dextrine)  +  Hp  =  QH^gO^  {Glucose). 

*  There  is  some  reason  to  believe  that  the  formation  of  glucose  from  starch  results  from 
a  change  simihir  to  that  bv  which  it  is  obtained  from  salicine  and  other  glucosides.     Thus 
2C6Hio03  +  HoO=CsH,o05  +  aH,206 
Dextrine.     Glucose. 


494  GERMINATION  OF  SEEDS. 

349.  Germination  of  seeds — Malting. — This  tendency  of  starch  to  com- 
bine with  the  elements  of  water  and  pass  into  glucose,  will  be  found  of 
immense  importance  in  the  chemistry  of  vegetation,  as  well  as  in  that  of 
food.  It  is,  indeed,  the  chief  chemical  change  concerned  in  the  develop- 
ment of  living  from  inanimate  matter,  being  one  of  the  first  processes 
involved  in  the  germination  of  a  seed — the  first  step  in  the  production  of 
vegetables,  which  must  precede  the  animals  whose  food  they  compose. 

The  components  of  all  seeds  are  similar  to  those  of  wheat,  which  have 
been  enumerated  above ;  and  if  they  be  perfectly  dried  immediately  after 
their  removal  from  the  parent  plant,  they  may  be  preserved  for  a  great 
length  of  time  unchanged,  and  without  losing  the  power  of  germinating 
under  favourable  circumstances.  The  essential  conditions  of  germination 
are  the  presence  of  air  and  moisture,  and  a  certain  temperature,  which  varies 
with  the  nature  of  the  seed.  These  conditions  being  fulfilled,  the  seed 
absorbs  oxygen  from  the  air,  and  evolves  carbonic  acid  gas,  produced  by  the 
combination  of  the  oxygen  with  the  carbon  of  one  or  more  of  the  most  alter- 
able constituents  of  the  seed,  such  as  the  vegetable  albumen  or  the  gluten. 
This  process  of  oxidation  is  attended  with  evolution  of  heat,  which  serves 
to  maintain  the  seed  at  the  degree  of  warmth  most  favourable  to  germina- 
tion. The  component  particles  of  the  albumen  or  gluten  having  been  set 
in  motion  by  the  action  of  the  atmospheric  oxygen,  induce  a  movement 
or  chemical  change  in  the  starch  with  which  they  are  in  contact,  causing 
it  to  pass  into  dextrine  and  glucose,  which,  unlike  the  starch,  being 
perfectly  soluble  in  water,  are  capable  of  affording  to  the  developing  shoot 
the  carbon,  hydrogen,  and  oxygen  which  it  requires  for  the  increase  of  its 
frame.  The  production  of  glucose  and  of  dextrine  in  germination  is 
well  illustrated  by  the  sweet  gummy  character  of  the  bread  made  from 
sprouted  wheat,  and  is  turned  to  practical  account  in  the  process  of 
malting. 

During  the  germination  of  all  seeds  there  is  formed,  apparently  by  the 
oxidation  of  one  of  the  more  alterable  constituents,  a  peculiar  substance 
containing  carbon,  hydrogen,  nitrogen,  and  oxygen,  which  has  never  yet 
been  obtained  from  any  other  source,  and  is  characterised  by  its  remark- 
able property  of  inducing  the  conversion  of  starch  into  dextrine  and  grape- 
sugar. 

This  substance  has  been  termed  diastase  (SiatrTacrts,  dissension;  metaph. 
fermentation),  but  has  never  yet  been  obtained  in  a  state  of  sufficient 
purity  to  enable  its  formula  to  be  satisfactorily  determined.  It  may  be 
extracted,  however,  from  malt,  by  grinding  it  and  mixing  it  with  half 
its  weight  of  warm  water,  which  dissolves  the  diastase ;  the  solution 
squeezed  out  of  the  malt  is  heated  to  about  170°  F,,  filtered  from  any 
coagulated  albumen,  and  mixed  with  absolute  alcohol,  which  precipitates 
the  diastase  in  white  flakes.  One  part  of  diastase  dissolved  in  water  is 
capable  of  inducing  the  conversion  of  2000  parts  of  starch  into  dextrine 
and  grape-sugar,  the  diastase  itself  being  exhausted  in  the  process.  A 
temperature  of  about  150°  F.  is  most  favourable  to  the  action  of  diastase, 
which  may  be  arrested  entirely  by  raising  the  liquid  to  the  boiling- 
point. 

The  great  importance  of  diastase  in  the  arts  of  the  brewer  and  distiller 
is  at  once  apparent.  In  the  process  of  malting  barley,  the  grain  is  soaked 
in  water,  and  afterwards  spread  out  in  thin  layers  upon  the  floor  of  a  dark 
r()om  (thus  imitating  the  natural  condition  under  which  the  seed  germi- 


PROCESS  OF  MALTING. 


495 


nates),  which  is  maintained  as  nearly  as  possible  at  a  constant  and  moderate 
temperature  (between  55°  and  62°  F.) ;  spring  and  autumn  are,  therefore, 
more  favourable  to  malting  than  summer  and  winter.  It  soon  evolves 
heat,  and  the  grains  begin  to  swell;  in  the  course  of  twenty-four  hours 
the  germination  commences,  and  the  radicle  makes  its  first  appearance  as 
a  Avhitish  protuberance ;  the  grain  is  turned  two  or  three  times  a  day,  in 
order  to  equalise  the  temperature.  In  about  a  fortnight  the  radicle  has 
grown  to  about  half  an  inch,  by  which  time  a  sufficient  quantity  of  dias- 
tase has  been  formed.  In  order  to  prevent  the  germination  from  proceed- 
ing further,  the  grain  is  killed  by  drying  it  at  a  temperature  of  90°  F.  on 
perforated  metallic  plates,  where  it  is  afterwards  heated  to  about  140°  F., 
so  as  to  render  it  brittle,  after  which  it  is  sifted  in  order  to  separate  the 
radicle,  which  is  now  easily  broken  off.  This  radicle  is  found  to  contain 
as  much  as  ith  of  the  total  quantity  of  the  nitrogen  present  in  the  barley, 
so  that  the  malt  dust,  as  the  sittings  are  called,  forms  a  valuable 
manure. 

One  hundred  parts  of  barley  generally  yield  about  80  parts  of  m-alt,  but 
a  part  of  the  loss  is  due  to  water  present  in  the  barley,  so  that  100  parts  of 
dry  barley  yield  90  parts  of  malt  and  4  parts  of  malt  dust,  the  difference, 
viz.,  6  parts,  representing  the  weight  of  the  carbon  converted  into  carbonic 
acid  gas,  of  the  hydrogen  (if  any)  converted  into  water  during  the  germina- 
tion, and  of  soluble  matters  removed  from  the  barley  in  steeping.  Malt 
contains  about  j^^^g^th  of  its  weight  of  diastase,  far  more  than  enough  to 
ensure  the  conversion  of  the  whole  of  its  starch  into  sugar. 

The  following  table*  illustrates  the  change  in  composition  suffered  by  barlej'' 
during  the  process  of  malting,  leaving  the  moisture  out  of  consideration  : — 


Sugar,      . 
Starch,     . 
Dextrine, 
Woody  fibre,    . 
Albuminous  matter, 
Mineral  matter, 

Bai-Iey, 

After 
Steeping. 

14J  days  on 
floor. 

Malt  after 
Sifting. 

Malt  nust. 

2-56 

80-42 

4-69 
9-83 
2-50 

1-56 

81-12 

5-22 
9-83 
2-27 

12-14 

70-09 

5-03 

10-39 

2-35 

11-01 

72-03 

4-84 
9-95 
2-17 

11-35 

43-68 

9-67 

26-90 

8 -40 

100-00          100  00 

100-00       1    100-00 

10000 

350.  Breioimj. — In  order  to  prepare  beer,  the  brewer  mashes  the  ground 
malt  with  water  at  about  180°  F.,  for  some  hours,  when  the  diastase 
induces  the  conversion,  into  dextrine  and  sugar,  of  the  greatest  part  of  the 
starch  which  has  not  been  so  changed  during  the  germination,  and  the 
wort  is  ready  to  be  drawn  off  for  conversion  into  beer.  The  undissolved 
portion  of  the  malt,  or  brewers'  grains,  still  contains  a  considerable  quantity 
of  starch  and  nitrogenised  matter,  and  is  employed  for  feeding  pigs. 

That  malt  contains  far  more  diastase  than  is  necessary  to  convert  its 
starch  into  sugar,  is  shown  by  adding  a  little  infusion  of  malt  to  the 
viscid  solution  of  starch,  and  maintaining  it  at  about  150°  F.  for  a  few 
hours,  when  the  mixture  will  have  become  far  more  fluid,  and  will  no 
longer  be  coloured  blue  by  solution  of  iodine.  In  distilleries,  advantage 
is  taken  of  the  excess  of  diastase  in  malt,  by  adding  three  or  four  parts  of 
unmalted  grain  to  it.  when  the  whole  of  the  starch  in  this  latter  is  also 

*  Lawes,  Report  of  the  Relative  Values  of  Unmalted  and  Malted  Barley  as  Food  for 
Stock,  1866. 


496  CHEMISTRY  OF  BREWING. 

converted  into  dextrine  and  sugar,  and  the  labour  and  expense  of  malting 
it  are  avoided. 

Tlie  wort  obtained  by  infusing  malt  in  water  contains  not  only  glucose, 
de.xtrine,  and  diastase,  but  a  considerable  quantity  of  nitrogenised  matter 
formed  from  the  gluten  (or  albuminous  matter)  of  the  barley.  Before 
subjecting  it  to  fermentation,  it  is  boiled  with  a  quantity  of  hops,  usually 
amounting  to  about  yV*"^  ^^  ^^^  weight  of  the  malt  employed,  which  is 
found  to  prevent,  in  great  measure,  the  tendency  of  the  beer  to  become 
sour  in  consequence  of  the  conversion  of  the  alcohol  into  acetic  acid. 

The  hop  contains  about  10  per  cent  of  an  aromatic  yellow  powder, 
called  hqmline,  which  appears  to  be  the  active  portion,  and  which  con- 
tains a  volatile  oil  of  peculiar  odour,  together  with  a  very  bitter  substance. 
The  hopped  wort  is  run  off  into  a  vat,  where  it  is  allowed  to  deposit 
the  undissolved  portion  of  the  hops,  and  the  clear  liquor  is  drawn  off 
into  shallow  coolers,  where  its  temperature  is  lowered  as  rapidly  as  pos- 
sible to  about  60°  F.,  the  cooling  being  usually  hastened  by  cold  water 
circulating  through  pipes  which  traverse  the  coolers.  If  the  wort  be 
cooled  too  slowly,  the  nitrogenised  matter  which  it  contains  undergoes 
an  alteration  by  the  action  of  the  air,  in  consequence  of  which  the  beer 
is  very  liable  to  become  acid. 

The  wort  is  now  transferred  to  the  fermenting  tun,  where  it  is  made 
to  ferment  by  the  addition  of  yeast,  usually  in  the  proportion  of  yuir^^ 
of  its  volume. 

Yeast  is  a  minute  fungoid  vegetable,  which  grows  in  solutions  con- 
taining sugar  together  with  some  nitrogenised  substance  {e.g.,  a  salt  of 
ammonium),  and  the  salts  (phosphates  of  potassium,  sodium,  calcium,  and 
magnesium),  which  are  essential  constituents  of  its  cells.  If  a  little  white 
of  egg,  cheese,  or  a  piece  of  flesh  (all  of  which  contain  carbon,  hydrogen, 
nitrogen,  oxygen,  and  phosphates),  be  placed  in  a  solution  of  sugar,  and 
allowed  to  undergo  decomposition,  a  grey  scum  forms  upon  the  liquid, 
which  is  seen  under  the  microscope  to  consist  of  irregularly  oval  cells, 
the  growth  of  which  may  be  watched  under  the  microscope  in  a  little  of 
the  liquid  from  which  they  were  obtained, 
when  they  will  be  found  to  multiply  rapidly 
by  the  production  of  new  cells  on  all  sides  of 
them  (fig.  286).  The  same  cells  will  be 
developed  very  rapidly  in  the  sweet  wort  of 
malt,  allowed  to  undergo  decomposition  be- 
tween 60°  and  70°  F. 

These  cells  contain  a  substance  somewhat 
resembling  albumen,  enclosed  in  a  thin  mem- 
brane, the  composition  of  which  is  similar  to 
that  of  cellulose.  They  also  contain  a  peculiar 
nitrogenised  body  resembling  diastase,  and 
capable  of  inducing  the  conversion  of  cane- 
Fig.  286.  sugar  (CjgHggOji)  into  glucose  (CgHjgOg). 
Accordingl}'^,  when  yeast  is  added  to  a  solution 
of  cane-sugar,  the  liquid  is  found  to  increase  in  specific  gravity  (a  solution 
of  cane-sugar  having  a  lower  density  than  one  containing  an  equivalent 
quantity  of  glucose),  previously  to  the  commencement  of  fermentation, 
and  the  application  of  tests  readily  proves  the  presence  of  glucose  in  the 
sulution. 


FERMENTATION.  497 

The  glucose  then  undergoes  the  decomposition  known  as  alcoholic 
fermentation,  which  results  in  the  production  of  alcohol,  carbonic  acid, 
lactic  acid,  succinic  acid,  glycerine,  and  a  pecuhar  brown  soluble  matter, 
together  with  other  substances,  the  true  nature  of  which  is  yet  undeter- 
mined. The  fermentation  is  attended  with  a  considerable  elevation  of 
temperature. 

Taking  into  consideration  only  the  alcohol  and  carbonic  acid  gas,  which 
are  the  chief  products,  their  formation  from  grape-sugar  may  be  repre- 
sented by  the  equation  CgH^gOg  =  SCgHgO  -f-  2C0^ 

During  the  fermentation  the  yeast  cells  are  gradually  broken  up,  so 
that  a  given  quantity  of  yeast  is  capable  of  fermenting  only  a  limited 
quantity  of  sugar.  On  an  average,  a  quantity  of  yeast  containing  between 
two  and  three  parts  of  solid  matter  is  required  to  complete  the  fermenta- 
tion of  100  parts  of  sugar.  The  solution  remaining  after  the  fermenta- 
tion is  found  to  contain  salts  of  ammonium,  which  have  been  formed  at 
the  expense  of  the  nitrogen  of  the  yeast. 

If  the  liquid  in  which  the  yeast  excites  fermentation  contains  nitro- 
genised  matters  and  phosphates,  the  yeast-plant  grows,  and  its  quantity 
increases;  thus,  in  the  sweet  wort  from  malt,  the  yeast  is  nourished  by 
the  altered  gluten  and  by  the  phosphates,  so  that  it  increases  to  six 
or  eight  times  its  original  weight. 

If  yeast  be  heated  to  the  boiling-point  of  water,  the  plant  is  killed, 
as  might  be  expected,  and  loses  its  power  of  inducing  alcoholic  fermenta- 
tion; but  it  may  be  dried  at  a  low  temperature,  or  by  pressure,  without 
losing  its  fermenting  power,  and  dried  yeast  is  an  article  of  commerce. 
German  dried  yeast  is  produced  in  the  fermentation  of  rye  for  making 
Hollands. 

Yeast  will  not  cause  fermentation  in  a  solution  containing  more  than 
one-fourth  of  its  weight  of  sugar,  and  the  fermentation  is  arrested  when 
the  alcohol  amounts  to  one-fifth  of  the  weight  of  the  liquid,  so  that  the 
strength  of  fermented  liquors  could  never  exceed  20  per  cent,  of  alcohol. 
The  fermentation  is  also  arrested  by  the  mineral  acids,  and  by  many  of 
the  substances  to  which  antiseptic  properties  are  commonly  attributed, 
such  as  common  salt,  kreasote,  corrosive  sublimate,  sulphurous  acid,  tur- 
pentine, &c. 

In  the  fermentation  of  beer,  the  yeast  is  carried  up  to  the  surface  by 
the  effervescence  due  to  the  escape  of  the  carbonic  acid  gas,  and  is 
eventually  removed,  in  order  to  be  employed  for  the  fermentation  of  fresh 
quantities  of  wort.  When  the  fermentation  has  proceeded  to  the  requii'ed 
extent,  the  beer  is  stored  for  comsumption. 

It  will  be  seen  that  the  chief  constituents  of  beer  are  the  alcohol, 
the  nitrogenised  substance  derived  from  the  albuminous  matter  of 
the  barley,  and  not  consumed  in  the  growth  of  the  yeast,  the  unaltered 
glucose  and  dextrine,  the  brown  or  yellow  colouring  matter  formed 
during  the  fermentation,  the  essential  oil  and  bitter  principle  of  the 
hop. 

Beer  also  contains  acetic  acid  (formed  by  the  oxidation  of  the  alcohol, 
page  498),  free  carbonic  acid,  which  gives  its  sparkling  character,  together 
with  the  lactic  and  succinic  acids  and  glycerine,  formed  as  secondary  pro- 
ducts of  the  fermentation,  and  ammoniacal  salts  derived  from  the  yeast. 
The  soluble  mineral  substances  from  the  barley  are  also  present,  minus 
the  phosphates  abstracted  by  the  yeast. 

2l 


498 


COMPOSITION  OF  BEER. 


The  proportions  of  the  constituents,  of  course,  vary  greatly,  as  Avill  be 
seen  from  the  following  examples  : — 


Percentage. 

AIlSOpp'8 

Ale. 

Bass's  Ale. 

Strong  Ale. 

Whltbread's 
Porter. 

Whitbiead-s 
Stout. 

Alcohol,  . 
Acetic  acid, 
Su^ar  and  otlier  solid  | 
matters,        .         .  ) 

6-00 
0-20 

5  00 

7-00 
0-18 

4-80 

8-65 
0-12 

6-60 

4-20 
0-19 

5-40 

6-00 
0-18 

6-38 

The  dark  colour  of  porter  and  stout  is  caused  by  the  addition  of  a 
quantity  of  hujh-dried  malt  which  has  been  exposed  to  so  high  a  tempera- 
ture in  the  kiln  as  to  convert  a  portion  of  its  sugar  into  a  dark  brown 
soluble  substance  called  caramel.  The  peculiar  aroma  of  beer  is  probably 
due  to  the  presence  of  acetic  ether,  produced  during  the  fermentation. 

In  some  cases,  when  the  operation  of  brewing  has  been  badly  con- 
ducted, the  beer  becomes  ropy,  or  undergoes  the  viscovs  fermentation.  In 
this  case  the  glucose  suffers  a  peculiar  transformation,  resulting  in  the  pro- 
duction of  a  mucilaginous  substance  resembling  gum  in  its  composition. 
This  change  may  be  induced  by  yeast  which  has  been  boiled,  or  by  water 
in  which  flour  or  rice  has  been  steeped.  White  wine  occasionally 
becomes  ropy  from  a  similar  cause,  but  red  wines  are  not  liable  to  this 
change,  apparently  because  the  tannin  which  they  contain  has  precipitated 
in  an  insoluble  form  the  ferment  which  induces  it.  During  this  viscous 
fermentation  a  part  of  the  glucose  is  often  converted  into  mannite 
(CoHi.O,). 

351.  AcBTiFicATioN — MANUFACTURE  OF  ViNBGAR. — Beer  wMch  has 
become  sour  is  often  said  to  have  undergone  the  acetous  fermentation ; 
but  this  is  not  strictly  correct,  the  change  being  more  similar  to  decay, 
since  it  is  one  in  which  the  oxygen  of  the  air  directly  takes  part.  The 
acidity  of  sour  beer  is  caused  by  the  acetic  acid  (CgH^Og)  formed  by  the 
action  of  atmospheric  oxygen  upon  the  alcohol,  according  to  the  equation — 

CgHgO  {Alcohol)  +02  =  CgH^Og  {Acetic  Add)   +  HgO. 

Pure  alcohol  may  be  exposed  to  the  air,  either  alone  or  when  mixed  with 
water,  for  any  period,  without  suffering  oxidation;  but  when  in  contact 
Avith  certain  changeable  organic  substances,  the  alcohol  undergoes  oxida- 
tion, and  is  converted  into  acetic  acid.  It  is  upon  this  circumstance  that 
the  different  methods  of  producing  vinegar  are  based. 

The  most  direct  application  of  this  principle  is  made  in  the  so-called 
quick  vinegar  jyrocess  in  use  in  continental  countries  where  alcohol  is 
free  of  duty.  Alcohol  of  about  80  per  cent,  is  mixed  with  6  parts  of 
water,  and  with  about  y  oVir^^^  P^^rt  of  yeast,  or  some  other  alterable  sub- 
stance containing  nitrogen.  This  mixture  is  heated  to  about  80°  F.,  and 
caused  to  trickle  slowly  from  pieces  of  cord  fixed  in  a  perforated  shelf  over 
a  quantity  of  wood  shavings*  previously  soaked  in  vinegar,  which  is  found 
materially  to  assist  the  acetification,  and  packed  in  a  tall  cask  (fig.  287) 
in  which  holes  have  been  drilled  in  order  to  allow  the  entrance  of  air.  The 
oxidation  of  the  alcohol  soon  raises  the  temperature  to  about  100°  F.,  which 
occasions  a  free  circulation  of  air  among  the  shavings.     The  mixtureis 

*  These  shavings  appear  to  favour  the  process  by  serving  as  points  of  attachment  for  a 
microscopic  vegetable,  which  encourages  the  oxidation  of  the  alcohol. 


MANUFACTURE  OF  VINEGAR. 


499 


Fiff.  287. 


passed  three  or  four  times  through  the  cask,  and  in  about  thirty-six  hours 
the  conversion  into  vinegar  is  completed.     The  oxidation  of  the  alcohol 
in  this  process  is  found  to  be  arrested 
by  the  presence  of  essential  oils,  or  of 
kreasote,    and  similar  antiseptic  sub- 
stances. 

The  necessity  of  affording  a  full 
supply  of  atmospheric  air  was  not 
appreciated  until  Liebig  had  proved 
the  existence  of  an  intermediate  stage 
in  the  process,  consisting  in  a  partial 
oxidation  of  the  alcohol  by  which 
it  became  converted  into  aldehyde 
(C.,H^O),  an  extremely  volatile  liquid 
(boiling  at  70°  R),  which  was  lost 
in  the  form  of  vapour,  thus  greatly 
diminishing  the  proportion  of  vinegar 
obtained — 

CgHgO  {Alcohol)  +  O  =  C2H4O  {Aldehyde)  +  HgO. 

If  a  sufficient  quantity  of  atmospheric  air  be  supplied,  the  production  of 
aldehyde  is  entirely  avoided. 

White  wine  vinegar  is  prepared  in  France  from  light  wines  by  a  process 
of  much  longer  duration.  A  little  boiling  vinegar  is  poured  into  a  cask, 
partially  open  at  the  top,  together  with  4  or  5  gallons  of  white  wine 
which  has  been  allowed  to  trickle  over  wood  shavings.  In  a  few  days, 
during  which  the  temperature  is  maintained  at  about  80°  F.,  a  fresh  quan- 
tity of  wine  is  poured  in,  and  in  the  course  of  a  fortnight  half  the  vinegar 
contained  in  the  cask  is  drawn  off,  and  replaced  by  a  fresh  portion  of  wine. 
In  this  way  an  occasional  renewal  of  the  air  in  the  upper  part  of  the  cask 
is  provided  for.  The  acetification  is  found  to  proceed  more  rapidly  in  old 
casks  than  in  new  ones,  wliich  is  attributed  to  the  presence  of  a  peculiar 
conferva  deposited  upon  the  sides  of  the  former,  and  styled  mother  of 
vinegar.  It  is  probably  for  a  similar  reason  that  the  acetification  is  pro- 
moted by  the  addition  of  ready-made  vinegar  at  the  commencement  of  the 
process. 

In  this  country  vinegar  is  chiefly  prepared  from  malt,  the  infusion  of 
which  is  allowed  to  undergo  the  alcoholic  and  acetous  fermentation. 

Vinegar  contains  on  an  average  about  5  per  cent,  of  acetic  acid,  together 
with  small  quantities  of  vegetable  and  mineral  substances,  varying  with 
the  source  from  which  it  was  obtained.  Its  pleasant  aroma  is  due  to 
the  presence  of  some  acetic  ether  (CaH-.CoHgOg)  formed  during  its  manu- 
facture. The  vinegar  of  commerce  is  allowed  to  be  mixed  with  y^o^^ 
of  its  weight  of  sulphuric  acid  in  order  to  prevent  it  from  becoming 
mouldy. 

Bread. 

352.  The  chemistry  of  fermentation  is  intimately  connected  with  the 
ordinary  process  of  bread-making.  It  will  be  remembered  that  wheaten 
flour  (page  490)  consists,  essentially,  of  starch  and  gluten,  with  a  little 
dextrine  and  sugar.  On  mixing  the  flour  with  a  little  water,  it  yields  a 
dough,  the  tenacity  of  which  is  due  to  the  gluten  present  in  the  flour.     If 


500  PROCESS  OF  BREAD-MAKING. 

this  dough  he  tied  up  in  a  piece  of  fine  muslin,  and  kneaded  iinder  a  stream 
of  water,  the  starch  will  he  suspended  in  the  water,  and  will  pass  through 
the  muslin,  whilst  the  gluten  -will  remain  as  a  very  tough  elastic  mass, 
which  speedily  putrefies  if  exposed  to  the  air  in  a  moist  state,  and  dries 
up  to  a  brittle  horny  mass  at  the  temperature  of  boiling  water. 

On  analysis,  gluten  is  found  to  contain  carbon,  hydrogen,  nitrogen,  and 
oxygen,  in  proportions  which  may  be  represented  by  the  empirical  formula 
C.,4H^o^'607>  though  it  cannot  be  regarded  as  a  single  independent  sub- 
stance, but  as  a  mixture  of  three  substances  very  closely  allied  in  compo- 
sition. 

When  gluten  is  boiled  with  alcohol,  one  portion  refuses  to  dissolve,  and 
has  been  named  vegetable  fibrine,  from  its  resemblance  to  the  substance 
forming  the  muscles  of  animals.  When  the  solution  in  alcohol  is  allowed 
to  cool,  it  deposits  a  white  flocculent  matter,  very  similar  to  the  casetne 
which  composes  the  curd  of  milk.  On  adding  water  to  the  cold  alcoholic 
solution,  a  third  substance  (glutine)  is  separated,  which  much  resembles 
the  albumen  found  so  abundantly  in  the  blood. 

The  presence  in  gluten  of  three  substances,  similar  to  the  three  principal 
components  of  the  animal  body,  leads  us  to  form  a  high  opinion  of  its 
value  as  a  nutritive  compound.  But  gluten  itself,  separated  from  the  flour 
by  the  process  above  described,  would  be  found  very  difficult  of  digestion, 
on  account  of  its  resistance  to  the  solvent  action  of  the  fluids  in  the 
stomach ;  indeed,  the  dough  composed  of  flour  and  water  is  proverbially 
indigestible,  even  when  baked.  In  order  to  render  it  fit  for  food,  it  must 
be  rendered  spongy  or  porous,  so  as  to  expose  a  larger  surface  to  the  action 
of  the  digestive  fluids  of  the  body ;  the  most  direct  method  of  effecting 
this  is  the  one  adopted  in  the  manufacture  of  the  aerated  bread,  and  con- 
sists in  mixing  the  flour  with  water  which  has  been  highly  charged,  under 
pressure,  with  carbonic  acid  gas  ;  the  mixing  having  been  efi'ected  in  a 
strong  closed  iron  vessel,  an  aperture  in  the  lower  part  of  this  is  opened, 
when  the  pressure  of  the  accumulated  gas  forces  the  dough  out  into  the 
air,  and  the  gas  which  had  been  imprisoned  in  the  dough  expands,  con- 
ferring great  porosity  and  sponginess  upon  the  mass  in  its  attempt  to 
escape.  In  another  process  for  preparing  7ivfermented  bread,  the  flour  is 
mixed  with  a  little  bicarbonate  of  soda,  and  is  then  made  into  a  dough 
with  water  acidulated  with  hydrochloric  acid ;  the  latter  decomposing 
the  bicarbonate  of  soda,  liberates  carbonic  aCid  gas,  which  renders  the 
hread  porous.  The  sodium  chloride  formed  at  the  same  time  remains 
in  the  bread.  In  the  preparation  of  cakes  and  pastry,  the  same  object  is 
sometimes  attained  by  adding  carbonate  of  ammonia  to  the  dough  ;  when 
heat  is  applied  in  the  baking,  the  salt  is  converted  into  vapour  which 
distends  the  dough. 

In  the  common  process  of  bread-making,  however,  the  carbonic  acid  gas 
destined  to  confer  sponginess  upon  the  dough  is  evolved  by  the  fermenta- 
tion of  the  sugar  contained  in  the  flour ;  the  latter  having  been  kneaded 
with  the  proper  proportion  (usually  about  half  its  weight)  of  water,  a  little 
yeast  and  salt  are  added,  and  the  mixture  is  allowed  to  stand  at  a  tempera- 
ture of  about  70°  F.  for  some  hours.  The  dough  swells  or  riiies  consider- 
ably in  consequence  of  the  escape  of  carbonic  acid  gas,  the  sugar  being 
decomposed  into  that  gas  and  alcohol,  as  in  ordinary  fermentation.  The 
spongy  dough  is  then  baked  in  an  oven,  heated  to  about  500=  F.,  when  a 
purcion  of  the  water  and  the  whole  of  the  alcohol  are  expelled,  the  carbonic 


PRODUCTION  OF  GRAPE-SUGAR  FROM  STARCH.  501 

acid  gas  being  also  much  expanded  by  the  heat,  and  the  porosity  of  the 
bread  increased.  The  granules  of  starch  are  much  altered  by  the  heat, 
and  become  far  more  digestible.  Although  the  temperature  of  the  inside 
of  the  loaf  does  not  exceed  212°  F.  the  outer  portion  becomes  torrefied  or 
scorched  into  crust. 

Occasionally,  instead  of  yeast,  leaven  is  employed,  in  order  to  ferment 
the  sugar,  leaven  being  dough  which  has  been  left  in  a  warm  place  until 
decomposition  has  commenced. 

The  passage  of  new  into  stale  bread  does  not  depend,  as  was  formerly 
supposed,  upon  the  drying  of  the  bread  consequent  upon  its  exposure  to 
air,  but  is  a  true  molecular  transformation  which  takes  place  equally  well 
in  an  air-tight  vessel,  and  without  any  loss  of  weight.  It  is  well  known 
that  when  a  thick  slice  of  stale  bread  is  toasted,  which  dries  it  still  further, 
the  crumb  again  becomes  soft  and  spongy  as  in  new  bread;  and  if  a  stale 
loaf  be  again  placed  in  the  oven,  it  is  entirely  reconverted  into  new  bread. 

"VVheaten  flour  is  particularly  well  fitted  for  the  preparation  of  bread  on 
account  of  the  great  tenacity  of  its  gluten.  Next  to  wheat  in  this  resj)ect 
stands  rye,  whilst  the  other  cereals  contain  a  gluten  so  deficient  in  tenacity 
that  it  is  impossible  to  convert  them  into  good  bread. 

Earley  bread  is  close  and  heavy,  since  its  nitrogenised  matter  is  chiefly 
present  in  the  form  of  albumen,  which  does  not  vesiculate  like  gluten, 
during  the  fermentation. 

Even  in  wheaten  flour  the  tenacity  of  the  gluten  is  liable  to  variation, 
and  in  order  to  obtain  good  bread  from  a  flour  the  gluten  of  which  is 
inferior  in  this  respect,  it  is  customary  to  employ  a  minute  proportion  of 
alum.  This  addition  being  considered  unwholesome  by  some  persons,  it 
would  be  better  to  substitute  lime-water,  which  has  been  found  by  Liebig 
to  have  a  similar  eflTect.  Sulphate  of  copper  improves  in  a  very  striking 
manner  the  quality  of  the  bread  prepared  from  inferior  flour,  but  this  salt 
is  far  more  objectionable  than  alum. 

The  Sugars. 

353.  The  conversion  of  starch  into  grape-sugar,  when  heated  in  contact 
with  diluted  acids  (page  493),  is  taken  advantage  of  for  the  preparation  of 
this  variety  of  sugar  on  the  large  scale.  For  this  purpose,  water  acidulated 
with  Y^th  of  sulphuric  acid  is  heated  to  ebullition,  and  a  hot  mixture  of 
starch  and  water  allowed  to  flow  gradually  into  it,  so  as  not  to  reduce  its 
temperature  below  the  boiling-point.  The  mixture  is  kept  boiling  for 
half  an  hour,  after  which  chalk  is  added  in  small  portions  at  a  time  to 
neutralise  the  sulphuric  acid,  and  the  sulphate  of  lime  having  been  allowed 
to  subside,  the  clear  syrup  is  drawn  off,  and  evaporated  to  the  crystallising 
point.  The  conversion  is  sometimes  accelerated  by  heating  under  pressure 
with  steam  at  320°  F. 

The  grape-sugar  or  glucose  thus  manufactured  cannot  be  employed  as  a 
substitute  for  the  sugar  extracted  from  the  sugar-cane,  on  account  of  its 
greatly  inferior  sweetening  power,  which  is  less  than  half  that  possessed 
by  cane-sugar.*  It  is,  moreover,  far  less  soluble  in  water,  1  part  of  grape- 
sugar  requiring  IJ  part  of  water  to  dissolve  it,  whilst  cane-sugar  requires 
only  \  part.     Grape-sugar  has  been  employed,  however,  for  the  adultera- 

*  Hence  the  loss  of  sugar  by  sweetening  tarts  before  baking  them,  part  of  the  sugar  being 
converted  into  grape-sugar  by  the  vegetable  acids  of  the  fruit. 


502  PRODUCTION  OF  SUGAR  FROM  CELLULOSE. 

tion  of  cane-sugar  and  honey.  The  fraud  is  easily  detected  in  cane-sugar 
by  boiling  a  portion  of  the  sample  with  a  little  solution  of  potash,  when 
the  grape-sugar  is  decomposed,  and  colours  the  liquid  intensely  brown, 
pure  cane-sugar  giving  very  little  brown  colour  unless  boiled  for  a  long 
time.  A  more  delicate  mode  of  detection  consists  in  adding  to  a  solution 
of  the  sugar  a  few  drops  of  solution  of  cupric  sulphate,  and  enough  solu- 
tion of  potash  to  form  an  intensely  blue  liquid.  The  cupric  oxide  is  nob 
precipitated  in  the  presence  of  either  of  the  sugars;  but  if  the  blue  liquid 
be  very  gently  heated,  a  red  precipitate  of  cuprous  oxide  will  separate  if 
grape-sugar  be  present,  whilst  with  pure  cane-sugar  the  precipitation  does 
not  take  place  unless  the  solution  is  boiled.  Calcium  sulphate  will 
generally  be  detected  in  sugar  or  honey  adulterated  with  glucose. 

Even  cellulose  is  transformed  into  dextrine  and  glucose  under  the 
influence  of  sulphuric  acid.  If  linen,  calico,  cotton- wool,  or  paper  be  dried 
and  gradually  moistened  with  1|  part  of  concentrated  sulphuric  acid,  avoid- 
ing elevation  of  temperature,  it  is  converted  in  the  course-  of  a  few  hours 
into  a  gummy  mass  which  dissolves  in  water,  and  is  very  similar  to  dex- 
trine. When  the  cellulose  has  been  left  in  contact  with  the  acid  for  a  day 
or  two,  it  should  be  dissolved  in  a  large  quantity  of  water,  and  boiled  for 
eight  or  ten  hours  hours  in  order  to  effect  the  conversion  into  glucose;  the 
acid  may  then  be  neutralised  with  chalk,  the  solution  filtered  from  the 
calcium  sulphate,  and  evaporated,  Avhen  it  furnishes  a  crystalline  mass  of 
glucose. 

Closely  connected  with  the  conversion  of  cellulose  into  dextrine  by  con- 
tact with  strong  sulphuric  acid,  is  that  very  remarkable  change  of  paper 
into  vegetable  parcliment.  If  dry  white  blotting-paper  be  drawn  through 
a  cooled  mixture  of  the  strongest  oil  of  vitriol  with  half  its  bulk  of  water, 
and  be  then  thoroughly  washed  in  a  large  volume  of  water,  it  becomes 
live  times  as  strong  as  before,  and  has  f  ths  of  the  strength  of  ordinary 
animal  parchment.  The  parchment  paper,  when  dry,  is  found  to  have 
suffered  no  alteration  in  weight,  and  analysis  shows  its  composition  to  be 
unchanged.  This  remarkable  increase  in  strength  must,  therefore,  be  re- 
ferred to  a  molecular  alteration.  The  paper  is  also  found  to  have  become 
almost  waterproof,  and  presents  a  somewhat  translucent  appearance  like 
paper  which  has  been  slightly  oiled.  It  receives  many  useful  applications, 
for  lugggage  labels  which  are  not  easily  torn  or  removed  by  rain,  and  as  a 
substitute  for  animal  membrane  in  tying  over  preserves,  &c. 

Hydroccllulosc  is  the  name  given  by  A.  Girard  to  the  brittle  substance  into  which 
cellulose  is  converted  by  the  action  of  mineral  acids  on  cellulose.  It  is  prejiared  by 
immersing  cellulose  for  twelve  hours  at  15°  C.  in  sulphuric  acid  of  sp.  gr.  1"453.  It 
differs  from  cellulose  in  the  facility  with  which  it  may  be  powdered,  and  in  its  greater 
susceptibility  to  oxidation  and  to  the  action  of  reagents.  Its  composition  is  represented 
by  Cj2Hjj.,0u,  which  would  be  2  molecules  of  cellulose,  CgHioOg,  with  addition  of  the 
elements  of  water.  Girard  believes  that  the  rotting  of  window  curtains  in  towns  is 
due  to  the  conversion  into  hydrocellulose  by  the  acid  vapours  in  the  air,  and  that  drrj 
rot  in  wood  is  due  to  a  similar  change  caused  by  acid  substances  generated  in  the 
wood  by  fermentation.  Hydrocellulose  yields  friable  pyroxyline  compounds  when 
treated  with  the  mixture  of  sulphuric  and  nitric  acids. 

The  susceptibility  of  conversion  into  grape-sugar  possessed  by  starch  and 
cellulose  affords  a  very  important  clue  in  tracing  the  changes  which  take 
place  in  living  vegetables.  It  has  been  already  seen  (page  494)  that  during 
the  gerniination  of  seeds,  their  starch  is  converted  into  sugar,  in  order  that 
it  may  be  carried  in  a  soluble  form  to  the  extending  limbs  of  the  vegetable 


EXTRACTION  OF  CANE-SUGAB.    _  503 

frame ;  but  it  would  appear  that  in  these  parts,  where  a  deposition  of 
cellulose  is  required,  the  sugar  (CgH^g^e)  ^^  reconverted  into  that  substance 
(CgHj^Oj).  In  the  ripening  of  the  fruit,  however,  the  ligneous  matter  and 
the  starch  seem  to  be  again  converted  into  sugar,  under  the  influence  of 
the  vegetable  acids  which  unripe  fruits  contain. 

The  sugar  contained  in  ripe  fruits  and  in  new  honey  is  usually  a  mix- 
ture of  about  equal  weights  of  grape-sugar  or  dextrose,  and  uncrystallisable 
sugar  or  levulose.  These  have  the  same  composition  (CgH^^Og),  but  levulose 
is  more  soluble  in  alcohol  than  dextrose,  and  rotates  the  plane  in  which  a 
ray  of  light  is  polarised  towards  the  left,  while  dextrose  turns  it  towards 
the  right  hand. 

When  starch  is  acted  on  by  infusion  of  malt,  it  is  converted  into  a 
particular  kind  of  sugar  termed  maltose  (CjgHggOij.HgO),  which  is  less 
soluble  in  alcohol  than  dextrose,  into  which  it  is  converted  by  the  action 
of  acids.  Its  production  seems  to  constitute  an  intermediate  stage  in  the 
transition  of  starch,  cellulose,  and  cane-sugar  into  grape-sugar.  Hence  it 
is  found  that  if  the  ebullition  with  diluted  sulphuric  acid  be  arrested  as 
soon  as  the  liquid  becomes  sweet,  no  crystals  can  be  obtained,  but  on 
further  ebullition  the  levulose  ox  fructose  is  converted  into  crystaUisable 
glucose.  When  honey  is  kept  for  some  time,  the  fructose  gradually 
becomes  converted  into  a  crystalline  mass  of  glucose.  The  same  change 
is  seen  to  take  place  in  raisins,  which  contain  granules  of  glucose,  though 
the  fresh  grapes  contain  only  fructose.  Cold  alcohol  extracts  about  35 
per  cent,  of  levulose  from  honey,  leaving  about  the  same  weight  of 
dextrose  Avhich  may  be  dissolved  in  boiling  alcohol  and  crystallised. 
These  crystals  are  anhydrous,  but  those  obtained  from  an  aqueous  solution 
are  CgHi.Pg.H.O. 

The  uncrystallisable  sugar  forms  the  chief  ingredient  of  molasses  and 
treacle,  for  although  the  fresh  juice  of  the  sugar-cane  contains  no  fructose, 
the  treatment  to  which  it  is  subjected  in  the  extraction  of  the  sugar 
occasioQs  a  copious  formation  of  the  uncrystallisable  sugar  at  the  expense 
of  the  cane-sugar.  The  simple  ebullition  of  a  solution  of  cane-sugar  for  a 
considerable  period  is  said  to  convert  a  portion  of  it  into  fructose,  and  if 
a  minute  quantity  of  any  uncombined  acid  be  present,  the  change  takes 
place  very  rapidily.  Pui-e  cane-sugar  dissolved  in  water  gradually  changes 
into  fructose  when  exposed  to  the  light. 

354.  Extraction  of  cane-sugar. — In  the  extraction  of  sugar  from  the. 
sugar-cane,  the  latter  is  cut  before  the  period  of  floAvering,  when,  as  might 
be  expected,  this  soluble  nutriment  of  the  plant  is  most  abundant.  For 
a  similar  reason,  the  canes  are  cut  off  close  to  the  ground,  since  in  the 
higher  joints  of  the  cane  much  of  the  sugar  has  already  been  consumed  for 
their  development.  A  specimen  of  sugar-cane  from  Martinique  was  found 
to  contain  90"1  per  cent,  of  juice  and  99  of  woody  fibre,  so  that,  theoreti- 
cally, 100  parts  of  cane  should  yield  as  much  as  90  parts  of  juice.  The 
canes  are  crushed  between  iron  cylinders,  which  express,  under  the  best 
arrangements,  only  65  parts  of  juice  from  100  of  cane.  It  has  been  found 
possible  to  increase  the  yield  by  steaming  the  canes  before  submitting 
them  to  a  final  pressure.  The  juice  thus  expressed  contains  about  18  per 
cent,  of  sugar,  together  with  the  usual  components  of  the  sap  of  plants, 
such  as  vegetable  acids,  albumen,  salts,  &c. 

In  the  tropical  climate  in  which  the  extraction  is  conducted,  the  albu- 


504  SUGAR-REFINING. 

men  of  the  juice  speedily  alters  when  exposed  to  the  air,  and  excites 
fermentation  in  the  sugar,  by  which  a  considerable  quantity  would  be  lost. 
If  the  fresh  juice  were  heated  to  coagulate  the  albumen,  the  free  acid  con- 
tained in  it  would  change  a  portion  of  the  sugar  into  the  uncrystallisable 
variety.  To  avoid  this,  the  juice  is  mixed  with  ^^th  part  of  slaked  lime, 
and  is  then  heated  to  140°  F.  in  large  flat  copper  pans.  The  coagulated 
albumen  rises  to  the  surface  of  the  heavy  syrup,  and  forms  a  thick  scum, 
which  is  taken  off,  and  the  clear  syrup  is  evaporated  till  it  is  strong  enough 
to  crystallise,  when  it  is  run  off  into  shallow  wooden  vats,  and  allowed 
to  cool  for  twenty-four  hours.  When  briskly  stirred,  it  congeals  to  a 
semi-solid  mass  of  crystals,  which  are  allowed  to  drain  for  three  weeks  in 
ca.sks  with  perforated  bottoms.  The  raw  sugar  thus  obtained,  after  dry- 
ing in  the  sun,  is  sent  into  commerce,  the  drainings  being  styled  molasses 
or  treacle.  The  weight  of  raw  sugar  seldom  exceeds  ^uth  of  the  juice, 
that  is,  about  half  the  quantity  which  the  juice  is  known  to  contain,  the 
remainder  having  been  converted  into  uncrystallised  sugar  during  the 
process  of  extraction.  The  loss  is  found  to  be  materially  diminished  by 
the  use  of  vacuum  pans,  in  which  the  evaporation  of  the  syrup  is  con- 
ducted under  diminished  pressure,  and  therefore  at  a  lower  temperature. 
Greater  economy  is  also  introduced  into  the  m.anufacture  by  the  use  of 
the  crushed  canes  as  fuel  for  the  evaporating  fires,  and  by  restoring  their 
ashes  to  the  land  as  food  for  ensuing  crops.  The  skimmings  of  the  clarified 
juice  are  also  advantageously  used  as  manure. 

The  raw  sugar  obtained  by  the  process  just  described  contains  about 
60  per  cent,  of  pure  cane-sugar,  the  remainder  consisting  of  water,  un- 
crystallisable  sugar,  colouring  matter,  and  various  salts  and  other  foreign 
substances  derived  from  the  cane-juice. 

In  the  ordinary  process  of  sugar-refining,  two  or  three  parts  of  raw 
sugar  are  dissolved  in  one  part  oif  water  containing  a  little  lime  in  solu- 
tion, and  mixed  with  three  or  four  parts  of  ground  bone-black  for  every 
hundred  of  sugar ;  a  small  quantity  of  serum  of  bullock's  blood  is  also 
sometimes  added.  This  mixture  is  heated  by  the  passage  of  steam  through 
it,  when  the  albumen  of  the  serum  is  coagulated,  and  rises  to  the  surface 
in  the  form  of  a  scum  which  entangles  the  floating  impurities  as  well  as 
the  bone-black,  and  leaves  the  syrup  much  lighter  in  colour,  a  consider- 
able part  of  the  colouring  matter  having  been  removed  by  the  charcoal. 

The  syrup  is  then  filtered  through  a  thick  layer  of  coarsely  powdered 
bone-black,  and  is  thus  rendered  perfectly  colourless  and  ready  for  evapora- 
tion, which  is  conducted  in  a  boiler  with  double  sides,  so  that  it  may  be 
heated  by  steam  admitted  between  the  two,  and  furnished  with  a  dome 
from  which  the  air  may  be  exhausted  in  order  to  allow  the  evaporation 
to  be  conducted  at  a  lower  temperature,  as  well  as  out  of  contact  with 
the  atmospheric  oxygen,  so  as  to  diminish  as  far  as  possible  the  produc- 
tion of  uncrystallisable  sugar.  The  boiling  down  of  the  syrup,  which 
would  require  a  temperature  of  230°  F.  at  the  ordinary  pressure,  may 
thus  be  conducted  at  160°  F.  When  sufficiently  evaporated,*  the  syrup 
is  transferred  to  a  heated  vat,  where  it  is  stirred  until  a  confused 
crystallisation  commences,  and  is  then  drawn  off"  into  inverted  sugar- 
loaf  moulds  of  iron  or  earthenware,  and   allowed   to  crystallise  during 

*  Tlie  state  of  concentration  of  the  syrup  is  known  by  the  degree  of  viscidity  which  it 
exhibits  between  the  finger  and  thumb,  by  the  length  of  the  thread  to  which  it  may  be 
drawn,  and  by  the  mode  iu  which  this  curls  after  breaking. 


BEET-EOOT  SUGAR.  505 

about  twenty  hours.  The  crystalline  mass  is  then  allowed  to  drain  by  the 
withdrawal  of  a  plug  at  the  apex  of  the  inverted  cone,  and  is  washed 
with  a  little  pure  syrup  to  remove  adhering  colouring  matter,  after  which 
the  loaf  is  dried  in  an  oven  and  finished  by  turning  in  a  lathe. 

The  operation  of  washing  with  syrup  is  often  referred  to  as  claying, 
being  sometimes  effected  by  placing  some  powdered  sugar  upon  the  base 
of  each  loaf,  and  over  this  a  cream  of  pure  pipeclay,  the  water  draining 
from  which  dissolves  the  powdered  sugar,  and  the  syrup  thus  formefl 
washes  the  loaf.  The  object  of  the  clay  appears  to  be  simply  to  allow 
the  water  to  flow  gradually  through  the  sugar. 

The  process  of  retining  is  sometimes  shortened  by  washing  the  raw 
sugar  with  strong  syrup,  so  as  to  remove  the  bulk  of  the  impurities  at 
the  commencement,  and  a  very  ingenious  method,  known  as  the  centri- 
fugal process,  has  been  devised  for  separating  the  syrup  from  the  sugar 
thus  washed.  The  pasty  mixture  of  sugar  and  syrup  is  introduced  into 
a  cylinder  of  strong  close  metallic  gauze,  which  is  rapidly  turned  upon 
its  axis,  when  the  liquid  syrup  of  course  flies  off  through  the  apertures 
of  the  gauze,  and  is  collected  by  a  box  surrounding  the  cylinder.  A  fresh 
quantity  of  syrup  is  then  introduced,  and  separated  in  the  same  manner, 
so  that  the  washing  may  be  rapidly  carried  as  far  as  may  be  deemed 
expedient. 

355.  During  the  wars  of  Ifapoleon,  when  the  importation  of  sugar  into 
France  was  suspended,  this  substance  was  extracted  from  the  beet-root, 
and  this  process  still  forms  a  very  important  branch  of  French  industry. 

The  white  beet  only  is  employed,  on  account  of  the  difficulty  of  separ- 
ating the  colouring  matter  existing  in  the  juice  of  the  red  variety.  The 
juice  contains  about  10  per  cent,  of  cane-sugar,  half  of  which  only  is 
usually  obtained  in  the  crystallised  state.  The  process  adopted  for  ex- 
tracting it  does  not  differ  in  principle  from  that  applied  to  the  juice  of 
the  sugar- cane. 

Cane-su>;ar  is  also  extracted  in  the  United  States  from  the  sap  of  the 
sugar-maple,  which  is  collected,  usually  in  the  spring,  from  deep  incisions 
through  the  bark,  into  each  of  which  a  pipe  of  reed  or  elder  is  inserted 
to  conduct  the  juice  into  pans  placed  for  its  reception,  whence  it  is  re- 
moved before  it  has  had  time  to  become  changed  by  fermentation.  The 
juice  is  evaporated  rapidly,  and  the  raw  crystalline  mass  sold  without 
further  refining.  On  an  average,  each  tree  furnishes  about  6  lbs.  of  sugar 
during  the  season. 

Sugar-candy  consists  simply  of  large  rhomboidal  prismatic  crystals  of 
sugar  deposited  upon  strings  stretched  across  crystallising  troughs,  in 
which  a  strong  syrup  is  slowly  evaporated  at  about  170°  F. 

Barley-sugar  is  prepared  by  evaporating  the  syrup  beyond  the  crystal- 
lising-point,  till  it  solidifies,  on  cooling,  to  a  vitreous  mass,  which  is  poured 
out  on  a  cold  surface  and  manipulated  to  the  requisite  forms.  When 
kept  for  some  time,  the  transparent  barley-sugar  becomes  crystalline  and 
opaque. 

Caramel  (CjoHjgOg)  is  a  dark  brown  substance  produced  by  the  action 
of  a  temperature  of  about  400°  F.  upon  melted  sugar.  It  is  very  soluble 
in  water,  and  gives  an  intensely  brown  liquid,  for  which  reason  it  is 
employed  for  colouring  sauces,  gravies,  brandy,  wines,  <fec. 

356.  Chemical  yn-opcrties  of  the  sugars. — Although  cane-  and  grape-sugar  appear  to 
be  essentially  indifterent  substances,  they  are  remarkably  prone  to  lorm  combinations 


506  CHKmCAL  PROPERTIES  OF  THE  SUGARS. 

with  many  basic  metallic  oxides.  Thus  a  solution  of  cane-sugar  is  capable  of  dissolv- 
ing a  large  quantity  of  lime,  forming  a  compound  (CaO.CioHjjOn)  which  is  much 
ixiore  soluble  in  cold  than  in  hot  water,  so  that  on  boiling  the  transparent  solution  it 
becomes  perfectly  opaque,  but  resumes  its  transparency  on  cooling.  This  has  been 
applied  for  separating  the  crystallisable  sugar  from  molasses,  the  compound  of  sugar 
and  lime,  precipitated  by  boiling,  being  redissolved  in  cold  water  and  treated  with 
carbonic  acid  to  separate  the  lime. 

On  boiling  lead  hydrate  with  a  solution  of  sugar,  it  is  dissolved,  and  as  the  solution 
cools,  a  white  powder  is  deposited,  which  has  the  composition  2PbO.C12H1gOg.H2O, 
the  water  being  expelled  at  a  temperature  of  212°.  The  composition  of  this  compound 
would  lead  to  the  belief  that  cane-sugar  contains  two  molecules  of  con.stitutioDal 
water,  and  that  its  formula  should  be  written  C10H18O9.2H2O.  By  carefully  heating 
cane-sugar,  the  compound  CijHgoOio,  saccharide,  has  been  obtained,  and  if  this  be 
further  heated  it  yields  CioHj^Og,  caramel.  When  a  solution  containing  1  part  of 
salt  and  4  parts  of  sugar  is  allowed  to  evaporate  spontaneously,  it  deposits  a  deli- 
quescent compound  containing  2(NaCl.Ci2Hi809).3H<jO. 

Many  metallic  oxides  form  compounds  with  sugar,  which  are  readily  soluble  in 
alkaline  licjuids,  so  that  the  addition  of  sugar  to  solutions  of  the  oxides  of  copper  and 
iron,  for  example,  prevents  the  precipitation  of  these  oxides  by  the  alkalies. 

Graj)e-sugar  also  combines  with  many  bases.  The  compounds  which  it  forms  with 
the  alkalies  are  very  unstable,  and  their  solutions,  which  are  at  first  alkaline,  soon 
become  neutral  in  consequence  of  the  conversion  of  the  grape-sugar  into  ghicic  acid 
(HjC'i-^HijOg)  by  the  loss  of  the  elements  of  water. 

By  saturating  a  solution  of  grape-sugar  with  common  salt,  a  liquid  is  obtained 
which  deposits  well-defined  crystals,  having  the  composition  2(CgHij,Og).NaCl.HaO. 
AVhen  dried  at  212°  it  becomes  2(CgHi20g).NaCl.  The  true  foimula  of  grape-sugar  is 
obviously  CgHijOg.  H^O,  for  if  it  be  dissolved  in  hot  strong  alcohol  (which  dissolves 
far  more  grape-sugar  than  cane-sugar)  it  crystallises  on  cooling,  in  prisms,  which 
have  the  formula  CgHiaOg.  A  molecule  of  water  maj'  also  be  expelled  from  ordinary 
grape-sugar  at  212°  F. 

The  ai;tion  of  sulphuric  acid  upon  cane-  and  grape-sugar  is  very  different ;  the 
former  is  carbonised  and  completely  decomposed,  whilst  the  latter  combines  with  the 
sulphuric  acid  to  form  sulphosaccharic  acid,  which  yields  soluble  salts  with  lime  and 
baryta.* 

The  optical  properties  of  solutions  of  the  sugars  are  now  often  turned  to  account  for 
their  identification,  and  even  for  the  determination  of  their  quantities.  Grape-sugar 
and  cane-sugar  both  rotate  the  plane  of  polarisation  of  a  ray  from  left  to  right,  cane- 
sugar  having  rather  a  more  powerful  action,  but  the  uncrystallisable  fruit-sugar 
rotates  the  plane  in  the  opposite  direction,  from  right  to  left.  If  a  solution  of  cane- 
sugar,  possessing  the  rotatory  power  from  left  to  right,  be  heated  with  hydrochloric 
acid,  it  acquires  the  power  of  rotating  the  plane  of  polarisation  from  right  to  left, 
in  consequence  of  the  conversion  into  uncrystallisable  (or  inverted)  sugar. 

Starch -sugar  exhibits  three  different  modes  of  action  upon  polarised  light,  for  a 
solution  which  has  been  kept  some  hours  rotates  the  plane  of  polarisation  only  half 
as  much  as  the  freshly  made  solution  ;  and  if  the  sugar  prepared  from  malt  be  dis- 
solved in  water,  the  solution  has  thrice  the  rotatory  power  which  it  possesses  after 
being  kept,  and  its  rotatory  power  is  one-third  higher  than  that  of  the  freshly -dis- 
solved starch-sugar.  All  these  may  be  reduced  at  once  to  the  lowest  rotatory  power 
by  heating  them  nearly  to  ebullition  and  allowing  them  to  cool. 

357.  Mannite  (CgHj^Og),  the  sweet  principle  of  manna  (the  concrete  juice  of  the 
Fraxinus  onms),  has  already  been  noticed  as  one  of  the  products  of  that  peculiar 
kind  of  fermentation  known  as  the  viscous,  to  which  beet-root  juice  is  especially 
liable.  It  is  also  found  in  certain  mushrooms,  in  sea-weeds,  celery,  asparagus,  and 
onions,  and  as  an  efflorescence  on  the  Laminuria  saccfuirina  or  sugar-wrack.  By 
treating  manna  with  hot  alcohol,  and  allowing  the  filtered  solution  to  cool,  the 
mannite  may  be  obtained  in  beautiful  prismatic  crystals,  which  have  a  sweet  taste, 
and  dissolve  readily  in  water.  Mannite  differs  widely  from  cane-  and  graj)e-sugar  in  not 
fermenting  when  placed  in  contact  with  yeast  ;  and  this  circumstance,  taken  in  con- 
junction with  its  composition,  which  differs  so  much  from  that  of  other  members  of 
tlie  saccharine  group,  has  always  led  to  the  belief  that  it  was  not  properly  classed 

*  Ethyle-gbicose,  a  bitter,  fragrant,  oily  substance,  has  been  obtained  by  acting  upon 
grape-sugar  with  ethyle  bromide  and  potash ;  it  may  be  represented  by"  the  fommla 
<^'6H8(C,H5)A. 


GUN-COTTON — PYROXYLTNE.  :  507 

among  these.  Recent  investigations  have  given  it  a  place  by  the  side  of  glycerine, 
the  sweet  principle  of  fats  and  oils,  as  will  be  seen  hereafter. 

Olycyrrhizine,  the  sweet  principle  of  the  liquorice  root,  somewhat  resembles  man- 
nite,  but  does  not  crystallise.  The  sweetness  of  liquorice  root  appears  to  be  due  to 
a  soluble  compound  of  glycyrrhizine  with  ammonia,  the  glycyrrhizine  itself  being 
almost  insoluble  and  tasteless. 

Sorbite,  having  the  same  composition  as  mannite,  is  a  crystalline  substance  extracted 
from  the  berries  of  the  mountain  ash  {Sorbus  aticuparia). 

GUN  COTTON  AND  SUBSTANCES  ALLIED  TO  IT. 

358.  Starch,  the  sugars,  and  cellulose,  when  acted  on  by  the  strongest 
nitric  acid,  furnish  compounds  which,  are  remarkable  for  their  explosive 
character.  By  far  the  most  important  of  these  is  pijroxyline  {irvpjire,  ^vXov, 
wood),  which  is  produced  by  the  action  of  nitric  acid  upon  the  dift'erent 
forms  of  woody  fibre,  including  wood,  cotton,  and  paper. 

If  a  piece  of  white  unsized  paper  (filter-paper)  be  soaked  for  a  few 
minutes  in  the  strongest  nitric  acid  (sp.  gr.  1'52),  then  washed  in  a  large 
volume  of  water  and  allowed  to  dry,  it  wiU  be  found  to  have  suffered 
little  alteration  in  appearance  or  texture,  but  to  have  acquired  the  pro- 
perty of  burning  very  rapidly  on  the  application  of  a  flame  or  even  of  a 
moderately  heated  glass  rod.  This  is  due  to  the  presence,  in  the  altered 
paper,  of  a  quantity  of  oxygen  in  the  form  of  NO3,  which  serves  to  burn 
up  the  paper  very  rapidly,  rendering  it  in  great  measure  independent  of 
any  extraneous  supply  of  oxygen. 

The  pyroxyline  so  obtained,  however,  is  always  associated  with  a  quan- 
tity of  unaltered  paper,  for  water  is  formed  by  the  oxidation  of  the 
hydrogen  in  the  paper,  and  dilutes  the  remaining  nitric  acid,  so  that  unless 
a  very  large  proportion  of  nitric  acid  were  employed,  the  acid  would  become 
so  far  weakened  towards  the  close  of  the  operation  as  to  be  incapable  of 
converting  the  last  portions  of  paper  into  pyroxyline.  Moreover,  since 
each  fibre  composing  the  paper  is  a  very  minute  tube,  often  folded  several 
times,  it  is  not  possible  for  the  nitric  acid  to  penetrate  its  entire  substance 
unless  the  paper  be  soaked  in  it  for  a  long  time. 

In  order  to  effect  a  more  complete  conversion  of  the  woody  fibre  into 
pyroxyline,  the  nitric  acid  must  be  mixed  with  strong  sulphuric  acid, 
which  will  combine  with  the  water  produced  by  the  action  of  the  nitric 
acid  upon  the  hydrogen  of  the  fibre,  and  will  thus  virtually  maintain  the 
nitric  acid  at  its  greatest  strength  throughout  the  operation.  Cotton-wool, 
from  the  looseness  of  its  texture,  is  more  easily  converted  into  pyroxyline 
than  paper. 

The  following  proportions  may  be 
recommended  for  preparation  of 
gun-cotton  on  a  small  scale  : — Dry 
1000  grains  of  pure  nitre  (page  416) 
at  a  very  moderate  heat,  place  it  in  a 
dr}'  retort  (tig.  288),  pour  upon  it  10 
drachms  (by  measure)  of  strong  sul- 
jihuric  acid,  and  distil  until  6 
drachms  of  nitric  acid  have  passed 
over  into  the  receiver.  Dry  some 
pure  cotton-wool,  and  weigh  out  30 
grains  of  it.  Mix  2^  measured 
drachms  of  the  nitric  acid  with  an  Fig.  288. 

equal  volume   of  strong   sulphuric 

acid  in  a  small  beaker.  Allow  the  mixture  to  cool,  immerse  the  cotton-wool  in 
separate  tufts,  pressing  it  down  with  a  glass  rod,  cover  the  beaker  with  a  glass  plate. 


508  MANUFACTURE  OF  GUN-COTTON. 

and  set  it  aside  for  fifteen  minutes.  Lift  the  cotton  out  \vith  a  glass  rod,  throw  it  into 
at  least  a  pint  of  water,  and  wash  it  thoroughly  in  a  stream  of  water  till  it  no  longer 
tastes  acid  or  reddens  blue  litmus  paper.  Cry  the  cotton  by  exposure  to  air  or  to  a 
very  moderate  heat. 

Very  great  great  attention  has  been  paid  to  the  manufacture  of  gun-cotton 
during  the  hist  few  years,  with  the  object  of  producing  a  perfectly  uniform 
product  which  might  be  employed  as  a  substitute  for  gunpowder. 

The  following  is  an  outline  of  the  process  now  generally  adopted  for 
the  production  of  large  quantities  of  gun-cotton  by  Abel's  process: — 

359.  Manufacture  of  gun-cotton. — The  cotton  is  employed  in  the  form  of  the  waste 
cuttings  from  spinning  machines  (cotton  waste),  and  is  thoroughly  cleansed. 

Tlie  proportions  in  which  it  is  found  most  advantageous  to  mix  the  nitric  and 
sulphuric  acids  are  1  part  of  nitric  acid  (sp.  gr.  1'52)  and  3  parts  by  weight  (or  2 '45 
by  volume)  of  sulphuric  acid  (sp.  gr.  1'84).  These  proportions  of  the  acids  are  placed 
in  separate  stoneware  cisterns  with  taps,  and  allowed  to  run  simultaneously,  in  slow 
streams,  into  another  stoneware  cistern  furnished  with  a  tap  and  an  iron  lid,  through 
a  second  opening  in  which  an  iron  stirrer  is  employed  to  mix  the  acids  thoroughly. 
The  mixture  is  set  aside  for  several  hours  to  become  perfectly  cool. 

A  quantity  of  the  mixed  acids  is  drawn  off  into  a  deep  stoneware  i)an  standing  in 
cold  water,  and  provided  with  a  perforated  iron  shelf,  upon  which  the  cotton  may  be 
drained.  The  well-dried  cotton  is  immersed,  a  little  at  a  time,  in  the  acid,  and 
stirred  about  in  it  for  two  or  three  minutes  with  an  iron  stirrer.  It  is  then  placed 
upon  the  perforated  shelf,  and  the  excess  of  acid  squeezed  out  with  the  stirrer. 
Enough  acid  is  drawn  from  the  cistern  to  replace  that  which  has  been  absorbed  by 
the  cotton,  and  more  cotton  is  treated  in  the  same  way.  Since  a  considerable  rise  of 
temperature  is  produced  by  the  action  of  the  nitric  acid  upon  the  cotton,  it  is  neces- 
sary to  keep  the  pan  surrounded  with  cold  water.  A  large  proportion  of  the  cotton 
is  doubtless  converted  into  gun-cotton  in  this  preliminary  immersion  in  the  mixed 
acids  ;  but  in  order  to  convert  the  remainder,  it  is  necessary  to  allow  the  cotton  to 
remain  in  contact  with  the  acid  for  a  much  longer  period,  so  as  to  ensure  its  pene- 
tration into  every  part  of  the  minute  twisted  tubes  of  the  fibre.  The  preliminary 
immersion  of  each  skein  has  the  advantage  of  wetting  every  part  with  the  acid,  which 
could  not  be  so  certainly  eff"ected  if  several  skeins  were  thrown  at  once  into  a  jar^ 
and  of  preventing  the  great  accumulation  of  heat  which  would  ensue  if  the  entire 
chemical  action  were  allowed  to  take  place  upon  anumber  of  skeins  at  the  same  time. 
The  amount  of  heat  evolved  during  the  subsequent  soaking  in  acid  is  comparatively 
small. 

The  skeins  are  next  transferred  to  a  jar  with  a  well-fitting  cover,  in  which  they  arc 
pressed  down  and  completely  covered  with  the  mixed  acids,  of  which  from  ]0  to  15 
times  the  weight  of  the  cotton  will  be  required,  according  to  the  closeness  with  which 
the  skeins  are  packed  in  the  jar.  The  jar  is  placed  in  cold  water,  and  the  cotton 
allowed  to  remain  in  the  acid  for  about  twelve  hours. 

The  skeins  are  then  removed,  with  the  aid  of  an  iron  hook,  to  a  centrifugal 
extractor,  which  is  a  cylinder  made  of  iron  gauze,  through  which  the  liquid  is  whirled 
out  by  the  rapid  rotation  of  the  cylinder  upon  an  axle.  In  this  they  are  whirled,  at 
first  slowly,  and  afterwards  at  800  revolutions  per  minute,  during  ten  minutes,  when 
the  bulk  of  the  acid  is  separated.  In  order  to  wash  away  the  remainder  of  the  acid, 
the  cotton  is  plunged,  suddenly,  into  a  cascade  of  water  ;  for  if  the  water  were 
allowed  to  come  slowly  into  contact  with  the  mixed  acids,  so  much  heat  would  be 
evolved  as  to  decompose  a  portion  of  the  pyroxyline.  The  cotton  is  then  drained 
in  the  centrifrugal  extractor,  and  again  rinsed  in  much  water.  After  two  or  three 
rinsings  it  is  reduced  to  pulp  in  a  rag-engine  such  as  is  employed  in  pajjcr-mills.  The 
pulp  is  thoroughly  washed  by  being  well  stirred  up  by  a  poachhig -engine  for  about 
forty-eight  hours  in  a  stream  of  warm  water,  so  as  to  remove  everj'  trace  of  acid, 
which  is  assisted  by  rendering  the  water  alkaline  with  a  little  lime  or  carbonate  of 
soda  or  with  ammonia.  The  pulp  is  then  drained,  moulded  into  discs  or  any  other 
required  form,  condensed  by  hydraulic  pressure  until  it  has  at  least  the  same  specific 
gravity  as  water,  and  dried  upon  heated  plates.  As  it  leaves  the  hydraulic  press,  the 
cotton  contains  about  one-fifth  of  its  weight  of  water,  so  that  it  may,  if  required,  be 
cut  up  or  bored  without  danger  of  explosion. 

The  finisiied  gun-cotton  is  examined  by  the  following  tests  : — 

1.  Four  grains  are  heated  in  a  test-tube  placed  in  an  oil-bath,  and  containing  a  slip 


COMPOSITION  OF  GUN-COTTON.  .  509 

of  moistened  paper  imbued  with  potassium  iodide  and  starch  (to  detect  nitrous 
vapours).  No  tinge  should  be  imparted  to  the  paper  till  thf:  temperature  of  the  oil 
reaches  190°  F. 

2.  The  experiment  is  repeated,  omitting  the  test-paper,  and  closing  the  tube  with 
a  disk  of  card.  No  brown  fumes  should  be  perceived  on  looking  down  the  axis  of  the 
tube  below  a  temperature  of  320°  F. 

3.  One  grain  is  heated  in  a  test-tube  placed  in  an  oil-bath  till  it  explodes,  which 
should  not  haj)pen  below  343°  F. 

4.  The  gun-cotton  sliould  dissolve  entirely  in  acetic  ether,  which  would  leave  any 
unconverted  cotton  undissolved. 

5.  Fifty  grains  of  the  gun-cotton  should  suffer  little  loss  in  weight  when  digested 
for  two  or  three  hours  with  four  ounces  of  a  mixture  of  1  volume  alcohol  and  2  volumes 
ethei-,  which  would  dissolve  any  collodion-cotton. 

3G0.  Cheviical  composition  of  gun-cotton. — Perfectly  pure  gun-cotton 
contains  carbon,  hydrogen,  nitrogen,  and  oxygen,  in  proportions  which 
correspond  to  the  empirical  formula  CgB^NgOj^,  The  determination  of 
its  rational  formula  is  attended  with  difficulty,  because,  being  an  indiffer- 
ent substance,  it  does  not  form  definite  combinations  with  other  bodies 
of  known  molecular  weight,  and  it  is,  of  course,  impossible  to  arrive  at  its 
volume  in  the  state  of  vapour  which  so  frequently  affords  valuable  assist- 
ance in  fixing  a  rational  formula. 

The  most  probable  formula  is  CgH-02(N03)3,  which  represents  it  as  the 
nitric  ether  of  cellulose,  according  to  which  view  cellulose  is  a  triatomic 
alcohol,  CgH-02(OH)3,  to  which  gun-cotton  has  the  same  relation  as  nitric 
ether,  CoHgNO^,  has  to  alcohol  C2H;^(0H).  The  action  of  nitric  acid  upon 
the  cotton  would  then  be  represented  by  the  equation — 

CgH,0.,(0H)3  +  3HXO3  =  3H2O  +  CgH,02(N03)3 

Cellulose.  Cellulo-tiinitrine. 

If  gun-cotton  be  digested,  at  a  gentle  beat,  for  about  fifteen  minutes,  in  an 
alcoholic  solution  of  KHS  (prepared  by  dissolving  KHO  in  alcohol  and 
thoroughly  saturating  with  H2S)  it  is  reconverted  into  cellulose — 

CgH-02(X03)3  -1-  3KHS  =  C^Yi^O^{OB)^  +  3KNO2  +  S3 

Gun-cotton.  Cellulose.  Potossiuui  nitiite. 

If  gun-cotton  were  trinitrocellulose,  CgH-(X02)305,  the  action  of  KHS 
miyht  be  expected  to  convert  it  into  an  organic  base,  just  as  it  converts 
nitrobenzene  CgH5(N02)  into  aniline  CgH^CXHg). 

361.  Products  of  the  explosifm  of  gun-cotton. — From  what  has  been 
stated  with  respect  to  the  products  of  explosion  of  gunpowder  (page  422), 
it  might  be  expected  that  those  furnished  by  gun-cotton  would  vary  accord- 
ing to  the  conditi(ms  under  which  the  explosion  takes  place.  When  a 
mass  of  the  gun-cotton  wool  is  exploded  in  an  unconfined  state,  the 
explosion  is  comparatively  slow  (though  appearing  to  the  eye  almost  in- 
stantaneous), since  each  particle  is  fired  by  the  flame  of  that  immediately 
ailjoiniug  it,  the  heated  gas  (or  flame)  escaping  outwards,  so  that  some 
time  elapses  before  the  interior  of  the  mass  is  ignited.  But  when  the 
gun  cotton  is  enclosed  in  a  strong  case,  so  that  the  flame  from  the  portion 
first  ignited  is  unable  to  escape  outwards,  and  must  spread  into  the  interior 
of  the  mass,  this  is  ignited  simultaneously  at  a  great  number  of  points, 
and  the  decomposition  takes  place  far  more  rapidly;  a  given  Aveight  of 
cotton  being  thus  consumed  in  a  much  shorter  time,  a  far  higher  tempera- 
ture is  produced,  and  the  ultimate  results  of  the  explosion  are  much  less 
complex,  as  would  be  expected  from  the  well-known  simplifying  effect  of 
higli  temperatures  upon  chemical  compounds. 


510  PRODUCTS  OF  EXPLOSION  OF  GUN-COTTON, 

If  a  tuft  of  gun-cotton  wool  be  placed  at  the  bottom  of  a  tall  glass  cylinder,  and 
inflamed  by  a  heated  wire,  it  will  be  seen  that,  immediately  after  the  explosion,  the 
gas  within  the  cylinder  is  colourless,  but  it  soon  becomes  red,  showing  that  nitric 
oxide  was  present  among  the  products,  and  became  converted  into  nitric  peroxide  by 
the  oxygen  of  the  air.  The  water  formed  by  the  combustion  of  the  hydrogen  converts 
the  nitric  peroxide  into  nitrous  and  nitric  acids  (p.  145),  and  hence  the  acid  character  of 
the  moisture  deposited  in  the  barrel  of  a  fowling-piece  in  which  gun-cotton  cartridges 
are  employed. 

A  little  hydrocyanic  acid  can  be  detected  among  the  products  of  combustion  of 
loo.se  gun-cotton. 

The  determination  of  the  products  of  explosion  of  confined  gun-cotton 
lias  been  effected  by  Karolyi,  by  enclosing  the  cotton  in  a  cast-iron  cylinder, 
strong  enough  to  resist  bursting  until  the  combustion  of  the  last  portion 
of  the  charge,  which  was  suspended  in  an  iron  globe  exhausted  of  air, 
and  exploded  by  the  galvanic  battery;  the  total  volume  of  the  gases 
collected  in  the  globe  was  then  determined  and  subjected  to  analysis. 
The  amount  of  gun-cotton  fired  was  about  10  grammes.  Unfortunately, 
the  formula  given  for  the  sample  of  gun-cotton  experimented  on  does  not 
represent  pure  gun-cotton,  being  CigHjj-NjOig,  instead  of  C^^^^i^QO.^ 
(representing  2  molecules  of  cellulo-trinitrine),  so  that  it  probably  con- 
tained some  unconverted  cotton. 

One  gramme  of  gun-cotton  gave  a  quantity  of  aqueous  vapour  and 
gaseous  products,  calculated  to  occupy,  at  0°  C.  and  760  mm.  Bar., 
753  cubic  centimetres,  supposing  the  aqueous  vapour  to  remain  uncon- 
densed  at  that  temperature.  The  analysis  of  the  gas  proved  that  100 
volumes  of  the  products  of  explosion  contain — 

Aqueous  vapour, 
Carbonic  oxide  (CO),  . 
Carbon  dioxide  (CO.^), 
Nitrogen,  . 
Hydrogen, 
Marsh  gas  (CH^), 

98-18 
If  the  marsh  gas  and  hydrogen  be  left  out  of  consideration,  the  follow- 
ing equation  will  account  for  the  other  products  of  the  explosion,  suppos- 
ing the  gun-cotton  to  be  pure — 

2C6H.02{N03)3  =  9C0  -J-  3CO2  +  7H2O  -t-  Nfi. 
According  to  this  equation,  1  gramme  of  gun-cotton  should  furnish  829 
cubic  centimetres  of  gas  and  vapour,  and  the  volume  of  the  products 
should  be — 

Aqueous  vapour,     ...         28  volumes, 
Carbonic  oxide,       .         .         .         36         ,, 
Carbon  dioxide,      .         .         .         12         ,, 
Nitrogen,        ....         12         ,, 

which  do  not  agree  with  the  experimental  results.  It  is  not  to  be  ex- 
j)ected,  however,  that  one  simple  equation  should  correctly  represent  all 
the  products  of  such  a  decomposition  (see  page  422). 

A  cubic  centimetre  of  compressed  gun-cotton,  of  the  same  density  as 
water,  weighs  1  gramme,  and  would  evolve,  according  to  the  above  equa- 
tion, 829  cubic  centimetres  of  gas  and  vapour  at  0°  C,  supposing  the 
steam  to  be  capable  of  remaining  uncondensed. 

The  quantity  of  heat  generated  in  the  explosion  of  gun-cotton  has  been 
determined  by  Roux  and  Sarrau  at  1056'3  centigrade  units.  The  specific 
heat  of  the  products  of  explosion  would  be  0"2855.     This  would  give 


25 

34  volumes. 

28 

•95 

20 

•82 

12 

•67 

3 

16 

7 

•24 

234  cub. 
234      „ 
166      „ 
107      „ 

cent. 

DETONATION  OF  GUN-COTTON.  511 

3700°  C.  for  tbe  temperature  of  the  gas  at  tbe  moment  of  explosion;  at 
this  temperature,  the  829  cubic  centimetres  of  gas  evolved  by  1  gramme 
of  gun-cotton  would  become  expanded  to  12,064  cubic  centimetres,  exert- 
ing a  pressure  of  81  tons  per  square  inch  if  the  gramme  of  gun-cotton 
occupies  one  cubic  centimetre.  The  experiments  of  Xoble  and  Abel  have 
indicated  4400°  C.  as  the  temperature  of  explosion,  and  a  pressure  con- 
siderably more  than  double  that  produced  by  gunpowder  when  fired  in  a 
space  which  is  entirely  filled  by  the  charge. 

Sarrau  and  Vieille,  employing  a  gun-cotton  containing  3  parts  of 
cellulo-trinitrine  and  1  part  of  cellulo-dinitrine,  CgH702.0H.(N03)2,  ob- 
tained, per  gramme  of  gun-cotton — 

Carbonic  oxide,    . 
Carbon  dioxide,    . 
Hydrogen, 
Nitrogen, 

Total,  .         .         .         .     741      „ 

At  low  pressures,  steam  was  also  produced,  together  with  more  carbonic 
oxide  and  less  carbon  dioxide. 

Berthelot  estimates  the  pressure  produced  by  the  detonation  of  gun- 
cotton,  compressed  to  a  density  of  1-1,  at  24,000  atmospheres,  or  about 
160  tons  per  square  inch,  being  only  half  the  pressure  assigned  by  him 
to  the  detonation  of  mercuric  fulminate. 

The  experiments  hitherto  made  have  been  unfavourable  to  the  employ- 
ment of  gun-cotton  as  a  substitute  for  gunpowder  in  artillery,  on  account 
of  the  injury  which  its  violent  explosion  occasionally  inflicts  upon  the 
gun.  For  use  in  fowling-pieces,  the  gun-cotton  pulp  is  diluted  with  a 
proportion  of  ordinary  cotton  pulp,  and  made  into  a  kind  of  paper  which 
is  rolled  up  to  form  the  cartridges.  Although  such  cartridges  leave  a  con- 
siderable carbonaceous  residue  when  fired  on  a  plate,  they  leave  little  or 
no  residue  when  fired  under  pressure. 

If  a  piece  of  compressed  gun-cotton  be  kindled  with  a  hot  wire,  it 
burns  rapidly  away,  producing  a  large  volume  of  flame,  but  without  any 
explosive  eff"ect.*  In  order  that  gun-cotton  fired  in  this  manner  might 
be  used  for  destructive  purposes,  it  was  found  necessary  to  confine  it  in 
strong  cases,  so  that  the  flame  of  the  portion  first  ignited  should  be  em- 
ployed in  raising  the  temperature  of  the  rest  to  the  exploding  point. 

The  discovery,  made  by  E.  0.  Brown,  of  a  method  by  which  the  icncon- 
fined  gun-cotton  could  be  made  to  explode  with  most  destructive  violence, 
has  opened  a  new  career  to  this  material,  rendering  it  far  superior  to 
gunpowder  for  all  blasting  operations,  torpedoes,  &c.  It  is  only  neces- 
sary to  explode  in  contact  with  the  compressed  cotton  a  detonating  fuze, 
consisting  of  a  little  tube  of  quill  or  thin  metal  charged  with  a  few  grains 
of  mercuric  fulminate,  to  cause  the  cotton  to  detonate  with  extreme 
violence ;  and  such  detonation  can  be  communicated  along  a  row  of 
pieces  of  compressed  cotton  placed  at  short  distances  from  each  other. 

*  Too  much  stress,  however,  should  not  be  laid  upon  this  as  rendering  gun-cotton  maga- 
zines safer  in  case  of  fire  than  gunpowder  magazines.  The  experiment  with  gunpowder 
mentioned  at  page  427,  shows  tliat  if  all  the  particles  of  an  explosive  be  raised  at  once  to 
nearly  the  inflaming  point,  the  first  particle  which  inflames  will  cause  the  detonation  of 
the  remainder.  Since  the  inflaming  point  of  gun-cotton  is  low,  the  above  condition  would 
be  easily  fulfilled  in  a  conflagration. 


512  PROPERTIES  OF  GUN-COTTON. 

This  capability  of  undergoing  what  may  be  termed  sympathetic  explo- 
don  is  by  no  means  confined  to  gun-cotton.  Previously  to  Brown's  dis- 
covery, Nobel  had  shown  it  to  exist  in  the  case  of  nitroglycerine,  and 
Abel  afterwards  proved  that  most  explosives,  including  even  gunpowder, 
can  be  made  to  detonate  in  a  similar  manner.  The  modus  operandi  of 
the  detonating  fuze  appears,  from  the  experiments  of  Abel,  as  well  as 
from  those  of  Champion  and  Pellet,  to  consist  in  the  influence  of  vibra- 
tory motion,  and  the  nature  of  the  motion  necessary  depends  upon  the 
nature  of  the  explosive.  That  it  is  not  a  result  of  the  action  of  heat 
is  proved  by  the  circumstance  that  wet  gun-cotton  may  be  exploded  by  a 
detonating  fuze,  so  that  torpedoes  may  be  charged  with  a  mixture  of  gun- 
cotton  pulp  and  water,  containing  15  per  cent,  of  the  latter,  if  a  small 
charge  of  dry  gun-cotton  be  placed  in  contact  with  the  fuze.  It  has 
been  found  that  the  wet  gun-cotton  is  more  easily  detonated  when  in  a 
frozen  state. 

The  very  destructive  effect  of  the  gun-cotton  exploded  in  this  way  is, 
of  coui'se,  due  to  the  sudden  manner  in  which  the  whole  mass  is  resolved 
into  gaseous  products. 

362.  Properties  of  gun-cotton  compared  tcith  those  of  gunpowder. — 
Gun-cotton  is  more  easily  exploded  than  gunpowder ;  the  latter  requires 
a  temperature  of  at  least  600°  F.,  whilst  gun-cotton  may  explode  at  277°  F., 
and  must  explode  at  400°  F.  It  is  very  diflScult  to  explode  gunpowder 
by  percussion,  even  between  a  steel  hammer  and  anvil;  but  gun-cotton 
invariably  detonates  in  this  way,  though  the  explosion  is  confined  to  the 
part  under  the  hammer.  The  explosion  of  gun-cotton  is,  of  course,  unat- 
tended by  any  smoke,  a  most  important  advantage  in  mines,  the  atmo- 
sphere of  which  is  sometimes  rendered  almost  intolerable  by  the  smoke 
of  gunpowder  used  in  blasting,  but  death  has  been  caused  by  the  large 
amount  of  carbonic  oxide  generated  by  the  gun-cotton.  The  absence  of 
residue  from  the  gun-cotton  prevents  the  fouling  of  guns,  and  renders  it 
unnecessary  to  sponge  them  after  each  discharge,  for  the  amount  of  incom- 
bustible mineral  matter  present  in  the  cotton  is  very  small  (from  1  to  2 
per  cent.),  and  is  entirely  scattered  by  the  explosion. 

It  has  already  been  mentioned  that  the  explosion  of  gun-cotton  does 
not  impart  so  much  heat  to  the  metal  of  the  gun  as  that  of  powder,  the 
difference  being  so  great  that,  after  tiring  100  rounds  with  gun-cotton,  the 
gun  was  not  so  much  heated  as  after  30  rounds  with  gunpowder.  This 
important  advantage  of  gun-cotton  is  probably  due  to  the  circumstance 
that  the  charge  of  gun-cotton  is  only  one-third  of  the  charge  of  powder, 
that  the  explosion  of  the  former  is  so  much  more  rapid,  leaving  less  time 
for  the  communication  of  heat  to  the  metal,  and  that  there  are  no  highly- 
heated  solid  products  left  in  contact  with  the  gun.  Gun-cotton  wool  may 
be  fired  upon  the  palm  of  the  hand  with  impunity,  or  upon  a  heap  of 
gunpowder  without  kindling  it ;  although  it  cannot  be  doubted  that  the 
temperature  of  the  flame  is  really  much  higher  than  the  inflaming  point 
of  powder.  That  the  recoil  of  a  gun  charged  with  gun-cotton  is  only  two- 
thirds  of  that  experienced  with  gunpowder,  is  probably  due  to  the  rapidity 
of  the  explosion,  which  allows  less  time  for  overcoming  the  inertia  of  the 
gun  ;  the  difference  in  recoil  taking  the  form  of  strain  upon  the  metal 
com])osing  the  gun. 

It  is  evident,  from  the  consideration  of  its  manufacture,  that  gun-cotton 


PREPARATION  OF  COLLODION.  513 

is  entirely  uninjured  by  water,  so  that  a  store  of  this  explosive  is  kept 
immersed  in  water;  whereas  gunpowder  is,  of  course,  rendered  useless  by 
contact  with  water,  which  dissolves  out  the  nitre.  Even  when  exposed 
to  very  damp  air,  gunpowder  is  liable  to  injury  from  the  effect  of 
moisture  in  partially  separating  the  nitre  from  the  other  ingredients,  whilst 
gun-cotton  only  requires  exposure  to  a  dry  atmosphere  for  a  short  time  to 
render  it  fit  for  use.  The  proportion  of  moisture  retained  by  gun-cotton, 
in  the  ordinary  state  of  the  atmosphere,  is  2  per  cent. 

As  an  objection  to  the  employment  of  gun-cotton  as  a  substitute  for 
gunpowder,  it  has  been  asserted  that  the  cellulo-trinitrine  is  liable  to 
undergo  spontaneous  decomposition,  which  might  at  any  time  render  the 
contents  of  a  magazine  unserviceable,  or  might  even  give  rise  to  the  evolu- 
tion of  a  sufficient  amount  of  heat  to  cause  an  explosion.  The  origin  of 
this  objection  is  to  be  traced  to  the  old  process  for  preparing  gun-cotton, 
in  which  the  acids  were  not  allowed  to  act  upon  the  cotton  for  a  sufficient 
length  of  time,  so  that  the  whole  of  the  cotton  was  not  converted  into 
true  gun-cotton,  but  some  less  stable  substitution  products  were  formed 
at  the  same  time.  Another  cause  of  spontaneous  alteration  is  the  imper- 
fect washing  of  the  gun-cotton,  whereby  minute  traces  of  acid  are  left  in 
the  fibre.  All  recent  experiments,  by  Abel  and  others,  appear  to  have 
proved  that,  considering  its  highly  complex  character,  pure  gun-cotton  is 
a  very  stable  compound  under  ordinary  conditions ;  although,  when  kept 
in  a  moist  state,  it  develops  traces  of  acid  products,  the  temperature  does 
not  rise  to  any  important  extent,  nor  is  the  explosive  quality  of  the 
material  at  all  injured. 

363.  Gun-cotton  is  somewhat  harsher  to  the  touch  than  ordinary 
cotton,  and  becomes  remarkably  electrical  when  rubbed  between  the  dry 
fingers.  It  is  insoluble  in  alcohol  and  ether,  as  well  as  in  a  mixture  of 
these  solvents,  though  ordinary  specimens  generally  yield  a  small  per- 
centage of  soluble  matter  when  treated  with  a  mixture  of  alcohol  and  ether, 
because  they  contain  extraneous  matters,  such  as  the  other  substitution 
products  to  be  mentioned  presently.  Acetic  ether  dissolves  it,  and  so  does 
a  mixture  of  ordinary  ether  with  ammonia.  Strong  sulphuric  acid  dissolves 
it  without  carbonisation,  unless  any  unconverted  cotton  should  happen  to 
be  present. 

364.  Collodion  cotton. — "When  cotton  or  paper  is  acted  upon  by  a  mix 
ture  of  nitric  and  sulphuric  acids  containing  more  water  than  is  present 
in  that  employed  for  the  preparation  of  gun-cotton  (page  508),  compounds 
are  formed  which  contain  less  NO^,  and  are  much  less  combustible  than 
the  cellulo-trinitrine,  from  which  they  are  also  distinguished  by  their 
solubility  in  mixtures  of  alcohol  and  ether. 

In  order  to  render  evident  the  relations  betAveen  these  compounds  and 
gun  cotton,  the  formula  of  the  latter  must  be  trebled,  when  we  have  the 
following  series  of  compounds  produced  by  the  mixture  of  nitric  acid, 
sulphuric  acid,  and  water,  to  which  they  stand  opposite : — 


Composition  of  the  mixed  acids. 

(1)  HX0,  +  H..S04 

(2)  HN03-^H.>l4-f-lfH.,0 

(3)  HN03-f-H.,S04  +  2H.p 

(4)  HN03-f-H.;,S04  +  2iH20 


Products  of  their  action  on  cellulose. 
C,8H.„0,;(N03)9 
Ci8H.,.,0-(N03)8 

C,8H.,40«(N03)6 


As  might  be  expected,  these  compounds  diminish  in  combustibility  in 
proportion  as  the  NO3  contained  in  them  diminishes.     The  second  is  that 

2  K 


514  XYLOIDINE  NITROMANNITE. 

em  ployed  for  the  preparation  of  photographic  collodion,  being  dissolved 
for  that  purpose  in  a  mixture  of  ether  and  alcohol. 

In  ortl»r  to  prepare  the  soluble  cotton  for  collodion,  3  measured  ounces  of  ordinary 
nitric  acid  (sp.  gr.  1  '429)  are  mixed  with  2  ounces  of  water  in  a  pint  beaker.  Nine 
measured  ounces  of  strong  sulphuric  acid  (sp.  gr.  1'839)  are  added  to  this  mixture, 
wliich  is  cDutinually  stirred  whilst  the  acid  is  being  added.  A  thermometer  is  placed 
in  the  mixture,  which  is  allowed  to  cool  to  140°  F.  ;  100  grains  of  dry  cotton  wool, 
in  ten  separate  tufts,  are  immersed  in  the  mixture  for  five  minutes,  the  beaker  being 
covered  witli  a  glass  plate.  The  acid  is  then  poured  into  another  beaker,  the  cotton 
squeezed  with  a  glass  rod,  and  thrown  into  a  large  volume  of  water ;  it  is  finally 
washed  in  a  stream  of  water  till  it  is  no  longer  acid,  and  dried  by  exposure  to  air. 

Collodion  bnllooiis.  — These  balloons  may  be  'made  in  the  following  manner  : — 6 
grains  of  the  collodion-cotton,  prepaied  according  to  the  above  directions,  are  dissolved 
in  a  niixt'ire  of  1  drachm  of  alcohol  (sp.  gr.  '835)  and  2  drachms  of  ether  (sp.  gr.  725) 
in  a  corked  test-tube.  The  solution  is  poured  into  a  dry  Florence  flask,  which  is 
then  turned  about  slowly,  so  that  every  part  of  its  surface  may  be  covered  with  the 
collodion,  the  excess  of  which  is  then  allowed  to  drain  back  into  the  tube.  Air  is 
then  blown  into  the  flask  through  a  long  glass  tnbe  attached  to  the  bellows  as  long 
as  any  smell  of  ether  is  perceptible.  A  pen-knife  blade  is  carefully  inserted  between 
the  flask  and  the  neck  of  the  balloon,  which  is  thus  detached  from  the  glass  all  round  ; 
a  small  piece  erf  glass  tubing  is  introduced  for  an  inch  or  two  into  the  neck  of  the 
balloon,  so  that  the  latter  may  cling  round  it.  Through  this  tube  air  is  drawn  out 
by  the  mouth,  until  one-half  of  the  balloon  has  left  the  side  of  the  flask  and  col- 
lapsed upon  the  other  half;  by  carefully  twisting  the  tube,  the  whole  of  the  balloon 
may  be  rietached  and  drawn  out  through  the  neck  of  the  fla.sk,  when  it  mu.st  be 
quickly  untwisted,  distended  by  blowing  through  the  tube,  tied  with  a  piece  of  silk, 
and  suspi-nded  in  the  air  to  dry.     The  average  weight  of  such  balloons  is  2  grains. 

Celluloid  or  artificial  ivory,  used  for  combs,  billiard  balls,  &c. ,  is  essentially  com- 
pressed collodion-cotton. 

When  collodion-cotton  is  kept  for  some  time,  especially  if  at  all  damp, 
it  undergoes  decomposition,  filling  the  bottle  with  red  fumes,  and  becom- 
ing converted  into  a  gummy  mass,  which  contains  oxalic  acid. 

365.  Xylf/idiTie  is  the  name  given  to  a  highly  combustible  substance 
analogous  to  pyroxyline,  which  is  obtained  by  dissolving  starch  in  the 
strongest  nitric  acid,  and  diluting  the  solution  with  water,  when  the 
xyloidine  falls  as  a  white  precipitate,  which  may  be  collected  upon  a 
filter,  and  washed  till  free  from  acid.  The  composition  of  xyloidine  is 
CgHg03(N03)2  representing  starch  (CgHjoOg),  in  which  2H0  have  been 
replaced  by  2NO3. 

Nitromannite  'C^^i^O^^  is  another  explosive  body  of  the  same  order, 
obtained  by  adding  powdered  mannite  (CgHj^Og),  in  small  portions,  to  a 
mixture  of  equal  measures  of  the  strongest  nitric  and  sulphuric  acids, 
which  immediately  dissolve  it,  and  presently  solidify  to  a  mass  of  minute 
needles  of  nitromannite,  wliich  may  be  washed  with  a  large  volume  of 
water,  and  crystallised  from  boiling  alcohol.  Under  the  hammer,  nitro- 
mannite explodes  with  a  very  loud  report.  When  heated,  it  fuses  before 
exploding. 

WINE  AND  SPIRITS. 

366.  Wine  is  essentially  composed  of  8  or  10  parts  of  alcohol,  with 
85  or  90  of  water,  together  with  minute  quantities  of  certain  fragrant 
ethers,  of  colouring  matter,  of  potassium  bitartrate,  and  of  the  mineral 
substances  derived  from  the  grape-juice.  Glycerine  and  succinic  acid 
have  also  bnen  found  in  wines,  and  appear  to  be  constant  secondary  pro- 
ducts of  the  alcoholic  fermentation. 


WINES,  515 

Those  wines  in  which  the  whole  of  the  sugar  has  been  fermented  are 
known  as  dry  wines;  whilst /r«%  wines  still  retain  a  considerable 
quantity  of  sugar. 

The  preparaiit>n  of  wines  differs  from  that  of  beer  in  the  circumstance 
that  no  addition  of  ferment  is  necessary,  the  fermentation  being  spon- 
taneous. Grape  juice  contains,  in  addition  to  grape-sugar,  vegetable 
albumen,  potassium  tartrate,  and  the  usual  mineral  salts  found  in  vegetable 
juices.  The  husks,  seeds,  and  stalks  of  the  grape  contain  a  considerable 
quantity  of  tannin,  together  with  certain  blue,  red,  and  yellow  colouring 
matters. 

When  the  expressed  juice  remains  for  a  short  time  in  contact  with  the 
air,  the  albuminous  substances  contained  in  it  enter  upon  a  state  of  change, 
exciting  the  vinous  fermentation  in  the  sugar,  and  a  scum  of  yeast  is 
formed  upon  the  surface.  If  this  fermentation  takes  place  in  contact  with 
the  husks  of  the  dark  grapes,  the  alcohol  dissolves  the  colouring  matter, 
and  a  red  wine  results ;  whilst  for  the  production  of  white  wines,  the 
husks,  &c.,  are  sei)arated  previously  to  the  fermentation,  and  the  juice  is 
exposed  as  little  as  possible  to  the  air. 

Wh'te  \7ines  are  rather  liable  to  become  ropy  from  viscous  fermenta- 
tion, but  this  is  prevented  by  the  addition  of  a  small  quantity  of  tannin, 
which  precipitdtHS  the  peculiar  ferment.  The  tannin  for  this  purpose  is 
extracted  from  the  husks  and  stalks  of  the  grapes  themselves. 

Red  wines,  sucli  as  port  and  claret,  are  often  very  astringent  from  the 
tannin  dissolved  out  of  the  husks,  &c.,  during  the  fermentation.  Port 
wine,  wlien  freshly  bottled,  still  retains  in  solution  a  considerable  quantity 
of  acid  potassium  tartrate  or  bitartrate  of  potash  (KHC^H^Og),  but  after 
it  has  been  kept  some  time,  and  become  more  strongly  alcoholic,  this  salt 
is  deposited,  together  with  a  quantity  of  the  colouring  matter,  in  the  form 
of  a  crust  upon  the  side  of  the  bottle.  Thus  a  dark  fri^ity  port  becomes 
tawny  and  dry  when  kept  for  a  sufficient  length  of  time,  the  sugar  having 
been  converted  into  alcohol. 

When  the  wine  contains  an  excess  of  tartaric  acid,  it  is  customary  to 
add  to  it  some  neutral  potassium  tartrate  (KgC^H^Og),  which,  precipitates 
the  acid  in  the  form  of  bitartrate. 

The  prep  t rati  on  of  champagne  is  conducted  with  the  greatest  care. 
The  juice  or  mud  is  carefully  separated  from  the  marc  or  husk,  and  is 
often  mixed  with  1  per  cent,  of  brandy  before  fermentation.  After 
about  two  months  the  wine  is  drawn  off  into  another  cask,  and  clarified 
with  isinglass  dissolved  in  white  wine,  and  added  in  the  proportion  of 
about  half  an  ounce  to  40  gallons.  This  combines  with  the  tannin  to 
form  an  insoluble  precipitate,  which  carries  with  it  any  impurities  float- 
ing in  the  wine.  After  another  interval  of  two  months,  the  wine  is  again 
drawn  off,  and  a  second  clarification  takes  place  ;  and  in  two  months 
more  the  wine  is  drawn  off  into  bottles  containing  a  small  quantity  of  pure 
sugar-candy  dissolved  in  white  wine.  The  bottles,  having  been  securely 
corked  and  wired,  are  laid  down  upon  their  sides  for  eight  or  ten  months, 
during  which  time  the  fermentation  of  the  newly  added  sugar  takes  place, 
and  the  carbonic  acid  produced  dissolves  in  the  wine,  whilst  a  quantity  of 
yeast  is  separated.  In  order  to  render  the  wine  perfectly  clear,  the  bottle 
is  left  for  about  three  weeks  in  such  a  position  that  the  deposit  may  subside 
into  the  neck,  against  the  cork,  which  is  then  unwired  so  that  the  pressure 
of  the  accumulated  carbonic  acid  gas  may  force  it  out  together  with  the 


516  WINES— DISTILLED  SPIRITS. 

deposit;  the  bottle  having  been  rapidly  filled  up  with  white  wine,  is 
attain  corked,  wired,  covered  with  tin  foil,  and  sent  into  the  market.  Pink 
champagne  is  prepared  from  the  must  which  is  squeezed  out  of  the  marc 
after  it  has  ceased  to  run  freely,  and  contains  a  little  of  the  colouring  matter 
of  the  husk.  The  colour  is  also  sometimes  imparted  by  adding  a  little 
tincture  of  litmus. 

The  proportion  of  alcohol  in  wines  varies  greatly,  as  will  be  seen 
from  the  following  statement  of  the  weight  of  alcohol  in  100  parts  of  the 


wme : — 

Port,     . 

15  to  17 

Claret,     . 

8  to9 

Sherry, 

14  to  16 

Kudesheimer,  . 

7  to  8- 

Champagne,  . 

11-5 

Sherry  contains  from  1  to  5  per  cent,  of  sugar,  port  from  3  to  7  per 
cent,  and  Tokay  17  per  cent.;  in  the  last  case,  the  sugar  is  increased" 
by  adding  some  of  the  must,  concentrated  by  evaporation,  to  the  wine 
previously  to  bottling. 

The  bouquet  or  fragrance  of  wine  is  due  to  the  presence  of  certain 
fragrant  ethers,  especially  of  oenanthic,  pelargouic,  and  acetic  ether,  formed 
during  the  fermentation  or  during  the  subsequent  storing  of  the  wine. 
It  is  to  the  increased  quantity  of  such  fragrant  ether  that  the  superior 
bouquet  of  many  old  wines  is  due. 

367.  Distilled  spirits. — The  varieties  of  ardent  spirits  are  obtained 
from  fermented  liquids  by  distillation,  so  that  they  consist  essentially  of 
alcohol  more  or  less  diluted  with  water,  and  flavoured  either  with  some 
of  the  volatile  products  of  the  fermentation,  or  with  some  essential  oil 
added  for  the  purpose. 

Brandy  is  distdled  from  wine,  and  coloured  to  the  required  extent 
with  burnt  sugar  (caramel).  Its  flavour  is  due  chiefly  to  the  presence 
of  oenanthic  ether  derived  from  the  wine.  The  colour  of  genuine  pale 
brandy  is  due  to  its  having  remained  so  long  in  the  cask  as  to  have  dis- 
solved a  portion  of  brown  colouring  matter  from  the  wood,  and  is  there- 
fore an  indication  of  its  age.  Hence  arose  the  custom  of  adding  caramel, 
and  sometimes  infusion  of  tea,  to  impart  the  colour  and  astringency  due 
to  the  tannin  dissolved  from  the  wood  by  old  brandy. 

Whisky  is  distilled  from  fermented  malt,  which  has  been  dried  over  a 
peat  fire,  to  which  the  characteristic  smoky  flavour  is  due. 

Gin  is  also  prepared  from  fermented  malt  or  other  grain,  and  is 
flavoured  with  the  essential  oil  of  juniper,  derived  from  juniper  berries 
added  during  the  distillation. 

Rum  is  distilled  from  fermented  molasses,  and  appears  to  owe  its 
flavour  to  the  presence  of  butyric  ether,  or  of  some  similar  compound. 

Arrack  is  the  spirit  obtained  from  fermented  rice. 

Kirschicasser  and  maraschino  are  distilled  from  cherries  and  their  stones, 
which  have  been  crushed  and  fermented. 

Some  varieties  of  British  brandy  and  whisky  are  distilled  from  fer- 
mented potatoes,  or  from  a  mixture  of  potatoes  and  grain,  when  there 
distils  over,  together  with  ordinary  alcohol,  another  spirit  belonging  to 
the  same  class,  but  distinguished  from  alcohol  by  its  nauseous  and 
irritating  odour.  This  substance,  which  is  known  as  potato-spirit,  amylic 
alcohol,  ov  f ousel  oil  (C5HJ2O),  also  occurs,  though  in  very  minute  quantity, 
in  genuine   wine-brandy.     The  manufacturers  of  spirit  from  grain  and 


THE  ALCOHOLS  AND  THEIR  DERIVATIVES.  517 

potatoes  remove  a  considerable  part  of  this  disagreeable  and  unwhole- 
some substance  by  leaving  the  spirit  for  some  time  in  contact  with  wood- 
charcoal. 

THE  ALCOHOLS  A^^D  THEIR  DERIVATIVES. 

368.  It  was  stated  at  page  437  that  the  alcohols  are  constructed  upon 
the  model  of  water  in  which  one-half  of  the  hydrogen  is  replaced  by  a 
compound  radical;  e.g.,  methyle  alcohol,  H3C.OH,  in  which  methyle, 
H3C,  occupies  the  place  of  the  atom  of  H  in  HOH  or  HgO. 

The  alcohols  are  designated  as  monatomic,  diatomic,  triatomic,  and  so 
on,  accordingly  as  they  are  constructed  upon  the  model  of  1,  2,  3,  or 
more  molecules  of  water. 


Model  or  Type. 

Alcohol. 

H.,0  =   H.OH 

H3C.OH 

monatomic    {Methyle  alcohol). 

2H:0  =   H^IOH)., 

H.CVOH), 

diatomic        {Ethylene  glycol). 

3H,0  =  H3(OH)3 

HA{0H)3 

triatomic       {Glycerine). 

&c. 

&c. 

Hence,  a  monatomic  alcohol  contains  one  hydroxyle  group  (OH),  a  diatomic 
alcohol  contains  two,  and  a  triatomic  alcohol  contains  three  hydroxyle 
groups. 

Monatomic  Alcohols. — The  simplest  type  of  these  is  the  methylic 
alcohol  {carbinol),  H3C.OH.  The  H  contained  in  the  hydroxyle  group  is 
termed  typical  hydrogen,  because  it  cannot  be  changed  without  altering 
the  type  upon  which  the  alcohol  is  formed;  but  the  H  in  the  methyle 
(H3C),  or  methylic  hydrogen,  admits  of  replacement,  and  it  is  in  this  way 
that  the  different  monatomic  alcohols  are  produced. 

The  monatomic  alcohols  are  again  subdivided  into  primary,  secondary, 
and  tertiary,  accordingly  as  1,  2,  or  3  atoms  of  the  methylic  hydrogen  in 
the  type  have  been  replaced  in  order  to  form  the  alcohol — 

Model  or  Type,  HHHC.OH  Carbinol. 

Primary  butj'lic  alcohol,  (C3H7)HHC.OH  Fropyl-carbinol. 

Secondary  ,,  (C2H5)(CH3)HC.OH  Melhyl-ethyl-carbinol. 

Tertiary  ,,  (CH3)(CH3)(CH3)C.0H  Trimethyl-carbiml. 

It  will  be  seen  that  these  three  alcohols  have  the  same  molecular  formula, 
C^HjqO,  but  their  properties  are  quite  different — 

Primary  butylic  alcohol,  liquid,  boiling  at  116°  C. 
Secondary  ,,  ,,  ,,         99°  C. 

m    .•  ^■  i    \  fusing  at    25°  C. 

Tertiary  „  solid,  j  j^^jli^^  ^^    g2°-5  C. 

Alcohols  are  said  to  be  normal  when  their  carbon-atoms  are  so  united 
as  to  form  a  single  chain  with  one  carbon  atom  at  each  end.     Thus,  normal 

n n Q Q 

butylic  alcohol  is  ^^  ^^  ^^   g^  qjj 

The  iso-alcohols  have  the  same  composition  as  the  normal  alcohols  (lo-os, 
equal,)  but  some  of  their  carbon-atoms  form  side-chains,  so  that  there  are 
more  than  one    carbon-atom  at  one  end  of  the  chain.     This  is  seen  in 

isobutylic  alcohol,  h3C^H~H2.0H. 

It  is  obvious  that  the  number  of  possible  iso-alcohols  will  increase  with 

the  number  of  carbon-atoms. 

The  monatomic  primary  alcohols  are  the  most  numerous  and  important. 


518 


MONATOMIC  ALCOHOLS. 


Monatomic  primary  alcohols. — The  following  table  includes  the  chief 
alcohols  of  this  series  which  are  at  present  known  : — 


Chemical  Kame. 

Soni-ce. 

Furmnla. 

Common  Name. 

].   Methylic  alcohol, 

Destructive  distillation  of  wood, 

C    H4O 

Wood-naphtha 

2.   Ethylic 

Vinous  fermentation  of  sugar, 

C.HeO 

Spirit  of  wine 

S.   I'ropylic       ,, 

Fermentation  of  gra|ie-husks, 

C3  H«  0 

4.   Butylic 

Fermentation  of  beet-root,    . 

C4  H,„0 

* 

5.  Ainylic         ,, 

Fermentation  of  potatoes,     . 

C,  H,,0 

Fousel  oil 

6.  Caproic        ,, 

Fermentation  of  grape-liusks. 

Cg  li„0 

7.  (Enanthic     „     j 

Distillation  of  castor  oil  with  ) 

potash ) 

Fermentation  of  grape-husks. 

C,  H,eO 

8.  Caprylic       ,, 

Cs  H.sO 

10.   Rutic 

Oil  of  rue,    .... 

CioH.«0 

12.   Laurie          „ 

Whale  oil,    .... 

CigHjgO 

16.  Cetylic 

Spermaceti, 

CigH.^0 

Ethal 

27.  Cerylic         „ 

Chinese  wax, 

CjyHssO 

Cerotene 

30.  Melissic        ,, 

Bees'  wax,    .... 

C.oH«,0 

Melissine 

The  regular  increase  of  these  alci)hols  by  the  addition  of  CHg  is  explained 
by  the  successive  replacements  of  H  by  CHg  {methyls).  Thus,  by  replac- 
ing H  in  HgO,  we  obtain  CH3.HO,  or  CH^O ;  by  again  replacing  H  in 
the  CHg,  we  obtain  CH2(CH3),  HO,  or  C^HgO,  &c.  (s,,e  page  438). 

The  usual  gradation  in  properties  attending  the  gradation  in  composition 
among  the  members  of  a  homologous  series,  is  siri  singly  exemplified  iti 
the  class  of  alcohols.  Methylic,  ethylic,  i  ropylic,  butylic,  amylic,  caproic, 
oenanthic,  and  caprylic  alcohols,  are  all  liquid  at  the  ordinary  temperature  ; 
they  all  possess  peculiar  and  powerful  odours,  and  may  be  readily  <iistilled 
unchanged.  The  two  Hrst,  methylic  and  ethylic  alcohuls,  may  be  mixed 
with  water  in  all  proportions,  but  the  tbiid,  propylic  alcohol,  though  freely 
soluble  in  water,  is  not  so  to  an  unlimited  extent ;  whilst  butylic  alcoliol 
is  less  solu'-le,  and  amylic  alcohol  may  be  gaid  to  be  sparingly  soluble  in 
water.  Caproic  alcohol,  the  next  member,  is  insoluble  in  water ;  whilst 
caprylic  is  not  only  insoluble,  but  poss^esses  an  oily  character,  leaving  a 
greasy  stain  upon  paper. 

In  their  Ijoiling-points,  and  the  specific  gravities  of  their  vapours,  a 
similar  gradation  is  observed. 


A'coliol. 

BoilinK-Point. 

Vapour  Density. 

Methylic, 

151°  F. 

112 

Ethylic, 

173° 

161 

Propylic, 

206° 

2  02 

Butylic, 

2:^3° 

2-59 

Amylic, 

269° -8 

315 

Caproic, 

299°-309'' 

8  5S 

(Enanthic,     . 

327^-343° 

Caprylic, 

356° 

4-50 

One  molecule  of  each  of  these  alcohols  yields  two  <JoZM?n<?6' of  vapour ; 
or,  in  other  words,  if  a  given  weight  of  the  alcohol  c<»riespoiiding  to  its 
molecular  weight  be  converted  into  vapour,  that  vapour  will  ociupy  twice 
as  much  space  as  would  be  occupied  by  one  part  by  weight  of  hydrogen 
at  the  same  temperature  and  pressur»\ 

The  higher  members  of  the  group  of  alcohols  are  solid  fusible  bodies 
more  neaily  approaching  to  waxy  or  fatty  matters  in  their  nature,  and 


ACETIC  SERIES  OF  ACIDS. 


519 


not  susceptible  of  distillation  without  decomposition.     Far  less  is  known 
of  these  than  of  the  alcohols  containing  less  carbon. 

The  true  chemical  definition  of  an  alcohol  of  this  series  rests  upon  the 
circumstance,  that  under  the  influence  of  oxidising  agents,  it  first  parts 
with  2  atoms  of  hydrogen,  and  is  converted  into  an  aldehyde  (alcohol 
dehydrogenated),  and  afterwards  absorbs  an  atom  of  oxyyen,  yielding  an 
acid.  Thus,  it  has  been  already  shown  (page  498)  tht  vinic  alcohol 
(CgHgO),  when  exposed  to  air  under  favourable  conditions,  yields  alde- 
hyde, CgH^O,  which,  by  absorbing  oxygen,  is  converted  into  acetic  acid, 

CgH^Og. 

The  formation  of  an  aldehyde  would,  therefore,  be  represented  by  the 
general  formula — 

C„Ho„+20  +  0  =  C„H2„0  +  H2O , 

Alcohoi.  Aldehyde. 

and  that  of  the  corresponding  acid  by 


C„Ho„+,0  +  O2 


C„H2„0, -f  H,0 


In  addition  to  this,  a  double  molecule  of  each  of  these  alcohols,  by 
the  loss  of  the  elements  of  a  molecule  of  water,  yields  an  ether,  corre- 
sponding to  ordinary  ether  {^.^^.fi,  which  differs  from  the  double 
molecule  of  vinic  alcohol,  CgHgU,  by  the  elements  of  a  molecule  of 
Avater. 

The  general  formula  representing  the  derivation  of  an  ether  from  an 
alcohol  of  the  above  series  is — 


2C„H2„+20 

Alcohol. 


H^O  =  (C„H2„+,)20. 

Ether. 


Hence,  every  alcohol  has  its  corresponding  aldehyde,  acid,  and  ether, 
so  that  there  are  homologous  series  01  aldehydes,  acids,  and  ethers,  just 
as  of  the  alcohols  from  which  they  are  derived. 

The  only  members  of  the  aldehyde  and  ether  series  which  have  received 
a  large  share  of  attention  on  account  of  their  practical  impnr(ance,  are 
those  derived  from  ordinary  alcohol ;  but  the  series  of  acids  contain  many 
members  of  importance,  to  some  of  which  no  corresponding  alcohols  are 
yet  known. 

The  very  important  homologous  series  of  acids*  composed  after  the 
general  formula  CnHgnOo,  includes — 


Acid. 

Source. 

Formula. 

1.    Kormic  acid, 

Red  auts,  nettles, 

C    H2O, 

2.   Acetic      ,, 

Vinegar,     .... 

C2  H4  O2 

.3.   Propylic  ,, 

Oxidation  of  oils, 

C3  He  0, 

4.   Butyric   ,, 

Rancid  butter,   . 

C4  Hg  O2 

5.   Valerianic  acid, 

Valerian  root,     . 

Cs  H10O2 

6.   Caproic          , , 

Rancid  butter.  . 

C«  H,202 

7.  OCuanthic      ,, 

Oxidation  of  castor  oil, 

C7  H]402 

8.  Caprylic        ,, 

Rancid  butter,  . 

Cs  H,A 

9.   Pelaigonic     ,, 

Geranium  leaves, 

C9  H,802 

10.   Rutic  or  capric  acid, 

Rancid  butter,    . 

CioH.jo'^>2 

11.  Euodict 

Oil  of  Rue, 

c„H2.A 

12.   Laurie                  ,, 

Bay  berries. 

C12H24O2 

*  Often  spoken  of  as  the  acetic  series  of  acids,  or  t\\t  fatly  acid  series. 
•(•  EvihSift,  fragratiL 


520 


FATTY  ACIDS. 


Homologous  Series  of  Acids — continued. 


Adds. 
13.  Cocinic            acid, 

Source. 

Foimultt. 

Cocoa  nut  oil,    . 

CisHjjflOa 

14.  Myristic              ,, 

Nutmeg  butter, 

C14H28O2 

15.   Beuic                  ,, 

Oil  of  beu. 

CiftHjoOj 

16.   Palmitic              ,, 

Palm  oil,   .... 

CjgHsjOj 

17.  Margaric            ,, 

Olive  oil  (?),       . 

C17H34O2 

18.  Stearic                 ,, 

Tallow,      .... 

CigHsaOj 

19.  Balenic 

C19H38O2 

20.  Butii(aracliidic),, 

Earth  nut, 

*-'8oH4oO<, 

21.  Nardic                ,, 

^21  "42*^2 

22.  Beheuic               „ 

^'J^ifii 

25.  Hytenic               ,, 

^25  "60^2 

27.  Cerotic 

Bees'  wax. 

P27H54O2         j 

30.  Melissic 

Bees'  wax. 

C3oHgo02 

1 

ITie  type  of  this  series  of  acids  is  formic  acid  H(OC.OH)  =  CHgOj, 
which  may  be  represented  as  composed  of  hydrogen  and  the  radical 
ojratyle  (OC.OH)  (see  page  437) ;  this  radical  remains  unchanged  through- 
out the  whole  series,  the  different  acids  being  produced  by  successive 
replacements  of  the  external  hydrogen.  Thus  acetic  acid  is  HgC.OCOH, 
or  methyle- formic  acid,  propylic  acid  is  HgCg-OCOH,  or  methyl-acetic  acid, 
and  so  on. 

It  is  by  the  replacement  of  the  H  in  the  oxatyle  group  by  metals  that 
these  acids  are  converted  into  salts,  and  therefore  all  the  acids  of  this 
series  are  monobasic  (page  250). 

A  very  gradual  transition  of  properties  is  observable  in  the  members  of 
this  extended  series  of  acids. 

The  first  nine  members  of  the  series  are  liquid,  the  remainder  solid  at 
common  temperatures.  Of  the  liquids,  formic  acid  boils  at  212°  F.,  and 
the  boiling-points  of  the  other  members  exhibit  a  gradual  rise  up  to  pelar- 
gonic  acid,  which  boils  at  500°  F.  The  melting-points  of  the  solid  acids 
also  ascend  from  86°  F.  for  rutic  acid  (CjoHgQOg)  to  192°  F.  for  melissic 

(^'■3oH6o92)- 

Formic  and  acetic  acids  may  be  mixed  with  water  in  all  proportions, 
like  their  corresponding  alcohols,  the  methylic  and  ethylic ;  propylic 
acid,  though  soluble  to  a  great  extent  in  water,  resembles  the  correspond- 
ing alcohol  in  not  mixing  indefinitely  with  water.  Butyric  acid  behaves 
in  a  similar  manner.  Valerianic,  caproic,  oenanthic,  and  caprylic  acids  are 
sparingly  soluble  in  water.  Pelargonic  and  capric  acids  are  very  sparingly 
soluble,  and  the  remaining  members  of  the  series  are  very  decidedly /a^^?/ 
acids,  insoluble  in  water,  and  forming  soaps  with  the  alkalies. 

The  members  of  the  series  of  alcohols,  under  the  action  of  powerful 
dehydrating  agents,  are  capable  of  parting  with  the  elements  of  a  mole- 
cule of  water,  furnishing  the  members  of  a  homologous  series  of  hydrocar- 
bons related  to  their  corresponding  alcohols,  as  olefiant  gas  or  ethylene 
(C0H4)  is  related  to  ethylic  alcohol. 

The  general  formula  for  the  production  of  the  homologues  of  ethylene 
(ur  oJcfines)  from  the  alcohols  may  be  thus  expressed — 


C„H 


,0  -  H2O  =  C..H.^ 


ALCOHOL. 


521 


The  chief  known  members  of  this  series  of  hydrocarbons  are— 


Name. 

Formula. 

Corresponding 
Aild. 

Corresponding 
Alcohol. 

2.  Ethylene, 

C0H4 

Acetic 

Alcohol 

3.  Propylene,*     . 

C3  Hg 

Propylic 

Propylic 

4.  Butylene, 

9*  J?8 

Butyric 

Butylic 

5.  Amylene, 

CsHjo 

Valerianic 

Fousel  oil 

6.  Caproylene, 

^6  H12 

Caproic 

Caproic 

7.  (Enantheue,     . 

C7  Hi4 

(Enanthic 

(Enanthic 

8.  Caprylene, 

Cg  H16 

Caprylic 

Caprylic 

9.   Elaene,    . 

C9  Hjg 

Pelargonic 

10.   Paramylene,    . 

C10H20 

Rutic 

Rutic 

16.  Cetylene, 

''le^aa 

Palmitic 

Ethal 

27.  Cerotene, 

C27H54 

Cerotic 

Cerotene 

30.  Melissene, 

CsqHbo 

Mellssic 

Melissine 

Of  these  hydrocarbons,  ethylene  and  propylene  are  gaseous;  butylene  is 
also  a  gas,  but  easily  condensed  to  a  liquid  state  ;  the  remainder  are  liquid 
at  the  ordinary  temperature,  except  cerotene  and  melissene,  which  are  solid. 

Since  one  molecule  of  each  of  these  hydrocarbons  in  the  state  of  vapour 
occupies  two  volumes,  it  must  follow,  if  their  composition  be  correctly 
stated,  that  their  vapour  densities  exhibit  a  progression  similar  to  that 
which  exists  in  the  formulae. 

That  this  is  the  case  will  be  seen  by  the  subjoined  table,  which  illus- 
trates very  clearly  the  importance  of  determining  the  specific  gravitj'  of 
the  vapour  of  a  volatile  substance  as  a  confirmation  of  the  results  of 
analysis : — 


Hydrocarbon 

Specific  gravity 
of  vapiiur. 

Hydrocarbon 

Specific  gravity 
of  vapour. 

Ethylene, 

C.,H4 

.     0-978 

Caprylene, 

CgHie 

3-90 

Propylene, 

CsHg 

.      1  -498 

Elaene, 

t'gHis 

4-48 

Butylene, 

O4H8 

.      1-852 

Paramvlene, 

C 10  "  20 

5-061 

Amj'lene, 

C'fiHifl 

.     2-386 

Cetylene, 

CieHsa 

8-007 

Caproylene, 

C0H12 

.     2-874 

It  will  be  seen  hereafter  that  each  of  these  defines  is  capable  of  giving 
rise  to  a  diatomic  alcohol  or  glycol,  derived  from  a  double  molecule  of 
water,  in  which  2  atoms  of  hydrogen  are  replaced  by  an  olefine ;  thus, 
(CoH^)H202  is  ethylene  glycol,  (C3Hg)H.,02  is  propylene-glycol. 

369.  Alcohol  may  be  studied  as  the  type  of  the  class  to  which  it  gives 
a  name. 

When  any  of  the  fermented  or  distilled  liquors  of  commerce  are  sub- 
jected to  distillation,  the  alcohol  passes  over  during  the  first  part  of  the 
process,  mixed  with  a  considerable  quantity  of  water ;  and  if  the  distilla- 
tion be  continued  as  long  as  any  alcohol  passes  over,  and  the  whole  of  the 
distilled  liquid  be  measured  or  weighed,  the  quantity  of  alcohol  present 
in  the  original  liquid  subjected  to  distillation,  may  be  inferred  (by  refer- 
ence to  a  table)  from  the  specific  gravity  of  the  aqueous  spirit  distilled 
from  it,  since  the  lighter  it  is  the  more  alcohol  it  contains,  the  specific 
gravity  of  pure  alcohol  being  0-794. 

*  These  hydrocarbons  are  sometimes  designated  by  names  which  refer  to  the  multiple  of 
CH,  which  they  contain.  Thus  propylene,  SlCHj),  is  sometimes  called  tritylene  ;  buty- 
lene, tetrylene  ;  caproylene,  Iiexyleiie,  kc. 


522  ALCOHOL — ETHER. 

The  strength  of  the  spirit  of  wine  of  commerce  is  ascertained  by  deter- 
mining its  specific  gravity.  Spiritus  rectijicatus  has  the  specific  gravity 
•838,  and  contains  84  per  cent,  by  weight  of  alcohol.  That  known  as 
jiroof  npirit  {sjdritKS  timuior)  has  the  specific  gravity  0'920,  and  is  so 
called  becanse  it  is  the  weakest  spirit  which  will  answer  to  the  rough 
proof  of  firing  gunpowder  which  has  been  moistened  with  it  and  kindled. 
Any  spirit  weaker  than  this  leaves  the  powder  moist,  and  does  not  explode 
it.  It  is  then  said  to  be  under  p)-oof,  whilst  a  stronger  spirit  is  spoken 
of  as  ooer  jiroof. 

Proof  spirit  contains  by  weight,  in  100  parts,  50"76  of  water,  and  49*24 
of  alcohol. 

A  spirit  would  be  spoken  of  as  30  per  cent.,  for  example,  over  proof , 
if  100  measures  of  it,  when  diluted  with  water,  would  yield  130  measures 
of  proof  spirit,  A  spirit  30  per  cent,  below  'proof  contains,  in  every  100 
measures,  70  measures  of  proof  spirit  By  repeatedly  rectifying  or  redis- 
tilling the  weak  spirit  obtained  from  a  fermented  liquid,  collecting  the 
first  portions  separately,  a  strong  spirit  may  be  obtained,  containing  90 
per  cent,  of  alcohol,  but  mere  distillation  will  not  effect  a  further  separa- 
tion of  I  he  water.  Weak  spirit  may  be  concentrated  to  a  greater  extent 
than  this,  by  leaving  it  enclosed  in  a  bladder  for  a  considerable  period, 
when  the  water  exudes  through  the  bladder  more  readily  than  the  alcohol, 
so  that  the  latter  accumulates  in  the  mixture  to  the  amount  of  95  percent. 

Another  method  of  separating  a  great  part  of  the  water  consists  in  add- 
ing dry  pntassiura  carbonate  to  the  weak  spirit  as  long  as  it  is  dissolved, 
when  the  mixture  separates  into  two  layers,  the  lower  consisting  of  solu- 
tion of  the  cariionate  in  water,  and  the  upper  one  of  spirit,  containing  89 
per  cent,  of  alcohol.  By  ettecting  the  separation  in  a  graduated  tube, 
this  method  is  sometimes  employed  for  roughly  ascertaining  the  proportion 
of  alcohol  in  a  fermented  or  distilled  liquid,  the  foreign  matters  in  which 
prevent  any  safe  inference  from  the  specific  gravity. 

The  last  portions  of  water  are  removed  from  alcohol  by  allowing  it  to 
stand  for  two  or  three  days  over  powdered  quicklime,  and  distilling,  when 
the  lime  retains  the  water  in  the  form  of  calcium  hydrate,  and  the  pure  or 
absolute  alcohol  distils  over.  It  must  then  be  preserved  in  well-stopped 
bottles,  since  it  readily  absorbs  moisture  from  the  atmosphere.  Its  attrac- 
tion for  water  causes  it  to  evolve  heat  when  mixed  with  that  liquid,  and 
the  volume  of  the  mixture  is  less  than  the  sum  of  the  volumes  of  its 
components,  showing  that  combination  has  taken  place. 

Pure  alcohol  does  not  freeze;  but  the  compound  C2Hg0.4H20  crystal- 
lises at  -  34°  C.  When  a  weak  spirit  is  cooled,  ice  separates  until  this 
ratio  is  reached,  when  the  temperature  remains  constant  till  the  whole  has 
solidified. 

370.  Ether,  oy,  as  it  is  sometimes  erronously  called,  sulphuric  ether 
(^4-^10^)'  is  obtained  by  distilling  a  mixture  of  two  measures  of  alcohol 
with  one  measure  of  concentrated  sulphuric  acid.  As  soon  as  the  mixture 
begins  to  blacken,  in  consequence  of  a  secondary  decomposition  of  the 
alcohol,  the  retort  is  allowed  to  cool,  another  half  measure  of  alcohol  is 
added,  and  the  mixture  again  distilled  as  long  as  ether  is  obtained. 

A  far  better  method  of  obtaining  ether  is  that  known  as  the  continuous 
process.  Alcohol  of  sp.  gr.  0-830  is  mixed  with  an  equal  measure  of  con- 
centrated sulphuric  acid,  and  introduced  into  a  retort  or  flask  (fig.  289), 


PREPARATION  OF  ETHER. 


523 


which  is  connected  with  a  small  cistern  containing  alcohol.  The  mixture 
in  the  flask  is  rapidly  raised  to  the  boiling-point,  and  alcohol  is  allowed  to 
pass  slowly  in  from  the  reservoir  through  a  siphon  furnished  with  a  stop- 
cock, so  as  to  keep  the  liquid  in  the  flask  at  a  constant  level.  A  thermo- 
meter should  be  immersed  in  the  liquid,  the  temperature  of  which  should 
be  maintained  at  284°  to  290°  F.  (140°  to  143°  C).  By  this  process,  one 
measure  of  sulphuric  acid  will  eflTect  the  conversion  into  ether  of  thirty 
measures  of  alcohol.  The  boiling-point  of  ether  being  very  low  (94°'8  F., 
35°  C.)  necessitates  the  employment  of  a  good  condensing  arrangement. 


Fig  289. — Continuous  etherification. 

The  liquid  which  distils  over  contains  about  two-thirds  of  its  weight 
of  ether,  with  about  one-sixth  of  water,  and  an  equal  quantity  of  alcohol. 
Traces  of  sulphurous  acid  are  also  generally  present  To  obtain  the  pure 
ether,  it  is  shaken  with  water  containing  a  little  potassium  carbonate,  when 
the  water  dissolves  the  alcohol,  and  the  potash  removes  the  sulphurous 
acid ;  the  ether  being  very  sparingly  soluble  in,  and  much  lighter  than 
water  (sp.  gr.  0'74  at  0°  C),  rises  to  the  surface,  holding  a  little  water  in 
solution.  This  upper  layer  is  drawn  off"  and  freed  from  water  by  distilla- 
tion in  a  water-bath,  at  a  very  low  heat,  over  quicklime. 

The  explanation  of  the  chemistry  of  this  process  of  etherificatiov,  will 
be  more  intelligible  after  some  other  changes  to  which  alcohol  is  liable 
have  been  studied. 

The  most  striking  properties  of  ether  are  its  peculiar  odour  and  its 
great  volatility ;  its  rapid  evaporation  when  poured  upon  the  hand  gives 
rise  to  a  sensation  of  intense  cold ;  and  if  a  little  ether  be  evaporated  by 
blowing  upon  it  in  a  watch-glass  with  a  drop  of  water  hanging  from  its 
convexity,  the  water  will  be  speedily  frozen.  Ether  is  also  exceedingly 
inflammable ;  and  since  its  vapour  is  very  heavy  (sp.  gi'.  2  "59),  and  passes 
in  an  unbroken  stream  through  the  air  for  a  considerable  distance,  great 
care  should  be  taken  to  avoid  pouring  it  from  a  bottle  in  the  neighbour- 
hood of  a  flame.  Its  flame  is  far  more  luminous  than  that  of  alcohol,  and 
much  acetylene  is  produced  during  its  imperfect  combustion  (page  94). 

The  high  specific  gravity,  volatility,  and  inflammability  of  ether  vapour  admit  of 
illustration  by  some  curious  experiments  :  — 


524  THE  ALCOHOL- KADICALS. 

A  piece  of  tow  wetted  with  ether  is  placed  at  the  top  of  a  sloping  wooden  trough 
over  6  feet  long  ;  a  match  applied  at  the  lower  end  tires  the  train  of  vapour. 

If  a  small  piece  of  sponge  be  saturated  with  ether  and  placed  in  the  centre  of  a 
laige  wooden  tray,  2  or  3  inches  deep,  the  latter  will  soon  be  entirely  hlled  with  the 
vapour,  as  may  be  shown  by  applying  a  lighted  match  to  one  corner.  A  jug  may  be 
warmed  by  rinsing  a  little  hot  water  round  it,  and  this  having  been  thrown  out,  a 
few  drachms  of  etlier  may  be  poured  into  the  jug,  which  will  immediately  become 
filled  with  ether  vapour,  anil  from  this  several  glasses  may  be  filled  in  succession,  the 
presence  of  the  ether  vapour  being  proved  by  a  lighted  taper. 

A  pneumatic  trough  may  be  filled  with  warm  water,  a  small  test-tube  filled  with 
ether  inverted  with  its  mouth  under  the  water,  and  the  ether  quickly  decanted  up 
into  a  gas  jar  also  filled  with  hot  water,  where  it  will  be  immediately  converted  into 
vapour,  and  may  be  decanted  through  the  water  into  other  vessels,  and  dealt  with 
like  a  permanent  gas.  Some  cold  water  poured  over  the  jar  containing  it  at  once 
proves  its  condensible  character. 

When  ether  is  acted  upon  by  hydrochloric,  hydrobromic,  or  hydriodic 
acid,  the  oxygen  of  the  ether  enters  into  combination  with  the  hydrogen 
of  the  acid,  and  the  chlorine,  bromine,  or  iodine  occupies  its  place. 

Thus,  with  hydrochloric  acid — 

(C2H5)20  {Ether)  +  2HC1  =  2C2H5CI  {Hydrochloric  ether)  +  H._jO . 
In  a  similar  manner,  hydrobromic  ether,  CaH^Br,  and  hydriodic  ether, 
C0H5I,  may  be  formed.  The  best  method  of  obtaining  the  two  last,  how- 
ever, consists  in  distilling  moderately  strong  alcohol  with  phosphorus  and 
either  bromine  or  iodine,  when  orthophosphoric  acid  and  hydriodic  ether 
are  formed — 

•      5(C2H5.0H)+    P  +  I5  =  5C2H5I  +  H3PO4  +  H2O. 

.,     ,    ,  Orthoplinsphoric 

Alcohol.  ^'jj   '' 

These  three  ethers  are  colourless,  fragrant,  volatile  liquids,  which  are 
of  the  greatest  value  in  the  investigation  of  the  constitution  of  complex 
organic  compounds. 

This  remark  applies  particularly  to  hydriodic  ether  {ethyle  iodide),  which 
is  less  volatile  than  the  others,  and  therefore  more  easily  manageable  in 
experiments  requiring  a  high  temperature. 

Iodide  of  cthyh,  or  ethylic  iodide,  is  prepared  by  distilling  1400  grains  of  ordinary 
alcohol  (sp.  gr.  0'84)  with  2000  grains  of  iodine,  and  100  grains  of  ordinary  vitreous 
phi)sphorus.  The  iodine  and  phosphorus  are  added  alternately,  in  small  portions,  to 
the  alcohol  in  the  retort,  which  is  immersed  in  cold  water  to  moderate  the  action, 
and  occasionally  shaken.  When  the  whole  has  been  added,  the  retort  is  connected 
with  a  Liebig's  condenser,  and  heated  in  the  water-bath,  when  about  2^  measured 
ounces  of  ethyle  iodide  mixed  with  alcohol  will  pass  over.  This  is  shaken  in  a 
stoppered  bottle  with  about  an  equal  measure  of  water,  which  dissolves  the  alcohol, 
leaving  the  ethyle  iodide  to  collect  at  the  bottom  as  an  oily  layer  (sp.  gr.  1'97). 
After  as  much  as  ]>ossible  of  the  upper  aqueous  layer  has  been  removed  with  a  siphon 
or  pipette,  the  iodide  is  poured  into  a  small  retort  containing  fused  calcium  chloride  in 
jiowiier  to  remove  the  water.  The  retort  is  closed  with  a  cork,  and  set  aside  for  some 
lioiirs,  when  the  ethyle  iodide  may  be  distilled  otf  in  the  water-bath,  and  condensed 
in  a  Liebig's  condenser. 

Another  process  consists  in  placing  1  part  of  amorphous  phosphorus  and  5  jwrts  of 
al  -ohol  in  a  retort,  adding  gradually  10  parts  of  iodine  in  powder,  setting  aside  for 
twelve  hours,  and  distilling. 

371.  Alcohol-radicals. — If  ethylic  iodide  be  poured  over  granulated 
zinc  contained  in  a  stout  glass  tube,  which  is  then  exhausted  of  air, 
hermeticidly  sealed,  and  heated  for  two  hours  in  an  oil-bath  to  300°  F., 
a  crystalline  substance  is  deposited,  which  is  a  compound  of  zinc  iodide 
witli  zinc  ethyle  (C2H5)2Zn,  whilst  a  colourless  liquid  separates,  consist- 
ing of  a  mixture  of  three  hydrocarbons,  which  have  been  liquefied  by  their 


DUPLICATE  NATURE  OF  THE  ALCOHOL-RADICALS.  525 

own  pressure.  On  breaking  the  extremity  of  the  tube  under  water,  this 
liquid  rapidly  escapes  in  the  form  of  gas,  which-  proves  on  examination 
to  contain  ethene  (CgH^),  ethane  (CgHg),  and  di-ethyle  (C2H.)2,  the  last 
of  which  may  be  obtained  nearly  pure  by  collecting  the  last  portions  of 
gas  separately,  since  it  is  the  least  volatile  of  these  hydrocarbons. 

Neglecting  the  secondary  decompositions  which  give  rise  to  the  other 
products,  the  formation  of  di-ethyle  would  be  represented  by  the  simple 
equation,  2C2H5I  +  Zn  =  Znig  +  (02115)2.  It  is  obtained  in  larger  quan- 
tity by  heating  ethylic  iodide  with  zinc  and  precipitated  copper  (page 
U). 

Di-ethyle  or  ethyle  is  a  colourless  gas,  having  a  faint  ethereal  smell, 
insoluble  in  water,  and  requiring  a  pressure  of  two  or  three  atmospheres 
for  its  liquefaction.  The  interest  which  attaches  to  it  is  due  to  its  being 
regarded  by  many  chemists  as  the  radical  or  starting-point  of  the  series  of 
compounds  derived  from  vinic  alcohol,  which  is  thence  spoken  of  as  the 
ethyle  series,  and  this  view  of  the  constitution  of  these  compounds  was 
in  favour  long  before  the  compound  (02115)2  was  obtained  in  the  separate 
state,  this  being  a  discovery  of  regent  date. 

Mention  has  already  been  made  of  the  existence  of  another  radical, 
methyle  (0113)2,  obtained  by  a  similar  process,  which  may  be  regarded  as 
the  starting-point  of  the  wood-spirit  series. 

Butyle  (0^119)2,  amyle  {G^-^])^,  and  caproyle  (CgHj3)2,  the  supposed 
radicals  of  the  butylic,  amylic,  and  caproic  alcohols,  have  also  been  ob- 
tained, these  being  liquids  with  progressive  boiling-points.  We  are'  thus 
in  possession  of  several  members  of  a  homologous  series  of  hydrocarbons, 
which  may  be  designated  the  alcohol-radicals,  and  represented  by  the 
general  formula  (CnR^n+ili' 

If  a  mixture  of  ethyle  iodide  and  amyle  iodide  (OgHj^I,  prepared 
from  f ousel  oil  just  as  ethyle  iodide  is  from  alcohol)  be  heated  with 
sodium,  a  colourless  liquid  is  obtained,  which  is  a  true  combination  of 
ethyle  and  amyle  (OgHg.OgH^^) — 

O2H5I    +    O5H11I    +    Nao    =    2Na.I    +    O2H5.O5H11  {EthyU-amyU). 

In  a  similar  manner,  ethyle-butyle  (CgHj.O^Hg),  methyle-caproyle 
(OH3.0gHj3),butyle-amyle  (C^Il9.C5Hjj),andbutyle-caproyle  (O^Hg-OgH^g), 
have  been  obtained. 

These  double  radicals  all  yield  two  volumes  of  vapour  for  each  mole- 
cule of  the  compound,  showing  that  the  empirical  formula  for  methyle 
(OH3),  which  furnishes  only  one  volume,  must  be  converted  into  that  of 
a  double  radical,  di-methyle  (OH3.OH3),  which  would  give  two  volumes 
of  vapour,  and  in  a  similar  manner,  ethyle  would  become  (03115,02115), 
butyle  (04Hf„04H9),  and  so  on. 

This  duplicate  nature  of  the  radicals  at  once  explains  the  circumstance 
that  they  do  not  unite  directly  with  chlorine,  bromine,  &c.,  as  might  have 
been  expected.  Thus  ethyle,  with  iodine,  does  not  combine  to  form 
ethyle  iodide,  because  the  ethyle  itself  is  an  ethylide  of  ethyle. 

Again,  the  formation  of  zinc-ethyle  (C^H-^.^Zw,  and  of  ethyle  hydride 
or  ethane  (O2H5H),  during  the  action  of  zinc  upon  ethyle  iodide,  becomes 
intelligible  upon  this  view.  Indeed,  the  first  stage  of  this  action  appears 
to  consist  in  the  formation  of  zinc-ethyle — 

2O2H5I    +    Zn2   =    (C2H5)2Zn   +    ZnJ^. 


CoHg.  CjHg 

C,Hg.H  =  C,He 

Ethane. 

C4H9.  C4H9 

C4H9.H  =  C4Hj(, 

Butane, 

C5H11.C5H1, 

C5Hii.H  =  CbHi2 

Pentane. 

526  OXALIC  ETHER. 

In  the  second  stage,  the  zinc-ethyle  acts  upon  a  fresh  portion  of  ethyle 
iodide,  producing  zinc  iodide  and  the  double  radical  ethyle — 

2C2H5I   +   {C,K,),Zn   =   Znl^   +    2{C,E,.C,K,). 

The  ethyle  hydride  itself  clearly  corresponds  to  the  double  radical 
ethyle,  one-half  of  which  is  replaced  by  an  atom  of  hydrogen  (C2H5.H). 

The  simultaneous  formation  of  ethyle  hydride,  and  of  olefiant  gas 
during  the  action  of  zinc  upon  ethyle  iodide,  might  be  represented  by 
the  equation — 

2C2H5I  +  Zn  =  Znl2  +  C2H5.H  +  C2H4. 

Ethyle  hydride  is  the  representative  of  a  series  of  homologous  hydro- 
carbons, of  which  the  first  member,  the  methyle  hydride  (CH3.H),  is 
identical  with  marsh  gas. 

The  following  table  exhibits  some  of  the  chief  members  of  the  marsh 
gas  series  of  hydrocarbons  (or  paraffins,  general  formula  C„H2„+2)>  ^^ 
well  as  the  corresponding  alcohol-radicals,*  having  the  general  formula 
2(C\H2»4-i)- 

Radical.  Hydride,  t 

Methyle,  .     CH3.CH3  CH3.H  =  CH4         Methane. 

Ethyle,  . 
Butyle,  . 
Amyle,    . 

The  three  first  of  these  hydrides  are  gaseous,  the  last  a  volatile  liquid. 

If  ethyle  (€2115)2  =  £2  be  accepted  as  the  radical  of  the  alcohol  series, 
then  ether  (€2115)20  would  become  the  ethyle  oxide,  and  alcohol  (C2H5HO) 
the  ethyle  hydrate  ;  and  it  will  be  seen  that  upon  this  view  a  considerable 
number  of  the  relations  of  these  bodies  can  be  readily  explained. 

372.  On  referring  to  the  action  of  hydrochloric  acid  upon  ether,  it  will 
be  seen  to  resemble  exactly  that  of  the  same  acid  upon  the  basic  oxide  of 
a  metal,  consisting  in  an  exchange  between  the  chlorine  of  the  acid  and 
the  oxygen  of  the  base.  Ethyle  chloride  may  also  be  produced  by  the 
action  of  hydrochloric  acid  upon  alcohol  (EHO),  just  as  potassium  chloride 
is  produced  by  the  action  of  that  acid  upon  caustic  potash — 

EHO  {Alcohol)  ■+-  HCl  =   ECl  {Ethyl  chloride)  -f  HgO . 

It  would  be  expected  that  the  action  of  other  acids  upon  alcohol  would 
correspond  to  their  action  upon  caustic  potash,  and  with  several  acids  this 
is  really  the  case,  although  it  is  far  more  difficult  to  break  up  the  alcohol 
than  the  caustic  potash. 

If  alcohol  be  boiled  for  many  hours  with  dry  oxalic  acid  (H2C2O4)  in 
a  flask  provided  with  a  long  tube,  so  that  the  volatilised  alcohol  may  run 
back,  it  is  found  that,  on  diluting  the  solution  with  water,  a  heavy  fra- 
grant liquid  separates,  which  has  the  composition  (€2115)20204,  and  is 
termed  oxalic  ether;  2EH0  -f-  H2C2O4  =  E2C2O4  -f  211^0. 

By  treatment  with  caustic  potash,  the  oxalic  ether  is  decomposed, 
yielding  potassium  oxalate  and  alcohol ;  thus — 

E2C2O4   -1-   2KH0   =   K2C2O4  -f-  2EH0. 

*  See  also  American  petroleum,  page  473. 

+  Each  of  these  hydrides  is  isomeric  with  the  radical  immediately  preceding  it.  Thus 
ethyle  hydride  has  the  same  composition  as  methyle,  and  is  regarded  by  some  chemists 
as  identical  with  it,  for  when  the  so-called  methyle  (or  dini^thyle)  is  treated  with  chlorine, 
it  yields  ethyle  chloride  precisely  as  ethyle  hydride  does. 


ETHERS.  527 

But  if  oxalic  ether  be  mixed  with  only  half  the  quantity  of  caustic  potash 
required  for  this  decomposition,  there  is  obtained,  instead  of  potassium 
oxalate,  a  salt,  crystallising  in  pearly  scales,  having  the  composition 
KEC2O4,  the  formation  of  which  is  easily  understood — 

Kfi^O^  +   KHO   =   KECA  +   EHO. 

Oxalic  ether.  Potassium  oxalovinatc. 

By  decomposing  this  salt  with  hydrofluosilicic  acid  (see  page  185)  to 
remove  the  potassium  in  an  insoluble  form,  a  new  acid  is  obtained,  which 
has  the  composition  HECgO^,  and  is  called  oxaloviidc  or  oxnletliylic  acid. 

Most  of  the  acids  form  ethers  corresponding  to  oxalic  ether ;  thus,  by 
distilling  acetic  acid  with  alcohol  and  sulphuric  acid,  and  diluting  the 
distilled  liquid  with  water,  acetic  ether  (EC.2H3O.2)  is  separated,  remark- 
able for  its  very  fragrant  odour,  which  has  a  share  in  the  perfume  of  cider, 
perry,  vinegar,  and  of  many  wines. 

The  ether  used  in  medicine  under  the  names  of  sweet  spirits  of  nitre, 
nitrous  ether,  and  nitric  ether,  is  essentially  a  solution  of  ni  lous  ether 
(C2H5)N0.2  in  alcohol,  and  is  prepared  by  distilling  alcohol  with  nitric 
and  sulphuric  acids  and  copper  wire,  when  a  complex  reaction  takes  place, 
the  formation  of  the  nitrous  ether  being  represented  by  the  equation — 

C2H5.HO  +  HNO3  +  H2SO4  +  Cu  =  C2H5.NO2  +  2H2O  +  CuSO^. 

Another  portion  of  the  alcohol  is  converted  into  aldehyde  by  the  oxidising 
action  of  the  nitric  acid. 

Nitrous  ether  is  a  very  volatile  liquid,  boiling  at  62°  F.,  characterised 
by  a  powerful  odour  of  rennet-apples,  and,  in  the  pure  state,  decomposing 
spontaneously,  evolving  nitric  oxide. 

Nitro-ethane  is  an  acid  liquid  having  the  same  composition  as  nitrous  ether,  and 
obtained  by  treating  ethyle  iodide  with  silver  nitrite  ;  iiasc^ent  hydrogen  converts 
it  into  ethylamine.  When  acted  on  by  sodium  hydrate  dissolved  in  alcohol,  it  forms 
an  explosive  compound  C.jH^NaNOa. 

True  nitric  ether  (ENO;,)  may  also  be  obtained  as  a  fragrant,  heavy  oilj'  liquid,  by 
distilling  alcohol  with  nitric  acid,  under  certain  precautions.  It  is  decomposed  with 
explosion  at  a  temperature  of  about  200°  F. 

By  the  action  of  nascent  hydrogen  upon  nitric  ether,  a  basic  substance  is  produced, 
which  has  been  named  hydroxijlamiiu,  in  allusion  to  its  reniHrkable  fonnu  a,  NH.,0, 
which  might  be  regarded  as  ammonia,  NH3,  in  which  one  atom  of  hyilrogen  is 
replaced  by  hydroxyle;  C.^HgNOs+Hg^C.^HjHO-f-H.jO -f-NHgO. 

In  order  to  obtain  this  base,  5  parts  of  nitric  ether  are  acted  on  by  12  parts  of  tin 
and  50  parts  of  concentrated  hydrochloric  acid.  When  the  action  is  over,  the  alcohol 
is  expelled  by  heat,  the  tin  precipitated  by  hydrosulphuric  acid,  the  solution  evapo- 
rated to  dryness,  and  the  residue  boiled  with  absolute  alcohol,  which  leaves  some 
ammonium  chloride  undissolved.  The  hydroxylamine  hydrochlorate  (NH3O.  HCl) 
crystallises  in  long  needles  from  the  alcoholic  solution.  From  the  hydroxylamine 
sulphate,  by  decomposition  with  baryta,  a  solution  of  the  base  itself  ma}-  be  obtained, 
but  pure  hydroxylamine  has  not  been  isolated  from  the  solution,  since  it  has  a  ten- 
dency to  decompose  into  ammonia,  water,  and  nitrogen — 

3NH3O   =   NH3  +    N2   -f   3H.,0. 

Hydroxylurea,  CH  ,(H0)N20,  or  urea  in  which  hydrogen  is  replaced  by  hydroxyle, 
has  also  been  obtained. 

The  chloric  ether  used  for  medicinal  purposes  is  not  an  ether  in  the  true  sense  of 
the  term,  but  a  solution  of  chloroform  (CHCI3)  in  alcohol.  Chloroform  will  be  more 
particularly  described  hereafter. 

Perchloric  ether,  {Q.2i\^)C\0^,  is  only  interesting  from  th''  circumstance  that, 
although  an  oily  liquid,  it  explodes  violently  under  a  sudden  Mow. 

Bonccic  ether,  which  has  the  formula  E3BO3,  is  form-d  when  iioron  trichloride  is 
decomposed  by  alcohol;  BCl3  +  3(EHO)=  E.BO.J+ 3HC1,  and  may  also  be  obtained 
by  heating  boracic  anhydride  with  an  excess  of  alcohol  under  pressure.     It  is  lighter 


528  SULPHOVINIC  ACID. 

than  water  (sp.  gr.  0'88),  and  boils  at  246°  F.  When  heated  with  boracic  anhydride 
it  is  converted  into  KjO.  B2O3,  which  is  decomposed  by  heat  into  EgBOjand  E^O.SB^Oj, 
the  latter  b  ing  a  vitreous  solid. 

When  silicon  tetrachloride  is  decomposed  by  alcohol,  the  compound  2EjO.SiOj,is 
produced;  SiCi4  +  4(EHO)  =  2R20-Si0.2  (Silicic  ether)  +  4HCI.  This  silicic  ether  is 
a  colourless  liquid,  of  sp.  gr.  0"93,  and  distilling  unchanged  at  330°  F.  It  has  an 
ethereal  odour,  and  burns  with  a  brilliant  flame  wliich  deposits  silica.  When  poured 
upon  the  surface  of  water,  it  gradually  decomposes,  with  separation  of  gelatinous 
hy.l rated  silica  ;  2F^O.SiOa  +  2H20  =  4(EHO)  {Alcohol) +  9,\.0.^ 

When  the  ether  is  kept  in  a  moist  atmosphere,  it  deposits  a  hard  transparent  mass 
of  silica,  known  as  artificial  quartz. 

Two  other  silicic  ethers  have  been  obtained,"  having  respectively  the  composition 
E.,O.SiO.,  and  £.^0.2810.2 ;  the  former  liquid,  the  latter  viscous. 

'Carbonic  ether  (EoCOs)  may  be  obtained  by  heating  silver  carbonate  with  ethyle 
iodide  in  a  sealed  tube  ;  Ag.jC03  +  2EI  =  E.iCOj+2AgI. 

The  compound  2¥,.f).C0^  or  C(0E)4  has  been  obtained  by  the  action  of  sodium 
upon  an  alcoholic  solution  of  chloropicrine — 

CCl3(N02)  +  4(EH0)  +  Na^  =  3NaCl  +  NaNOj  +  j  2E?0.0a      j  +  "<• 
Chloropicrine.        Alcoliol.  Ethyle  ortho-carbonate. 

When  carbonic  acid  gas  is  passed  through  a  solution  of  potassium  hydrate  in 
absolute  alcohol,  the  potassium  carbovinate  is  obtained  in  crystals  having  the  com- 
position KECO3,  corresponding  to  KHCO3. 

By  the  action  of  syrupy  phosphoric  acid  upon  alcohol,  the  compound  HjEP04, 
phosphnhylic  acid,  is  formed,  and  by  neutralising  it  with  a  base,  a  phosphethylate 
may  be  obtained,  composed  after  the  general  formula  M'2EP04.  A  second  acid  is 
formed  at  the  same  time,  having  the  formula  HE.2PO4,  its  salts  being  M'EjP04.  The 
true  phosphoric  ether  E3PO4  is  also  said  to  have  been  obtained. 

The  true  sulphuric  ether  {Ya^SO^)  may  be  formed  by  passing  the  vapour  of  anhy- 
drous sulphuric  acid  into  ether,  or  by  decomposing  ethyle  iodide  with  silver  sulphate. 
It  is  an  oily  liquid  heavier  than  water,  and  decomposed  by  heat,  olefiant  gas  and 
alcohol  being  found  amongst  the  products. 

The  fragrant  liquid  known  as  heavy  oil  of  wine,  which  is  formed  towards  the  latter 
part  of  the  preparation  of  ether  and  of  olefiant  gas,  has  been  found  by  Harting  to 
contain  ethyl-amyle  ether  (C.^Hs.CjHu.O),  ethyl-amyle  ketone  (CjHj.CjHu.CO),  and 
methyl -hexyle  ketone  (CHj.CgHu.CO). 

373.  When  ether  or  alcohol  is  added  to  concentrated  sulphuric  acid, 
much  heat  is  evolved,  in  consequence  of  the  formation  of  sulphiwinic  or 
sulpliethylic  acid,  HESO4,  corresponding  in  composition  to  KHSO4.  If 
baryta  be  now  added  to  the  solution,  the  uncombined  sulphuric  acid  will 
be  precipitated  in  the  form  of  barium  sulphate,  but  the  sulphovinic  acid  wiU 
form  the  barium  sulphovinate,  which  may  be  obtained  by  evaporating  the 
solution,  in  rhombic  prisms  which  have  the  formula  BaE.3(S04)22Aq.,  and 
are  easily  soluble  in  water.  By  cautiously  adding  sulphuric  acid  to  the 
•solution  of  barium  sulphovinate  till  the  whole  of  the  barium  is  precipitated 
as  sulphate,  and  evaporating  the  filtered  liquid  in  vacuo,  the  pure  sul- 
phovinic acid  is  obtained  as  a  syrupy  liquid  liable  to  spontaneous  decom- 
position, and  readily  decomposed,  when  heated  with  water,  into  alcohol 
aud  sulphuric  acid — 

HESO4   +   H,0   =   H2SO4   4-   EHO. 

Sulphoviiiic  acid.  Alcoliol. 

The  sodium  sulphovinate,  prepared  by  decomposing  the  barium  salt 
with  sodium  carbonate,  is  used  medicinally  in  Germany. 

374.  Vinic  acids  are  not  formed  by  monobasic  acids. — It  must  be 
noticed  that  although  the  greater  number  of  the  acids  are  capable  of 
Ibrming  ethers,  only  a  few  of  them  produce  vinic  acids.  Indeed,  only 
tliose  acids  form  vinic  acids  which  are  polybasic,  i.e.,  require  more  than 


THEORY  OF  FORMATION  OF  ETHER.  529 

one  atom  of  a  metal  for  the  formation  of  a  normal  salt  (page  250),  the 
tendency  to  form  a  vinic  acid  depending  upon  the  possibility  of  replacing 
a  portion  of  the  hydrogen  in  the  acid  by  ethyle.  In  the  case  of  nitric 
acid,  which  is  undoubtedly  a  monobasic  acid,  and  does  not  form  acid 
salts,  no  vinic  acid  can  be  produced ;  the  formula  of  the  acid  being 
HNO3,  the  hydrogen  must  be  entirely  or  not  at  all  replaced  by  the 
ethyle. 

375.  Theory  of  etherification. — When  sulphovinic  (or  sulphethylic) 
acid  is  decomposed  by  heat,  especially  in  the  presence  of  excess  of  alcohol, 
a  large  proportion  of  ether  is  found  among  the  products,  and  this  lias 
given  rise  to  a  very  general  opinion  among  chemists,  that  the  production 
of  sulphovinic  acid  is  an  intermediate  stage  in  the  formation  of  ether,  by 
the  ordinary  process  of  distilling  alcohol  with  sulphuric  acid.  At  first 
sight  it  would  appear  that  the  etherification  of  alcohol  in  this  process  was 
sufficiently  explained  by  reference  to  the  attraction  of  sulphuric  acid  for 
Avater,  and  consisted  in  a  simple  removal  of  water  from  the  alcohol  by  the 
acid,  for  2C2H6O  -  HP  =  C^n^^O. 

Alcoiiol.  Ether. 

AVhen  it  is  found,  however,  that  a  continuous  stream  of  alcohol,  flowing 
into  heated  sulphuric  acid  in  a  retort,  is  converted  into  ether  and  water, 
which  is  not  retained  by  the  sulphuric  acid,  but  distils  over  with  the 
ether,  and  that  this  may  go  on  almost  without  limit,  this  explanation  is 
no  longer  tenable. 

Accordingly,  the  formation  of  ether  from  alcohol  by  the  action  of  sul- 
phuric acid  is  generally  referred  to  the  formation  of  sulphovinic  acid,  as 
soon  as  the  alcohol  and  the  acid  are  brought  in  contact,  and  the  subse- 
quent decomposition  of  this  sulphovinic  acid,  in  the  presence  of  alcohol, 
into  sulphuric  acid,  water,  and  ether  ;  thus — 

HESO4   +   EHO    =   H^SO^   -J-   E2O. 

Sulphovinic  acid.       Alcohol.  Ether. 

The  sulphuric  acid  thus  set  free  would  of  course  give  rise  to  the  fonna- 
tion  of  a  fresh  quantity  of  sulphovinic  acid,  which  would  be  decomposed 
in  its  turn,  and  so  on  without  limit. 

A  strong  argument  in  favour  of  this  view  is  deducible  from  the  follow- 
ing experiment : — 

When  araylic  alcohol  (the  amylic  hydrate  CgH^^HO)  is  mixed  with 
concentrated  sulphuric  acid,  it  forms  sulphamylic  acid  (C5Hjj)HS04, 
corresponding  to  sulphovinic  acid,  and  if  this  be  heated  in  a  retort,  and 
alcohol  be  allowed  to  flow  into  it  as  in  making  ether,  the  first  portion  which 
distils  over  is  found  to  be  a  true  double  ether  molecule  (CoHg.CgH^^.O),  the 
production  of  which  would  be  represented  by  the  equation — 

H(C5Hii)S04   +   C0H5HO   =   CoH^.C^H.^.O   +   H.^SO^ . 

Sulphamylic  acid.  Alcohol.  .\mylethj'lic  et:ier. 

On  continuing  the  distillation,  nothing  but  ordinary  ethylic  ether  is 
obtained. 

The  existence  of  these  double  ethers  might  have  been  anticipated  from 
what  has  been  said  with  respect  to  the  double  radicals  (page  525),  but 
the  mode  of  formation  in  the  above  instance  certainly  aftbrds  support  to 
the  view,  that  ether  results  from  the  decomposition  of  sulphovinic  acid 
by  alcohol  in  the  ordinary  etherifying  process. 

2l 


530  CONSTITUTION  OF  ALCOHOL  AND  ETHER. 

On  the  other  hand,  this  theory  of  etherification  is  shaken  by  the  circum- 
stance, that  if  vapour  of  alcohol  be  passed  into  boiling  sulphuric  acid  of 
sp.  gr.  1*52  (boiling  at  290°  F.)  almost  the  whole  of  the  alcohol  is  resolved 
into  water  and  ether,  which  distil  over,  so  that  either  no  sulphovinic  acid 
is  formed,  or  it  is  only  formed  to  be  immediately  decomposed.  If  the 
acid  have  the  sp.  gr.  1'61  (boiling  at  330°  F.),  no  ether  is  obtained,  the 
alcohol  being  resolved  into  olefiant  gas  and  water. 

Moreover,  hydrated  phosphoric  acid  cannot  be  substituted  for  the 
sulphuric  acid  in  the  preparation  of  ether,  notwithstanding  that  it  also 
forms  a  vinic  acid. 

Hence,  many  chemists  are  inclined  to  attribute  to  sulphuric  acid  a 
specific  action  by  contact  {catalytic  action)  upon  alcohol,  causing  its 
resolution  into  water  and  ether,  or  olefiant  gas,  according  to  the  tem- 
perature. This  view  receives  some  confirmation  from  the  behaviour  of 
sulphuric  acid  towards  cellulose  and  certain  other  substances,  in  which  it 
causes  important  transformations,  without  itself  appearing  to  take  part  in 
the  change. 

In  connexion  with  this  subject,  it  is  remarkably  interesting  to  observe, 
that  alcohol  may  actually  be  reproduced  from  olefiant  gas  and  water 
under  the  influence  of  sulphuric  acid.  If  concentrated  sulphuric  acid  be 
violently  agitated  in  a  vessel  containing  olefiant  gas,  the  latter  is  absorbed, 
and  on  diluting  the  acid  with  water  and  distilling,  a  quantity  of  alcohol 
is  obtained. 

376.  Alcohols  and  ethers  re/erred  to  the  water-type. — ^When  potassium 
or  sodium  is  thrown  into  absolute  alcohol,  the  metal  is  dissolved  with 
disengagement  of  heat  and  rapid  evolution  of  hydrogen,  and  a  crystalline 
compound  is  formed,  known  as  potassium  ethylate  or  sodium  ethylate,  and 
containing  an  atom  of  the  metal  in  the  place  of  an  atom  of  hydrogen  ;  the 
action  of  potassium  upon  alcohol  would  be  thus  represented — 

C2H5HO  {Alcohol)    -f    K    =    C2H5KO  [Potassium  ethylate)    +    H . 

Other  alcohols  behave  in  a  similar  manner.  No  one  can  fail  to  be  struck 
with  the  similarity  which  exists  between  the  action  of  potassium  upon 
alcohol  and  upon  water,  and  chemists  have  naturally  endeavoured  to  refer 
both  actions  to  a  common  type. 

The  decomposition  of  water  by  potassium  is  represented  by  the 
equation — 

Alcohol  may  be  represented  with  equal  fitness,  as  water  in  which  half 
the  hydrogen  is  replaced  by  ethyle  (CgHg),  or  EHO,  and  the  action  of 
potassium  upon  it  may  be  thus  expressed — 


h}o  +  k=e|o  +  h 


In  a  similar  manner  sodium  ethylate  would  be  formed. 

This  substance  has  been  found  useful  in  surgery  as  a  caustic  antiseptic, 
since  it  is  decomposed  by  water,  when  applied  to  a  wound,  yielding 
caustic  soda  and  alcohol,  to  which  the  antiseptic  action  is  due. 

Aluminium  does  not  act  upon  alcohol,  but  if  a  little  iodine  be  dis- 
solved in  the  alcohol,  and  the  solution  heated  with  aluminium,  hydrogen 
is  evolved  and  aluminium  ethylate,  Al2(C2Hj^O)g,  is  produced.     Probably 


MERCAPTAN.  531 

the  aluminium  iodide  first  produced  decomposes  with  the  alcohol,  forming 
aluminium  ethylate  and  hydric  iodide ;  the  latter,  being  acted  on  by  the 
excess  of  aluminium,  evolves  hydrogen  and  forms  more  aluminium  iodide, 
which  decomposes  a  fresh  portion  of  alcohol,  and  thus  a  small  quantity 
of  iodine  carries  on  a  continuous  action.  Other  aluminium  alcohols  are 
produced  in  a  similar  manner. 

Thallium -ethylate,  C.^HgTlO,  has  also  been  obtained  as  a  colourless  liquid  remark- 
able for  its  high  specific  gravity  (3 '55)  and  great  refractive  and  dispersive  action  upon 
light.  Barium-ethylate,  (C.2H50)2Ba,  is  obtained  by  the  action  of  anhydrous  baryta 
on  absolute  alcohol.  A  trace  of  water  precipitates  barium-hydrate  from  the  solution. 
On  heating  the  alcoholic  solution,  the  barium-ethylate  precipitates,  being  less  soluble 
in  hot  alcohol.  The  alcoholic  solution  absorbs  carbonic  oxide  at  the  ordinary 
temperature,  yielding  a  salt  isomeric  with  barium  propionate;  (C2H50)2B.a -I- 2C0 
=  Ba(C3HA)-2- 

When  sodium  ethylate  is  heated  in  a  sealed  tube  with  the  iodide  of 
one  of  the  alcohol-radicals,  the  sodium  combines  with  the  iodine,  whilst 
the  alcohol-radical  enters  into  the  place  of  the  sodium,  and  a  double 
ether  is  formed. 

Thus,  if  methyle  iodide  (CH3I)  be  decomposed  by  sodium  ethylate — 

CH3I    +    ^     >  0  (Sodium-ethylate)  =  Nal   +      pW    (  ^  [Methyl-ethylic  ether). 
In  a  similar  manner  amyl-ethylic  ether,  ^  -^     J-  0,  would  be  produced. 

Again,  if  ethyle  iodide  be  decomposed  by  sodium-alcohol,  common 
ether  is  obtained,  and  the  action  must  in  consistency  be  similarly  ex- 
plained— 

C  TT  T   4-  ^2^5   I  O    =    NaT    4-       2  "5  I  n 

377.  Compounds  have  been  obtained  corresponding  to  alcohol  and  ether,  in  which 
the  place  of  the  oxygen  is  occupied  by  sulphur,  and  which  bear  the  same  relation  to 
hyilrosulphuric  acid  as  alcohol  and  ether  bear  to  water. 

XT    J 

Type — Hydrosulphuric  acid,  „  [  S 

Hydrosulphuric  ether,  C.,H»  )  a    -r,  .      ■  lu-i  l^lc 

^    (ethyle  sulphide)!  aH^  i  ^   Potassium  sulphide,  j,  \  b 

Mercaptan,       .         .       ^tt'  [  S   Potassium  hydrosulphate,  g^  r  S  • 

These  compounds  are  distinguished  for  their  powerful  odour  of  garlic.  This  is 
especially  the  case  with  mercaptan,  which  is  notoriously  one  of  the  most  evil-smelling 
chemical  compounds.  It  is  prepared  by  distilling  solution  of  potassium  hydrosul- 
phate (obtained  by  saturating  potash  with  hydrosulphuric  acid)  with  sulphovinate  of 
potassium,  or  better,  of  calcium — 

KaF[gS04  +  §  I    S         r.        ^-^^  j  S  +  K.,S04. 

Potassium  Mercaptan. 

sulphovinate. 

Mercaptan  is  a  light,  very  volatile  and  inflammable  liquid,  sparingly  soluble  in 

water.     That  it  is  constituted  after  the  type  of  hydrosulphuric  acid  is  shown  by  its 

action  upon  metals  and  their  oxides.     Potassium  acts  upon  it  precisely  as  it  iloes  upon 

alcohol — 

C  H   )  C  H   ) 

^TT^  t  S  (Mercaptan)    -I-    K  =^      ^t^*  >  S  (Potassium-mercaptan)    -f-  H . 

Its  name  was  bestowed  in  allusion  to  its  action  upon  mercuric  oxide,  when  it 
forms  a  white  crystalline  inodorous  compound,  insoluble  in  water,  but  soluble  in 
alcohol — 

2(aH5)HS  +  Hg"0  =  (C2H5)2S.Hg"S  -f  H.O . 
Mercaptan.  ilcrcaptide  of  mercury. 


582  ARSENICAL  ALCOHOL  OR  ALCARSIN. 

378.  Hydrocyanic  ether  (CaHg.CN=-ECy),  or  ethyle  cyanide,  is  obtained  by  heat- 
ing ethyle  iodide  with  silver  cyanide  ;  C2H5l  +  AgCN  =  C2H5.CN  + AgL 
Ethyle  cyanide  is  a  volatile  poisonous  liquid,  smelling  strongly  of  garlic. 


KAKODYLE  SERIES— OEGANO-METALLIC  BODIES. 

379.  One  of  the  most  pleasing  results  of  the  progress  of  investigation 
in  chemistry  is  the  discovery  of  the  true  position  among  classified  com- 
pounds which  is  to  be  assigned  to  some  substance  hitherto  regarded  as 
anomalous,  and  as  destroying  by  its  presence  the  symmetry  and  complete- 
ness of  an  otherwise  perfect  classification.  Such  was  the  case,  until 
within  the  last  few  years,  with  kakndijle,  and  the  bodies  derived  from  it. 
Discovered  long  before  the  science  of  organic  chemistry  was  prepared  to 
receive  it,  it  taxed  the  ingenuity  of  chemists  to  find  a  place  for  it  in  their 
arrangement  of  organic  compounds,  and  always  occupied  an  anomalous 
and  isolated  position.  Modern  research  has  now  brought  to  light  a  whole 
series  of  compounds,  which  would  not  have  been  complete  without  kako- 
dyle,  and  this  hitherto  incomprehensible  substance  has  at  length  been 
assigned  its  proper  place. 

AVhen  a  mixture  of  equal  weights  of  white  arsenic  and  dry  potassium 
acetate  is  submitted  to  distillation,  a  heavy  poisonous  liquid  is  obtained, 
which  has  a  most  disgusting  odour  of  garlic,  and  takes  fire  spontaneously 
when  exposed  to  the  air.  This  liquid,  which  has  long  been  known  under 
the  names  of  alcarsin  (arsenical  alcohol)  and  Cadet's  fuming  liqibor,  has 
the  composition  04X1^2-^^2^'  ^^^  ^^^  production  may  be  represented  (if  the 
various  secondary  products  be  neglected)  by  the  equation — 

4KC2H3O2    +    AS2O3   =    C.H.gAsgO   -f    2K2CO3   +    2CO2. 

Potassium  acetate.  Alcarsin. 

The  spontaneous  combustibility  of  the  crude  product  is  due  to  the  presence  of 
kakodyle. 

If  acetic  acid  be  represented  as  derived  from  formic  acid  by  the  substitution  of 

iiiftthyle  for  hydrogen,  the  formation  of  alcarsin  would  be  easily  explained.    Potassium 

K      ) 
acetate  would  then  be  represented  by  the  formula  ,-,„   |  CO.^,  and  its  action  upon 

arsenious  anhydride  might  be  thus  expressed — 


AsO  >   0  -I-  '  ^^ 


AsO  i  -  -  ^  CH3  i  CO^  =    IsScS:!:  i  0  +  2K,C03  +  2C0, 

Alcarsin. 

Alcarsin  has  the  properties  of  a  base  ;  it  is  capable  of  combining  with 
the  oxygen  acids  to  form  cry.stalline  salts,  and  in  contact  with  the  hydro- 
gen acids  it  furnishes  water,  together  with  a  salt  of  the  radical  of  the  acid. 
Thus,  with  hydrochloric  acid,  we  have — 

C4H,2As20  +  2HC1  =  2As(CH3)2Cl  -H  HgO. 

Alcarsin.  Kakodyle  chloride. 

The  best  method  of  obtaining  this  chloride  consists  in  dissolving  the 
alcarsin  in  alcohol,  and  adding  an  alcoholic  solution  of  corrosive  sublimate, 
Avhen  a  white  crystalline  solid  is  obtained,  composed  of  C4Hi2As20.HgCl2; 
and  on  distilling  this  with  hydrochloric  acid  (out  of  contact  with  air),  a 
spontaneously  inflammable  liquid  is  obtained,  of  insupportable  odour,  and 
composed  of  C2HgAsCl.  By  distilling  this  chloride  with  zinc  in  an  atmo- 
s])here  of  carbonic  acid  gas,  a  third  unbearable  liquid  is  procured,  which 
has  the  formula  C^H^gAsg,  and  has  been  named  kukodijle,  in  allusion  to 


KAKODYLE  SEKIES.  533 

its  intolerable  odour  (KaK6<i,  had).  This  substance  is  obviously  the  radical 
from  which  the  compounds  just  mentioned  are  immediately  derived; 
thus — 

Kakodyle,  C4Hi2As2  =  Kd2 

Alcarsin,  or  kakodyle  oxide,  C4H^oAs.,0  =  Kd.,0 
Kakodyle  chloride,  C2HgAsCl  =  Kd0l. 

The  remarkable  properties  of  kakodyle  leave  no  doubt  as  to  its  being 
really  the  radical  of  these  compounds,  in  the  same  sense  in  which  potas- 
sium is  the  radical  of  the  oxide  and  chloride  of  that  metal,  for  kakodyle 
enters  into  direct  combination  with  chlorine  and  with  oxygen,  its  attrac- 
tion for  the  latter  being  so  energetic  as  to  cause  its  spontaneous  inflamma- 
tion in  the  air. 

The  discovery  of  this  radical,  comporting  itself  in  all  respects  like  a 
metal,  was  of  the  utmost  importance  in  its  effect  upon  organic  chemistry, 
affording  very  strong  ground  for  belief  in  the  existence  of  other  quasi- 
metallic  radicals,  such  as  ethyle,  methyle,  &c.,  which  have  only  recently 
been  isolated.  A  similar  service  had  been  previously  rendered  to  the 
science  by  the  discovery  of  the  compound  radical  ci/anogen  (CX)  belong- 
ing to  the  electro-negative  class  opposed  to  the  metals,  and  for  a  long  time 
these  two  remained  the  only  compound  radicals  which  had  been  obtained 
in  a  separate  form. 

When  kakodyle  is  brought  gradually  in  contact  with  oxygen,  it  is  first 
converted  into  kakodyle  oxide  ((C2HgAs)20),  and  subsequently,  if  water 
be  present,  into  kakodijlic  acid  (HCgHgAsOg  =  HKd02),  which  forms  pris- 
matic crystals,  unaltered  by  air,  and  destitute  of  poisonous  character. 
When  treated  with  hydrochloric  or  hydrosulphuric  acid,  it  yields  trichloride 
(KdClg)  and  sesquisulphide  of  kakodyle  (KdgSg). 

The  most  poisonous  member  of  this  series  is  kakodyle  cyanide 
(C2HgAs.CX  =  KdCy),  which  is  easily  obtained  in  crystals  by  decompos- 
ing mercuric  cyanide  in  solution  with  kakodyle  oxide — 

HgCy2  +  KdgO  =  HgO  +  2KdCy. 

A  very  minute  quantity  of  this  substance  diffused  in  vapour  through  the 
air  has  the  most  dangerous  effect  upon  those  inhaling  it. 

The  following  are  the  most  important  members  of  the  kakodyle  series : — 

Kakodyle,  (C.^HeAs),  =  Ktl, 

Kakodyle  oxide,  (aH6As)oO  =  KdoO 

sulphate,  (aHgAs^ASOs^^Kd.vSO^ 

„        sulphide,  (C2HsAs).,S=Kd.,S 

chloride,  C.,HfiAsCl=KdCl 

Kakodylic  acid,  HCoHb AsO^ = H KdO., 

Silver  kakodylate,  AgC.,HfiAsO._,  =  AgKdOg 

Kakodyle  sesquisulphide,  (CoHgAs)2S3=Kd.2S3 

■ ,,         trichloride,  C2HgAsCl3=KdCl3 

380.  Orr/ano-7netalUc  compounds. — The  only  way  of  referring  kakodyle 
to  any  known  series  was  to  regard  it  as  an  association  of  arsenic  with  2 
atoms  of  methyle  (CHg),  and  this  supposition  necessitated  the  existence 
of  other  compounds  of  a  similar  nature,  formed,  that  ip,  by  the  association 
of  an  inorganic  element  with  a  quasi-metallic  radical.  Accordingly, 
within  the  last  few  years,  it  has  been  discovered  that  by  heating  the 
iodides  of  methyle,  ethyle,  and  amyle  with  zinc,  compounds  of  those 
radicals  with  the  metal  can  be  obtained,  and  these  compounds,  like  kako- 
dyle, are  distinguished  by  their  remarkable  attraction  for  oxygen. 


534 


PREPARATION  OF  ZINC-ETHYLE. 


Nor  are  arsenic  and  zinc  the  only  elements  with  which  these  radicals  can 
be  associated;  boron,  potassium,  sodium,  magnesium,  aluminium,  cadmium, 
tin,  antimony,  bismuth,  lead,  and  mercury  may  be  made  to  furnish  similar 
compounds,  and  the  principle  is  now  fully  established  that  the  alcohol- 
radicals  can  enter  into  combination  with  metals  to  form  compounds  which 
are,  in  some  cases,  capable  of  direct  union  with  oxygen  and  other  electro- 
negative elements,  for  which  they  exhibit  a  greater  attraction  than  the 
metals  themselves. 

The  members  of  this  class  of  organo-metallie  bodies  which  have  been 
the  subjects  of  some  of  the  most  important  researches  deserve  special 
attention. 

Zinc-ethyle  is  prepared  by  the  action  of  zinc  upon  ethyle  iodide — 

2C2H5I  +  Zug  =  (C2H5)2Zn  +  Znl2. 

Eight  hundred  grains  of  bright  freshly  granulated  and  thoroughly  dried  zinc  are 
)ilaced  in  a  half-pint  flask  (E,  fig.  290),  which  is  connected  with  the  carbonic  acid 
apparatus  (A),  from  which  the  gas  is  passed  through  strong  sulphuric  acid  in  the 
bottles  (B  and  C)  where  it  is  thoroughly  dried.  A  second  perforation  in  the  cork  of 
tlie  flask  (E)  allows  the  passage  of  the  tube/,  which  passes  through  the  two  corks  in 
rlie  wide  tube  F,  and  dips  into  a  little  mercury  in  D.  A  stream  of  cold  water  is 
kept  running  througli  the  wide  tube  (F),  being  conveyed  by  the  caoutchouc  tubes  1 1. 
AVhen  the  whole  apparatus  has  been  filled  with  carbonate  acid  gas  the  cork  of  the 


Preparation  of  zinc-ethyle. 


flask  (E)  is  removed,  and  400  grains  of  ethyle  iodide  (perfectly  free  from  moisture)  are 
introduced,  the  cork  being  then  replaced.*  The  carbonic  acid  gas  is  again  passed 
for  a  short  time,  and  then  cut  off  by  closing  the  nipper-tap  (T)  upon  a  caoutchouc 
connector,  when  the  gas  escapes  through  the  tube  (G),  which  dips  into  mercury.  A 
gentle  heat  is  then  applied  by  a  water-bath  to  the  flask  (E)  till  the  ethyle  iodide  boils 
1  iriskly,  the  vapour  being  condensed  in  the  tube  /,  and  running  back  into  the  flask. 
In  about  five  hours  the  conversion  is  complete,  and  the  iodide  ceases  to  distil.  The 
nipper-tap  (T)  is  again  opened,  and  a  slow  current  of  carbonic  acid  gas  is  allowed  to 
l)ass  ;  the  position  of  the  condenser  (F)  is  reversed  (fig.  291),  and  the  tube/ is  con- 
nected by  the  cork  K,  with  the  short  test-tube  0  ;  the  longer  limb  of  a  very  narrow 
siphon  (I)  of  stout  tube  passes  through  a  second  perforation  in  the  cork  (K),  the 
shorter  limb  passing  into  the  very  short  test-tube  (P),  the  cork  of  which  is  also 
furnished  with  the  short  piece  of  moderately  wide  tube  (L).  For  receiving  and  pre- 
serving tlie  zinc-ethyle,  a  number  of  small  tubes  are  prepared  of  the  form  shown  in 

*  The  jirocess  is  said  to  be  much  accelerated  if  about  A  of  zinc-ethyle  is  dissolved  in  the 
ethvle  iodide. 


ZINC-ETHYLE.  535 

g.  292.  The  long  narrow  neck  (R)  of  one  of  these  is  passed  down  the  short  tube  (L) 
to  the  bottom  of  P,  the  other  end  (N)  of  the  tube  being  connected  with  an  apparatus 
for  passing  dry  carbonic  acid  gas.  The  whole  of  the  apparatus  being  filled  with  this 
gas,  the  nipper-tap  is  closed,  and  the  Ihisk  (E)  heated  on  a  sand-bath,  so  that  the  zinc- 
cthyle  may  distil  over,  a  slow  stream  of  carbonic  acid  gas  being  constantly  passed 
into  P,  the  excess  escaping  through  L.  When  enough  zinc-ethyle  has  collected  in 
the  tube  (0)  a  blowpipe  flame  is  applied  to  the  narrow  tube  (N),  which  is  drawn  off 


Fig.  291. — Collection  of  zinc  ethj'ie. 

and  sealed  ;  the  siphon  tube  (I)  is  then  gradually  pushed  down,  so  that  its  longer 

limb  may  be  sufficiently  mmersed  in  the  zinc-ethyle,  and  the  nipper-tap  (T,  fig.  290) 

is  opened,  when  the  pressure  of 

the  carbonic  acid  gas  forces  over 

a  part  of  the  zinc-ethj'le  into  the 

tube  P.     By  heating  the  tube  (M) 

with  a  spirit-lamp,  so  as  to  expel 

part  of  the  gas,   allowing   it  to  Fig.  2v?.. 

cool,  it  will  become  partly  filled 

with  zinc-ethyle,  and  may  be  withdrawn  and  quickly  sealed  by  the  blowpipe.     The 

spontaneous  inflammability  of  the  zinc-ethyle,  and  its  easy  decomposition  by  water, 

reader  great  care  necessary  in  its  preparation.     If  an  alloy  of  zinc  with  one-fourth  its 

weight  of  sodium  be  employed,  the  conversion  may  be  effected  in  an  hour. 

If  any  moisture  were  present  in  the  materials  employed,  it  would 
decompose  a  corresponding  quantity  of  the  zinc-ethyle,  yielding  zinc  oxide 
and  gaseous  ethyle  hydride — • 

{C^B.,}^Zn  +  H,0  =  2(CoH5.H)  +  ZnO . 

Zinc-ethyle  is  a  colourless  liquid  of  povi'erful  odour,  heavier  than  water 
(sp.  gr.  1"18),  and  boiling  at  244°  F.  In  contact  with  atmospheric  air, 
it  takes  fire  spontaneously,  burning  with  a  dazzling  greenish-blue  flame 
which  emits  white  clouds  of  zinc  oxide.  If  a  piece  of  porcelain  be 
depressed  upon  the  flame,  a  deposit  of  metallic  zinc  is  formed,  surrounded 
by  a  ring  of  oxide,  which  is  yellow  while  hot,  and  white  on  cooling. 

When  oxygen  is  allowed  to  act  very  gradually  upon  zinc-ethyle,  zinc 
ethylate  is  formed,  corresponding  to  potassium  and  sodium  ethylates, 
which  have  been  already  described;  (C2H5).,Zn-FO,  =  Zn(C2H5)202. 

Under  the  gradual  action  of  other  electro-negative  elements,  zinc-ethyle 
is  decomposed  into  compounds  of  zinc  and  ethyle  with  the  particular 
element  employed ;  (C2H5)2Zn  4- 14  =  2C2H5I  +  Znl.,. 

Zinc-methyle  (CH3)2Zn  is  prepared  by  the  action  of  zinc  upon  the 
methyle  iodide  (CH3I),  and  resembles  zinc-ethyle  in  its  general  character ; 
it  is,  however,  far  more  volatile  and  more  energetic  in  its  reactions  than 
zinc-ethyle,  and  is  decomposed  with  inflammation  and  explosion  when 


536  ARSEXAIO-TRIETHYLE. 

brought  in  contact  with  water,  yielding  zinc  oxide  and  marsh  gas  (methyle 
hydride);  (CH3)2Zn  +  H20  =  2(CH3.H)  +  ZnO. 

Zinc-amyle  {G^H.-^^)^Zn  is  not  so  violent  in  its  reactions;  it  does  not 
inflame  when  exposed  to  air,  but  absorbs  oxygen  very  rapidly. 

Potassmm-ethyle  and  sodium-ethyle  (CgH^.K  and  CgHg.Na)  have  as 
yet  been  obtained  only  in  combination  with  zinc-ethyle,  by  heating  this 
liquid  in  a  sealed  tube  with  potassium  or  sodium,  when  metallic  zinc  is 
separated,  and  the  alkali-metal  takes  its  place — 

3(C2H,),Zn  +  Na,  =  2{Zn{C,^,\^2^C^ll,)  +  Zn. 

Tlie  double  compound  of  sodium-ethyle  with  zinc-ethyle  is  a  crystalline 
solid  which  decomposes  water  with  great  violence,  forming  soda,  zinc 
oxide,  and  ethyle  hydride.*  Its  behaviour  with  carbonic  acid  gas  is  very 
interesting  and  important. 

When  the  crystalline  compound  of  sodium-ethyle  with  zinc-ethyle  is 
introduced  into  a  bulb  tube  through  which  dry  carbonic  acid  gas  is 
passed,  much  heat  is  evolved,  zinc-ethyle  distils  off,  and  a  white  solid  is 
left  in  the  bulb,  which  is  found  to  consist  of  the  sodium  propylate 
NaCgHgOg  formed  according  to  the  equation — 

CgHjNa  +  CO2  =  NaCgHjOa. 

This  reaction  is  one  of  very  great  importance,  representing  the  first 
successful  attempt  to  produce  directly  one  of  the  organic  acids  from 
carbon  dioxide,  and  indicating  a  general  method  for  the  formation  of  the 
other  acids  of  the  same  series. 

Thus,  if  sodium-methyle  be  treated  in  the  same  way,  it  yields  sodium 
acetate ;  CHgNa  -|-  COg  =  NaCgHgOg. 

By  heating  methyle  iodide  in  a  sealed  tube  with  a  compound  of 
ai'senic  and  sodium,  kakodyle  or  arsenio-dimethyle  is  obtained — 

2CHgI  -1-  AsNa^  =  As(CHg)2  +  2NaI, 

and  thus  kakodyle  finds  its  place  among  the  organo-metallic  bodies,  the 
existence  of  which  it  foreshadowed. 

When  ethyle  iodide  is  treated  in  a  similar  manner,  arsenio-diethylef 
As(C2H5)2,  or  ethylic-kakodyle,  is  obtained. 

381.  Arsenio-trimethyle  or  trimethylarsine,  As(CH3)3,  and  arsenio- 
triethyle  or  triethylarsine,  As(C2H5)g,  may  be  obtained  by  acting  upon 
the  iodides  of  methyle  and  ethyle  with  a  compound  of  arsenic  with 
3  atoms  of  sodium  — 

3CH3I  -f  AsNag  =  As(CH3)3  -f-  3NaI; 

or  by  decomposing  zinc-methyle  or  zinc-ethyle  with  arsenic  chloride; 
3Zn(C2H5)2  -f  2 ASCI3  -  2 As(C2H5)3  +  SZnCla- 

Arsenio-triethyle  has  a  kakodyiic  odour,  but  does  not  take  fire  when 
exposed  to  air,  although  it  oxidises  with  great  rapidity.  Like  kakodyle,  it 
is  capable  of  producing  a  base  by  combination  with  oxygen,  which  has 
the  formula  As(C2H5)30,  and  is  called  arsenic  trietlioxide.  Similar  com- 
pounds have  been  obtained  in  which  the  oxygen  is  replaced  by  chlorine, 
iodine,  and  sulphur. 

Other  arsenical  compounds  of  ethyle  and  methyle  have  been  produced 

*  Strange  to  say,  when  this  compound  of  sodium-ethyle  with  zinc-ethyle  is  heated,  it 
leaves  metallic  sodium  and  zinc. 


ALUMINIUM  ETHIDE — TKIBORETHYLE.  537 

containing  four  atoms  of  the  alcohol-radical,  but  the  oxide  of  teti-ethyl- 
arsonium  [As(C2H5)^].,0  and  its  congeners  are  really  substances  belonging 
to  the  ammonium  family,  and  they  will  be  again  alluded  to  elsewhere. 

Stibethijle,  Sb(C2H-)3,  or  stibiotriethyle,  and stibiotrimethyle,  Sb(CH3)3, 
are  obtained  by  processes  similar  to  those  which  furnish  the  corresponding 
compounds  of  arsenic,  which  they  much  resemble. 

Stibethyle  has  a  powerful  odour  of  onions,  and  takes  fire  spontaneously 
in  air.  It  combines  with  oxygen,  chlorine,  iodine,  and  sulphur  with  great 
energy.  So  powerful  is  its  attraction  for  chlorine,  that  it  displaces  hydrogen 
from  concentrated  hydrochloric  acid — 

Sb(C2H5)3  +   2HC1  =   ^\y{C^^)yQ\^  {StihethyU  dichlm-ide)  +  H2. 

Stibethyle  oxide  is  a  basic  substance.  The  iodide  of  tetrethylstibonium, 
Sb(C2H5)4l,  belongs  to  the  ammonium  family. 

Mercuric  methide  Hg(CH3)2  and  ethide  Hg(C2H5)2  are  formed  by  the 
action  of  zinc-methyle  and  zinc-ethyle  upon  mercuric  chloride — 

Zn(C2H5)2  -t-  HgCl2  =  ZnCl2  +  Hg(C2H5)2. 

The  methyle  compound  is  the  heaviest  liquid  (except  metallic  mercury) 
which  is  known;  its  specific  gravity  is  3*07,  so  that  glass  floats  upon  its 
surface. 

Aluminmm  ethide,  A].2(C2^r,)Q,  is  obtained  by  decomposing  mercuric 
ethide  with  aluminium,  SHgE^  +  Alg  =  Hg2  +  Al2Eg.  It  is  a  colourless 
liquid,  spontaneously  inflammable,  and  decomposed  by  water.  The 
corresponding  methyle  compound,  Al2(CH3)g,  solidifies  at  a  little  above 
32°  F.  into  a  transparent  crystalline  mass. 

Trihorethyle,  3(02115)3,  has  been  obtained  by  the  action  of  zinc-ethyle 
upou  boracic  ether — 

2E3BO3    +    3ZnE2    =    2BE3    +    3ZnE.,02 

Boracic  etlier.  Zinc-etlixle.       Tribor-eiliyle.     Etliylate  of  zinc. 

It  distils  over  as  a  very  light  (sp.  gr.  0*69)  colourless  liquid,  which  has 
an  irritating  odour,  and  is  insoluble  in  water.  It  inflames  spontaneously 
in  air,  burning  with  a  beautiful  green  flame,  and  explodes  when  brought 
in  contact  with  pure  oxygen.  By  gradual  oxidation  it  is  converted  into 
the  compound  BE3O0,  which  may  be  distilled  in  vacuo  without  decom- 
position. When  this  liquid  is  mixed  with  w^ater  it  is  decomposed,  yield- 
ing alcohol,  and  a  volatile  white  crystalline  body,  BH2EO2 — 

BE3O2  +  2H2O  -  BH2EO2  +  2(EH0). 

This  substance  has  an  agreeable  odour,  and  a  most  intensely  sweet 
taste  ;  it  is  very  soluble  in  water,  alcohol,  and  ether. 

Boric  methide,  B(CH3)3,  is  foi-med  by  the  action  of  a  strong  ethereal 
solution  of  zinc-methyle  upon  boracic  ether —  < 

2E3BO3  +  3ZnMe2  =  2BMe3  +  3ZnE202 

Boracic  etlier.     Zinc-methyle.     Boric  metliyde.     Zinc  etliylate. 

Boric  methide  is  a  heavy  (sp.  gr.  1  -93)  colourless  gas,  having  an  intoler- 
ably pungent  tear-exciting  odour,  and  capable  of  liquefaction  under  a 
pressure  of  three  atmospheres  at  50''  F.  When  it  issues  very  slowly  into 
the  air  from  a  tube,  it  undergoes  partial  oxidation,  and  produces  a  lam- 
bent blue  flame,  invisible  in  daylight,  and  incapable  of  burning  the 
fingers ;  but  when  it  comes  rapidly  into  contact  with  air,  it  burns  with  a 
bright  green  hot  flame,  remarkable  for  the  immense  quantity  of  large 


538 


BORIC  METHIDE — SILICIUM-ETHYLE, 


flakes  of  carbon  which  it  disperses  through  the  air,  apparently  "because 
the  BgOg  produced  envelopes  them  and  prevents  their  combustion. 
Boric  methide  combines  with  an  equal  volume  of  ammonia  gas,  producing 
a  white,  volatile  compound  NHg.BMeg,  which  is  deposited  in  fine  crystals 
from  its  ethereal  solution,  and  may  be  sublimed  without  decomposition. 
Its  vapour,  like  that  of  sal-ammoniac,  occupies  four  volumes  instead  of 
two.  Water  absorbs  very  little  boric  methide,  but  alcohol  dissolves  it 
readily.  Solutions  of  the  alkalies  and  alkaline  earths  also  absorb  it,  and 
potash  decomposes  the  ammonia  compound,  but  the  combinations  of  boric 
methide  with  the  alkalies  do  not  crystallise,  and  are  decomposed  even  by 
carbonic  acid  gas. 

Silicium-ethyle,  SiE^,  results  from  the  decomposition  of  silicon  tetra- 
chloride with  zinc-ethyle;  it  is  not  decomposed  by  water  or  by  solution  of 
potash,  is  lighter  than  water,  and  burns  with  a  bright  flame.  Silioium- 
ethyle  is  especially  interesting  as  the  source  of  a  new  alcohol  in  which  a 
part  of  the  carbon  appears  to  be  replaced  by  silicon.  The  formula  of  this 
alcohol  is  said  to  be  SiCgHooO,  which  may  be  represented  as  the  (missing, 
see  page  518)  alcohol  CgH^oO  (nonyle-alcohol),  in  which  an  atom  of  carbon 
is  replaced  by  an  atom  of  silicon. 

Silicium-hexethyle,  SigEg,  corresponding  in  composition  to  aluminium 
cthide,  is  also  an  inflammable  liquid,  the  vapour  of  which  has  the  high 
specific  gravity  7  "96. 

Silicium-methijle,  SilCHg)^,  is  obtained  by  the  action  of  SiCl4  upon 
methyle  iodide  in  the  presence  of  zinc.  It  is  a  liquid  which  burns  with 
a  luminous  flame,  producing  white  fumes  of  silica. 

382.  The  following  table  exhibits  the  composition  of  the  principal  com- 
pounds of  alcohol-radicals  with  inorganic  elements  which,  have  yet  been 
analysed,  omitting  some  of  the  compound  ammonias,  which  will  be  noticed 

hereafter : — 


Compounds  of  alcohol-radicals 
with  inorganic  elements. 

Formula. 

Inorganic 
Type. 

Sodium-ethyle, 
Magnesiiun-ethyle, 
Aluiuinium-etltyle, 
Zinc- methyle, 
Zinc-ethyle,   . 

Zinc-amyle 

Stau-methyle, 
Stan-ethyle,  .       '  . 
Sesquiethide  of  tin, 
Diethiodide  of  tin, 
Stannic  etiiide, 
Stannic  ethylomethide,  . 
Stannic  iodethide, 
Bisniuthous  etliide, 
Bismuthous  dielilorethide, 
Plumbic  etliide,     . 
Mercuric  ethide,     . 
Mercuric  methide, 
Stibethyle,     . 
Antimonic  triethoxide,  . 

NaE 

MgE, 

A1,E« 

ZuMco 

ZnEg- 

ZnAylj 

SuMca 

SuEg 

SiL^Eg 

Sn^EJ, 

SnE, 

SnE.,Me..* 

SnEJa  " 

BiE; 

BiECL 

PbE. 

Hg.E 

HgMe^ 

SbEa 

SbEgO 

NaCl 

MgCl^ 

AlaCls 

ZnOlg 

ZnClj 

ZnCl, 

SnCl," 

SnCi; 

SujiOs 

SnaOs 

SnCl4 

Sn0l4 

SnCl4 

BiClg 

BiCL 

PbOs 

HgCl, 

HgCL, 

SbCls 

SbClj 

*  Formed  by  the  action  of  zinc-raethyle  upon  the  stannic  iodethide,  ZnMe.>  +  SuEo 
=  SuE.jMe2  -t-  Zulg. 


CONSTITUTION  OF  ORGANO-METALLIC  BODIES. 


539 


j               Compounds  of  alcoliol -radicals 

r  onuulfl. 

luorcanic 

'                    with  inorganic  elements. 

Tj-pe. 

Iodide  of  letrethyl-stibonium, 

SbE4l 

SbCij 

Kakodyle, 

AsMe, 

AsjS., 

Kakodyle  oxide,     .... 

AsgMe^O 

As.,03 

Arsenious  oxymethide,  . 

AsMeO 

ASCI3 

Trimethyl-arsine,  .         .         ... 

AsMcj 

ASCI3 

Mouomethyl  arsenic  oxide, 

AsMeO., 

AsClj 

Kakodylic  acid,      .... 

HAsMejO., 

HAs03(?) 

Sulphokakodylic  acid,    . 

(A8Me,).,S; 

AS2O5 

Kakodyle  trichloride,     . 

AsMe.,Cl.^ 

ASCI5 

Ethyl-kakodylic  acid,     . 

(AsE.;),03 

As,05 

Arsenic  triethoxide, 

ASE3O 

AsCIg 

Tetreth3'^larsonium  oxide. 

(AsEJ^O 

As-Ps 

Diuiethyl-diethylarsonium  oxide,  . 

{AsMe2E,)20 

As-A 

Triborethyle,          .... 

BE3        ' 

BCI3 

Boric  methide,       .... 

BMe3 

BCl, 

Silicium-ethyle 

SiE^ 

SiCii 

Silicium-methyle,  .... 

SiMe^ 

SiCl4 

These  compounds  are  evidently  formed  upon  the  types  of  the  inorganic 
combinations  of  the  respective  elements.  Those  elements  which  combine 
in  only  one  proportion  with  oxygen  or  sulphur,  also  combine  in  one  pro- 
portion with  an  alcohol-radical;  whilst  those  which  form  more  than  one 
compound  with  oxygen  and  sulphur  also  generally  form  corresponding 
compounds  with  alcohol-radicals. 

Thus  zinc,  which  combines  with  only  2  atoms  of  chlorine  or  bromine, 
also  associates  itself  with  2  of  methyle,  ethyle,  or  amyle.  Aluminium 
also  combines  only  in  one  proportion  Avith  the  alcohol-radicals,  but  that 
l)roportion  corresponds  with  the  composition  of  alumina,  the  only  oxide 
of  aluminium. 

Tin,  on  the  other  hand,  forms  three  distinct  series  of  compounds  with 
the  alcohol-radicals,  composed  according  to  the  types  of  SnO,  SugOg  and 
Sn02,  respectively.  And  it  must  be  observed  that  as  long  as  the  type  is 
adhered  to,  the  particular  radical  occupying  a  place  in  the  compound 
apjjears  to  be  a  matter  of  indifference;  thus  we  find,  in  the  bodies  com- 
posed after  the  type  of  SugOj,  one  in  which  the  places  of  the  3  atoms  of 
oxygen  are  occupied  by  ethyle,  and  another  in  Avhich  only  two  of  the 
places  are  occupied  by  ethyle  (an  electro-positive  or  quasi-metallic  or 
hasylous  radical),  Avhilst  the  third  is  filled  by  iodine  (an  electro-negative 
or  chlorous  radical). 


ORGANIC  ALKAKOIDS— AMMONIA  DERIVATIVES. 

38.3.  The  attraction  which  the  vegetable  alkaloids  have  always  possessed 
for  the  chemical  inquirer  is  easily  accounted  for;  composing,  as  they  do,  so 
very  small  a  portioa  of  the  plants  in  which  they  are  found,  and  yet  repre- 
senting, in  many  cases,  the  Avhole  virtue  and  activity  of  such  plants  in 
their  action  upon  the  animal  body,  it  is  very  natural  that  their  composi- 
tion should  have  been  very  carefully  studied,  with  a  view  to  explain  the 
changes  by  which  they  are  produced  in  the  plants,  and,  if  possible,  to 
imitate  those  changes  in  order  to  obtain  these  valuable  remedies  by  arti- 
ficial means.  In  this  study,  however,  the  chemist  has  to  contend  with 
difficulties  of  no  insignificant  character;  for  even  in  the  determination  of 
the  ultimate  composition  of  these  alkaloids,  their  high  molecular  weights 


540 


COMPOSITION  OF   THE  ALKALOIDS. 


and  comparatively  small  proportion  of  hydrogen  render  the  exact  determin- 
ation of  this  element  a  matter  of  great  difficulty,  so  that  even  at  the 
present  time  the  composition  of  some  of  the  less  known  alkaloids  can 
hardly  he  said  to  he  definitely  established. 

The  following   table  includes  the  most  important  of   those  alkaloids 
which  are  extracted  from  plants  : — 


Alkaloid. 

Source. 

Formula. 

Morphine 

Opium          .... 

C17H19NO3 

Codeine 

j» 

C18H21NO3 

Narcotine 

9f 

C.,.^H.^N07 

Papaverine 

ft 

C20H21NO4 

Quinine 

Cinchona  bark     . 

C2o"24^2^2 

Cinchonine 

>> 

CjoH^.N^O 

Quinidine 

>> 

C,oH24N20.i 

Quinamine 

J) 

C^aH^^NA 

Caffeine 

Coffee 

1  C»  H,„N^Oo 

Theine 

Tea     . 

1   ^8  "lO-^  4^4 

Theobromine 

Cacao-nut    . 

C,  Hg  N4O2 

Strychnine 

Nux  vomica 

CaiHojN^Oj 

Brueine 

»j 

c^h;„n.a 

Nicotine 

Tobacco 

^10"l4-*'2 

Solanine 

Potato-shoots 

C43HnNOi6 

Atropine 

Deadly-nightshade 

I  C„H„,NO 

Daturine 

Stramonium 

>  v^l7Al23^^^'3 

Cocaine 

Coca-leaves . 

Cj^H^i  NO4 

Hyoscyamine 

Henbane 

C15H23NO3 

Emetine 

Ipecacuanlia 

C3nH44NA 

Aconitine 

Aconite 

C27H39NO,„ 

Vera  trine 

White  hellebore  . 

^32  "52  ^2^8 

Coniine 

Hemlock     , 

CgHisN 

Piperine 

Pepper 

C17H19NO3 

Capsicine 

Cayenne  pepper  . 

Sparteine 

Common  broom   . 

C'i8"26^2 

Curarine 

Curara  poison 

CioHi^N 

Pilocarpine 

Jaborandi leaves . 

CnHjeNjOs 

From  this  table  it  is  seen  that  the  alkaloids  invariably  contain  nitrogen  ; 
and  though  this  element  generally  forms  a  comparatively  small  part  of  the 
weight  of  the  alkaloid,  not  exceeding  31  per  cent,  in  theobromine,  which 
is  the  richest  in  nitrogen^  and  falling  as  low  as  3 '4  per  cent,  in  narcotine, 
Avhich  is  the  poorest,  it  is  from  this  element  that  chemists  have  always  started 
in  their  speculations  upon  the  constitution  of  these  important  bodies. 

The  earliest  view  of  any  importance  respecting  the  constitution  of  the 
alkaloids  was  that  of  Berzelius,  who,  resting  upon  the  constant  presence 
of  nitrogen  and  hydrogen  in  these  substances,  regarded  them  as  compounds 
of  certain  neutral  substances  (then  unknown  in  the  separate  state)  with 
ammonia,  to  which  they  owed  their  alkaline  characters,  and  this  opinion 
was  much  strengthened  when  it  was  discovered  that  certain  organic  bases 
(though  not  those  actually  found  in  plants)  could  be  produced  by  the 
direct  combination  of  ammonia  with  neutral  substances ;  thus  oil  of 
mustard  (C4H5NS),  when  combined  with  ammonia  (NH3),  yields  the  base 
tldosinnamine  (C^HgNgS). 

To  this  view  it  was  objected,  that  ammonia  could  not  be  detected  in 
these  organic  bases,  and  as  the  doctrine  of  the  displacement  of  one  element 
by  another,  or  by  a  quasi-element,  gained  ground,  it  was  suggested  that 
the  organic  bases  might  be  really  constituted  in  the  same  manner  as 


ETHYLATED  AMMONIAS.  541 

ammonia  itself,  the  place  of  a  portion  of  the  hydrogen  being  occupied  by 
a  group  composed  of  carbon  and  hydrogen,  or  of  carbon,  hydrogen,  and 
oxygen.  This  view  of  the  constitution  of  the  alkaloids,  therefore,  would 
at  once  propose  ammonia  as  the  type  of  this  large  class. 

In  the  earlier  attempts  to  refe'r  the  organic  bases  to  ammonia  as  their 
type,  it  was  said  that  just  as  that  substance  is  composed  of  4  atoms  (1 
of  nitrogen  and  3  of  hydrogen),  so  are  the  organic  bases,  but  that  these 
contain  only  2  separate  hydrogen  atoms,  the  place  of  the  third  atom  of 
that  element  being  occupied  by  a  compound  which  discharges  the 
functions  of  that  third  atom  of  hydrogen,  and  does  not  destroy  the  alka- 
line character  of  the  original  ammonia  type. 

To  apply  this  view  to  one  of  the  least  complex  of  the  organic  bases, 
aniline  (CgH^N),  we  might  represent  it  as  ammonia  (NHg),  in  which  the 
third  atom  of  hydrogen  had  been  displaced  by  the  hypothetical  compound 
radical  phenyle  (C^Hj)  for  CgH-^N"  =  NHg.CgHj,  phenylaraine. 

This  view  of  the  constitution  of  aniline  was  supported  by  the  fact,  that 
aniline  may  be  obtained  by  the  action  of  heat  upon  ammonium  phenate, 
thus;  NH^. CgH- O  (^m?)io?uum  2>^e?i«<e)  —  HgO  =  KHg. CgH^  {Aniline);  and 
as  the  substances  derived  from  ammoniacal  salts  by  the  loss  of  a  mole- 
cule of  water  were  called  amides  (being  supposed  to  contain  amidogen, 
NHg)  this  theory  was  spoken  of  as  the  amide-theory  of  the  constitution 
of  organic  bases. 

Later  research  has  only  extended  this  theory,  having  proved  that 
ammonia  is  the  type  of  at  least  the  greater  number  of  organic  bases,  and 
that  not  only  one,  but  all  three  of  the  hydrogen-atoms,  are  movable,  and 
may  be  displaced  by  compound  radicals,  whilst  even  the  nitrogen  of  the 
type  also  admits  of  replacement  by  other  elements  of  the  same  chemical 
family,  viz.,  by  phosphorus,  arsenic,  and  antimony. 

A  more  instructive  example  of  the  elasticity  of  a  type  cannot  be  given. 

384.  Ethylated  ammonias  and  their  derivatives. — When  ethyle  iodide 
(CgHgl)  is  heated  in  a  sealed  tube  with  an  alcoholic  solution  of  ammonia, 
in  the  proportion  of  single  molecules,  a  crystalline  compound  is  formed^ 
which  might  at  first  be  regarded  merely  as  a  combination  of  the  two 
bodies  employed  to  produce  it  (CgH^LNHg)  ;  but  when  this  substance  is 
distilled  with  potash,  it  furnishes,  instead  of  ammoniacal  gas,  a  vapour 
which  condenses,  under  the  ordinary  pressure,  in  a  receiver  cooled  by 
ice,  to  a  very  light  colourless  liquid  which  boils  at  65° '6  F.,  and  has  a 
powerful  ammoniacal  odour.  By  analysis,  this  liquid  is  found  to  have 
the  composition  C^HyN",  being,  in  fact,  ammonia  in  which  one-third  of  the 
hydrogen  has  been  displaced  by  ethyle.  That  this  is  the  true  view  of  its 
constitution  does  not  admit  of  a  doubt,  since  it  so  nearly  resembles 
ammonia  in  all  its  characters,  that  it  might  easily  be  mistaken  for  that 
substance.  The  ethyl-ammonia  or  ethylia,  or  ethylamine,  has  not  only  the 
modified  odour  of  ammonia,  but  it  is  powerfully  alkaline,  and  combines 
readily  with  acids,  forming  salts,  many  of  which  may  be  crystallised.  It 
is,  as  might  be  expected,  more  inflammable  than  ammonia. 

The  crystalline  compound  formed  by  the  action  of  ethyle  iodide  upon 
ammonia  is  the  ethylamine  hydriodate — 

C2H5I  +  N-   H  =  X  <^      H   >.HI, 


542  TETBETHYLIUM. 

the  hydrogen  expelled  from  the  ammonia  having  taken  the  place  of  the 
ethyle  in  the  iodide,  forming  hydriodic  acid,  which  remains  in  combina- 
tion with  the  ethylamine. 

Ethyle  chloride  and  bromide,  when  heated  with  ammonia,  yield, 
respectively,  the  hydrochlorate  and  hydrobromate  of  ethylamine,  but 
the  ethyle  iodide  is  preferred  for  this  and  similar  experiments,  as  being 
less  volatile,  and  therefore  more  manageable  in  sealed  tubes. 

If  ethylamine  be  again  acted  upon  by 'ethyle  iodide,  a  second  atom  of 
hydrogen  may  be  displaced  by  ethyle,  and  the  hydriodate  of  diethyla- 
mine  is  obtained — 

NJ      H   V  +C,H,I  =  NJC^H    '>.HI, 

Ethylamine.  Todidif  Dietliylamine  hydriodate. 

and  from  the  hydriodate  the  diethylamine  is  obtained  by  distillation  with 
potash,  as  a  colourless  and  inflammable  liquid,  strongly  ammouiacal,  and 
having  a  much  higher  boiling-point  than  ethylamine  (134° '6  F.).  In  its 
chemical  relations  diethylamine  is  a  decided  ammonia. 

In  order  to  remove  the  third  atom  of  hydrogen,  it  is  only  necessary  to 
subject  diethylamine  to  the  action  of  ethyle  iodide — 

Diethylamine.  iodide^  Triethylamlne  hydriodate. 

When  this  last  hydriodate  is  distilled  with  potash,  the  triethylamine  is 
obtained  as  a  colourless  liquid,  presenting  the  strongest  evidence  of  its 
relationship  to  ethylamine  and  diethylamine  as  well  as  to  ammonia.  It 
is  powerfully  alkaline,  and  boils  at  a  higher  temperature  than  diethylamine. 

But  the  action  of  ethyle  iodide  does  not  stop  here,  for  if  triethylamine 
be  again  heated  with  it,  a  molecule  of  that  base  combines  with  a  mole- 
cule of  the  iodide  to  form  the  compound  ^(02115)3.021151,  which  may  be 
represented  as  triethylamine  hydriodate,  in  which  the  place  of  the  hydrogen 
in  the  hydriodic  acid  is  occupied  by  ethyle. 

But  it  will  be  remembered  that  the  hydriodate  of  ammonia  (NH3.HI) 
is  regarded  as  the  iodide  of  a  hypothetical  compound  metal  ammonium 
(NH4),  and  it  would  appear  admissible  to  view  the  above  compound  as 
ammonium  iodide  (NH^I),  in  which  the  4  atoms  of  hydrogen  are  displaced 
by  ethyle ;  it  would  then  be  called  iodide  of  tetrethylammonium  (NE^I), 
or  tetrethylium  iodide. 

That  this  is  the  true  view  of  the  compound  has  been  inferred  from  the 
circumstance  that  the  salt,  obtained  by  the  action  of  ethyle  chloride  on 
(limethylamine,  is  identical  with  that  resulting  from  methyle-chloride  with 
diethylamine.  Its  formula  must  therefore  be  NEgMcgOl,  whereas  if  it 
were  formed  upon  the  type  of  NH3.HCI,  the  former  reaction  would  have 
given  the  salt  NMe2EE01,  and  the  latter,  NE2Me.Me01. 

Unlike  the  preceding  compounds,  tetrethylium  iodide  may  be  boiled 
with  solution  of  potash  without  decomposition,  but  if  a  solution  of  this 
substance  be  treated  with  silver  oxide,  silver  iodide  is  formed,  and  when 
the  solution  is  filtered  and  evaporated  in  vacuo  over  sulphuric  acid,  it 
deposits  needle-like  crystals  having  the  composition  N(02H5)4HO,     This 


AMMONIA  BASES.  543 

substance,  which  is  called  the  tetrethylium  hydrate,  is  exactly  similar  in 
properties  to  the  hydrates  of  potassium  and  sodium ;  it  is  deliquescent, 
absorbs  carbonic  acid  gas  eagerly  from  the  air,  is  exceedingly  alkaline 
and  caustic,  expels  ammonia  from  its  salts,  forms  soap  with  the  fats,  and 
behaves  in  every  respect  like  a  fixed  alkali.  Its  taste  is  very  bitter  as 
well  as  alkaline. 

It  is  obviously  not  an  ammonia,  but  is  composed  after  the  type  of 
caustic  potash  (KHO),  and  contains,  in  place  of  the  potassium,  the 
hypothetical  radical  tetrethylium  ^(CgHg)^,  or  ammonium  (J^H^),  in 
which  the  4  atoms  of  hydrogen  have  been  displaced  by  ethyle. 

The  action  of  oxide  of  silver  upon  the  tetrethylium  iodide  is  now 
intelligible — 

2NE^I    4-    AggO    +  H2O    =    2NE^H0    +    2AgI. 

Tetrethylium  iodide.  Tetrethylium  hydrate. 

The  new  alkali  is  easily  decomposed;  even  at  a  temperature  below  the 
boiling-point  of  water,  it  is  resolved  into  triethylamine,  olefiant  gas,  and 
water;  X(C2H.)^H0  =  N(C2H5)3  +  C2H4-|-H20. 

It  will  be  remembered  that  the  solution  of  ammonia  in  water  may  be 
regarded  as  containing  ammonium  hydrate,  i^Hg  +  H2O  =  NH^HO,  which 
latter  woidd  be  the  true  type  of  tetrethylium  hydrate,  but  so  great  is 
the  want  of  stability  in  this  case,  that  all  attempts  to  isolate  ammonium 
hydrate  have  resulted  in  the  production  of  ammonia  and  water. 

Like  potash,  tetrethylium  hydrate  is  capable  of  forming  salts  with  the 
acids — 

Potassium  sulphate,  .         .         KgSO^ 

Tetrethylium  sulphate,         .         .         (NE4)2SO^. 

It  would  naturally  be  expected  that  by  the  action  of  the  iodides  of 
other   alcohol-radicals  upon   ammonia,   compounds   should   be   obtained 
corresponding  to  those  belonging  to  the  ethyle  series;  thus  we  have — 
( Type  ;  ammonia  NH3). 

Methylamine,  *NH,.CHs  Diamylamine,  NH.(C5Hii)o 

Ethylamine,  NH2.C2H3  Trimethylamine,  N(CH,,)3 

Amylamine,  NHj.CjHn  Triethylamine,  N^C.^Hgij 

Dimethylamine,      NH.(CH3)2  Triamylamine,+  N(C5Hji)3 

Diethylamine,         NH.(C2H5)2  I 

{Type;  imaginary  ammonium  hydrate,  KH^HO). 

Hydrate  of — 

Tetramethylium,     N(CH3)4HO 

Tetrethylium,  X(C,H5)4HO 

Tetramylium,  N(C"5Hii)4HO . 

But  even  here,  the  elasticity  of  the  types  and  the  replacing  power  of 
the  alcohol-radicals  are  not  exhausted. 

If  methylamine  (XH2.^Ie)  be  acted  upon  by  ethyle  iodide,  the  hydrio- 
date  of  methyl-ethylamine  is  formed — 

NHg-Me  +  EI  =  NHMeE.HI, 

and  by  distilling  this  with  potash,  the  methyl-ethylamine,  much  resem- 
bling the  other  ammonia  bases,  is  obtained. 

*  Methylamine,  whicli  is  a  gas  at  the  ordinary  temperature,  is  far  more  soluble  in  water 
than  any  other  gas  ;  water  dissolves  1150  volumes  of  methylamine,  the  solution  exactly 
resembling  that  of  ammonia, 

+  Even  the  hypothetical  hydrocarbon  cetyle  (C16H33),  the  radical  of  ethal,  has  been  sub- 
stituted for  the  nitrogen  in  ammonia.  The  base  tricetylamiru,  ^{Gxs^'^>3i  which  is  thus 
formed,  contains  only  2  per  cent,  of  nitrogen. 


544  PHENYLAMINE. 

Again,  on  subjecting  this  base  to  the  action  of  aniyle  iodide,  and  dis- 
tilling the  product  with  potash,  a  new  ammonia  base  is  procured,  in  which 
all  3  atoms  of  hydrogen  are  replaced  by  different  radicals ;  this  base  is 
called  methyl-ethyl- amy lamine,  and  its  composition  is  represented  by  the 
formula  N(CH3)  (C2H5)  (C5H11)  =  NMeEAyl. 

If  we  had  started  with  aniline  (phenylamine,  NH^CgHg)  in  the  above 
experiment,  treatment  M-^ith  methyle  iodide  would  have  furnished  methyl- 
an dine  or  methyl-phenylamine,  KH.CgHjCH^  ;  and  by  treating  this  with 
ethyle  iodide,  we  should  obtain  ethyl-methyl-phenylamine,  NCgHj.CHg. 
CHg ;  the  action  of  amyle  iodide  upon  this  last  ammonia  would  give 
methyl-ethyl-amylo-phenylium  iodide,  and  on  decomposing  this  with  silver 
oxide,  there  would  be  obtained  methyl-ethyl-amylo-phen) Hum  hydrate 
N(CH3)  (C2H5)  (C5H11)  (C6H5)HO,  a  base  formed  upon  the  hypothetical 
type  of  ammonium  hydrate,  in  which  each  of  the  4  atoms  of  hydrogen  is 
replaced  by  a  different  radical. 

This  complex  substance  affords  an  excellent  example  of  the  difference 
between  an  empirical  and  a  rational  formula ;  its  empirical  formula, 
Cj^HgsNO,  which  simply  shows  the  result  of  its  ultimate  analysis,  teaches 
nothing  with  respect  to  its  constitution,  which  is  at  once  clear  when  the 
rational  formula  as  above  written  is  placed  before  us. 

Phenylamine,  NH2(C8H5),  is  found  among  the  products  of  the  destructive  distilla- 
tion of  rosanillne  (page  461),  whilst  ethyle-rosaniline  (aniline-violet)  yields  ethyl- 
phenylamine  or  ethyl-aniline,  NH(CgH5)  (C^Hj),  and  phenyl  rosanillne  {aniline  blue) 
yields  di -phenylamine  ov  phenyl  aniline,  NH(CgH5)2. 

Diphenylamine  has  also  been  obtained  by  digesting  aniline  hydrochlorate  witli 

free  aniline  at  a  high  temperature,  when  diphenylamine  hydrochlorate  is  obtained, 

which  is  decomposed  by  a  large  excess  of  warm  water,  the  diphenylamine  rising  to 

he  surface  as  an  oil  which  solidifies  on  cooling.     The  change  may  be  expressed  by 

the  following  equation  : — 

NH,(C6Hj).HCl  -f-  NHjiCgHs)  =  NH(CeH5),.HCl  -^  NH3. 
Aniline  hydrochlorate.       Aniline.  KcSe" 

By  boiling  diphenylamine  with  benzyle  chloride,  benzyldiphenylamine  is  ob- 
tained— 

NH(C«Hj),  +  C7H7CI  =  NC^HyCCgHs),  +  HCl. 

By  heating  the  new  product  with  hydrochloric- and  arsenic  acids,  it  is  converted  into 
a  tine  green  dye,  known  as  viridine  or  alkali-green. 

DUoluy lamine,  'NB.{Cy'Hj)^,  may  be  procured  in  a  similar  way  by  digesting  toluidine 
hydrochlorate  with  toluidine. 

Phenyl-toluylamine,  NH(C6H5)  (CgHy),  is  formed  by  the  action  of  aniline  on 
toluidine  hydrochlorate,  or  by  that  of  toluidine  on  aniline  hydrochlorate. 

Under  the  action  of  nitric  acid,  di-phenylamine  gives  rise  to  di-nitro-diphenyla- 
niine,  NH[CgH4(N0.2)]j,  in  which  the  same  type  is  preserved  though  nitric  peroxide 
(NOj)  is  substituted  for  one-fifth  of  the  hydrogen  in  the  phenyle.  The  intense  blue 
colour  which  is  produced  renders  the  diphenylamine  a  most  delicate  test  for  nitric 
acid. 

When  heated  with  benzoyle  chloride  (C7H5O.CI),  diphenylamine  yields  diphenyl- 
beuzoylaniine,  N(C6H5)j(C7H50). 

It  will  be  observed  that  certain  of  these  bases  derived  from  the  alcohols 
have  the  same  empirical  formulae  as  those  derived  from  coal-tar  and  other 
sources,  with  which,  however,  they  are  by  no  means  identical.  Thus,  tolui- 
dine (C7H9N)  has  the  same  composition  as  methyl-aniline  (NH.CgH5.CH3) ; 
but  the  former  is  a  crystalline  solid,  and  the  latter  an  oily  liquid. 
Again,  when  ethyle  iodide  acts  upon  toluidine,  an  atom  of  hydrogen  is 
displaced  by  ethyle,  and  ethylotoluidijie  is  obtained.  The  composition 
of  this  base,  C7Hg(C2H5)N,  is  the  same  as  that  of  methyl-ethyl-aniline, 


POLY-AMMONIAS.  545 

N(CH3)(C2H5)  (CgHg),  and  as  that  of  cumidine  (CpHjj;^^) ;  but  in  their 
chemical  properties  these  bodies  exhibit  such  a  difference  as  would  be 
expected  from  the  difference  in  their  constitution. 

385.  Investigation  of  the  constitution  of  the  alkaloids. — It  will  be 
evident  that  the  principles  developed  in  the  experiments  just  described 
may  be  applied  in  investigating  the  constitution  of  the  bases  extracted 
from  plants.  Let  it  be  supposed  that  ethylamine  (C2H-X)  was  a  vege- 
table alkali  of  unknown  constitution ;  when  it  was  found  that  by  the 
action  of  ethyle  iodide  2  out  of  the  7  atoms  of  hydrogen  could  be  dis- 
placed, it  would  be  at  once  inferred  that  these  2  atoms  occupied  a  very 
different  position  from  the  other  5,  and  that  the  constitution  of  the 
compound  would  be  more  properly  expressed  by  writing  the  formula 
C^Hg.HoX.  On  applying  the  same  principle  to  the  examination  of  the 
natural  alkaloid  coniine  (CgHj^N),  it  was  found  possible,  by  the  action  of 
methyle  iodide,  to  remove  only  1  atom  of  the  hydrogen,  so  that  the 
formula  CgHj^.HX  would  more  correctly  represent  the  constitution  of 
coniine,  which  might  be  then  regarded  as  ammonia  in  which  2  atoms  of 
the  hydrogen  have  been  displaced  by  the  group  CgH^^,  or  in  which 
each  of  these  atoms  has  been  displaced  by  the  group  C4H7. 

If  we  were  acquainted  with  an  iodide  of  this  group,  wo  have  every 
reason  to  expect  that  its  action  upon  ammonia  would  lead  us  to  the  artificial 
formation  of  coniine. 

Nicotine,  morphine,  and  codeine,  when  acted  upon  by  the  iodides  of 
alchohol-radicals,  yield  iodides  upon  the  type  NH^I,  from  which  may  be 
obtained  fixed  alkalies  resembling  tetrethylium  hydrate.    Thus  we  have — 

Methyl-morphyl-ammonium  hydrate,  ]Sr(Ci7Hi903)"'(CH3)HO 
Ethyl-codyl-ammonium  „         N(Ci8H2i03)"'(C2H5)HO 

Ethyl-nicotyl-ammonium  „         N(C5H7)"'(C2H5)HO. 

Monamines,  as  the  bases  formed  on  the  type  of  one  molecule  of  ammonia 
are  called,  are  classified  as  primary,  secondary,  and  tertiary  monamines, 
accordingly  as  one,  two,  or  three  of  the  hydrogen  atoms  of  the  ammonia 
have  been  replaced  by  another  radical  They  may  be  distinguished  by 
heating  their  hydrochlorates  with  silver  nitrite. 

A  primary  monamine  then  yields  the  corresponding  alcohol;  thus 
XH.,C2H5.HC1  (ethylamine  hydrochlorate)  +  AgNOg  =  C2H5OH  (ethyle- 
alcohol)  +  AgCl  +  H2O  +  N2. 

A  secondary  monamine  yields  a  "  nitroso-corapound  ;"  X'H(C2H.)2.HC1 
(di-ethylamine  hydrochlorate)  +  AgX02  =  X(C2H5)2NO  (nitroso-diethy- 
lamine)  +  AgCl  +  HgO. 

A  tertiary  monamine  is  not  decomposed  by  silver  nitrite. 

386.  Pohj  ammonias. — In  speculating  upon  the  constitution  of  the 
vegetable  bases,  it  must  not  be  forgotten  that  some  of  them  contain 
2  atoms  of  nitrogen ;  this  is  the  case,  for  example,  with  cinchonine 
(C00H24X2O),  quinine  (C20H24X2O2),  and  strychnine  (C21H22X2O2).  If 
the  whole  of  the  nitrogen  in  these  bases  be  due  to  the  ammonia  type, 
they  must  be  composed  after  the  type  of  a  double  atom  of  ammonia, 
X<,Hg.  In  the  case  of  strychnine,  it  is  found  that  the  action  of  ethyle 
iodide  fails  to  remove  any  portion  of  the  hydrogen,  so  that  if  the  base  be 
really  composed  after  the  ammonia  type,  it  must  be  represented  by  2  atoms 
of  ammonia  (X2^6)»  ^^  which  the  whole  of  the  hydrogen  has  been  dis- 

2  M 


546  DIAMINES. 

placed  by  the  group  (C21H22O2),  when  its  formula  would  be  'i^oi^ 21^12^ iY^ 
the  replacing  group  in  this  case  being  hexaiomic,  or  equivalent  to  6  atoms 
of  hydrogen.  That  it  is  by  no  means  necessary  for  each  atom  of  hydrogen 
to  be  displaced  by  a  single  group  or  radical,  is  seen  in  a  great  many  organic 
compounds ;  thus,  in  chloroform  (CH)Cl3,  we  have  the  triatomic  group 
CH  (commonly  called  formyle)  occupying  the  position  of  3  atoms  of 
hydrogen  which  would  be  required  to  combine  with  the  3  atoms  of 
chlorine  ;  again,  in  Dutch  liquid  (C2H4)Cl2,  we  have  the  diatomic  group 
C2H4  (ethylene)  occupying  the  place  of  2  atoms  of  hydrogen. 

If  the  view  above  explained  with  respect  to  the  constitution  of  some  of 
the  natural  alkaloids  be  correct,  it  ought  to  be  possible  to  form  artificially 
a  base  in  which  2  or  3  atoms  of  hydrogen  have  been  displaced  by  means 
of  a  diatomic  or  triatomic  radical 

387.  Diamines. — When  olefiant  gas  or  ethylene,  C2H4,  is  brought  in 
contact  with  bromine,  the  compound  C^^^v^,  corresponding  to  Dutch 
liquid  (C2H4CI2),  is  obtained,  and  from  the  action  of  ammonia  upon  this 
ethylene  dihromide,  there  is  derived  a  new  alkaline  base,  having  the 
composition  N2H^(C2H4)",  or  2  molecules  of  ammonia  (NgHg),  in  which 
the  diatomic  ethylene  replaces  2  atoms  of  hydrogen.  Such  bases,  formed 
upon  the  double  ammonia  type,  are  called  diamines.  The  base  above  men- 
tioned is  named  ethylene-diamine.  The  diamines,  like  the  double  molecule 
of  ammonia  from  which  they  are  derived,  are  capable  of  combining  with 
2  molecules  of  hydrochloric  or  any  similar  acid,  which  is  implied  by 
stating  that  they  are  diacid. 

When  Dutch  liquid  {ethylene  dicliloride  (C2H4)"Cl2)  is  heated  to  300°  F.  with  strong 
ammonia  in  a  sealed  tube,  an  action  takes  place  corresponding  to  that  of  a  double 
molecule  of  hydrochloric  acid  (HjCl^)  upon  a  double  molecule  of  ammonia  (NjHj), 
which  would  give  rise  to  a  double  molecule  of  NH4CI ;  in  the  product  of  the  action  of 
Dutch  liquid  upon  ammonia  (N2H4(C.2H4)/'Cl2),  the  places  of  4  atoms  of  hydrogen 
are  occupied  by  2  of  the  diatomic  group  (C2H4).  But  here  the  correspondence  ceases, 
for  whilst  the  ammonium  chloride,  when  decomposed  with  silver  oxide,  would  yield 
ammonia  and  silver  chloride,  the  new  compound,  when  thus  treated,  yields  a  fixed  alka- 
line base,  resembling  caustic  potash,  and  having  the  composition  N2H4(C2H4)j".H20j, 
which  represents  a  double  molecule  of  the  hypothetical  ammonium  hydrate  2(NH4HO), 
in  which  4  atoms  of  hydrogen  have  been  disjJaced  by  2  of  the  diatomic  ethylene. 
The  name  dwthylene-diaminoniicm,  hydrate  expresses  the  composition  of  this  substance, 
which  is  remarkable  for  its  stability,  a  temperature  above  300°  F.  being  required  to 
effect  its  decomposition,  when  it  furnishes  a  volatile  alkali,  having  the  composition 
NjHj(CjH4)g",  and  called  diethylene-diamine,  being  evidently  formed  from  a  double 
molecule  of  ammonia,  in  which  four  atoms  of  hydrogen  are  replaced  by  two  of  the 
diatomic  ethylene.     Its  production  may  be  explained  by  the  equation — • 

N2H4(C2H4),"H202  =  N2H2(C2H4)2"  +  2H2O . 

By  acting  upon  the  new  ammonia  with  ethyle  iodide  (C2H5I),  the  2  atoms  of  hydrogen 
may  be  displaced  by  ethyle,  yielding  diethyl-diethylene-diamine,  N2(C2H5)2(C2H4)./,  or 
a  double  molecule  of  ammonia  (NjHb),  in  which  Hj  are  replaced  by  two  of  ethyle, 
and  H4  by  two  of  ethylene. 

By  treating  phenylamine  (aniline),  NHaCCeHj),  with  ethylene  dichloride  (Dutch 
liquid),  the  diphenyl-diethylene-diamine,  N2(C8H5)2(C2H4)2",  is  obtained,  which  repre- 
sents a  double  molecule  of  ammonia  (NjHg),  in  which  'H2  are  replaced  by  two  of 
phenyle,  and  H4  by  two  of  ethylene.  By  the  action  of  chloroform  upon  aniline, 
formyle-diphcnyl-diaminc,  N2(CH)"'(CgHB)2H,  has  been  obtained,  in  which  H3  are  re- 
placed by  the  triatomic  formyle  (CH),  and  H,  by  phenyle. 

It  has  been  seen  that  phenylamine  is  produced  by  the  deoxidising  action  of  ferrous 
acetate  upon  nitrobenzene  (CflHjNO,).  When  di-nitrobenzene  is  treated  in  a  similar 
%\  ay,  phenylenc-diamine,  N2H4(CgH4J'',  is  obtained,  which  is  evidently  derived  from  a 
double  molecule  of  ammonia,  in  which  H,  are  replaced  by  the  diatomic  group  phcjiy- 
Icne  (CgH4),  which  bears  the  same  relation  to   phenyle   (CgHj)  as  ethylene  (CJH4) 


TRIAMINES  OR  TRIPLE  AMMONIAS.  547 

bears  to  ethyle  (C2H5).  By  treating  di-nitrotoluene  and  di-uitrocumene  with  ferrous 
acetate,  tohjleiie-diamine  and  cumyklie-diamine  are  obtained,  which  are  diammouias, 
in  which  Hj  are  replaced  by  the  diatomic  radicals  tolylene  (CyHg)"  and  cumylene 
(^\Hij)".  These  three  diamines  are  called  the  aromatic  diamines,  since  the  diatomic 
groups  phenyleue,  tolylene,  and  cumylene  are  closely  connected,  through  benzene 
(CgHg),  toluene  (CyHg),  and  cumene"  (CgHja),  with  the  aromatic  acids,  benzoic 
(C-HgOo),  toluic  (CgHgOg),  and  cuminic  (C10H12O2). 

Paraniliiic  (CJ2HJ4N2)  is  obtained  as  a  secondary  product  in  the  manufacture  of 
aniline,  with  \yhich  it  is  polymeric.  Its  properties  are  very  difiTerent  from  those  of 
aniline,  for  it  is  solid  at  the  ordinary  temperature,  forming  silky  needles  which  melt 
when  heated,  and  boil  beyond  the  range  of  the  thermometer,  distilling  unchanged. 
It  combines  with  acids,  forming  beautiful  crystalline  salts,  the  study  of  which  proves 
it  to  be  a  diamine. 

388.  Triamines. — The  triamines  are  formed  upon  the  type  of  a  treble 
molecule  of  ammonia  (X3H9),  in  which  the  hydrogen  is  replaced 
either  entirely  or  in  part  by  other  radicals.  Thus,  diethylene-triamine, 
-^3^5(^2^4)2",  and  triethylene-triamine,  'S ^Yi.^{C^^" ^,  are  obtained  by 
the  action  of  ethylene  di-bromide  (CgH^Brg)  upon  ammonia.  They  are 
powerfully  alkaline  liquids,  which  are  capable  of  absorbing  carbonic  acid 
gas  from  the  air.  The  triamines  are  generally  capable  of  forming  three 
classes  of  salts,  the  monacid,  diacid,  and  triacid  salts,  containing  respec- 
tively one,  two,  and  three  molecules  of  acid. 

Di-ethylene-di-ethyl-triamine,  N3H3(C2H4)2"(C2Hg)2,  is  produced  by  the  joint  action 
of  ethylamine  and  ammonia  upon  ethylene  dibromide — 

2(C2H,)Br2  +   3NH2(C2H5)  +   NH3 
=N3H3(C2H,)2"(C2H5)2.3HBr  +  NH2(C2H5).HBr. 

It  forms  splendidly  crystallised  salts,  and  is  evidently  derived  from  3  molecules  of 
ammonia  (N3H9),  by  the  substitution  of  (02114)2"  for  H4,  and  of  (02115)2  for  Hj. 

Carbotriamine  (guanidine),  NjHgC'^,  is  a  treble  molecule  of  ammonia,  in  which 
4  atoms  of  hydrogen  are  replaced  by  1  atom  of  tetratomic  carbon.  It  is  formed  by 
heating  ammonia  with  ethyl  subcarbonate  in  a  sealed  tube  to  about  300°  F. 

2(C2H5)2O.0O2  +  3NH3  +   H2O  =   N3H5O.H2O  +   4(02H5.HO). 

The  change  is  more  clearly  explained  by  representing  the  ethyle  subcarbonate  as 
formed  upon  the  type  of  4  molecules  of  water  (H8O4)  in  which  H4  are  replaced  by 
(02115)4,  and  the  remaining  H4  by  C   . 

(CoHsj/  j  Q^  ^   gj^jj^  ^   jj^Q  _   N3H5CWH2O   +   (^2H5)4  j  O4 

Ethyle  subcarbonate.  Guanidine.  4  mols.  alcohol. 

Guanidine  may  also  be  obtained  by  heating  chloropicrine  in  a  sealed  tube,  with  an 
alcoholic  solution  of  ammonia,  to  212°  F.,  when  the  following  reaction  ensues — 

2CCl3(N02)   +   6XH3  =  2(N3H5C.H01)   =    +   4H01  +  N2O3  +   H2O . 
Cloropicrlne.  Guanidine  hydrochlorate. 

It  will  be  remembered  that  eth}'le  subcarbonate  itself  is  obtained  by  the  action  of 
sodium  upon  an  alcoholic  solution  of  chloropicrine  (page  528). 

Guanidine  is  also  formed  by  heating  ammonium  sulphocyanide  for  two  hours  to 
190°-200°  0. 

3XH4OXS   =   l^^Yifi.YiClS^  [OiiMnidine  svlphocyanate)  +   2NH3  +   CS2. 

Mclanilinc,  C^^y^^,  a  crystalline  base,  produced  by  the  action  of  cyanogen 
chloride  upon  aniline,  may  be  regarded  as  diphenyl-guanidine,  ^3113(05115)20,  or 
guanidine  in  which  two  of  phenyle  have  replaced  two  of  hj'drogen. 

The  beautiful  aniline  dyes  appear  to  be  salts  of  certain  triamines  formed  by  the 
replacement  of  the  hydrogen  in  a  treble  molecule  of  ajnmonia  by  hydrocarbon 
radicals. 

According  to  Hofmann,  rosaniline,  the  base  of  the  aniline  red  produced  by  the 
action  of  oxidising  agents  upon  aniline  containing  toluidine,  is  possibly  phenylen^- 
ditolylene-triaminc,  X3(0,.,H4)"(0-H6).,"H3.H.,O,  the  phenylene  being  derived  from  the 
aniline,  XHo(06H5),  and  the  tol^'lene  from  the  toluidine,  XH2(07H7).  Aniline  bine, 
formed  by  the  action  of  aniline  upon  aniline  red,  would  be  phcnylene-ditolyleneo 


548  TETRAMINES. 

fnphenyl-triamine,  N3(CeH4)*(C7H6)2"(CgH5)3.H,0,  having  been  formed  from  roaani- 
line  by  the  substitution  of  three  of  phenyle  for  Hj.  Aniline  violet,  the  result  of 
the  action  of  ethyle  iodide  upon  rosaniline,  would  be  phcmjlene-ditolylene-ti-icthyl- 
triamine,  Ns(CgH4)"(C7Hg)2"(C2H5)3.  HjO,  or  rosaniline  containing  three  of  ethyle  in 
place  of  Hj. 

The  trichloride  of  diethylene-triammonium,  N3(C2H4)2"H8.Cl3,  has  also  been  ob- 
tained. 

389.  Tetramines  are  formed  npon  the  type  of  4  molecules  of  ammonia, 
and  therefore  contain  4  atoms  of  nitrogen,  and  are  able  to  combine  with  4 
molecules  of  a  hydrogen  acid.  Thus,  if  ethylene  dibromide  be  allowed  to 
act  upon  ethylene-diamine  in  the  presence  of  hydrobromic  acid,  the  hydro- 
bromate  of  triethylene-tetramine  is  obtained — 

{C,n,)"Bv^    -f-   2N2(C2H,)"H4   +   2HBr     =     N,(C2Hj3"H6.4HBr 

Ethylene  dibromide.  Ethylene-diamine.  Triethylene-tetramine  hydrobromate, 

and  if  this  be  decomposed  with  silver  oxide,  a  strongly  alkaline  solution 
is  obtained,  which  contains  triethylene-tetramine,  N4(C2H4)3"Hg,  or  a 
quadruple  molecule  of  ammonia  (N^Hjg),  in  which  half  of  the  hydrogen 
is  replaced  by  three  of  diatomic  ethylene. 

By  acting  on  CoH4Br.2  with  ethylamine,  a  salt  is  obtained,  having  the  composi- 
tion N4(C.,H4)5"(CoHg)4H2>B''4,  representing  4  molecules  of  ammonium  bromide 
(N4H,fiBr4),  in  whfch  Hi„  are  replaced  by  5(C2H4)",  and  H4  by  (02115)4.  From  this 
bromide  a  strongly  alkaline  base,  peiitethylene-tetrethyl-tetrammonium  hydrate 
[N4(C2H4)5"(C2Hb)4H2]H404  is  obtained,  which  is  formed  upon  the  type  of  4  molecules 
of  the  imaginary  ammonium  hydrate  (NH4HO). 

The  action  of  ethyle  iodide  (C^HjI)  upon  this  base  replaces  each  of  the  remaining 
atoms  of  hydrogen  by  ethyle,  yielding  (N4(C2H4)5"(C2H5)5H]H404,  and  [N4(C2H4)5" 
(aHB)glH;04. 

When  diethylamine  NH(C2H5)2  acts  upon  ethylene  dibromide,  the  bromide  of 
tri-ethylene-octethyl-tetrammonium,  N4{C2H4)3"(C2H.,)8H5.  V>r^,  is  obtained,  which  also 
furnishes  a  powerfully  alkaline  base  [N4(C2H4)3"(C2H5)8H2]H404. 

390.  We  are  not  entirely  dependent  upon  purely  artificial  processes  for 
the  ammonia  bases  containing  alcohol-radicals.  Many  processes  of  putre- 
faction furnish  certain  of  these  bases  which  had  hitherto  been  overlooked 
in  consequence  of  their  resemblance  to  ammonia.  Thus,  putrefying  flour 
yields  ethylamine,  trimethylamine,  and  amylamine ;  trimethylamine  is  also 
found  in  the  roe  of  herrings,  as  also  in  putrefied  nrine  and  in  the  Cheno- 
podium  vulvaria  ;  it  may  also  be  obtained  by  distilling  ergot  of  rye  with 
potash.  Methylamine,  ethylamine,  ■pro'pylam.me  (NH2.C3H-),  hutylamine 
(NH2.C^H9)  or  peti7iine,  ami  amylamine,  are  found  among  the  products  of 
the  destructive  distillation  of  bones. 

Trimethylamine  is  obtained  in  quantity  by  distilling  the  refuse  or  vinasses  of  the 
French  beet-sugar  refineries.  It  is  used  for  converting  potassium  chloride  into 
potassium  carbonate  by  a  process  resembling  the  ammonia-soda  process  (p.  264), 
which  depends  on  the  fact  that  bicarbonate  of  soda  is  less  soluble  in  water  than  sal- 
ammoniac  ;  but  bicarbonate  of  potnsh  has  about  the  same  solubility  as  sal-ammoniac, 
so  that  trimethylamine,  whose  hydrochlorate  is  much  more  soluble  than  that  of 
ammonia,  is  substituted  for  the  latter.  The  hydrochlorate  of  trimethylamine  is 
us(mI  as  a  source  of  methyle  chloride,  which  is  obtained  from  it  by  distillation  ; 
3NMe3HCl  =  2MeCl-l-2NMe3-l-NH2Me  +  HCl.  The  MeCl  comes  off  as  a  gas  which 
is  condensed  by  a  pressure  of  about  four  atmospheres  into  an  ethereal  liquid, 
boiling  at  -  23-  C. 

It  is  used  for  making  aniline  colours  and  for  producing  artificial  cold. 

Hy  the  action  of  trimethylamine  on  ethyle'ne  oxide  in  the  presence  of  water,  a 
strongly  alkaline  base  is  obtained,  which  is  known  as  choline  or  neurine,  and 
was  originally  found  in  bile,  but  is  extracted  in  larger  quantity  from  the  brain ; 
N(CH3)3  +  C2H4O  +  W.fi  =  C5H15NO2  {neurine). 


TRIETHYLPHOSPHIXE.  549 

391.  Ammonias  and  ammonium  hoses  containing  pJwsphorus,  arsenic, 
and  antimony. — It  might  be  expected  tliat  the  ammonia  type  was  not 
susceptible  of  any  further  modifications,  but  it  has  been  found  that  even 
the  nitrogen  of  that  type  may  be  represented  by  other  elements  which  are 
chemically  related  to  it. 

Antimony,  arsenic,  and  phosphorus,  it  wiU  be  remembered,  aU  form 
compounds  with  3  atoms  of  hydrogen,  SbHg,  AsHg,  and  PHg,  which  may 
be  regarded  as  formed  upon  the  ammonia  type.  Xeither  of  these  sub- 
stances, however,  possesses  any  alkaline  character,  the  last  alone  being 
capable  of  combining  with  certain  acids  (hydrobromic  and  hydriodic). 

Mention  has  already  been  made  of  the  circumstance  that  compounds 
corresponding  to  antimonietted,  arsenietted,  and  phosphuretted  hydrogen 
may  be  obtained,  in  which  the  place  of  the  hydrogen  is  occupied  by  cer- 
tain alcohol-radicals ;  but  in  these  cases  the  hydrogen  does  not  admit  of 
partial  replacement,  only  those  compounds  which  correspond  to  triethyla- 
mine  and  trimethylamine  having  been  obtained. 

Triethyhtihine,  Sb(C2H5)3,  and  tnethylarsine,  As(C2H5)3,  have  already 
been  noticed  amongst  another  class  of  bodies  to  which  they  seem  properly 
to  belong,  since  they  are  not  capable  of  forming  salts  corresponding  to 
those  of  ammonia  (see  page  536). 

With  triethylphosphine,  however,  the  case  is  different ;  this  substance, 
P(C2H.)3,  is  a  true  ammonia,  capable  of  forming  salts  with  the  acids,  like 
ethylamine,  although  exhibiting,  unlike  that  body,  a  very  powerful  ten- 
dency to  combine  directly  with  an  atom  of  oxygen  or  sulphur,  to  form 
compounds  resembling  those  of  the  arsenic  and  antimony  series  (see 
page  536),  and  formed  upon  the  type  of  phosphoric  chloride  (PCI5). 
Thus  we  have — 

Triethylphosphine  oxide,     .         .     PE3O 
Sulphide, PE3S, 

and  the  corresponding  compounds  containing  methyle. 

Triethylphosphine  is  obtained  by  the  action  of  phosphorus  trichloride 
upon  zinc-ethyle,  2PCI3  +  3ZnE.,  =  2PE3  -|-  3ZnCl2.  It  is  a  volatile  liquid 
of  a  very  peculiar  powerful  odour,  the  vapour  of  which,  when  mixed 
with  oxygen,  explodes  with  great  violence  at  a  temperature  far  below 
212°. 

By  acting  upon  triethylstibine,  or  stibio-triethyle,  with  ethyle  iodide, 
an  iodide  is  obtained  which,  when  decomposed  by  silver  oxide,  yields 
tetrethylstibonium  hydrate  (SbE^HO),  formed  after  the  type  of  ammonium 
hydrate  (XH^HO). 

In  a  similar  manner  there  are  obtained  tetrethylarsonium  hydrate 
(AsE^HO)  and  tetrethylphosphonium  hydrate  (PE^HO),  and  their  corre- 
sponding methyle  compounds. 

These  substances  are  precisely  similar  in  properties  to  tetrethylium 
hydrate,  being  powerfully  caustic  alkalies  bearing  a  close  resemblance  to 
caustic  potash. 

A  very  remarkable  base  has  also  been  obtained,  composed  after  the  type 
of  a  double  molecule  of  the  imaginar}^  ammonium  hydrate  (XgHgHgOg), 
in  which  1  atom  of  nitrogen  has  been  replaced  by  phosphorus,  and  the 
other  by  arsenic,  whilst,  of  the  hydrogen,  2  atoms  are  replaced  by  the 
diatomic  radical  ethylene  (CgH^)",  and  the  remainder  by  ethyle.  This 
base  has  been  styled  ethylene-hexethyle-diphospharsonium  hydrate,  and 
its  formula  is  PAs(C2H4)"(C2HJgH202.     It  combines  with  2  molecules 


550  AMIDES. 

of  acids  to  form  salts,  and  behaves  in  every  respect  as  a  double  molecule 
of  caustic  potash  would  do. 

By  acting  upon  triethylphosphine  with  chloroform  (CHCI3)  containing 
the  triatoraic  radical  formyle  (CH)'",  a  chloride  has  been  obtained  which 
is  composed  upon  the  type  of  3  molecules  of  ammonium  chloride  (SNH^Cl 
=  N3Hj2Cl3),  in  which  one-fourth  of  the  hydrogen  is  replaced  by  formyle 
and  the  rest  by  ethyle ;  the  composition  of  this  chloride  is  therefore 
(P3(CH)"'(C2H5)9Cl3) ;  from  this  compound  various  salts  have  been  ob- 
tained, containing  the  corresponding  oxide  combined  with  3  molecules  of 
the  acids,  but  the  hydrate  itself  has  not  been  obtained — 

3P(C2H5)3    +    (CH)"'Cl3    =    P3(CH)"'(CA)«Cl3 

Triethylphosphine.  ChWonn.  '^'^'^'XVosSfur"'''^'- 

392.  The  insight  into  the  constitution  of  the  bases  derived  from  ammonia,  which 
has  been  acquired  in  the  researches  detailed  above,  has  induced  chemists  to  endeavour 
to  apply  the  same  principles  to  certain  inorganic  bases  derived  from  ammonia  by  the 
action  of  metallic  salts. 

Thus,  by  the  action  of  platinous  chloride  upon  ammonia  (see  page  396),  a  compound 
is  obtained  which  may  be  regarded  as  simply  PtCl2(NH3)2,  but  when  this  is  treated 
with  silver  oxide,  the  CI  is  removed  in  the  form  of  silver  chloride,  and  a  caustic 
alkaline  base  is  separated,  which  has  the  formula  PtO.(NH3),,  or  rather,  viewed 
upon  the  type  of  ammonium  oxide,  NjHgPtO,  platammonium  oxide. 

By  employing  ethylaniine  instead  of  ammonia,  there  would  be  obtained  N2H4E2PtO, 
ethyloplatammonium  oxide. 

When  the  compound  PtCl2(NH3)2  (or  rather  N2HgPt.Cl2,  platammonium  chloride) 
is  again  treated  with  ammonia,  it  yields  N2H(jPt.Cl2(NH3)2,  and  when  this  is  decom- 
posed with  silver  oxide,  another  caustic  alkali  is  obtained,  having  the  composition 
N2HfiPt(NH3)2H202,  which  may  be  regarded  as  N2H4Pt(NH4)2Ho02,  platammon- 
ammonium  hydrate  (diplatosamine  hydrate)  ;  it  would  then  become  a  double  mole- 
cule of  ammonium  hydrate  (NH4HO),  in  which  2  atoms  of  hydrogen  are  replaced  by 
platinum  and  2  by  ammonium. 

Very  remarkable  and  beautiful  crystalline  compounds  have  also  been  obtained,  which 
are  formed  after  the  type  of  platammonium  chloride,  but  contain  either  phosphorus, 
antimony,  or  arsenic,  in  place  of  nitrogen,  and  ethyle  in  place  of  hydrogeu ;  these 
are — 

Plcdo-triethyl-dipliospJionium  chloride,         .  P2Pt(CoH5)g.  CL 

arsonium  „  .  Aa2Pt((32H5)g.Cl2 

stibwiium  ,,  .  Sb2Pt(C2H5)g.Cl2. 

Corresponding  salts  have  also  been  obtained  containing  gold  in  the  place  of 
platinum,  and  forming  beautiful  colourless  crystals. 

In  some  bases,  chlorine,  bromine,  and  even  nitric  peroxide  (NO2)  have 
been  introduced  in  the  place  of  hydrogen  into  the  alcohol-radical,  but  in 
all  these  cases  the  basic  energy  is  diminished  by  such  substitution,  and  in 
some  altogether  destroyed. 

Thus,  in  the  aniline  (phenylamine)  series,  we  have — 


Chloraniline, 

Dichloraniline, 

Trichloraniline, 

Nitraniline, 

Dinitraniline, 


NH2(C8H4C1),  weak  base. 
NH2(C8H3Cl2),  weaker  base. 
NH2(C8H2Cl3),  neutral. 
NH2[CeH4(N02)],  weak  base. 
NH2[C6H3(N02)2],  neutral. 


393.  Amides. — When  ammonium  oxalate  (NH4)2C204  is  subjected  to 
distillation,  a  white,  crystalline,  sparingly  soluble  substance  is  obtained, 
which  has  been  named  oxamide,  and  is  represented  by  the  formula 
(NHo).,C,0<,.  This  substance  is  derived  from  the  ammonia-salt  by  the 
loss  of  2  molecules  of  water  (NH4)2C204  -  2H2O  =  (NH2)2C202,  and  its 
close  relationship  to  ammonium  oxalate  is  shown  by  the  circumstance 
that  it  is  reconverted  into  that  salt,  if  heated  with  watei;  in  a  sealed  tube 


NITRILES.  551 

to  436°  F.,  or  by  simply  boiling  it  with  water  to  Avhich  a  little  acid  or 
alkali  has  been  added. 

Oxamide  is  more  readily  prepared  by  decomposing  oxalic  ether  with 
ammonia,  when  it  is  obtained  as  a  white  crystalline  precipitate — 

(C,H,),CA  +  2XH3  =  2C2H,HO  +  {^n,),c,o. 

Oxalic  ether.  AlcohoL  Oxamide. 

If  one  of  the  compound  ammonias,  such  as  ethylamine  and  aniline,  be 
employed  instead  of  ammonia,  ethyloxamide  and  oxanilide  are  produced — 

(CgHJ.Cp^  +  2(NH2.C2H.)  =  2C2H5HO  +  (NH.C2H5)2C202 

Oxalic  etiier.  Ethylamine.  Ethyluxxkmide. 

{Q.B..^fi.p,  +  2(NH2.CeH,)  =  2C2H,HO  +  (NRC^H^AO^ 

Aniline.  Oxanilide. 

Oxamide  is  the  representative  of  a  large  class  of  bodies,  known  as  the 
amides,  which  may  be  defined  as  substances  capable  of  being  converted, 
by  the  assimilation  of  the  elements  of  water,  into  the  ammonium-salts  from 
which  they  are  derived. 

Some  other  interesting  members  of  this  class  are  here  enumerated, 
together  with  the  corresponding  ammonium-salts — 

Formamide,  .  .  .  NHo.CHO  1     Ammonium  foraiiate,  (NH4).CH0._j 

Acetamide,  .  .  .  NHZ-CoH^^O  ,,  acetate,  (NH^j.CaHjOa 

Butyramide*,  .  .  .  NH2.C4H7O  ,,  bntyrate,  (NH4).C4H702 

Benzamide,  .  .  .  NHj.C-HjO  |  ,,  benzoate,  (XH4).C7Hg02 

It  is  evident  that  these  amides  may  be  regarded  as  derived  from  ammonia 
by  the  substitution  of  a  compound  group  for  one  of  the  3  atoms  oi 
hydrogen. 

"When  hydro-ammonic  oxalate  (NH^HC204)  is  distilled,  at  a  moderate 
heat,  a  solid  acid  substance  is  left  in  the  retort,  which  is  known  as  oxamic 
add,  NH2.HC2O3,  and  forms  soluble  crystallisable  salts  with  lime  and 
baryta,  both  which  bases  yield  insoluble  salts  Avith  oxalic  acid. 

When  the  solution  of  oxamic  acid  in  water  is  boiled,  it  is  reconverted 
into  the  original  oxalate ;  XH2HC2O3  +  np  =  NH^HCgO^. 

Oxamic  acid  is  the  representative  of  a  limited  class  of  acids  formed  in  a 
similar  manner. 

394.  Nitriles. — When  ammonium  oxalate  is  mixed  with  phosphoric 
anhydride  and  distilled,  it  loses  4  molecules  of  water,  leaving  cyanogen 
(NH,)2C20,-4H20  =  2CK 

In  a  similar  manner,  ammonium  benzoate  yields  henzonitrile — 

^n^C-H502  {Ammoniuin  benzoate)   —   2II2O   =   C-H-N  (Benzonitrile). 
The  new  compound  is  an  oil  which  has  a  powerful  odour  of  bitter 
almonds,  and  is  reconverted  into  ammonium  benzoate  by  boiling  with 
dilute  acids  or  alkalies. 

The  term  nitrile  is  applied  to  all  similar  substances  which  are  derived 
from  ammoniacal  salts  by  the  loss  of  2  molecules  of  water,  and  are  capable 
of  reconversion  into  those  salts.  Many  of  these  nitriles  are  isomeric  with 
the  cyanides  of  the  alcohol-radicals,  from  which  they  may  sometimes  be 
obtained  by  the  action  of  a  high  temperature. 

Oxalonitrile,    NC         =      Cy,  cyanogen. 
Formonitrile,  KCH      =      HCy,  hydrocyanic  acid. 
Acetonitrile,    NC0H3  =     CH3.CX,  methyle  cyanide. 
Propionitrile,  NC3H5  =      C2H5.CX,  ethyle 
Benzonitrile,  ^C^H^  =      C^H^.CX,  phenyle      „ 


552  IMIDES. 

The  nitriles  are  distinguished  by  their  ready  tranformation  into 
ammonia  and  an  acid  containing  the  same  number  of  carbon-atoms  as  the 
nitrile,  under  the  influence  of  caustic  alkalies;  thus — 

C3H5N  +  KHO  +  H2O  =  NH3  +  KC3H5O2 

Prop'ioniti  ile.  Potassium  propionate. 

Again,  diluted  acids  have  little  action  upon  the  nitriles,  whilst  the 
cyanides  of  the  alcohol  radicals  (or  carhamines)  are  converted  into  formic 
acid,  and  an  ammonia  in  which  the  alcohol  radical  is  substituted  for 
hydrogen;  thus — 

C2H5.CN  +  HCl  +  2H2O  =  CH2O2  +  NH2.C2H5.HCI, 

Ethyle  cyanide.  Fonnic  acid.    Ethylamine  liydroclilorate, 

a  reaction  corresponding  to  that  of  hydrocyanic  acid  with  hydrochloric 
acid ;  HCN  +  HCl  +  2H2O  =  CH2O2  +  NH3.HCI. 

A  by  no  means  numerous  class  of  substances,  frequently  spoken  of  as 
the  imides*  are  obtained  by  the  action  of  heat  upon  the  acid  ammonium 
salts  of  certain  dibasic  acids,  by  ihe  loss  of  2  molecules  of  water,  thus — 

NH.HCioHi^O^  -  2H2O  =  NRC10H14O2 

Hydro-ammunic  cainphorate.  Camphoritnide. 

395.  If  the  amides  be  regarded  as  immediately  derived  from  ammonia  by  substi- 
tution, their  want  of  alkaline  properties  must  be  ascribed  to  the  introduction  of  an 
electro-negatiye  radical  in  place  of  the  hydrogen. 

Thus,  if  oxalic  acid  be  regarded  as  112(0202)03,  then  oxamide  may  be  viewed  as  a 
double  molecule  of  ammonia,  in  which  2  atoms  of  hydrogen  have  been  displaced  by 
(CA);N2  j^^^Oa)" 

Again,  if  benzoic  acid  and  salicylic  acid,  respectively,  be  regarded  as  (CyHjOjHO 
and  (C7H502)HO,  then  their  amides  would  be  represented  as — 

Benzamide,  N  j  (^7^5^)'  Salicylamide,  N  j  (^THjOaX 

and  it  should  be  possible  to  procure  them  from  ammonia  by  processes  similar  to  that 
which  furnishes  ethylamine,  &c.  It  is  found  that  when  benzoyle  chloride  is  heated 
with  ammonia,  benzamide  is  really  produced — 

C7H5O.CI  (Benzoyle  chloride)  +  2NH3  =  NHJ.C7H5O  {Benzamide}  +  NH4CI. 

But  we  ought  also  to  be  able  to  carry  the  substitution  farther  by  displacing  the 
remaining  hydrogen ;  accordingly,  when  benzainide  and  salicylamide  are  heated 
together,  ammonia  is  disengaged,  and  benzoyl-salicylamide  obtained — 

C^HjO  (CrHjOa  I  C7H5O 


N{     H         -^     N    ^      H       -     N^CyH.Oj  -I-  NH, 
H  (      H  (      H 

Benzamide.  Salicylamide.  Benzdyl-salicylamide. 

Amides  have  even  been  obtained  in  which  the  3  atoms  of  hydrogen  in  ammonia  are 
displaced  by  different  radicals. 

It  is  evident  that  the  imides  might  be  regarded  as  ammonia  in  which  2  atoms  of 
hydrogen  have  been  replaced  by  a  diatomic  radical,  thus — 


Camphorimide,  N  j  (^oHuOa)" 


and  the  nitriles,  as  ammonias  in  which  all  the  hydrogen  has  been  replaced  by  a 
triatomic  radical,  but  experimental  evidence  is  scarcely  in  favour  of  these  views. 

If  the  amides  be  really  derivatives  from  ammonia,  it  would  be  expected  that 
similar  bodies  shonld  be  derived  from  phosphine  (PHj).  An  example  of  these  is  fur- 
nished by  tribenzoyl-phosphide,  Y{CjYifi)^  which  is  obtained  by  the  action  of  benzoyle 
chloride  upon  phosphine — 

PH3  +  3(CVH»0.C1)  =  PlCVHsO)^  +  3HC1. 

*  This  designation  was  originally  employed  upon  the  supposition  that  these  bodies  con- 
tain the  imaginary  radical  imidogen,  NH ;  and,  in  a  similar  manner,  the  amides  were 
supix)sed  to  contain  amidogen,  NHj. 


METAL- AMIDES — DERIVATIVES  OF  THE  ALCOHOLS.  553 

396.  Metal-amides. — The  possibility  of  substituting  metals  for  the 
hydrogen  in  ammonia  has  only  recently  been  fully  established,  though  it 
had  long  been  known  that  when  potassium  and  sodium  were  heated  in 
gaseous  ammonia,  hydrogen  was  evolved,  and  potassamide  and  sodamide 
were  produced,  XH3  +  K  =  NH^K  +  H.  When  potassamide  is  heated, 
ammonia  is  evolved,  and  tripotassamide  (NK,)  produced,  3(NH2K) 
=  NK3  +  2XH3. 

If  aramoniacal  gas  be  passed  into  an  ethereal  solution  of  zinc-etbyle, 
ethyle  hydride  is  evolved,  and  a  white  amorphous  precipitate  of  zincamide 
separates :  2NH3  +  (C2H5)2Zn  =  (NH2)2Zn  +  2(C2H5.H).  When  zincamide 
is  brought  in  contact  with  water,  it  is  decomposed  with  evolution  of  heat, 
yielding  zinc  hydrate  and  ammonia — 

(NH2)2Zn  +  2H2O  =  2NH3  +  Zn(H0)2. 

The  decomposing  action  of  zinc-ethyle  upon  the  bases  derived  from 
ammonia  is  parallel  with  that  upon  ammonia  itself.  Thus,  with  aniline ; 
2(NH2.CsH,)  +  (C2H,)2Zn  =  (XH)2Zn(C6H,)2  +  ^C^^.B) 

Aniline.  Zinc-ethyle.  Zinc-phenylimide.  Ethyle  hydiiae. 

When  the  zinc-phenylimide  is  treated  with  water,  of  course  aniline  is 
reproduced. 

When  diethylamine  is  treated  with  zinc-ethyle — 

2X(C2H,)2H  +  {C^n,)^n  =  N,(C,lI,),Zn  +  2(C2H5.H) . 

Diethylamine.  Diethylzincamine. 

When  zincamide  is  heated  above  400°  F.,  it  is  decomposed  into  am- 
monia and  zinc  nitride  (NgZug),  which  represents  2  atoms  of  ammonia, 
in  which  the  6  atoms  of  hydrogen  are  replaced  by  zinc — 

3(NH2)2Zn  {Zincamide)   =  X'2Zn3  {Zinc  nitride)   +   4NH3 . 

The  zinc  nitride  is  a  grey  powder,  which  is  unaffected  by  a  red  heat 
if  air  be  excluded.  If  it  be  moistened  with  water  it  becomes  red  hot, 
being  decomposed  with  great  violence,  according  to  the  equation — 

N'2Zn3  +  6H2O  =  2NH3  -1-  3Zn(OH)2. 

It  might  be  anticipated  that  if  the  amides  be  truly  formed  after  the 
ammonia- type,  they  should  behave  towards  zinc-ethyle  in  the  same  manner 
as  ammonia  and  aniline. 

By  heating  oxamide  with  zinc-ethyle,  2  of  its  atoms  of  hydrogen  may 
be  replaced  by  zinc — 

X2H4.C2O2  +  Zn(C2H5)2  =  X2H2Zn.C202  +  2(C2H5.H). 

Oxamide.  Zinc-oxamide. 

In  a  similar  manner  acetamide  (NH2C2H3O)  is  converted  into  zinc- 
acetamide  N2H2Zn(C.,H30)2.  These  bodies  are  reconverted  into  their 
corresponding  amides  and  zinc  oxide,  when  treated  with  water. 

Derivatives  of  the  Alcohols. 

397.  Chloroform. — Among  the  useful  substances  prepared  from  members 
of  the  alcohol  series,  cliloroform  (CHClg)  occupies  a  prominent  position. 

It  is  prepared  by  distilling  1  part  of  alcohol  (sp.  gr.  "834)  with  10  parts 
of  chloride  of  lime,  and  40  parts  of  water,  at  65°  C,  until  about  1|  part 
has  passed  over ;  the  distilled  liquid,  consisting  chiefly  of  water  and 
cliloroform,  separates  into  two  layers,  the  heavier  being  chloroform 
(sp.  gr.   rS).     The  upper  aqueous  layer  having  been  drawn  off  by  a 


554  CHLOROFORM. 

siphon,  the  chloroform  is  shaken  witli  oil  of  vitriol  to  remove  certain 
volatile  oils,  wliich  have  distilled  over  with  it,  and  as  soon  as  it  has 
risen  to  the  surface  of  the  oil  of  vitriol,  it  is  drawn  off  and  rectified  by 
distillation,  until  it  boils  regularly  at  61°  C.  (142°  R). 

The  chemical  change  involved  in  the  preparation  of  chloroform  is 
expressed  in  the  equation  2C2HgO  +  4Ca(C10)2  =  2CHCl3  {chloroform) 
+  Ca(CH02)2  {calcium  formiate)  +  CaCla  +  2Ca(HO)2  +  2H2O. 

Chloroform  is  remarkable  for  its  very  fragrant  odour,  and  for  the  power 
of  its  vapour  to  produce  insensibility  to  pain,  for  which  purpose  it  is 
often  used  in  surgical  operations.  This  property  is  not  peculiar  to  chloro- 
form, but  is  possessed  in  different  degrees  by  most  other  liquids  of  power- 
ful ethereal  odour,  such  as  ordinary  ether,  carbon  disulphide,  carbon 
tetrachloride,  &c.  Chloroform  is  also  used  for  dissolving  caoutchouc, 
which  it  takes  up  more  readily  and  abundantly  than  an}"-  other  liquid, 
and  is  employed  for  extracting  the  poisonous  alkaloids  (particularly 
strychnine),  when  mixed  with  organic  matters.  The  name  chloroform 
has  been  conferred  upon  this  substance  on  the  supposition  that  it  con- 
tained the  radical  of  formic  acid  (formyle  CH),  and  it  is  sometimes  styled 
the  trichloride  of  formyle.  This  belief  is  encouraged  by  its  behaviour 
with  an  alcoholic  solution  of  potash,  when  it  yields  potassium  formiate 
and  potassium  chloride — 

CHCI3  +  4KH0  =  KCHO2  +  3KC1  +  2H2O. 

Chloroform.  Potassium  formiate. 

But  the  processes  by  which  it  may  be  formed  would  lead  us  to  regard  it 
as  a  substitution-product  from  marsh  gas  (methyle  hydride,  CH3.H).  If 
mar.sh  gas  be  diluted  with  an  equal  volume  of  carbonic  acid  gas  and  to  1 
volume  of  this  mixture  at  least  1 J  volume  of  chlorine  be  added,  chloro- 
form is  slowly  produced ;  CH^  +  Clg  =  3HC1  +  CHCI3.  Chloroform  is  also 
formed  by  the  action  of  chlorine  upon  methyle  chloride — 

CH3CI  +  CI4  =  CHCI3  +  2HC1 . 

Wood-spirit  (methyle  hydrate)  may  be  employed  instead  of  alcohol  for 
the  preparation  of  chloroform. 

If  chloroform  be  distilled  in  a  current  of  chlorine,  it  is  converted  into 
carbon  tetrachloride,  CHCI3 -t- CI2  =  CCI4  +  HCl.  When  chloroform  is 
heated  with  potassium  amalgam,  acetylene  (C2H2)  is  disengaged,  which  is 
polymeric  with  the  hypothetical  radical  formyle  CH. 

On  heating  chloroform  w4th  aniline  (phenylamine)  and  alcoholic  solu- 
tion of  potash,  phenylecarbamine  (CgHjNC)  is  produced,  and  may  bo 
recognised  by  its  most  remarkable  odour,  which  permits  the  detection  of  a 
very  minute  quantity  of  chloroform — 

HCCI3  +  H2NCeH5  +  3K0H  =  C^Yi^'^C  +  3KC1  +  3H2O. 

Chlorofonn.        Phenylamine.  Phenyle-carbamine. 

When  chloroform  is  heated  with  sodium  ethylate,  it  yields  tribasic  formic 
ether — 

HCCI3  -1-  3NaOC2H5  =  3NaCl  +  (CH)03  {C.^^)^ . 

Bromoform  (CHBrg)  and  Iodoform  (CHI3)  have  no  practical  interest. 

The  production  of  iodoform  is  sometimes  turned  to  account  in  testing 
for  alcohol ;  a  little  potash  being  dissolved  in  the  suspected  liquid,  and 
some  iodine  added ;   on  heating  the  solution,  the  iodoform  is  recognised 


CHLORAL.  555 

Vy  its  odour,  resembling  chloroform ;  if  there  be  much  iodoform  it  forms 
a  yellow  precipitate.     Iodoform  is  sometimes  used  in  medicine. 

Chloral  (CgHClgO),  which  has  been  mentioned  as  resulting  from  the 
action  of  chlorine  upon  alcohol,  may  be  regarded  as  aldehyde  (C2H4O),  in 
which  3  atoms  of  hydrogen  are  replaced  by  chlorine. 

It  is  prepared  by  passing  thoroughly  dried  chlorine  into  absolute 
alcohol,  which  must  be  placed  in  a  vessel  surrounded  by  cold  water  at 
the  commencement,  because  the  absorption  of  chlorine  is  attended  by 
great  evolution  of  heat.  The  passage  of  chlorine  is  continued  for  many 
hours,  and  when  the  absorption  takes  place  slowly,  the  alcohol  is  gradu- 
ally heated  to  boiling,  the  chlorine  being  still  passed  in  until  the  liquid 
refuses  to  absorb  it.  The  principal  reaction  is  CgHgO  {alcohol)  +  Clg 
=  €2110130  (c/iZorrtZ) +  5HCL*  But  a  secondary  reaction  takes  place 
between  the  hydrochloric  acid  and  the  alcohol;  (02H5)HO  {alcohol) 
+  HOI  =  HgO  +  (02115)01  {hydrochloric  ether).  The  water  thus  formed 
combines  with  the  chloral,  forming  a  heavy  oily  liquid  which  solidifies 
on  standing  to  a  white  crystalline  mass  of  chloral  hydrate,  C2HOI3O.H0O. 
To  obtain  chloral  itself,  this  must  be  distilled  with  twice  its  volume  of 
oil  of  vitriol  to  remove  the  "water,  and  with  quicklime  to  remove  the 
hydrochloric  acid. 

In  the  preparation  of  chloral  hydrate  on  the  large  scale,  chlorine  is 
passed  into  alcohol  of  at  least  96  per  cent,  for  twelve  or  fourteen  days. 
The  crude  product  is  heated  with  an  equal  weight  of  strong  sulphuric 
acid  in  copper  vessels  lined  with  lead.  Hydrochloric  acid  escapes  at  first, 
and  the  chloral  distils  over  at  about  212"  F.  The  distillate  is  rectified, 
and  mixed  with  water  in  glass  flasks,  when  chloral  hydrate  is  formed, 
Avhich  is  poured  into  large  porcelain  basins  where  it  solidifies. 

Ohloral  is  a  colourless  liquid,  with  a  peculiar  pungent  odour  exciting 
to  tears.  Its  sp.  gr.  is  1'5,  and  it  boils  at  201°  F.  It  makes  a  greasy 
mark  on  paper,  and  mixes  with  water,  alcohol,  and  ether. 

"When  mixed  with  a  small  quantity  of  water,  combination  takes  place, 
with  evolution  of  heat,  and  the  crystallised  hydrate  is  produced.  Ex- 
posed to  moist  air,  it  absorbs  water  and  forms  the  hydrate.  The  chloral 
hydrate  itself  readily  absorbs  water  from  the  air;  it  may  be  sublimed 
without  decomposition,  though  its  vapour  undergoes  dissociation. 

When  kept,  chloral  suffers  a  change  somewhat  resembling  that  of  alde- 
hyde, becoming  an  opaque  white  mass,  insoluble  chloral,  insoluble  in 
water,  alcohol,  and  ether,  and  reconvertible  into  liquid  chloral  by  distilla- 
tion. Left  in  contact  with  water,  it  becomes  gradually  converted  into 
chloral  hydrate.  Ohloral  is  decomposed  by  solution  of  potash;  CgHOlgO 
{chloral)  +  KHO  =  KOHOg  (potassium  formiate)  +  OHOI3  {chloroform). 

Chloral  hydrate  has  been  lately  much  used  medicinally  for  procuring 
sleep.  The  distillation  of  starch  or  sugar  with  hydrochloric  acid  and 
manganese  dioxide  furnishes  chloral  together  with  other  products. 

If  aldehyde  be  cooled,  saturated  with  chlorine,  heated  to  100°  C.  and  again  saturated 
with  chlorine  at  that  temperature,  it  is  converted  into  croton-ehloral — 

2Q^llfi  (Aldehyde)   +   Clg  =   C^YLj:^\^0  {Croton-ehloral)   +   H^O   +   3HC1. 

Croton-ehloral  is  derived  from  C^HgO  croton-aldehycle  {crotonic  acid,  C4Hg02,  is  obtained 

*  An  intermediate  compound  of  chloral  and  alcohol,  CgHClaO.CoHfiO,  also  appears  to  be 
formed.  It  is  a  solid  crystalline  body,  fusing  at  115°  F.,  boiliug  at  234°  F.,  and  difficultly 
soluble  in  water,  which  distinguishes  it  from  chloral  hydrate.  Heat  decomposes  it  into 
chloral  and  alcohol. 


556  PERFUME-ETHERS — ALDEHYDES. 

rom  croton  oil).  Croton-cliloral  is  an  oily  liquid  of  a  pungent  smell,  boiling  at  164' 
C.  It  combines  with  water  to  form  a  hydrate  which  dissolves  in  hot  water,  and 
crystallises,  on  cooling,  in  plates  which  have  a  very  irritating  odour.  It  has  been 
used  in  medicine. 

398,  Perfume  ethers — Fruit  essences. — Certain  of  the  compound  ethers, 
formed  by  the  acids  of  the  acetic  series,  are  employed  in  perfumery  and 
confectionery. 

Thus,  ethyle  hutyrate  or  butyric  ether  (C2H5.C4H7O2),  prepared  by  dis- 
tilling potassium  hutyrate  with  alcohol  and  sulphuric  acid,  has  a  decided 
flavour  of  pine  apples.  Formic  ether  is  used  for  flavouring  rum  and  arrack. 
Amyle  acetate  {C^^^yQ>^^0^  has  a  very  strong  resemblance  in  taste  and 
smell  to  the  jargonelle  pear ;  it  is  obtained  by  distilling  fousel  oil  (amyle 
hydrate)  with  sodium  acetate  and  sulphuric  acid. 

The  armjle  valerianate,  which  has  the  flavour  of  apples,  and  is  known 
as  apple  oil,  is  obtained  by  distilling  fousel  oil  with  sulphuric  acid  and 
potassium  dichromate,  when  the  chromic  acid  of  the  latter  oxidises  one 
portion  of  the  amyle  hydrate  (CsHj^.HO),  converting  it  into  valerianic 
acid  CjHjpOg),  which  then  forms  amyle  valerianate  (CjHj^.CjHgOg). 

399.  Aldehydes — Vinic  or  acetic  aldehyde. — It  has  been  already 
noticed  (p.  499)  that  a  considerable  loss  of  alcohol  has  occasionally  taken 
place  in  the  manufacture  of  vinegar,  in  consequence  of  the  formation  of 
aldehyde  (CgH^O)  instead  of  acetic  acid  (CgH^Og)  by  partial  oxidation 
of  the  alcohol.  In  order  to  prepare  aldehyde  in  quantity,  alcohol  is  dis- 
tilled with  sulphuric  acid  and  manganese  dioxide,  or  with  sulphuric 
acid  and  potassium  dichromate,  or  it  may  be  oxidised  by  chlorine  in  the 
presence  of  water. 

Three  parts  of  bichromate  of  potash,  in  crystals  free  from  powder,  are  placed  in  a 
flask  or  retort  surrounded  by  ice  (or  by  a  mixture  of  sulphate  of  soda  crystals  with 
half  their  weight  of  hydrochloric  acid),  and  a  mixture  of  2  parts  ordinary  alcohol,  4 
parts  sulphuric  acid,  and  12  parts  of  water,  also  previously  cooled  in  ice,  is  added. 
The  flask  or  retort  is  then  connected  with  a  Liebig's  condenser  containing  iced  water, 
and  the  refrigerating  mixture  removed,  when  the  whole  of  the  aldehyde  will  generally 
be  distilled  over  by  the  heat  attending  the  reaction. 

In  these  processes  the  alcohol  is  oxidised  according  to  the  equation — 

CgHgO  {Alcohol)  +   0   =   C2H4O  {Aldehyde)  +  HgO  . 

In  the  first  process  the  oxygen  is  derived  from  the  manganese  dioxide, 
leaving  manganous  sulphate  (MnO.SOg)  in  the  retort ;  in  the  second 
process,  the  dichromate  furnishes  the  oxygen,  chromium  sulphate 
^'■2(^^4)3  ^cing  formed.  As  might  be  expected,  a  portion  of  the  alcohol 
is  oxidised  to  a  higher  degree,  and  converted  into  acetic  acid  (CgH^Og), 
so  that  some  acetic  ether  comes  over  together  with  the  aldehyde.  Another 
product,  acetal,  is  also  found  in  the  distillate,  which  has  the  composition 
CgHj^Oj,  and  may  be  regarded  as  resulting  from  the  union  of  ether,  formed 
bv  a  secondary  action  of  the  sulphuric  acid  upon  the  alcohol,  with  aldehyde 
((C2H5)oO.C2H,0). 

By  redistilling  the  aldehyde  with  an  equal  weight  of  fused  calcium  chloride  in  a 
gently  heated  water-bath,  it  may  be  freed  from  most  of  the  water  and  alcohol,  which 
are  left  behind  in  the  retort,  the  boiling-point  of  aldehyde  being  only  67°'8  F.  After 
rectification,  it  may  be  separated  from  the  acetic  ether  and  acetal,  by  taking  advan- 
tage of  its  property  of  combining  with  ammonia  to  form  a  compound  which  is 
insoluble  in  ether  ;  the  rectified  aldehyde  is  mixed  with  twice  its  volume  of  ether, 
jtlaced  in  a  bottle  surrounded  by  ice,  and  saturated  with  gaseous  ammonia  (page  125), 
when  white  needle-like  crystals  of  aldehyde  ammonia  (NH3.C2H4O)  are  deposited. 


ALDEHYDK  557 

By  distilling  this  compound  with  diluted  sulphuric  acid,  and  condensing  the  vapour 
in  a  thorouglily  cooled  receiver,  pure  aldehyde  is  obtained,  from  which  the  last  por- 
tions of  water  may  be  removed  by  standing  over  fused  calcium  chloride  and  a  final 
distillation. 

Aldehyde  may  be  recognised  by  its  peculiar  acrid  odour,  which  affects 
the  eyes,  as  well  as  by  its  volatility  and  inflammability.  It  absorbs 
oxygen  from  air  even  at  the  ordinary  temperature,  and  is  gradually  con- 
verted into  acetic  acid.  Its  attraction  for  oxygen  enables  it  to  reduce  the 
salts  of  silver  to  the  metallic  state,  and  a  characteristic  test  for  aldehyde 
consists  in  adding  a  little  silver  nitrate  and  a  trace  of  ammonia ;  on 
heating,  the  silver  is  deposited  as  a  mirror  on  the  sides  of  the  test-tube. 
In  contact  with  potassium  hydrate,  aldehyde  undergoes  decomposition, 
yielding  a  brown  substance  {resin  of  aldehyde)  and  a  solution  of  acetate 
and  formiate  of  potassium.  By  distilling  a  mixture  of  these  two  salts,  alde- 
hyde may  be  reproduced — 

KC2H3O2     -f-      KCHO2      -      K2CO3    +     CaH.O 

Potassium  acetate.       Potassium  fonniate.  Aldehyde. 

These  reactions  lend  some  support  to  the  opinion,  that  aldehyde  should 
be  represented  as  being  framed  upon  the  model  of  a  molecule  of  hydrogen 
(HH),  in  which  the  place  of  1  atom  of  hydrogen  is  occupied  by  acehjle 
(C2H3O),  the  hypothetical  radical  of  acetic  acid.  For  if  potassium 
formiate  be  distilled  with  caustic  potash,  it  yields  potassium  carbonate 
and  2  atoms  of  hydrogen,  KCHOg  +  KHO  =  KoCOg  +  HH;  and  if  potassium 
acetate  be  employed  instead  of  the  hydrate,  aldehyde  is  obtained  instead 
of  hydrogen,  KCHO2  -f-  K(C2H30)0  =  K2CO3  +  (C2H30)H. 

On  this  view  it  is  easy  to  explain  the  tendency  of  aldehyde  to  undergo 
oxidation,  forming  acetic  acid,  just  as  hydrogen  is  converted  into  water 
by  oxidation. 

Type. — Molecule  of  hydrogen,  H.H    I  Type. — Molecule  of  water,  H.^O 
Aldehyde,  CgHgO.H  |  Acetic  acid,  (C2H30)HO  . 

As  might  be  anticipated,  it  is  found  that  when  vapour  of  aldehyde  is 
passed  over  heated  caustic  potash  (mixed  with  lime)  it  yields  potassium 
acetate  and  hydrogen,  C2H3O.H  +  KHO  =  H.H  -h  K(C2H30)0. 

By  the  action  of  potassium,  the  atom  of  hydrogen  may  be  displaced 
from  the  aldehyde,  and  the  compound  (C2H30)K  obtained. 

In  contact  with  water  and  sodium  amalgam,  aldehyde  combines  with 
the  nascent  hydrogen,  and  produces  alcohol.  Chlorine  displaces  three- 
fourths  of  the  hydrogen  from  aldehyde,  producing  chloral,  C2CI3HO, 
which  has  been  already  noticed  as  yielding  chloroform  when  acted  on  by 
alkalies. 

Perfectly  pure  aldehyde  can  be  kept  unchanged ;  but  in  the  presence  of  a  very 
small  quantity  of  hydrochloric  or  sulphurous  acid,  or  carbon  oxychloride,  it  undergoes 
a  polymeric  transformation  into  paraldehyde  [or  elaldehyde),  CgHigOj,  which  ciystallises 
in  prisms  when  cooled  to  10°  C,  and  boils  at  a  much  higher  temperature  than  aldehyde, 
into  which  it  may  be  reconverted  by  distillation  witli  sulphuric  or  hydrochloric  acid. 
If  aldehyde  be  cooled  in  a  freezing  mixture,  and  a  few  bubbles  of  hydrochloric  or 
sulphurous  acid  passed  in,  inetaldehyde  crystallises  out.  This  body  may  be  recon- 
verted into  aldehyde  by  distillation  with  diluted  sulphuric  acid,  or  by  heating  in  a 
sealed  tube  to  240°  F. 

PCI5  converts  aldehyde  into  ethylidene  dichloride  CgH^C^,  which  is  isomeric  with 
Dutch  liquid,  but  not  identical  with  it. 

In  contact  with  moderately  strong  hydrochloric  acid,  aldehyde  gradually  becomes 
converted  into  aldol  CjEgO^,  which  possesses  some  of  the  chemical  properties  both  of 


are — 

Acetic  aldeliyde,     . 
Propionic  aldehyde, 
Butyric  aldehyde,  . 
Valeric  aldehyde,    . 
CEnanthic  aldehyde, 

.     C2H4  0* 
.     CjHeO 
.     C4H8O 
.     C5H10O 
.     C,Hi40 

558  ALDEHYDES. 

an  aldehyde  and  an  alcohol.  Tlie  action  appears  to  take  place  in  two  stages ;  in  the  first, 
the  HCl converts  the  aldehyde  into  a  chlorhydrin  ;  CH3.CHO  +  HCl  =  CH3.CH(0H)C1  ; 
in  the  second,  the  chlorhvdriu  is  acted  on  by  the  aldehyde,  forming  aldol  and  hydro- 
chloric acid  ;  CH3.CH(OH)Cl  +  CH3.CHO  =  HCl  +  CH3.CH(OH).CH2.CHO. 

When  aldehyde  is  treated  with  a  saturated  sohition  of  sodium  bisul- 
phite (NaHSOg),  it  forms  a  crystalline  compound  which  is  soluble  in 
water,  but  insoluble  in  tho  saline  solution,  and  contains  the  elements  of  2 
molecules  of  the  aldehyde  and  1  molecule  of  the  bisulphite. 

If  the  view  above  referred  to  be  correct,  which  represents  aldehyde  as 
the  hydride  of  acetyle  (the  radical  of  acetic  acid),  each  of  the  acids 
belonging  to  the  acetic  series  would  be  expected  to  have  a  corresponding 
aldehyde.  Accordingly,  just  as  calcium  acetate,  when  distilled  with 
calcium  formiate,  yields  acetic  aldehyde,  so  valerianic,  cenanthic,  and 
caprylic  aldehydes  may  be  obtained  by  distilling  the  corresponding  calcium 
salts  with  calcium  formiate. 

The  chief  aldehydes  of  this  series  which  have  at  present  been  examined 

Caprylic  aldehyde,  .  .  Cg  HjgO 

Rutic  aldehyde,  .  .  CjoHjoO 

Euodic  aldehyde,  .  .  CuHjjO 

Laurie  aldehyde,  .  .  C12H24O 

The  radicals  corresponding  to  acetyle,  which  may  be  regarded  as  asso- 
ciated with  hydrogen  in  these  aldehydes,  have  not,  for  the  most  part,  been 
isolated  ;  a  substance  having  the  same  composition  as  butyryle  (C4H-O). 
the  supposed  radical  of  butyric  acid  (C^HgOg),  has,  however,  been  obtained 
from  that  acid  by  an  indirect  process. 

Acetic,  propionic,  and  butyric  aldehydes  have  been  found  among  the 
products  of  the  oxidising  action  of  a  mixture  of  manganese  dioxide  and 
sulphuric  acid  upon  fibrine,  albumen,  and  caseine. 

Valeric  aldehyde  is  obtained,  like  acetic  aldehyde,  by  distilling  the 
corresponding  alcohol  (amyle-alcohol,  CgH^gO)  with  sulphuric  acid  and 
potassium  dichromate. 

Capric  (rutic),  euodic,  and  lauric  aldehydes  arc  found  in  essential  oil  of 
rue.  The  higher  aldehydes  of  the  series  are  not  so  easily  oxidised  as  those 
containing  a  lower  number  of  carbon  atoms. 

"WTien  an  aldehyde  is  heated  with  one  of  the  bases  derived  from 
ammonia  by  the  substitution  of  an  alcohol-radical  for  1  atom  of  hydro- 
gen, the  other  2  atoms  of  hydrogen  of  the  ammonia  are  replaced  by  the 
diatomic  hydrocarbon  of  the  aldehyde  ;  thus — 

2XH,C,H,,  +  2C,H,,0  =  2H,0  +  ^.,{C,n,,),{C,-R,,)''. 

Araylamine.  ^^u^f"  Di-oenanthvlene-di- 

'  aldehyae.  ainylamme. 

This  reaction  has  been  recommended  for  the  determination  of  the  re- 
placeable (or  typical)  hydrogen  in  organic  bases. 

400.  Acetones  or  Ketones. — If  the  calcium  salts  of  the  acids  of  tho 
acfitic  series,  instead  of  being  distilled  with  calcium  formiate,  as  for  the 
preparation  of  the  aldehydes,  be  distUled  alone,  or  with  quicklime,  in  an 

*  It  will  be  remarked  that  these  aldehydes  are  polymeric  with  the  compound  ethers 
t'oruied  by  their  acids  ;  thus,  acetic  aldehyde  is  polymeric  with  acetic  ether,  for — 

2C2H4O  =  CaHs.CjHsOa, 
but  the  sp.  gr.  of  aldehyde  vapour  (1'53)  is  only  half  that  of  acetic  ether  vapour  (3"06). 


ACETONES  OR  KETONES.  559 

iron  tube  placed  in  a  combustion  furnace  (page  84)  and  heated  gradually 
from  back  to  front,  a  series  of  homologous  products  is  obtained,  each  of 
Avhich  is  isomeric  with  the  aldehyde  of  the  series  next  below  it  in  the  table, 
though  totally  different  from  that  aldehyde  in  properties. 

Thus,  by  distilling  calcium  acetate  with  lime,  the  liquid  acetone  or 
pifi'o-acetic  spirit  (CgtlgO)  is  obtained,  which  has  been  already  noticed 
among  the  products  of  the  distillation  of  wood — 

03(0211302)2  {Calcium  acetaic)  =  OaOOg   +   OgHgO  (Acetone). 

The  ketones  bear  the  same  relation  to  the  secondary  monatomic  alcohols 
(p.  517)  as  the  aldehydes  bear  to  the  primary  alcohols,  and  may  be  ob- 
tained from  them  by  oxidation  in  a  similar  manner.  Propyle  alcohol, 
when  oxidised,  yields  propyle  aldehyde — 

C2H5.H2.OH  +  0  =  O2H..H.O  +  H2O. 

c"  c" 

Propyle-alcohol.  Propyle-aldehyde. 

But  isopropyle-alcohol,  which  is  a  secondary  alcohol,  yields  acetone — 
OH3.OH3.H.OH  +  0  =  OHg-OH-gO   +  H2O. 


0  0 

Isopropyle-alcohol.  Acetone. 

When  the  ketones  are  treated  with  water  and  sodium- amalgam  (to  yield 
nascent  hydrogen),  they  give  secondary  alcohols,  whilst  the  aldehydes  give 
primary  alcohols. 

The  ketones  form  crystalline  compounds  with  acid  sodium  sulphite,  but 
do  not  reduce  silver-nitrate  like  the  aldehydes. 

By  distilling  a  mixture  of  two  salts  of  acids  of  the  acetic  series,  double 
ketones  are  obtained.  Thus,  if  potassium  acetate  be  distilled  with  potas- 
sium propionate,  acetoue-propione  is  obtained — 

KC2H3O2     -f     KO3H5O2     =     O^HgO      +     K2OO3. 

Posassium  acetate.     Potassium  propionate.    Acetone-propione. 

The  constitution  of  a  ketone  may  be  inferred  from  the  products  of  its 
oxidation  by  chromic  acid  or  by  potassium  hydrate  ;  thus  acetone  yields 
acetic  (02H^02)  acid  and  formic  (OHO2),  ethyl-amyle  ketone  yields  valeric 
(C5H10O2),  and  propionic  (C3H602)- 

It  will  be  seen  that  the  ketones  form  a  homologous  series  of  which  the  odd 
members  are  single  ketones,  and  the  even  members  are  double  ketones— 

Acetone, 

Acetone-propione, 
Propione, 

Propio  n  e-bu  ty  roue, 
Butyrone, 
and  so  on. 

Acetone  may  be  obtained  by  the  action  of  zinc-methyle  on  carbon  oxy- 
chloride  — 

•    0001.    +    Zn(0H3),    =  ZnOl,    +    00(OH3)2 

Carbon  oxychloride.    Zinc-methyle.  Acetone. 

Acetone  may  also  be  prepared  by  distilling  sugar  with  eight  times  its 
weight  of  quicklime,  when  it  is  accompanied  by  another  liquid,  metacetone, 
OjjHjqO,  which  differs  from  acetone  in  being  insoluble  in  water. 


CsHg 

0 

C4H8 

0 

CgHioO 

CgHjoO 

C-H, 

4O 

560  OIL  OF  BITTER  ALMONDS  AN  ALDEHYDE. 

401.  The  description  above  given  of  the  properties  of  aldehyde  will 
have  recalled  those  of  some  of  the  essential  oils  containing  oxygen.  Thus 
essential  oil  of  bitter  almonds  (CyHgO),  when  exposed  to  air,  absorbs 
oxygen,  and  is  converted  into  benzoic  acid  (C^H^Oo),  just  as  aldehyde 
(C^H^O)  passes  into  acetic  acid  (CgH^Oa).  Moreover,  oil  of  bitter  almonds 
forms  a  crystalline  compound  with  sodium  disulphite,  similar  to  that 
formed  by  aldehyde,  and  its  conversion  into  this  compound  is  sometimes 
resorted  to  in  order  to  obtain  the  pure  oil. 

In  constitution,  also,  oil  of  bitter  almonds  (benzoyle  hydride,  C-H5O.H) 
closely  resembles  aldehyde  (acetyle  hydride,  C2H3O.H),  and  just  as  the 
latter  may  be  obtained  by  distilling  potassium  acetate  with  potassium 
formiate,  so  benzoic  aldehyde  (oil  of  bitter  almonds)  may  be  obtained  from 
potassium  benzoate — 

KC-HjQg     +     KCHO2     =     K2CO3     +     C7H5O.H 

Potassium  benzoate.      Pota8:iium  furmiate.  Benzoic  aldehyde. 

Oil  of  bitter  almonds  is  produced,  together  with  some  aldehydes  of  the 
acetic  series  of  acids  (page  558),  when  certain  albuminous  bodies  are  oxi- 
dised by  sulphuric  acid  and  manganese  dioxide. 

When  benzoic  aldehyde  is  acted  on  by  an  alcoholic  solution  of  potash, 
an  oily  liquid  is  obtained,  which  stands  in  the  .same  relation  to  benzoic 
aldehyde  as  alcohol  bears  to  acetic  aldehyde — 

2(C-H.0.H)   +  KHO   =  K(C,H50)0   +   C^HgO 

{Benzoic  aldehyde.  Potassium  benzoate.     Benzoic  alcohol. 

The  conversion  of  bitter  almond  oil  into  benzoic  alcohol  may  also  be 
eifected  by  the  action  of  water  and  sodium  amalgam  (to  furnish  nascent 
hydrogen) ;  whereas,  by  treatment  with  zinc  and  hydrochloric  acid,  it  is 
converted  into  hydrobenzoine  (C7H7O). 

The  hydrochloric  ether  of  benzoic  alcohol,  C7H-CI,  is  sometimes  called 
benzyle  chloride,  the  radical  henzyle,  C^H-,  being  supposed  to  have  the 
same  relation  to  the  benzoic  series  as  ethyle  has  to  the  acetic  series.  By 
the  action  of  ammonia  upon  benzyle  chloride,  henzylamine,  NH2(C;H;), 
and  tri-henzylamine,  N(C7H-)g,  have  been  obtained  ;  the  former  is  isomeric 
with  toluidine,  but  is  by  no  means  identical  with  it ;  for  benzylamine  is 
a  liquid  having  basic  properties  far  more  powerful  than  those  of  toluidine, 
and  it  is  very  readily  soluble  in  water,  which  dissolves  but  little  of  the 
latter  base. 

By  distilling  benzyle  chloride  with  potassium  cyanide,  phenylaceto- 
nitrile,  CgH5.CH2.CN,  is  obtained.  This  liquid  forms  the  principal  part 
of  the  oil  of  cress  and  oil  of  nadurtium. 

The  benzoic  acetone  or  henzone  (C^gHj^O)  has  been  obtained  by  the 
distillation  of  calcium  benzoate.  It  is  often  called  benzopJienone,  being 
regarded  as  an  association  of  benzoyle  with  phenyle,  C-HjO.CgHj;  for 
when  distilled  with  potash,  it  yields  potassium  benzoate  and  benzene 
(phenyle  hydride) ;  C-HjO.CgH^  +  KHO  =  K(C-H-0)0  +  CgHg.H 

Benzuphenone.  Potassium  benzoate.      Benzene. 

Oil  of  cinnamon  (page  482),  or  cinnamyle  hydride  (CgH^O.H),  is  the 
iildehyde  of  cinnamic  acid  (CgHgOj)  ;  and  essential  oil  of  cummin  contains 
the  aldehyde  (CiqHj^O.H)  of  cuminic  acid  (CjoH^gO-i)*  ^^^  yields  cuminic 
alcohol  (CjoHj^O)  when  treated  with  alcoholic  solution  of  potash.  Oil  of 
spiraea  or  salicyle  hydride  (C7H5O2.H)  is  the  aldehyde  of  salicylic  acid 
(C-HgOa).     Anisyle  hydride  (CgH-O^-H),  obtained  by  the  oxidation  of 


POLYATOMIC  ALCOHOLS.  561 

oil  of  aniseed,  is  the  aldehyde  of  anisic  acid  (CgHgOg),  and  of  anisic 
alcohol  (CgH^oO).  These  aldehydes  allow  their  associated  atom  of  hydro- 
gen to  be  displaced  by  chlorine  more  readily  than  the  aldehydes  of  the 
acetic  series,  to  form  chlorides  of  their  respective  radicals  (page  481). 

Glycol — Polyatomic  Alcohols. 

402.  It  has  been  already  shown  (page  530)  that  alcohol  may  be  con- 
veniently regarded  as  composed  after  the  fashion  of  a  molecule  of  water 
(HgO)  in  which  half  the  hydrogen  has  been  displaced  by  ethyle  (CgH^)  ; 
according  to  this  view  alcohol  is  represented  by  the  formula  H(C2H5)0  ; 
and  it  is  a  monatomic  alcohol,  for  it  contains  the  monatomic  radical, 
(CgHg)'.  But  if,  following  the  same  plan,  a  diatomic  radical,  such  as 
ethylene  (CgH^)",  were  to  displace  half  the  hydrogen  in  water,  the  dis- 
placement could  not  be  effected  in  less  than  2  molecules  of  water  (H4O9), 
and  a  diatomic  alcohol  would  result. 

Glycol  (CgHgO^)  is  the  representative  of  the  diatomic  alcohols,  and  may 
be  regarded  as  2  molecules  of  water,  in  which  half  the  hydrogen  is 
replaced  by  ethylene  {H^{G.^^"0^.  It  is  obtained  by  heating  50 
grammes  of  ethylene  dibromide  with  40  grammes  of  potassium  carbonate, 
and  100  grammes  of  water  for  eighteen  hours  in  a  flask  provided  with 
a  reversed  condenser  (fig.  290);  G^n^Bv^  +  Y^^GO^  +  B.f>  =  C^B.^{Oli)., 
-f2KBr-hC02. 

Glycol  was  originally  obtained  by  the  action  of  ethene  di-iodide  (formed 
by  the  absorption  of  olefiant  gas  by  iodine)  upon  silver  acetate — 

2AgC2H302     +     C2HJ2     =     2AgI  +  G,U,(C^llf>^\ 

Silver  acetate.  Ethene  di-iodide .  Glycol  diacetate. 

The  glycol  diacetate  thus  formed  corresponds  to  the  acetic  ether 
((€0115)0211302)  derived  from  common  alcohol ;  but  since  ethene  is 
diatomic,  it  displaces  the  hydrogen  in  2  molecules  of  acetic  acid.  When 
the  result  of  this  action  is  distilled,  the  glycol  diacetate  passes  over 
as  a  colourless  liquid,  which  sinks  in  water,  and  boils  at  365°  F. 
(197°C.).* 

Glycol  can  be  obtained  from  the  diacetate  by  digesting  it  with  potash 
for  some  time  at  360°  F.,  and  distilling,  when  the  glycol  passes  over,  its 
boiling-point  being  387°  F.  It  is  a  colourless  liquid,  having  a  sweet  taste, 
whence  it  derives  its  name  (yXuKv's,  sweet).  Like  common  alcohol,  it 
mixes  with  water  in  all  proportions,  and  may  be  distilled  without  decom- 
position. It  also  gives  an  inflammable  vapour,  and  has  never  been  frozen  ; 
but,  unlike  alcohol,  it  is  heavier  than  water  (sp.  gr.  1'125),  and  does  not 
mix  with  ether,  though  alcohol  dissolves  it  reatlily. 

The  action  of  hydrochloric  acid  upon  glycol  does  not  perfectly  corre- 
spond with  its  action  upon  common  alcohol,  for  instead  of  yielding 
ethene  dichloride,  it  gives  a  compound  of  hydrochloric  acid  with  ethene 
oxide;  C.,H,(0H)2   +   HCl   =   C2H4(0H)C1   -f    H2O. 

Glycol.  Chlorhydiine  of  glycol. 

By  decomposing  this  compound  with  potash,  the  ethene  oxide  (C2H4)"0 
is  obtained,  as  a  colourless  liquid,  which  boils  at  56°  F.,  and  is,  therefore, 

*  A  liquid  isomeric  with  binacetate  of  glycol,  but  boiling  at  336"  F.,  is  obtained  by  heat- 
ing aldehyle  in  a  sealed  tube  with  acet'c  anhydride. 

2  N 


562  GLYCOL. 

not  identical  with  aldehyde  (which  boils  at  68°  F.),  though  it  has  the 
same  composition.  It  is  obvious  that  glycol  might  be  represented  as 
(C9H^)".H202,  ethene  hydrate,  and  this  view  is  favoured  by  the  cir- 
cumstance that  glycol  may  be  formed  by  heating  ethene  oxide  with  water 
in  a  sealed  tube :  but,  on  the  other  hand,  when  glycol  is  treated  with  zinc 
chloride,  to  dehydrate  it,  ordinary  aldehyde  (CgH^O),  and  not  the  ethene 
oxide,  is  produced. 

By  the  action  of  phosphoric  chloride  upon  glycol,  the  ethene  dichloride, 
or  Dutch  liquid,  is  obtained — 

C.^H,(0H)2  +  2PCI5  =  (CaHJClj  +  2HC1  +  2POCI3. 

It  will  be  observed  that  this  equation  is  the  exact  counterpart  of 
that  which  represents  the  action  of  phosphoric  chloride  upon  Avater, 
substituting  diatomic  ethene  for  monatomic  hydrogen — 

H2(OH)2  +  2PCI5  =  (H2)''Cl2  +  2HC1  +  2POCI3. 

Sodium  acts  upon  glycol  in  the  same  manner  as  upon  ordinary  alcohol, 
but  in  consequence  of  the  diatomic  character  of  glycol,  the  reaction 
takes  place  in  two  stages,  producing,  successively,  mono-sodium  glycol, 
Yi'^?i{G.^^"0.2,  and  di-sodium  glycol,  Na2(C2H^)"02,  both  which  are 
solid. 

AA^hen  glycol  is  exposed  to  the  action  of  oxygen  in  the  presence  of 
platinum-black,  or  when  it  is  cautiously  oxidised  with  nitric  acid,  it 
becomes  converted  into  glycoUc  acid,  C2H4O3,  which  bears  the  same  rela- 
tion to  it  as  acetic  acid  bears  to  common  alcohol,  as  will  be  evident  from 
the  folloAving  equations  :  * — 

C2H5OH  -{-02  =  (C2H30)OH  +  H2O 

Alcohol.  Acetic  Ecid. 

C2H,(OH)2  +  02  =  (C2H20)(OH)2  +  H2O, 

Glycol.  Glycolic  acid. 

in  which  the  change  consists,  in  both  cases,  in  the  substitution  of  0  for 
Ho  in  the  radical  of  the  alcohol,  acetic  acid  being  formed  upon  the  type 
of  a  molecule  of  water  (HgO)  in  which  H  is  replaced  by  C2H3O,  and  gly- 
colic acid  upon  the  type  of  2  molecules  (H^Og),  in  which  H2  are  replaced 
by  CgHoO.  If  the  oxidation  with  nitric  acid  be  carried  farther,  the 
remainder  of  the  hydrogen  in  this  last  radical  is  replaced  by  oxygen,  and 
oxalic  acid  is  produced — 

(C2H20)(OH)2  +  0^  =  (C202)(OH)2  -h  H2O. 

Glycolic  acid.  Oralic  acid. 

By  the  action  of  nascent  hydrogen  upon  oxalic  acid,  the  0  in  the 
radical  may  be  again  displaced  by  Hg,  so  that  glycoHc  acid  is  repro- 
duced. 

Glycolic  acid  forms  a  syrupy  liquid  which  resembles  lactic  acid,  but  is 
distinguished  from  it  by  giving  a  precipitate  with  lead  acetate.  Unlike 
oxalic  acid,  glycolic  is  a  monobasic  acid,  only  1  atom  of  its  hydrogen 
being  replaceable  by  a  metal  Glycolic  acid  is  found  together  with 
o.xalic  acid  among  the  products  of  the  action  of  nitric  acid  upon  alcohol 

*  The  aldehyde  of  glycol,  glyoxal,  CiH-^Oo,  is  found  among  the  products  of  the  deconi- 

liositiou  of  nitrous  ether  in  contact  with  water. 


LACTIC  SEEIES  OF  ACIDS. 


563 


in  the  preparation  of  mercuric  fulminate,  which  is  easily  accounted  for 
by  the  connection  between  alcohol  and  ethylene,  which  is  best  exhibited 
by  writing  the  formula  of  alcohol  (C2H4).H20. 

Glycolic  acid  is  the  first  member  of  a  series  of  homologous  acids,  of 
which  the  most  important  is  lactic  acid,  these  acids  standing  in  the  same 
relation  to  the  glycols  in  which  the  members  of  the  acetic  series  stand  to 
the  alcohols. 


Lactic  Series  of  Acids. 


Kame. 

Formula. 

Source. 

Glycolic  acid, 

C2H4O3 

Oxidation  of  glycol  and  of  alcohol. 

Lactic  acid,    . 

CjHgOj 

Fermentation  of  cane  and  milk  sugars. 

Butylactic  acid,  . 

C4H8O3 

Oxidation  of  butyl-glycol. 

Valerolactic  acid, 

C5H10O3 

\  Decomposition   of   bromo-valerianic 
\          acid  with  silver  oxide. 

Leucic  acid,   .     . 

CgHiaOjj    ' 

Action  of  nitric  acid  on  leucine. 

It  will  be  observed  that  these  acids  are  intermediate,  with  respect  to 
the  number  of  atoms  of  oxygen  which  they  contain,  between  the  acetic 
and  the  oxalic  series  of  acids ;  thus — 


Acetic  acid, 
Glycolic  „ 
Oxalic 


CgH.O, 
C2H2O4 


Propionic  acid, 
Lactic  „ 

Malonic 


C3H6O2 

CgHgOg 
CgH.O, 


These  three  series  of  acids,  therefore,  present  a  relation  to  each  other 
similar  to  that  between  the  three  series  of  alcohols,  represented  by — 


Vinic  alcohol,     . 

.      c^n.o 

Glycol,       . 

C2Hg02 

Glycerine, 

CgHgOg 

Just  as  acetic  and  glycolic  acids  are  formed  by  the  oxidation  of  alcohol 
and  glycol,  so  the  oxidation  of  glycerine  by  nitric  acid  furnishes  glyceric 
acid,  CgHgO^. 

The  transition  from  the  oxalic  series  to  the  lactic  series  of  acids  has 
been  effected  in  the  case  of  leucic  acid,  which  has  been  artificially  formed 
from  oxalic  acid,  by  converting  it  into  oxalic  ether,  and  acting  upon  this 
with  zinc-ethyle,  when  leucic  ether  is  obtained,  from  which  leucic  acid  is 
easily  prepared.  The  reaction  is  rendered  intelligible  if  the  two  acids  be 
thus  formulated — 


Oxalic  acid, 
Leucic     „ 


C2H2O, 
62112(02115)203 


from  Avhich  it  appears  that,  neglecting  intermediate  stages,  the  zinc 
of  the  zinc-ethyle  removes  an  atom  of  oxygen  from  the  oxalic  acid, 
leaving  ethyle  in  its  stead,  so  that  leucic  acid  may  be  regarded  as  dieth- 
oxalic  acid,  or  oxalic  acid  containing  two  of  ethyle  instead  of  one  of 
oxygen.  If  methyle  oxalate  be  substituted  for  ethyle  oxalate  in  this 
experiment,  methyle  leucate,  CHg.CgHj^^Og,  is  obtained,  and  when  this 
is  decomposed  by  baryta,  and  the  barium  leucate  treated  with  sulphuric 
acid,  fine  crystals  of  leucic  acid  are  obtained,  which  are  readily  soluble  in 
water,  alcohol,  and  ether,  and  sublime  slowly  at  the  ordinary  tempera- 


564  POLYATOMIC  ALCOHOLS. 

ture.*  By  the  reaction  between  methyle  iodide,  methyle  oxalate, 
and  amalgamated  zinc,  dimethoxalic  acid,  03112(0113)203,  has  been  obtained, 
Avhich  may  be  regarded  as  oxalic  acid  containing  two  of  methyle  in  the 
place  of  an  atom  of  oxygen.  Dimethoxalic  acid  is  isomeric  with  butylactic 
or  acetonic  acid  (04HgO3);  it  crystallises  in  prisms  resembling  those  of 
oxalic  acid,  which  may  be  sublimed  at  122°  F.,  and  volatilise  slowly  even 
at  the  ordinary  temperature. 

From  the  other  hydrocarbons  of  the  olefiant  gas  series  (page  521),  glycols 
may  be  prepared  by  processes  similar  to  that  which  furnishes  ethene- 
glycol.  Thus  propene  (CgHg)  yields  propene-glycol,  (C3Hq)"(OH)2  ; 
butene  (O^Hg),  hutene-glycol  (C4Hg)"(0H)2 ;  amylene  (OgHj^),  amylene- 
Hhjcol,  (C5Hjq)"(0H)2  ;  it  is  a  very  remarkable  circumstance  that  the 
boiling-points  and  specific  gravities  of  these  liquids  decrease  as  the 
complexity  of  the  formula  increases,  which  is  quite  contrary  to  ordinary 
exj)erience  ;  thus  amylene-glycol  (CjHjgOg)  has  the  sp.  gr.  0'987,  and 
boils  at  351°  F.,  whilst  propylene-glycol  (OgHgOg)  has  the  sp.  gr.  1"051, 
and  boils  at  371°  F. 

When  propylene-glycol  is  slowly  oxidised,  it  is  converted,  into  lactic 
arid,  exactly  as  glycol  is  converted  into  glycolic  acid — 

(C3H,)"(OH)2  +  02  =  (C3H40)"(0H)2  +  H2O. 

Piopyleue-glycol.  Lactic  acid. 

The  difference  between  the  diatomic  character  of  glycol  and  the  mona- 
tomic  character  of  ordinary  alcohol,  is  strongly  marked  in  their  behaviour 
with  the  organic  acids,  for  whilst  the  monatomic  alcohol  yields  (with 
monobasic  acids)  only  one  series  of  compound  ethers  derived  from  one 
molecule  of  acid,  the  diatomic  glycol  yields  two  series  derived  respectively 
from  one  and  two  molecules  of  acid;  thus  we  have  glycol  monacetate 
(C2H4)".HO.(02H30)0  and  glycol  diacetate  (02H4)".(C2H3O)2.O2.  In 
the  last  series,  it  is  not  necessary  that  the  two  molecules  shoidd  con- 
sist of  the  same  acid,  as  may  be  seen  in  the  acetobutyrate  of  glycol, 
(C2HJ".C2H3O.04H7O.O2. 

Just  as  polyatomic  ammonias  are  formed  upon  the  type  of  several 
molecules  of  ammonia,  so  polyatomic  alcohols  may  be  produced  by  the 
.substitution  of  compound  radicals  for  hydrogen  in  a  multiple  alcohol 
type.  Thus,  by  heating  glycol  in  a  sealed  tube  with  ethene  oxide,  di- 
rtlicne  tri-alcohol,  H2(02H4)"203,  is  produced,  which  is  formed  upon  the 
ty])e  of  three  molecules  of  alcohol,  H3(02H5)303.  In  a  similar  manner; 
tri-othylene  tetralcohol,  lil^iC^j^^'O^,  is  formed  upon  the  quadruple 
alcohol  type,  114(02115)404. 

It  will  be  seen  hereafter  that  glycerine  (CgllgOg),  the  sweet  principle 
of  oils  and  fats,  is  a  triatomic  alcohol,  formed  upon  the  type  of  three 
molecules  of  water  (HgOg),  in  which  half  the  hydrogen  is  replaced  by 
the  triatomic  radical  (Cgil-)'",  ghjcen-yle,  the  formula  of  glycerine  being 
I[,(C3H,)"'O3or(0gHJ"(OH)3. 

It  is  easy  to  convert  a  diatomic  into  a  monatomic  alcohol ;  for  example, 
if  the  chlorhydrine  of  glycol  be  treated  with  sodium  amalagam  in  the 
]iresence  of  water,  it  becomes  converted  into  ordinary  (monatomic)  alco- 
\vA ;  CoH.ClO  +  H2O  +  Nag  =  C^H/)  +  XaHO  -1-  NaOl . 

Clilorhydrine  .,     .    , 

of  glycol.  AlcohoU 

*  It  is  said  that  this  leucic  acid,  though  closely  resembling  that  obtained  from  oxalic 
cthtT,  is  not  iJeutical  with  it. 


WATER-TYPE  VIEW  OF  POLYATOMIC  ALCOHOLS.  565 

The  relation  of  the  alcohols  to  water  as  their  primary  type  is  here 
exhibited — 

Type,  one  molecule  of  water,  HgO  =        xr  (  0 

TT      ) 
Vinic  alcohol,  CoHgO  =        /n  xr  \'  r  C) 

Type,  two  molecules  of  water,  H^Og        =        Tf^  \^'> 

Glycol,  CsHeO,  =       (C.hV}^^ 

Type,  three  molecules  of  water,  HgOg       =        TI,  '>  O3 

h;j 

Diethylene-trialcohol,  C4H^q03         =        /p  tt^,,,  |  ^ 

(C^H,)"  ) 
TT        ) 
Glycerine,  CgHgOa  =       (chV'/^^ 

TT    ) 
Type,  four  molecules  of  water,  HgO^        =        tt'^  \  0^ 

TT        ) 

Triethylene-tetralcohol,  CgHj^O^       =       /r  tt^"    1^4 

W2^4/  3  J 

The  compounds  formed  by  the  action  of  acids  upon  these  alcohols  would 
then  be  represented  by  such  formulae  as  the  following: — 

Acetic  ether,     .         .         .  ^S??l?\'  1 0 

(^2^5)  J 

Glycol  monacetate,    .         •      ^   ^^    }       (.  q 

(^^2^4)   J 

„     diacetate,        .         .       ^^fS'^SH  \  ^-2 

('^2^4)   J 
(C2H3O)'  ) 
„     acetobutyrate,  .       (C4H-O)'  VO, 

Monacetine,       .         .         .    ^  ^^A^X^^.  \  O., 

mils)    J 

Diacetine,  .         .         •        '  /P  TT  V"  I  ^3 

Triacetine,         .         .         .  (h  h  v"  \  O3 

ACETIC  ACID— THE  FATTY  ACID  SERIES. 

403.  The  most  useful  of  the  acids  belonging  to  the  acetic  series  (see 
page  519)  is  acetic  acid  itself,  the  preparation  of  which  has  been  already 
described  (page  471). 

Many  of  its  salts  are  extensively  employed  in  the  arts.  Aluminium 
acetate  is  used  as  a  mordant  by  the  dyer  and  calico-printer.  Lead  acetate 
or  sugar  of  lead,  Pb(C2H302)23Aq.,  is  prepared  by  dissolving   litharge 


566  ACETONE. 

(PbO)  in  an  excess  of  acetic  acid,  when  the  solution  deposits  prismatic 
crystals  of  the  acetate,  which  are  easily  dissolved  by  water  and  alcohol. 

On  the  large  scale,  hot  acetic  acid  vapour  is  passed  through  copper 
vessels  with  perforated  shelves  on  which  litharge  is  placed. 

Goulard's  extract,  or  trihasic  lead  acetate,  is  prepared  by  dissolving 
litharge  in  solution  of  lead  acetate;  it  may  be  obtained  in  needle-like 
crystals,  which  have  the  composition  Pb(C2H302)22PbO.H20. 

Verdigris,  or  basic  copper  acetate,  Cu(C2H302)2-Cu0.6H20,  is  pre- 
pared by  piling  up  sheets  of  copper  with  layers  of  fermenting  husks  of 
grapes  (the  marc  of  the  wine-press)^  when  the  copper  oxide,  formed  at 
the  expense  of  the  oxygen  of  the  air,  combines  with  the  acetic  acid  fur- 
nished by  the  oxidation  of  the  alcohol. 

Sodium  acetate  dissolved  in  water  is  used  in  foot-warmers  for  railway 
carriages,  on  account  of  the  continuous  evolution  of  heat  during  its 
crystallisation.  It  is  four  times  as  effective  as  an  equal  volume  of 
water. 

Acetone  (CgHgO)  is  obtained  by  the  destructive  distillation  of  calcium 
acetate,  Ca(CoH302)2  =  CaCOg  +  CgHgO,  a  decomposition  which  possesses 
some  genera]  interest,  since  the  calcium  salts  of  the  other  acids  of  the 
acetic  series  yield  ketones  in  a  similar  manner  (see  page  559). 

The  acetone  thus  obtained  is  an  ethereal  liquid  lighter  than  water,  boil- 
ing at  133°  F.,  and  burning  with  a  luminous  flame.  It  is  easily  miscible 
with  water,  but  separates  when  potassium  hydrate  is  added,  rising  to  the 
surface. 

Under  the  action  of  chlorine,  acetic  acid  loses  an  atom  of  hydrogen, 
taking  chlorine  in  its  place,  and  forming  chlor acetic  acid,  H.C2H2CIO2;  * 
and  if  the  action  be  promoted  by  sun-light,  tricJdoracetic  acid  may  be 
formed,  H.CgClgOg,  which  may  be  crystallised.  This  latter  acid  has  a 
peculiar  interest  on  account  of  its  being  concerned  in  the  production  of 
acetic  acid  from  inorganic  materials,  which  was  one  of  the  first  examples 
of  the  actual  synthesis  of  organic  compounds. 

The  synthesis  of  acetic  acid  has  been  effected  by  the  action  of  carbon 
oxychloride  upon  marsh  gas,  when  hydrochloric  acid  and  acetic  oxychloride 
are  formed  ;  CH^  +  COCI2  =  (C2H30)C1  {Acetic  oxychloride)  +  HCl. 

When  the  acetic  oxychloride  is  decomposed  by  water,  acetic  acid  is  pro- 
duced ;  (C2H30)C1  +  H2O  =  H(C2H30)0  -F  HCl. 

This  appears  to  be  an  example  of  a  general  method  of  synthesis  of  the 
volatile  fatty  acids,  starting  from  the  marsh  gas  hydrocarbons  derived  from 
them;  thus,  amyle  hydride,  C5H^2>  treated  in  a  similar  manner,  yields 
caproic  acid,  HCgH^^Og. 

404.  Anhydrides  of  organic  acids — Acetic  anhydride.- — The  course  of 
investigation  by  which,  of  late  years,  much  light  has  been  thrown 
upon  the  true  constitution  of  acetic  acid,  and  therefore  of  many  other 
organic  acids,  is  of  a  very  instructive  character.  The  strongest  acetic 
acid  which  can  be  prepared  (see  p.  471)  is  known  as  glacial  acetic 
acid,  from  its  crystallising  in  icy  leaflets  at  about  55°  F.  This  acid  has 
the  composition  C^fi^,  and  may  be  regarded  as  a  molecule  of  water  in 
which  half  the  hydrogen  is  replaced  by  the  hypothetical  radical  acetyle, 

When  this  acid  is  distilled  with  phosphorous  chloride,  a  colourless,  very 
*  Dichloracetic  acid,  H.CsHClj03,  has  also  been  obtained. 


ACETIC  ANHYDRIDE.  567 

pungent  liquid  is  obtained,  which  is  commonly  spoken  of  as  acetic  oxy- 
chloride,  C0H3OCI — 

2H(C2H30)0  +  PCI3  =  HCl  +  HPO2  +  2(C2H30)C1. 

That  this  acetic  oxychloride  (or  acetyls  chloride)  really  bears  a  very 
close  relationship  to  acetic  acid,  is  shown  by  the  action  of  water,  which 
acts  with  explosive  violence  and  reproduces  the  acetic  acid — 

(C2H30)C1  +  H2O  =  H(C2H30)0  +  HCl. 

If  potash  be  allowed  to  act  upon  the  chloride  of  acetyle — 

(C2H30)C1  +  KHO  =  H(C2H30)0  +  KCl. 

T5ut  if  potassium  acetate  (KC2Hg02)  be  employed  instead  of  potassium 
hydrate;  (C2H30)C1  +  K(C2H36)0  =  CgHgO.CgHgO.O  +  KCl. 

Acetic  oxychloride.    Potassium  acetate.  Acetic  aniiydride. 

Glacial  acetic  acid  may  be  used  instead  of  the  potassium  salt. 

Acetic  anhydride  has  also  been  obtained  by  heating  dry  acetate  of  lead 
or  of  silver  with  carbon  disulphide  in  a  sealed  tube  to  about  326°  F.  for 
several  hours,  the  tube  being  occasionally  opened  to  relieve  the  pressure 
of  the  carbonic  acid  gas  evolved — 

2Pb(C2H30)202  +  CS2  =  2PbS  +  CO2  +  2(C2H30)20. 

The  acetic  anhydride  is  a  neutral  oily  liquid  which  may  be  distilled  oft" 
in  the  above  experiment.  Its  smell  recalls  that  of  acetic  acid,  but  affects 
the  eyes  strongly.  It  sinks  in  water,  but  dissolves  slowly,  with  evolution 
of  heat  and  formation  of  acetic  acid.* 

The  most  convincing  proof  that  this  anhydride  is  really  formed  after  the 
type  of  a  molecule  of  water,  is  obtairied  by  acting  upon  the  acetate  of 
potash  with  the  benzoic  instead  of  the  acetic  oxychloride — 

(C.H50)C1  +  K(C2H30)0  =  KCl  +  C7H5O.C2H3O.O, 

Benzoic  Potassium  Benzo-acetic 

oxychloride.  acetate.  anhydride. 

and  the  true  nature  of  this  double  anhydride  is  seen  by  its  conversion 
into  a  mixture  of  benzoic  and  acetic  acids  when  left  in  contact  with 
water. 

By  methods  similar  to  that  employed  for  acetic  acid,  the  anhydrides  of 
many  other  organic  acids  may  be  obtained. 

Peroxides  of  organic  radicals. — Considerable  support  has  been  offered 
to  that  view  of  the  constitution  of  the  organic  acids,  which  represents 
them  as  composed  after  the  type  of  water,  by  the  discovery  of  certain 
compounds  which  bear  the  same  relation  to  the  anhydride  as  peroxide  of 
hydrogen  bears  to  water. 

When  barium  dioxide  is  acted  on  by  hydrochloric  acid,  barium  chloride 
and  hydric  peroxide  are  formed — 

BaOg  +  2HC1  =  BaCla  +  H2O2. 
If  barium  dioxide  be  acted  on  by  benzoic  oxychloride  (benzoyle  chloride), 
the    products    are    barium    chloride    and    benzoic   peroxide    (benzoyle 
peroxide) — 

Ba02  +  2(C7H50)C1  =  BaCla  +  (C.H50)202. 

*  If  acetic  anhydride  be  heated  with  an  excess  of  barium  dioxide,  it  yields  barium 
acetate,  carbon  dioxide,  and  methyle  gas  (page  526) — 

2(C.,H30)oO  +  BaOa  =  BaiC.^HsOa).,  +  2CH3  +  2C0.,. 
By  absorbing  the  carbon  dioxide  with  potash,  the  pure  methyle  gas  is  easily  obtained. 


568  FORMIC  ACID. 

The  benzoic  peroxide  may  be  obtained  in  fine  crystals  from  its  ethereal 
solution,  but,  likehydric  peroxide,  it  is  easily  decomposed  at  about  212°  F. 
with  explosive  violence.  By  the  action  of  alkalies  it  is  resolved  into 
benzoic  acid  and  oxygen,  just  as  hydric  peroxide  yields  water  and 
oxygen — 

(C7H50)202  +  2KH0  =  2K(C7H50)0  +  0  +  HgO. 

By  acting  upon  acetic  anhydride  with  barium  dioxide,  the  acetic  peroxide 
(or  acetj-ie  peroxide)  is  obtained — 

BaO^  +  2(C,H30),0  =  M^,^z0.^2  +  (C^^sOyp, 

Bavinin  acetate.  Acetic  peroxide. 

The  acetic  peroxide  is  an  oily  liquid,  insoluble  in  water,  and  exploding 
with  great  violence  when  heated.  It  has  the  powerful  oxidising  pro- 
perties which  would  be  expected  from  its  chemical  resemblance  to  hydric 
peroxide. 

Ethyle  peroxide  (0.35)403  has  been  obtained  by  the  action  of  ozone  on 
ether.  It  forms  a  syrupy  liquid  which  explodes  when  heated,  and  is 
decomposed  by  water,  forming  alcohol  and  hydric  peroxide. 

405.  Formic  acid  (H.CHOg)  is  regarded  with  great  interest  by  the 
chemist,  from  its  occurring  both  in  the  animal  and  vegetable  kingdoms, 
and  from  the  ease  with  which  it  may  be  artificially  obtained.  This  acid 
is  found  in  the  leaves  of  stinging-nettles,  and  was  originally  obtained  by 
distilling  the  red  ants  [Formica  rufa),  whence  it  derives  its  name. 

It  has  long  been  prepared  in  laboratories  by  the  oxidation  of  various 
organic  substances,  particularly  by  distilling  starch  with  manganese 
dioxide  and  sulphuric  acid.  Another  more  modern  process,  which  yields 
it  more  abundantly,  consists  in  distilling  oxalic  acid  with  enough  glycerine 
to  cover  it,  when  it  is  resolved  into  carbonic  acid  gas  and  formic  acid  ; 
HgCgO^  {Oxalic  acid)  —  HCHO2  {Formic  acid)  +  COg. 

The  glycerine  appears  to  act  by  producing  an  unstable  compound  with 
the  formic  acid  (analogous  to  the  stearines  and  acetines,  see  p.  565)  which 
is  afterwards  decomposed.  The  solution  thus  obtained  contains  75  per 
cent,  of  formic  acid.  If  dried  oxalic  acid  be  heated  in  the  aqueous 
formic  acid,  and  the  solution  allowed  to  crystallise,  the  oxalic  acid  retains 
the  water,  and  when  the  liquid  is  decanted  from  the  crystals  and  distilled, 
pure  formic  acid  is  obtained,  and  may  be  crystallised  at  a  low  temperature. 

But  the  most  remarkable  method  of  obtaining  formic  acid  is  that  in 
which  it  is  formed  from  inorganic  materials.  When  formic  acid  is  heated 
with  strong  sulphuric  acid,  it  is  resolved  into  water  and  carbonic  oxide, 
HCHO2  =  HgO  +  CO.  It  might,  therefore,  be  expected  to  be  reproducible 
by  the  combination  of  those  two  substances,  and  accordingly,  if  moistened 
caustic  potash  be  heated  for  some  hours  to  212°  F.  in  a  flask  filled  with 
carbonic  oxide,  the  gas  is  absorbed,  and  potassium  formiate  produced,  from 
which  the  formic  acid  may  be  obtained  by  distillation  with  diluted  sulphuric 
acid ;  KHO  +  CO  =  KCHO2  {Potassium  formiate). 

This  is  a  far  simpler  example  of  the  synthesis  of  an  organic  compound 
from  inorganic  materials  than  that  of  the  acetic  acid  above  referred  to, 
and  since  the  carbonic  oxide  may  be  prepared  by  heating  barium  carbonate 
with  metallic  iron,  this  method  of  synthesis  is  quite  independent  of  any 
organic  source  of  carbon.  Sodium  ethylate,  !N"aC2H50,  also  absorbs 
oaibonic  oxide,  ionning  soditim  etkpl-formiate  NaC(C2H5)02,  isomeric  with 
sodium  propionate,  a  little  of  this  salt  also  being  formed. 


FURFUROLE — BUTYRIC  ACID.  569 

In  properties,  formic  acid  bears  a  great  general  resemblance  tp  acetic 
acid,  but  has  a  more  powerful  action  upon  the  skin  when  in  the  concen- 
trated form.  It  is  employed  in  the  manufacture  of  one  of  the  blue  colours 
derived  from  coal-tar. 

Furfurole  or  furfural  (CgH402),  or  oil  of  ants,  accompanies  the  fonnic  acid  ob- 
tained by  distilling  amylaceous  matters  with  manganese  dioxide  and  sulphuric  acid. 
It  is  prepared  in  quantity  by  distilling  bran  (freed  from  starch  and  gluten  by  steep- 
ing in  a  cold  weak  solution  of  potash)  with  half  its  weight  of  sulphuric  acid  (pre- 
viously diluted  with  an  etpial  bulk  of  water),  a  current  of  steam  being  forced  through 
the  mixture  ;  the  furfurole  distils  over  with  the  water,  from  which  it  may  be  sepa- 
rated by  fractional  distillation.  Furfurole  has  also  been  obtained  by  the  action  of 
steam  at  100  lbs.  pressure  upon  wood.  It  is  a  colourless  oily  substance,  smelling  of 
bitter  almonds,  becoming  brown  when  exposed  to  the  air,  and  but  slightly  soluble  in 
water.  Strong  sulphuric  acid  dissolves  it  to  a  purple  liquid,  from  which  water  pre- 
cipitates it  unchanged.  Furfurole  resembles  the  aldehydes  in  its  property  of  reducing 
silver  oxide,  and  in  forming  a  crystalline  compound  with  sodium  disulphite.  It  is 
convertible  by  oxidation  into  pyromucic  acid  (C5H4O3),  the  acid  obtained  by  distil- 
ling the  mucic  acid  derived  from  the  oxidation  of  gum  or  milk-sugar.  The  systematic 
name  for  furfurole,  therefore,  would  he  pyromucic  aldehyde. 

Just  as  oil  of  bitter  almonds  (benzoic  aldehj'de),  when  acted  on  by  ammonia,  is 
converted  into  hydrobenzamide,  so  furfurole  yields  furfirainide — 

SC^H/)  {Oil  of  bitter  almonds)  -I-2XH3  =  C^^Yi.i^2{Hydrobenmmide)  -hSHaO 
3C5H4O2  (F^«r/Mro^e)  -f-  2NH3  =  C^^Yi-^^^ ^0^  (Furfxiraviide)  +  SHgO. 

And,  just  as  hydrobenzamide,  when  boiled  with  solution  of  potash,  j-ields  the  iso- 
meric base  amarine  or  benzoline  (CjiHigNo),  so  furfuramide  when  boiled  with  pota.sh 
gives  furf}tri7ie  (C15H12N2O3),  which  is  isomeric  with  it. 

Butyric  add  (HC4H7O.,)  is  found  not  only  in  rancid  butter,  but  in 
the  juice  of  muscular  flesh,  and  is  a  frequent  product  of  fermentation. 
Indeed,  the  best  mode  of  obtaining  this  acid  consists  in  exciting  fermen- 
tation in  sugar  by  contact  with  cheese;  the  liquid  soon  becomes  acid,  in 
consequence  of  the  formation  of  lactic  acid  (the  acid  of  sour  milk),  and  if 
it  be  neutralised  from  time  to  time  with  chalk,  this  fermentation  continues 
until  the  whole  is  converted  into  a  pasty  crystalline  mass  of  calcium 
lactate  Ca(C3ll503)2.  The  formation  of  lactic  acid  from  sugar  becomes 
intelligible  on  comparing  the  formulae — 

1  molecule  cane-sugar,  0^211^20^^ ;  4  molecules  lactic  acid,  C^^S-^^Oy^' 

After  a  time  the  mass  becomes  more  fluid,  at  the  same  time  evolving 
bubbles  of  gas,  which  contain  carbonic  acid  gas  and  hydrogen,  for  the 
calcium  lactate  is  undergoing  a  fermentation,  by  which  it  is  converted 
into  butyrate — 

2Ca(C3H503)2  -t-  H.2O  =  Ca(C4H.02)2  +  CaCOg  +  3CO2  +  Hg. 

Calcium  lactiite."  "  Calcium  butyrate. 

By  distilling  the  butyrate  with  dilute  hydrochloric  acid,  an  aqueous  solu- 
tion of  butyric  acid  is  obtained,  and  on  saturating  this  with  calcium 
chloride,  the  acid  collects  as  an  oily  layer  upon  the  surface.  It  is  remark- 
able for  its  powerful  odour  of  rancid  butter.* 

Synthetical  formation  of  acids  of  the  acetic  series. — By  a  very  remark 
able  process  of  substitution,  butyric  acid  has  been  derived  from  acetic 
acid.     When  sodium  is  heated  with  acetic  ether,  it  is  gradually  dissolved, 
and  the  liquid  solidifies,   on   cooling,   to  a  crystalline  mass  containing, 

*  Butyric  acid  and  some  of  its  homologues  (as  valerianic  and  caproic)  appear  to  be  present 
in  the  perspiration  of  the  skin,  and  to  cause  the  disagreeable  odour  of  close  rooms. 


570  SYNTHESIS  OF  ACIDS  OF  THE  ACETIC  SERIES. 

among  o^her  products,  sodacetic  ether,  or  acetic  ether,  in  which  1  atom  of 
the  hydrogen  has  been  displaced  by  sodium.  The  reaction  appears  to 
take  place  in  two  stages — 

(1)  3(C2H5.C2H30.0)  +  Na^  =  3(C2H5.Na.O)  +  :N'a(C2H30)3 

Acetic  ether.  Sodium-alcohol.  Sodium-triacetyle. 

(2)  CHsNaO  +  C2H5.C2H3O.O  =  C2H5.H.O  +  C2H5.C2(H2Na)0.0 

Sodium-alcohol.  Acetic  ether.  Alcohol.  Sodacetic  ether. 

l>y  digesting  the  sodacetic  ether  with  ethyle  iodide  for  several  hours  in 
a  close  vessel,  at  212°  F.,  the  atom  of  sodium  is  exchanged  for  ethyle,  and 
ethacetic  etlier,  or  butyric  ether,  is  produced — 

C2HvC2(H2Na)02  +  C2H5I  =  Nal  +  C2H5.C2H2(C2H5)02 

Sodacetic  ether.  Ethyle  iodide.  Ethacetic  or  butyric  ether. 

From  this  ether  the  ethacetic  acid,  €2113(02115)02,  has  been  prepared,  and 
found  to  be  identical  with  butyric  acid,  C4H8O2.  The  connexion  thus 
established  between  butyric  acid  and  the  ethyle  series  helps  to  explain 
the  production  of  that  acid  in  the  fermentation  of  sugar. 

But  butyric  ether  has  also  been  obtained  by  another  process.  The 
substitution  of  sodium  for  hydrogen  in  acetic  ether  may  extend  to  2 
atoms  of  hydrogen,  and  if  the  disodacetic  ether  so  produced  be  digested 
with  methyle  iodide,  butyric  ether  is  obtained — 

C2H5.C2(HXa2)02  +  2CH3I  =  2NaI  +  C2n5.C2H(CH3)202 

Disodacetic  ether.  Methyle  iodide.  Dimethacetic  or  butyric  etlier. 

So  that  butyric  acid  may  be  regarded,  according  to  the  method  by  which 
it  is  produced,  either  as  ethacetic  acid,  formed  from  acetic  acid  by  the 
substitution  of  an  atom  of  ethyle  for  one  of  hydrogen,  or  as  dimethacetic 
acid,  resulting  from  the  substitution  of  two  atoms  of  methyle  for  two  of 
hydrogen. 

When  disodacetic  ether  is  acted  on  by  ethyle  iodide,  it  yields  dieth- 
acetic  ether — 

C2H5.C2HNa202  +  2C2H5I  =  2NaI  +  C2H5.C2H(C2H5)202 

Disodacetic  ether.  Ethyle  iodide,  Diethacetic  ether. 

This  ether  has  an  odour  resembling  peppermint,  and  its  composition  is 
the  same  as  that  of  caproic  ether  C^^.G^-^^O^;  but  the  diethacetic  acid 
prepared  from  it,  though  isomeric  with  caproic  acid  (CgHj202),  is  not 
identical  with  it. 

The  acid  next  in  the  series,  cenanthic  (HC7Hj30)2,  may  be  obtained 
from  the  ether  produced  by  the  action  of  amyle  iodide  upon  sodacetic 
ether;  C2H5.C2(H2Na)02  +  C^B.^,!  -  Nal  +  C2H5.C2H2(C5Hii)02. 

Sodacetic  ether.  Amyle  iodide.  Arayl-acetic  ether. 

From  this  ether,  the  amyl-acetic  acid,  H. €2112(0511^^)02,  which  appears 
to  be  identical  with  cenanthic  acid,  has  been  obtained. 

These  reactions  help  to  explain  the  production  of  several  of  the  alcohols 
corresponding  to  the  acetic  series  of  acids,  during  the  fermentation  of 
grape  husks  (marc  of  the  wine-press). 

Among  the  products  of  the  action  of  sodium  and  ethyle  iodide  upon  acetic  ether,  is 
a  Hijuid  having  the  composition  C8H14O3,  which  when  distilled  with  barium  hydrate 
yields  dhylatcd  acetone,  €3115(02115)0,  isomeric  with  propione;  CoHi40o4-Ba(HO)2 
=  CgHioO  -f  CaHgO  +  BaCOg. 

Another  liquid  produced  by  the  action  of  ethyle  iodide  upon  disodacetic  ether  has 
tlie  composition  CjoHjgOg,  which  furnishes  diethylated  acetone,  C3H4(C2Hb)20,  when 
distilled  with  baryta  water  ;  CioHi803-fBa(HO)2  =  C7Hi40-f  CoHfiO  +  BaCOg. 

Diethylated  acetone  is  a  liquid  smelling  of  camphor,  and  boiling  at  280"  F.     It  is 


VALERIANIC  ACID.  571 

isomeric  with  butyrone,  •which  boils  at  290°  F.,  and  with  oenanthic  aldehyde  or 
oenanthole,  which  boils  at  312°  F. 

By  treating  acetic  ether  with  sodium  and  methylic  iodide,  the  corresponding 
methylated  acetones  may  be  obtained. 

Methylated  acetone,  C3Hg(CH3)0,  has  the  odour  of  chloroform,  and  is  identical  with 
the  ethyl-acetyle,  C2H3O.C2H5,  obtained  by  the  action  of  zinc-ethyle  upon  acetyle 
chloride. 

Dimethylated  acetone,  03114(0113)20,  has  an  odour  of  parsley. 

Valerianic  add  (H.CgHgOo)  derives  interest  from  the  circumstance 
that  some  of  its  salts,  particularly  the  zinc  valerianate,  are  used  medi- 
cinally. This  acid  is  found  in  valerian  root  and  in  the  berries  of  the 
guelder-rose.  It  is  one  cause  of  the  peculiar  odour  of  decaying  cheese, 
and  of  whale  and  seal  oils. 

Artificially,  it  is  best  obtained  by  distilling  fousel  oil  (amylic  alcohol, 
CjH^gO)  ^vith  sulphuric  acid  and  potassium  dichromate,  when  the  oxygen 
of  the  chromic  acid  converts  part  of  the  amylic  alcohol  into  valerianic 
acid;  CjH^g^  {Fousel  oil)  +  Og  =  CjH^^jOg  ( Valerianic  acid)  +  HgO. 

The  distilled  liquid  is  really  a  mixture  of  valerianic  acid  and  amyle 
valerianate  (CjH^j.CjHgOg),  but  when  treated  with  caustic  potash,  the 
latter  is  decomposed,  yielding  fousel  oil  and  potassium  valerianate — - 

C5H11.C5H9O2  -I-  KHO  =  C5H11.HO  -I-  KC^H^Og 

Amyle  valerianate.  Fousel  oil.       Potassium  valerianate. 

By  distilling  potassium  valerianate  with  sulphuric  acid,  the  valerianic 
acid  is  obtained  as  an  oily  liquid  of  very  remarkable  odour,  which  recalls 
that  of  butyric  acid. 

406.  The  separation  of  the  volatile  acids  belonging  to  the  acetic  series 
is  a  problem  which  frequently  presents  itself  to  the  chemist,  and  is 
effected  by  a  very  instructive  process  of  partial  saturation,  founded  upon 
the  principle,  that  when  a  mixture  containing  two  acids  with  different 
boiling-points  is  partially  neutralised  by  an  alkali  and  distilled,  the  more 
volatile  of  the  two  acids  {i.e.,  that  having  the  lower  boiling-point)  will 
pass  over,  whilst  the  other  remains  in  combination  with  the  alkali. 

In  applying  this  method,  for  example,  to  a  mixture  of  valerianic  acid 
(boiling  at  347°  F.)  and  butyric  acid  (boiling  at  315°  F.),  in  unknown 
proportions,  the  liquid  would  be  divided  into  two  equal  parts,  one  of 
which  would  be  exactly  neutralised  with  potash  and  then  distilled  to- 
gether with  the  other  half.  If  there  were  just  enough  valerianic  acid  to 
combine  with  the  potash,  pure  potassium  valerianate  would  be  left  in  the 
retort,  and  the  more  volatile  butyric  acid  would  pass  over.  If  there  were 
more  valerianic  acid  than  would  be  required  to  combine  with  the  potash, 
the  excess  of  that  acid  would  distil  over,  together  with  the  butyric  acid, 
whilst  potassium  valerianate  alone  would  be  left  in  the  retort.  By  distil- 
ling this  salt  with  sulphuric  acid,  the  pure  valerianic  acid  would  be  ob- 
tained, and  the  separation  of  the  rest  of  the  valerianic  from  the  butyric 
acid  would  be  effected  by  one  or  two  repetitions  of  the  process. 

If  the.  valerianic  acid  present  in  the  mixture  were  not  in  sufficient 
quantity  to  combine  with  the  potash  added,  then  potassium  butyrate,  as 
well  as  valerianate,  would  be  left  in  the  retort,  and  pure  butyric  acid  would 
distil  over.  By  distilling  the  mixture  of  potassium  valerianate  and  buty- 
rate with  sulphuric  acid,  a  mixture  of  the  two  acids  would  be  obtained 
which  would  require  a  repetition  of  the  process.  In  any  case,  it  will  be 
observed  that  this  process  must  yield  one  of  the  acids  in  a  state  of  purity. 


572  CHEMISTRY  OF  SOAP. 

The  same  principle  applies  to  the  separation  of  three  or  more  volatile 
acids,  but  the  process  involves,  of  course,  a  greater  number  of  distillations. 

407.  Soap. — The  manufacture  of  soap  affords  an  excellent  instance  of 
a  process  which  was  in  use  for  centuries  before  anything  was  known  of 
the  principles  upon  which  it  is  based,  for  it  was  not  till  the  researches  of 
Chevreul  were  published,  in  1813,  that  any  definite  ideas  were  entertained 
with  respect  to  the  composition  of  the  various  fats  and  oils  from  which 
soaps  are  made. 

The  investigations  of  Chevreul  are  conspicuous  among  the  labours 
which  have  contributed  in  so  striking  a  manner  to  the  rapid  advancement 
of  chemistry  during  the  present  century ;  undertaken  when  the  chemistry 
of  organic  substances  had  scarcely  advanced  beyond  the  dignity  of  an  art, 
when  the  principles  of  classification  were  almost  entirely  empirical,  and 
hardly  any  research  had  been  published  which  would  serve  as  a  model, 
these  researches  reflect  the  remarkable  sagacity  and  accuracy  of  their  author. 

The  sense  of  our  obligation  to  this  eminent  chemist  is  further  increased, 
when  we  remember  that  the  ultimate  analysis  of  organic  substances  w^as 
then  eff"ected  by  a  very  difficult  and  laborious  process,  whilst  the  doctrine 
of  combining  proportions  was  so  imperfectly  understood,  that  it  could 
afford  but  little  assistance  in  confirming  or  interpreting  the  results  of 
analysis. 

All  soaps  result  from  the  action  of  the  alkalies  upon  the  oils  and  fats. 

In  the  manufacture  of  soap,  potash  and  soda  are  the  only  alkalies  em- 
ployed, the  former  for  soft,  the  latter  for  hard  soaps. 

The  fatty  matters  employed  by  the  soap-maker  are  chiefly  tallow,  palm 
oil,  cocoa-nut  oil,  and  kitchen  stuff,  for  hard  soaps,  and  seal  oil  and  whale 
oil  for  soft  soaps. 

In  the  manufacture  of  hard  soap,  the  alkali  is  prepared  by  decomposing 
or  caustifying  sodium  carbonate  (soda-ash)  with  slaked  lime,  iN^agCOg 
-l-Ca{HO)2  =  CaC03+ 2NaH0,  the  clear  solution  of  sodium  hydrate,  or 
soda-leij,  being  drawn  off"  from  the  insoluble  calcium  carbonate. 

The  tallow  is  at  first  boiled  with  a  weak  soda-ley,*  because  the  soap 
which  is  foi-med  is  insoluble  in  a  strong  alkaline  solution,  and  would 
enclose  and  protect  a  quantity  of  undecomposed  tallow;  in  proportion 
as  the  saponification  proceeds,  stronger  leys  are  added,  until  the  whole 
of  the  grease  has  disappeared.  In  order  to  separate  the  soap  which  is 
dissolved,  advantage  is  taken  of  the  insolubility  of  soap  in  solution  of  salt; 
a  quantity  of  common  salt  being  thrown  into  the  boiler,  the  soap  rises  to 
the  surface,  when  the  spent  ley  is  drawn  off"  from  below,  and  the  soap 
transferred  to  iron  moulds  that  it  may  harden  sufficiently  to  be  cut  up 
into  bars. 

In  order  to  understand  the  chemistry  of  this  process,  it  is  necessary  to 
know  that  tallow  contains  two  fatty  substances,  one  of  which  steaj-mef 
(Cj,-HjjQOg),  is  solid,  and  the  other,  oleine  (Cg^Hjo^Og),  liquid,  the  quantity 
of  stearine  being  about  thrice  that  of  oleine. 

^Vhen  these  fats  are  acted  upon  by  soda,  they  undergo  decomposition, 
furnishing  stearic  and  oleic  acids,  which  combine  with  the  soda  to  form 
soap,  whilst  a   peculiar  sweet    substance,  termed  glyc&rine,  passes   into 

*  Soap  is  now  sometimes  made  by  the  action  of  the  sodium  carbonate  upon  the  fat,  thus 
saving  the  expense  of  caustifying  (Morfit's  process). 
+  ^reap,  talUnv. 


ACTION  OF  ALKALIES  ON  FATS.  573 

solution;  the  nature  of  the  decomposition  in  each  case  will  be  understood 
from  the  following  equations  : — 

C3H,.(C,sH3,0)3.03  +  3XaH0  =  3Xa(C,3H3,0)0  +  C3H3O3, 

Steariiie.  Sodium  stearate.  Glycerine. 

C3H,.(CjsH330)3.03  +  3XaH0  =  3Xa(C,3H330)0  +  C3HSO3 , 

Oleine.  Sodium  oleate.  Glycerine. 

so  that  the  soap  obtained  by  boiling  tallow  with  soda  is  a  mixture  of  the 
sodium  stearate  with  about  a  third  of  its  weight  of  sodium  oleate  and 
20  to  30  per  cent,  of  water. 

Palm  oil  is  composed  chiefly  of  palmitine  (Cg^H^gOg),  a  solid  fat  which 
is  resolved,  by  boding  with  soda,  into  sodium  palmitate  (pahn  oil  soap) 
and  glycerine — 

C3H,.(C,,H3,0)303  +  3NaH0  =  m^{C;,B.,,0)0  +  C3H3O3. 

Palmitine.  Sodium  palmitate.  Glyceiine. 

In  the  fish  oils  the  predominant  constituent  is  oleine,  so  that  when 
boiled  with  potassium  hydrate,  they  yield  potassium  oleate  (KCJ8H33O2), 
which  composes  the  chief  part  of  soft  soap. 

Castile  soap  is  made  from  olive  oil,  which  contains  oleine  and  a  solid  fat 
known  as  margarine.  The  latter  appears  to  be  really  composed  of  palmi- 
tine and  stearine,  so  that  the  Castile  soap  is  a  mixture  of  oleate,  palmitate, 
and  stearate  of  sodium. 

The  peculiar  appearance  of  mottled  soap  is  caused  by  the  irregular  dis- 
tribution of  a  compound  of  the  fatty  acid  with  oxide  of  iron,  which 
arranges  itself  in  veins  throughout  the  mass.  If  the  soap  contained  too 
much  water,  so  as  to  render  it  very  fluid  when  transferred  to  the  moulds, 
this  iron  compound  would  settle  down  to  the  bottom,  leaving  the  soap 
clear,  so  that  the  mottled  appearance  is  often  regarded  as  an  indication 
that  the  soap  does  not  contain  an  undue  proportion  of  water ;  it  is  imi- 
tated, however,  by  stirring  into  the  pasty  soap  some  ferrous  sulphate  and 
a  little  impure  ley  containing  sodium  sulphide,  so  as  to  produce  the  dark 
sulphide  of  iron  by  double  decomposition.* 

In  the  manufacture  of  yellow  soap,  in  addition  to  tallow  and  palm  oil, 
a  considerable  proportion  of  common  rosin  (see  page  476)  is  added  to  the 
soap  shortly  before  it  is  finished. 

Soft  soap  is  not  separated  from  the  water  by  salt  like  hard  soap,  but  is 
evaporated  to  the  required  consistency. 

Transparent  soaps  are  obtained  by  drying  hard  soap,  dissolving  it  in  hot 
spirit  of  wine,  and  pouring  the  strong  solution  into  moulds  after  the  greater 
part  of  the  spirit  has  been  distilled  ofi". 

Silicated  soap  is  a  mixture  of  soap  with  silicate  of  soda. 

Glycerine  soap  is  prepared  by  heating  the  fat  with  alkali  and  a  little 
water  to  about  400°  F.  for  two  or  three  hours,  and  running  the  mass  at 
once  into  moulds.     It  is,  of  course,  a  mixture  of  soap  and  glycerine. 

The  proportion  of  water  in  soaps  is  very  variable,  some  specimens  con- 
taining between  70  and  80  per  cent.  The  smallest  proportion  is  about  30 
per  cent. 

The  theory  of  saponification,  stated  above,  has  received  the  strongest 
confirmation  within  the  last  few  years,  by  the  synthetic  production  of  the 
fats  from  glycerine  and  the  fatty  acids  formed  in  their  saponification. 

*  A  soap  which  contains  much  more  than  30  per  cent,  of  water  is  said  not  to  admit  of 
mottling. 


574  STEARIC  AND  OLEIC  ACIDS. 

Preparation  of  the  fatty  acids. — All  the  soaps,  when  mixed  with  acids, 
undergo  decomposition,  their  alkalies  combining  with  the  acid  added, 
whilst  the  fatty  acids  separate,  either  in  the  solid  form  (in  the  case  of 
stearic  and  palmitic  acids),  or  as  an  oily  liquid  (in  the  case  of  oleic  acid). 
Thus,  if  soap  obtained  by  boiUng  tallow  with  soda  be  dissolved  in  hot 
water,  and  mixed  with  an  excess  of  tartaric  acid,  an  oil  rises  to  the  surface 
Avhich  concretes  into  a  buttery  mass  on  cooHng.  This  mass,  composed  of 
stearic  and  oleic  acids,  is  submitted  to  pressure  in  order  to  separate  the 
greater  part  of  the  liquid  oleic  acid,  and  the  stearic  acid  which  is  left  is 
purified  by  crystallisation,  first  from  alcohol,  and  afterwards  from  ether. 

Stearic  acid  is  thus  obtained  in  transparent  colourless  plates  which  have 
the  composition  HC18H35O.2 ;  they  are,  of  course,  insoluble  in  water,  but 
dissolve  in  hot  alcohol,  the  solution  being  acid  to  test-papers. 

By  repeated  distillation  under  pressure,  stearic  acid  is  completely  de- 
composed into  HgO  and  COg,  and  hydrocarbons  of  the  parafiin  (C„H2„  g) 
and  olefine  CpH^n)  series. 

All  the  stearates  are  insoluble  in  water  except  those  of  the  alkalies,  so 
that  if  a  solution  of  common  soap  (containing  sodium  stearate)  be  mixed 
with  a  solution  of  calcium  or  magnesium,  a  stearate  of  calcium  or  mag- 
nesium is  separated  in  the  insoluble  form,  and  it  will  be  remembered  that 
this  decomposition  of  soap  is  produced  by  the  action  of  hard  waters 
(page  45). 

408.  Canbles. — Since  tallow  fuses  at  about  100°  F.,  and  stearic  acid 
not  below  159°,  it  is  evident  that,  independently  of  other  considerations, 
the  latter  would  be  better  adapted  for  the  manufacture  of  candles,  for  such 
candles  would  never  soften  at  the  ordinary  atmospheric  temperature  in 
any  climate,  and  would  have  much  less  tendency  to  gutter  in  consequence 
of  the  excessive  fusion  of  the  fuel  around  the  base  of  the  wick.  The 
gases  furnished  by  the  destructive  distillation  of  stearic  acid  in  the  wick 
of  the  candle  burn  with  a  brighter  flame  than  those  produced  from  taUow. 
Accordingly  the  manufacture  of  stearine  (or  more  correctly,  stearic  acid) 
candles*  has  now  become  a  very  important  and  instructive  branch  of 
industry. 

The  original  method  of  separating  the  stearic  acid  from  tallow  on  the 
large  scale  consisted  in  mixing  melted  tallow  with  lime  and  water,  and 
heating  the  mixture  for  some  time  to  212°  by  passing  steam  through  it. ' 

The  tallow  was  thus  converted  into  the  insoluble  stearate  and  oleate  of 
calcium,  which  was  drained  from  the  solution  containing  the  glycerine, 
and  decomposed  by  sulphuric  acid.  The  mixture  of  stearic  and  oleic  acids 
thus  obtained  was  cast  into  thin  slabs,  which  were  packed  between  pieces 
of  cocoa-nut  matting,  and  well  squeezed  in  a  hydraulic  press,  which  forced 
out  the  oleic  acid,  leaving  the  stearic  and  palmitic  acids  in  a  fit  state  for 
the  manufacture  of  candles. 

The  separation  of  the  solid  fatty  acids  from  tallow  and  other  fats  may 
also  be  effected  by  the  action  of  the  sulphuric  acid,  a  process  extensively 
applied  in  this  country  to  palm  and  cocoa-nut  oils.  These  fats  are  mixed 
in  copper  boilers  with  about  one-sixth  of  their  weight  of  concentrated  sul- 
phuric acid,  and  heated  by  steam  to  about  350°  F.  for  some  hours,  when 
jtart  of  the  glycerine  is  converted  into  sulphoglyceric  acid  (CgHgOg.SOg), 
and  the  remainder  is  decomposed  by  the  sulphuric  acid,  carbonic  and  sul- 

*  Composite  candles  are  made  of  a  mixture  of  stearic  and  palmitic  acids. 


DECOMPOSITION  OF  FATS  BY  SULPIIUEIC  ACID.  575 

phiirous  acid  gases  being  disengaged,  whilst  a  dark-coloured  mixture  of 
palmitic,  stearic,  and  oleic  acid  is  left.  A  part  of  the  oleic  acid  becomes 
converted  in  this  process  into  elaidic  acid,  which  has  the  same  composition, 
but  differs  from  oleic  acid  in  fusing  at  about  113°  F.,  so  that  the  amount 
of  solid  acid  obtained  by  this  process  is  much  increased.  This  mixture  is 
well  washed  from  the  adhering  sulphuric  and  sulphoglyceric  acids,  and 
transferred  to  a  copper  still  into  which  a  current  of  steam  is  passed, 
which  has  been  raised  to  about  600°  F.  by  passing  through  hot  iron  pipes. 
These  fatty  acids  could  not  be  distilled  alone  without  decomposition,  but 
under  the  influence  of  a  current  of  steam  they  pass  over  readily  enough, 
leaving  a  black  pitchy  residue  in  the  retort,  which  is  employed  in  making 
black  sealing-wax,  and  for  other  useful  purposes. 

The  distilled  fatty  acids  are  broken  up  and  pressed  between  cocoa-nut 
matting  to  remove  the  oleic  acid. 

One  great  advantage  of  this  process,  which  is  commonly,  though  incor- 
rectly, styled  the  saponification  by  sulphuric  acid,  is  its  allowing  the  con- 
version of  the  worst  kinds  of  refuse  fat  into  a  form  fit  for  the  manufacture 
of  candles  ;  thus  the  fat  extracted  from  bones  in  the  manufacture  of  glue, 
and  that  removed  from  wool  in  the  scouring  process,  may  be  turned  to 
profitable  account. 

It  will  be  remarked  that  in  this  process  the  palmitic,  stearic,  and  oleic 
acids  are  formed  from  the  palmitine,  stearine,  and  oleine  existing  in  the 
fats,  by  the  assimilation  of  the  elements  of  water  and  the  subsequent 
separation  of  glycerine,  just  as  in  the  ordinary  process  of  saponification  by 
means  of  alkalies. 

Strictly  speaking,  the  action  appears  to  consist  of  two  stages ;  for  when 
concentrated  sulphuric  acid  is  allowed  to  act  upon  the  natural  fats  in  the 
cold,  it  combines  with  each  of  their  ingredients,  forming  the  acids  known 
as  sulphostearic,  sulphopalmitic,  sulpholeic,  and  sulphoglyceric,  which 
are  soluble  in  water,  though  not  (with  the  exception  of  the  last)  in  water 
containing  sulphuric  acid. 

The  second  stage  consists  in  the  decomposition  of  the  sulpho-fatty  acids 
by  the  high  temperature  in  contact  with  steam,  the  sulphoglyceric  acid 
having  been  in  great  measure  decomposed  into  secondary  products  before 
the  distillation  is  commenced. 

Within  the  last  few  years  the  extraction  of  the  solid  acids  from  the 
natural  fats  has  been  effected  by  a  process  known  as  saponification  by 
steam,  which  allows  the  glycerine  also  to  be  obtained  in  a  pure  state.  It 
is  only  necessary  to  subject  the  fat,  in  a  distillatory  apparatus,  to  the  action 
of  steam,  at  a  temperature  of  about  600°  F.,  to  cause  both  the  fatty  acids 
and  the  glycerine  to  distil  over;  the  former  may  be  separated  as  usual 
into  solid  and  liquid  portions  by  pressure,  whilst  the  glycerine,  which  is 
obtained  in  aqueous  solution  below  the  layer  of  fatty  acids,  is  concentrated 
by  evaporation,  and  sent  into  commerce  as  a  very  sweet  colourless  viscid 
liquid.  The  saponification  of  palmitine,  for  instance,  by  steam,  would  be 
represented  by  the  equation — 

C3H,.(C,,H3,0,)3  +  3H,0  =  3{K.C,,-a,,0,)  +  C3H,(HO)3. 

ralmitine.  Palmitic  acid.  Glycerine. 

409.  In  the  artificial  formation  of  natural  fats,  this  change  has  been 
reversed,  for  by  heating  3  molecules  of  stearic,  palmitic,  or  oleic  acid  with 
1  molecule  of  glycerine,  in  a  sealed  tube  for  several  hours,  to  about  500° 


576  SYNTHESIS  OF  NATURAL  FATS. 

F.,  3  molecules  of  water  are  eliminated,  and  stearine,  palmitine,  or  oleine 
is  produced. 

By  a  similar  process,  compounds  have  been  formed  from  glycerine  with 
1  and  2  molecules  of  the  fatty  acids,  so  that  we  are  acquainted,  in  the 
stearine   series,  for  example,  with — 

Stearic  add.  Glycerine. 


Monostearine, 

•    C21H42O4   = 

^18^36^2           + 

CgHgOg 

-       H2O 

Eistearine,     . 

•      CggHygOg      ^- 

2(Ci8H3602)     + 

CgHgOg 

-       2H2O 

Terstearine,  . 

'     ^b1^\\<p6  = 

3(C,8H3e02)   + 

CgHgOg 

-  SHgO 

The  last  representing  stearine  as  it  exists  in  the  natural  fats. 

Xor  is  it  only  with  the  fatty  acids,  properly  so  called,  that  glycerine 
will  furnish  glycerides,  as  these  bodies  are  termed,  similar  compounds 
having  been  obtained  with  acetic  and  benzoic  acids. 

By  heating  together  molecular  weights  of  glycerine  and  boracic  acid  as 
long  as  steam  is  evolved,  Barfi"  obtained  horo-glyceride  C3H5BO3  as  a  hard 
glacial  mass  soluble  in  water,  and  very  efficacious  for  preserving  milk  and 
flesh. 

The  hydrogen-acids  are  also  capable  of  acting  upon  glycerine  in  a  similar  manner. 
Thus,  when  glycerine  (CgHgOj)  is  acted  on  by  hydrochloric  acid,  an  oily  liquid, 
chlorhydrine  C3H5(H0)2C1  is  obtained. 

Dichlorhydrine  C3H5(HO)Cl2,  and  trichlorhydrine  (C3H5CI3),  have  also  been  ob- 
tained. 

By  the  action  of  silver  oxide  in  presence  of  water,  the  chlorhydrines  may  be 
reconverted  into  glycerine.  The  examination  of  these  chlorhydrines  has  pointed  out 
the  method  of  effecting  the  conversion  of  a  triatomic  alcohol  (glycerine)  into  a  diatomic 
alcohol  (glycol),  for  if  chlorhydrine  be  acted  on  by  sodium  dissolved  in  mercury,  in 
the  presence  of  water,  it  is  converted  into  the  glycol  of  propylene — 

C.,H6(H0).,C1   +   H2O   +   Naa  =  C3Hfi(HO)2  +   NaHO   +  NaCl . 
Chlorhydrine.  Propyl-glycol. 

This  tendency  of  glycerine  to  form  compounds  with  the  acids,  the 
formation  of  which  is  attended  (like  that  of  the  ethers  from  alcohol)  with 
separation  of  the  elements  of  water,  has  led  chemists  to  look  upon  glyce- 
rine as  an  alcohol — a  view  which  is  also  supported  by  its  combining  with 
sulphuric  and  phosphoric  acids  to  form  sulphoglyceiic  (€3115(110)211804 
and  phosphogbjcenc  acids,  just  as  alcohol  forms  sulphethylic  and  phos- 
phethylic  acids.  A  compound  has  even  been  obtained,  which  is  believed 
to  stand  to  glycerine  in  a  relation  similar  to  that  which  ether  bears  to 
alcohol ;  the  formula  of  this  glyceric  ether,  as  it  is  called,  is  (03115)203, 
differing  from  2  molecules  of  glycerine  (CgHjgOg)  by  the  elements  of  3 
molecules  of  water. 

Gylcerlc  aldehyde,  CgHgOg,  is  said  to  be  obtained  by  electrolysing  a 
mixture  of  glycerine  with  dilute  sulphuric  acid. 

Monosudium  glyceride  C^^^sS}^,  and  disodium  glyceride  CgHgNajOg, 
Lave  been  obtained  by  the  action  of  sodium  on  glycerine. 

The  formation  of  stearine  from  stearic  acid  and  glycerine  is  quite 
analogous  to  that  of  acetic  ether,  for  example,  from  acetic  acid  and  alcohol, 
as  will  be  seen  by  comparing  the  two  equations — 

H.C2Hg02  +     C2H5.HO  =     C2H5.C2Hg02  4   H2O 

Aceiic  acid.  Alcohol.  Acetic  ether. 

3(H.Ci,H3502)  +  CgH^.HgOg  =  C^^,.ZC,,U,,0,  +  3H2O. 

stearic  acid.  '"'1^^^!''  S'-'"^- 


GLYCEKINK  577 

The  only  difference  between  the  two  reactions  is,  that  in  the  latter,  3 
molecules  of  acid  are  concerned,  and  3  molecules  of  water  are  fonned, 
This  circumstance,  taken  together  with  some  other  features  of  glycerine, 
has  induced  those  chemists  who  consider  alcohol  as  formed  upon  the  type 
of  a  molecule  of  water,  to  look  upon  glycerine  as  derived  in  a  similar 
manner  from  3  molecules  of  water,  in  which  half  the  hydrogen  is  replaced 
by  the  triatomic  radical,  glycet^yle  (C3H5)'" ;  thus — 


Type, 


0 

Type, 

1:1^3 

0 

Glyceric  alcohol, 
or  glycerine, 

(C3H5)'" 
H3 

0 

Glyceric  ether, 

(C3H5)'" 
(C3H5)'" 

Alcohol,     .      ^^Hs  J  0  ...^|.«oc  »u;ouu.,  v^jris;     j  q^ 

Ether,        .     ^^^  \  0  Glyceric  ether,     ^^^Z^[.„  [  O3 

410.  Glycerine  is  obtained  on  the  small  scale  by  boiling  olive  oil  with 
litharge  and  water,  until  the  stearic,  oleic,  and  palmitic  acids  are  converted 
into  their  lead-salts  (lead  plaster),  which  are  insoluble,  whilst  the  glyce- 
rine, together  with  a  little  lead  oxide,  pass  into  solution.  The  lead  is 
precipitated  by  hydrosulphuric  acid,  and  the  filtered  liquid  concentrated 
by  evaporation. 

The  chief  uses  of  glycerine  as  an  application  to  the  skin,  and  a  remedy 
in  cases  of  deafness,  depend  itpon  its  oily  consistency,  and  its  want  of 
volatility,  which  preserves  surfaces  to  which  it  is  applied  in  a  moist  and 
supple  condition. 

Glycerine  boils  at  290°  C,  but  cannot  be  distilled  alone  without 
decomposition,  though  it  has  been  seen  to  be  capable  of  distillation 
in  a  current  of  highly  heated  steam,  Wheu  decomposed  by  distilla- 
tion, it  evolves  very  irritating  vapours  of  acrolelne  (CgH^O),  which 
is  a  constant  product  of  the  destructive  distillation  of  fats  containing 
glycerine,  and  gives  rise  to  the  peculiar  disgusting  odour  of  a  smouldering 
tallow  candle ;  composite  candles,  being  made  of  stearic  and  palmitic 
acid  (without  glycerine)  do  not  emit  this  odour  of  acroleine  when  blown 
out. 

Acroleine  is  obtained  in  the  pure  state  by  distilUng  glycerine  with 
phosphoric  anhydride,  which  removes  2  molecules  of  water  (CgHgOg 
-  2H2O  =  CgH^O).  It  may  also  be  prepared  by  strongly  heating  100  grms. 
of  glycerine  with  50  grms.  of  hydropotassic  sulphate,  in  a  1500  c.c.  flask, 
and  distilling  into  a  receiver  placed  in  ice.  It  is  a  colourless  liquid, 
distinguished  by  its  intensely  irritating  vapour,  which  affects  the  eyes 
very  strongly.  From  a  chemical  point  of  view  it  is  interesting,  as  being 
the  aldehyde  of  the  allyle  series  (see  p.  486),  and,  therefore,  another  link 
connecting  that  series  Avith  glycerine.  By  treatment  with  silver  oxide, 
acroleine  is  converted  into  acrylic  acid  (0311^0.2),  bearing  the  same  relation 
to  acroleine  (CgH^O)  that  acetic  acid  (CoH^O^)  bears  to  ordinary  aldehyde 
(CoH^O).  Allyle  iodide  and  ally  lie  alcohol  have  been  already  noticed 
(page  486). 

The  allyle  series,  therefore,  is  perfectly  parallel  with  the  ethyle 
series,  and  it  seems  very  probable  that  allylic  alcohol  is  a  member  of 
a  homologous  series  of  alcohols  having  the  general  formula  CHgnO, 
with  a  series  of  acids  corresponding  to  the  acetic  series,  but  having 
the  general  formula  C^Hgn-oOg,  of  which  the  following  members  are 
known : — 

2o 


578 


ACIDS  OF  THE  ACRYLIC  SERIES. 


Acrylic  Series  of  Adda. 


Add. 

Foi-mnld. 

Source. 

Acrylic,  . 

CjH.Oa 

Oxidation  of  acroleine. 

Crotonic, 

CjIlflOj 

Croton-seed  oil. 

Angelic, 

CjHsO, 

Angelica  root. 

Pyroterebic,    . 

CeHioOa 

Turpentine. 

Damaluric, 

C7H12O2 

Cow's  urine  {Sdfia\os,  a  calf). 

Campholic, 

CioHigOj 

Camphor. 

Cimicic, . 

*-'14"26^2 

Tree-bug. 

Moringic, 

^is^as^j 

Moringa  aptcra  (oil  of  ben). 

Hypogeic, 

f  CjbHjoOj 

1  Oil  of  ground  nut. 

Physetoleic,    . 

1  Sperm-whale  oil  (Physeter  macrocephalus). 

Oleic,      . 

t-'igH  34(^2 

Most  oils. 

Doeglic, 

C'lgHatjOj 

Doegling  train  oil. 

Brassic, 

1  C^jHi^Oa 

J  Mustard  seed  (fixed)  oil. 

Erucic,   . 

1  Colza  oil  {Brassica  oleifera). 

These  acids  are  monobasic,  their  salts  being  formed  by  the  replacement  of  1  atom 
of  hydrogen  by  a  metal.  Each  of  these  acids,  when  fused  with  potassium  hydrate, 
yields  potassium  acetate  together  with  the  potassium  salt  of  some  other  member  of 
the  acetic  series  ;  C3H4O2  (acrylic)  +2KHO  =  KC2H302  (acetate)  +  KCHOj  (formiate) 
+  H.2.  In  a  similar  way,  crotonic  acid  yields  two  molecules  of  the  acetate  ;  angelic 
yields  acetate  and  propylate  ;  oleic  yields  acetate  and  palmitate. 

The  following  table  exhibits  the  principal  members  of  the  allyle  series,  together 
with  the  corresponding  members  of  the  ethyle  series  : — 


Ethyle  Series. 


Ethyle, 
Ether, 

Alcohol,    .    . 
Ethyle  iodide, 
Acetic  ether. 
Aldehyde,    . 
Acetic  acid, 
Ethyle  sulphide, 
Triethylamine, 
Tetrethylium      hy- 
drate. 


CjHg.  C.jHj 

(CaHs).^ 

C^Hg.HO 

C2H5.  C2H3O2 

C2H4O 

C.H^O^ 

(C2H.,)2S 

N(C2HJ3 
N(C„H5)4.HO 


Allyle, 
Allylic  ethei', 
AUylic  alcohol, 
Allyle  iodide,     . 
Allyle  acetate,   . 
Allyle  aldehyde, 
Acrylic  acid, 
Allyle  sulphide, 
Triallylarnine,    . 
Tetrallylium  hy 
drate, 


Allyle  Series. 

C3HS.HO 

C3H5.C2H3O2 

C3H4O  (acroleine) 

C3H4O2 

(03115)28  (oil  of  garlic) 

N(C3H5)3 

N(C3H3)4.HO. 


It  has  been  seen  (page  486)  that  glycerine,  when  distilled  with  Pig 
yields  allyle  iodide  (C3H5I).  When  this  liquid  is  treated  with  bromine, 
it  yields  a  crystallisable  allyle  tribromide,  CgH^Br^  ;  and  if  this  be  decom- 
l^osed  by  silver  acetate,  it  furnishes  the  glyceride  known  as  teracetine, 
thus — 


CgH.Brg 


+    SAgCHoO,   =    CoH,.3CoHoO.,    +    3AgBr 


Silver  acetate. 


Triacetine. 


3Ba(C2H302)2 

Barium  acetate. 


Allyle  tribromide. 

When  triacetine  is  submitted  to  the  action  of  barium  hydrate,  glycerine 
is  reproduced — 

2{C,^,.ZC.^f,^)   +   3Ba(HO)2   =    2C3H,(HO)3   + 

Triacetine.  Glycerine. 

This  affords  an  interesting  example  of  the  conversion  of  a  monatomic 
radical,  allyle  (C3II-)',  into  a  trialomic  radical,  glyceryle  (C3H5)'". 

Glycerine  may  be  obtained  from  propane  by  the  following  reactions  : — (1)  C3Hg 
(propane)  +Cl4  =  C3H6Cl2  (propene  dichloride)  +2HC1.  (2)  C3HfiC!,  +  ICl  =  C3HBCl3 
(glyoyle  trichloride)  +HI.     (3)  C3H5Cl3  +  3H20  =  C3H6(OH)3  (glycerine)  +3HC1. 

411.  A  very  interesting  chemical  similarity  has  been  pointed  out 
between  glycerine  and  mannite  (CgHj^Og).  It  will  be  remembered  that 
the  former  is  a  constant  product  of  the  alcoholic  fermentation,  and  the 


GLUCO-TARTARIC  ACID — NITROGLYCERINE.  579 

latter,  of  a  peculiar  kind  of  fermentation  (the  viscous),  to  which  saccha- 
rine liquids  are  subject. 

When  mannite  is  heated,  under  pressure,  with  the  acids  of  the  acetic 
series,  it  forms  compounds  corresponding  to  those  obtained  when  glycerine 
is  so  treated.     Thus,  with  stearic  acid — - 

Mannite.  Steailc  acid.  Mannite  steari:ie. 

But  it  will  be  observed  that  7  molecules  of  water  are  here  eliminated 
instead  of  3,  as  in  the  case  of  glycerine.  The  further  examination  of 
mannite  explains  this,  for  it  is  not  that  substance  which  is  the  true  ana- 
logue of  glycerine,  but  one  which  is  obtained  by  heating  mannite  to  400° 
F.,  when  it  loses  a  molecule  of  water,  and  is  converted  into  mannitane— 

Mannite.  Mannitane. 

This  mannitane  or  mannite-glycerine  is  a  viscous  substance,  presenting 
a  very  strong  resemblance  to  glycerine,  so  that  it  is  not  unlikely  to  have 
been  mistaken  for  this  substance  in  examining  some  of  the  natural  fats. 
The  manHite-glycerides,  or  compounds  formed  by  heating  mannite  with 
the  fatty  acids,  are  scarcely  to  be  distinguished  from  stearine,  palmitine, 
&c.      They  are  saponified  by  alkalies  in  exactly  the  same  manner. 

Cane-susar  and  grape-sugar  are  capable  of  forming  compounds  corre- 
sponding to  those  obtained  by  the  action  of  acids  upon  glycerine  and 
mannite.  Thus,  if  grape-sugar  be  heated  to  250°  f .  for  several  hours  in 
contact  with  stearic  acid,  it  is  converted  into  a  fusible  solid,  insoluble  in 
water,  but  soluble  in  alcohol  and  ether — 

C,H,A   +    2C,,H3,02  =   C4.H,A   -f    SH^O. 

fanlfymw^'.  Stearic  acid.  Stearic  glucose. 

When  grape-sugar  is  heated  with  tartaric  acid,  a  similar  reaction  takes 
place,  but  the  resulting  product  is  a  new  acid — 

QH,,0,   +   2HAHA  =   H^C.^Hj.Oi,   +   3H,0. 

GraiX'-snjrar  Tartaric  acid.  GUico-tartaric  add. 

(anhydrous). 

Cane-sugar  behaves  in  a  similar  manner. 

412.  Nitroglycerine  or  (jlonoine. — This  violently  explosive  substance  is 
very  easily  prepared  h^  dissolving  glycerine  in  a  mixture  of  equal  measures 
of  the  strongest  nitric  and  sulphuric  acids,  previously  cooled,  and  pouring 
the  solution  in  a  thin  stream  into  a  large  volume  of  water,  when  the 
nitroglycerine  is  precipitated  as  a  colourless  heavy  oil  (sp.  gr.  1'6).  It  is 
advisable  to  add  the  glycerine  to  the  mixed  acids  in  very  small  quantities 
at  a  time,  and  to  cool  the  mixture  in  a  vessel  of  water  after  each  addition. 
When  the  nitroglycerine  has  subsided,  the  water  may  be  poured  oiF,  and 
the  oil  shaken  several  times  with  water,  so  as  to  wash  it  thoroughly. 

Nitroglycerine  is  the  nitric  ether  of  glycerine,  and  its  formation  is 
explained  in  the  following  eqnation — 

C.HsO^  -I-  3(HX03)  =  C.,H,(X03)3  +  Zn.ff . 

Glycerine.  Nitroglycerine. 

On  a  larger  scale,  a  mixture  of  concentrated  nitric  acid  (sp.  gr.  1  "47  to  1  '49)  with 
twice  its  weight  of  concentrated  sulphuric  acid  is  employed.  The  mixture  is  placed 
in  stone  jars  containing  about  7  lbs.  each,  which  are  immersed  in  running  water,  and 
about  1  ib.  of  glycerine  (sp.  gr.  l'2o)  is  gradually  added,  with  frequent  stirring,  to  the 
contents  of  each  jar,  care  being  taken  that  the  temperature  does  not  rise  above  80°  F. 


5  80  NITROGLYCERINE. 

The  mixture  is  allowed  to  settle  for  a  quarter  of  an  hour,  and  poured  gradually  into 
5  or  6  gallons  of  water.  The  oily  nitroglycerine  which  falls  to  the  bottom  is  well 
washed  by  stirring  with  water,  a  little  alkali  being  added  in  the  last  washings.  One 
per  cent,  of  magnesia  is  sometimes  added  to  the  nitroglycerine  in  order  to  neutralise 
any  acid  arising  from  decomposition. 

This  oil  is  very  violent  in  its  explosive  eflTects.  If  a  drop  of  nitro- 
glycerine be  placed  on  an  anvil  and  struck  sharply,  it  explodes  with  a 
very  loud  report,  even  though  not  free  from  water;  and  if  a  piece  of 
j^aper  moistened  with  a  drop  of  it  be  struck,  it  is  blown  into  small  frag- 
ments. On  the  application  of  a  flame  or  of  a  red  hot  iron  to  nitro- 
glycerine, it  burns  quietly ;  and  when  heated  over  a  lamp  in  the  open  air 
it  explodes  but  feebly.  In  a  closed  vessel,  however,  it  explodes  at  about 
360°  r.  with  great  violence.  For  blasting  rocks,  the  nitroglycerine  is 
poured  into  a  hole  in  the  rock,  tamped  by  filling  the  hole  with  water, 
and  exploded  by  the  concussion  caused  by  a  detonating  fuze  (see  page  512). 
It  has  been  stated  to  produce  the  same  effect  in  blasting  as  ten  times  its 
weight  of  gunpowder,  and  much  damage  has  occurred  from  the  accidental 
explosion  of  nitroglycerine  in  course  of  transport.  When  nitroglycerine 
is  kept,  especially  if  it  be  not  thoroughly  washed,  it  decomposes,  with 
evolution  of  nitrous  fumes  and  formation  of  crystals  of  oxalic  acid;  and 
it  may  be  readily  imagined  that,  should  the  accumulation  of  gaseous  pro- 
ducts of  decomposition  burst  one  of  the  bottles  in  a  case  of  nitroglycerine, 
the  concussion  would  explode  the  whole  quantity. 

Nitroglycerine,  like  gun-cotton,  is  particularly  well  fitted  for  blasting, 
because  it  will  explode  with  equal  violence  whether  moisture  be  present 
or  not,  but  it  has  the  advantage  of  containing  enough  oxygen  to  convert 
all  its  carbon  into  carbonic  acid  gas.  On  the  other  hand,  it  is  very 
poisonous,  and  is  said  to  affect  the  system  seriously  by  absorption  through 
the  skin,  and  the  gases  resulting  from  its  explosion  are  exceedingly  acrid. 
Again,  its  fluidity  prevents  its  use  in  any  but  downward  bore-holes.  To 
overcome  these  objections,  and  to  diminish  the  danger  of  transport,  several 
blasting  compounds  have  been  proposed,  of  which  nitroglycerine  is  the 
•basis. 

Dynamite  is  composed  of  a  particularly  porous  siliceous  earth  (Kiesel- 
(lufir),  obtained  from  Oberlohe  in  Hanover,  impregnated  with  about 
70  or  75  per  cent,  of  nitroglycerine. 

Kieselguhr  contains  63  per  cent,  of  soluble  silica,  about  1 8  of  organic 
matter,  11  of  sand  and  clay,  and  8  of  water.  It  is  incinerated  to  expel 
the  organic  matter,  and  mixed  with  the  nitroglycerine  in  wooden  troughs 
lined  with  lead. 

When  used  in  solid  rock,  dynamite  is  6  or  7  times  as  strong  as  blasting- 
powder. 

NuheVs  detonators  for  nitroglycerine  contain  7  parts  of  mercuric  ful- 
minate and  3  parts  of  potassium  chlorate,  pressed  into  small  copper  tubes. 

Fatal  accidents  have  occurred  in  using  dynamite,  in  consequence 
of  exudation  of  .nitroglycerine  from  the  dynamite,  caused  by  contact  with 
Avater  in  the  bore-holes;  this  nitroglycerine  having  been  afterwards 
exploded  by  the  drill  in  boring  fresh  holes. 

Glyoxyline  is  a  name  given  to  gun-cotton  pulp  and  saltpetre  mixed  with 
nitroglycerine.  Lithofradeur  is  a  more  complex  mixture  containing 
about  half  its  weight  of  nitroglycerine,  together  with  nitrate  of  soda, 
sulphur,  powdered  coal,  sawdust,  and  siliceous  earth.     Diialine  is  com- 


•    OILS  AND  FATS.  581 

posed  of  nitroglycerine  and  sawdust.  Nitromagnite  contains  nitroglycerine 
and  magnesia. 

Blasting  gelatine  is  made  by  dissolving  collodion-cotton  (p.  513)  in 
about  nine  times  its  weight  of  nitroglycerine;  its  detonation  is  even  more 
powerful  than  that  of  nitroglycerine  itself.  The  readiness  with  which  it 
may  be  exploded  by  a  detonating  fuze  charged  with  mercuric  fulminate  is 
greatly  increased  by  incorporating  it  with  about  one-tenth  of  its  weight 
of  gun-cotton.  On  the  other  hand,  its  liability  to  accidental  detonation 
may  be  reduced  by  intimately  mixing  it  with  a  small  proportion  of 
camphor,  the  action  of  which  does  not  appear  to  be  understood. 

Nitroglycerine  is  readily  soluble  in  ether  and  in  wood-naphtha,  but 
somewhat  less  so  in  alcohol;  it  is  reprecipitated  by  water  from  these  last 
solutions.  It  becomes  solid  at  40°  F.,  a  circumstance  which  is  unfavour- 
able to  its  use  in  mining  operations,  partly  because  it  is  then  less  sus- 
ceptible of  explosion  by  the  detonating  fuze,  and  partly  because  serious 
accidents  have  resulted  from  attempts  to  thaw  the  frozen  nitroglycerine 
by  heat,  or  to  break  it  up  with  tools.  It  is  remarkable  that  when  made 
on  the  small  scale,  the  nitroglycerine  may  generally  be  cooled  down 
to  0°  F.  without  becoming  hard.  This  and  other  observations  render 
it  probable  that  some  other  substitution  product  is  occasionally  mixed 
with  it. 

Nitroglycerine  C3H5(N03)3  stands  in  the  same  relation  to  the  triatomic  alcohol 
glycerine  C3Hb(HO)3,  in  which  nitric  ether  C2Hg(N03)  stands  to  ordinary  monatomic 
alcohol  C2Hg(H0).  Berthelot  finds  that,  in  the  lormation  of  nitric  ether  by  the  action 
of  nitric  acid  upon  alcohol,  5800  heat  units  are  disengaged  for  each  molecule  of  nitric 
acid  entering  into  the  reaction,  whereas,  in  the  formation  of  nitroglycerine,  only  4300 
heat  units,  per  molecule  of  nitric  acid,  are  disengaged.  Less  energy  having  been 
converted  into  heat  in  the  latter  case,  more  is  stored  up  in  the  nitroglycerine,  and 
hence  its  formidable  effect  as  an  explosive.  In  the  formation  of  gun-cotton,  each 
molecule  of  nitric  acid  disengaged  11,000  heat  units,  to  which  Berthelot  attributes 
the  stability  and  inferior  explosive  effect  of  guu-cotton  in  comparison  with  nitro- 
glycerine. 

Oils  and  Fats. 

413.  A  very  remarkable  feature  in  the  history  of  the  fats  is  the  close 
resemblance  in  chemical  composition  and  properties  which  exists  between 
them,  whether  derived  from  the  vegetable  or  the  animal  kingdom.  They 
all  contain  two  or  more  neutral  substances  which  furnish  glycerine  when 
saponified,  together  with  some  of  the  acids  of  the  acetic  series  or  of  series 
closely  allied  to  it. 

One  of  the  most  useful  vegetable  fatty  matters  is  palm  oil,  which  is 
extracted  by  boiling  water  from  the  crushed  fruit  of  the  Elais  guineerms, 
an  African  palm.  It  is  a  semi-solid  fat,  which  becomes  more  solid  when 
kept,  since  it  then  undergoes  a  species  of  fermentation,  excited  apparently 
by  an  albuminous  substance  contained  in  it,  in  consequence  of  which  the 
palmitine  (CsjHggOg)  is  converted  into  glycerine  and  palmitic  acid.  The 
bleaching  of  palm  oil  is  effected  by  the  action  of  a  mixture  of  sulphuric 
or  hydrochloric  acid  and  potassium  dichromate,  which  oxidises  the  yellow 
colouring  matter. 

Cocoa-nut  oil  is  also  semi-solid,  and  is  remarkable  for  the  number  of 
acids  of  the  acetic  series  which  it  yields  when  saponified,  viz.^  caproic, 
caprylic,  rutic,  lauric,  myristic,  and  palmitic. 

These  fats  are  chiefly  used  in  the  manufacture  of  soap  and  candles. 

iSalad  oil  or  sweet  oil  (olive  oil)  is  obtained  by  crushing  olives,  and  an 


582 


OXALIC  ACID  SERIES. 


inferior  kind  which  is  used  for  soap  is  obtained  by  boiling  the  crushed 
fruit  with  water.  When  exposed  to  a  temperature  of  about  32°  F.  a  con- 
siderable portion  of  the  oil  solidifies;  this  solid  portion  is  generally  called 
margarine  {C^jfi-^QiOQ) ;  it  is  much  less  soluble  in  alcohol  than  stearine, 
though  more  so  than  palmitine.  When  saponified,  margarine  yields 
glycerine  and  margaric  add  (C17H34O2).  This  acid  appears  to  be  really 
composed  of  stearic  and  palmitic  acids,  into  which  it  may  be  separated  by 
repeated  crystallisation  from  alcohol,  when  the  palmitic  acid  is  left  in 
solution.  The  fusing-point  of  margaric  acid  is  140°  F.,  that  of  stearic 
being  159°,  and  that  of  palmitic,  144°,  but  a  mixture  of  10  parts  of  pal- 
mitic with  1  part  of  stearic  acid  fuses  at  140°. 

That  portion  of  the  olive  oil  which  remains  liquid  below  32°  con- 
sists of  oldne  (Cg'^Hjo^O,-,),  and  forms  nearly  three-fourths  of  its  weight. 
Oleine  is  not  so  easily  saponified  as  the  solid  fats,  and  is  resolved  by 
that  process  into  glycerine  and  oleic  acid  (Cj8^34^2)>  '^^ich  differs  from  the 
other  fatty  acids  by  remaining  liquid  at  temperatures  above  40°  F.,  and 
by  absorbing  oxygen  from  the  air,  when  it  is  converted  into  a  new  acid 
which  is  not  solidified  by  cold. 

Oleic  acid  is  used  in  greasing  wool  for  spinning,  being  much  more 
easily  removed  by  alkalies  than  olive  oil,  which  was  formerly  employed. 
(31eate  of  ammonia  is  sometimes  employed  as  a  mordant  for  the  aniline 
dyes  on  cotton. 

The  characteristic  feature  of  oleic  acid  is  its  furnishing  a  solid  crys- 
tallised acid  when  submitted  to  destructive  distillation ;  this  acid  is  called 
sebacic  acid,  and  is  one  of  a  series  of  dibasic  acids,  most  of  the  other  mem- 
bers of  which  may  be  obtained  from  oleic  acid  by  the  action  of  nitric 
acid. 

Oxalic  Acid  SeHes  or  Dibasic  Fatty  Acid  Series. 


Acid. 

Formula. 

Source. 

Oxalic, 

Malonic, 

Succinic, 

Lipic,    . 

Adipic, 
1  Piinelic, 
1  Suberic, 

Anchoic,* 

Lepargylic,t 

Sebacic, 

C,H,04 
C3H4O4 

C5H8O4 

C6Hio04 
^  CgHi804 

C10H18O4 

Oxalis  acetosella  (wood  sorrel),  &c. 
Oxidation  of  malic  acid. 
Amber  (succinum). 
Oxidation  of  oleic  acid  (\liros,  fat). 

„                ,,         (adcps,fat). 

,,                 ,,          {ir7fie\-fi,  fat.). 
Oxidation  of  stearic  acid,  and  of  cork  {suber). 

Oxidation  of  Chinese  wax,  and  of  cocoa-nut  oil. 

Distillation  of  oleic  acid. 

The  normal  salts  of  the  acids  of  this  series  are  formed  by  the  displace- 
ment of  2  atoms  of  hydrogen  by  a  metal.  Thus,  potassium  succinate 
has  the  composition  04(114X2)04. 

It  is  worthy  of  remark,  that  nine  acids  of  the  series,  CJl^n^o  (from 
acetic  to  capric  inclusive),  are  found  among  the  products  of  the  action  of 
nitric  acid  upon  oleic  acid. 

It  is  well  known  that  salad  oil  becomes  rancid,  and  exhales  a  disagree- 
able odour  after  being  kept  for  some  time.  This  appears  to  be  due  to  a 
fermentation  similar  to  that  noticed  in  the  case  of  palm  oil,  originally 
started  by  the  action  of  atmospheric  oxygen  upon  albuminous  matters 

^       •  From  ayxio,  to  throttle,  from  its  suffocating  vapours. 
+  From  Xeirapyoi,  having  white  skvti. 


FIXED  OILS.  583 

present  in  the  oil;  the  neutral  fatty  matters  are  thus  partly  decomposed, 
as  in  saponification;  their  corresponding  acids  being  liberated,  and  giving 
rise  (in  tlie  case  of  the  higher  members  of  the  acetic  series,  such  as  caproic 
and  valerianic)  to  the  disagreeable  odour  of  rancid  oil.  By  boiling  the 
altered  oil  with  water,  and  afterwards  washing  it  with  a  weak  solution  of 
soda,  it  may  be  rendered  sweet  again. 

Almond  oil,  extracted  by  a  process  similar  to  that  employed  for  olive  oil, 
is  also  very  similar  in  composition;  but  colza  oil,  obtained  from  the  seeds 
of  the  Brassica  oleifera,  contains  only  half  its  weight  of  oleine,  and  hence 
solidifies  more  readily  than  the  others. 

Colza  oil  is  largely  used  for  burning  in  lamps,  and  undergoes  a  process 
of  purification  from  the  mucilaginous  substances  which  are  extracted  with 
it  from  the  seed,  and  leave  a  bulky  carbonaceous  residue  when  subjected 
to  destructive  distillation  in  the  wick  of  the  lamp.  To  remove  these,  the 
oil  is  agitated  with  about  2  per  cent,  of  oil  of  vitriol,  which  carbonises 
the  mucilaginous  substances,  but  leaves  the  oil  untouched.  When  the 
carbonaceous  flocks  have  subsided,  the  oil  is  drawn  off,  washed  to  remove 
the  acid,  and  filtered  through  charcoal. 

Linseed  oil,  obtained  from  the  seeds  of  the  flax  plant,  is  much  richer  in 
oleine  than  any  of  the  foregoing,  exhibiting  no  solidification  till  cooled 
to  15°  or  20°  F.  below  the  freezing-point.  It  exhibits,  however,  in  a  far 
higher  degree,  a  tendency  to  become  solid  when  exposed  to  the  air,  which 
has  acquired  for  it  the  name  of  a  drying  oil,  and  renders  it  of  the  greatest 
use  to  painters.  This  solidification  is  attended  with  absorption  of  oxygen, 
which  takes  place  so  rapidly  in  the  case  of  linseed  oil,  that  spontaneous 
combustion  has  been  known  to  take  place  in  masses  of  rag  or  tow  which 
have  been  smeared  with  it.* 

The  tendency  of  linseed  oil  to  solidify  by  exposure  is  much  increased  by 
heating  it  with  about  -^^th  of  litharge,  or  y^th  of  black  oxide  of  manganese ; 
these  oxides  are  technically  known  as  dryers,  and  oil  so  treated  is  called 
boiled  Unseed  oil.  The  action  of  these  metallic  oxides  is  not  well  under- 
stood. 

The  strong  drying  tendency  of  linseed  oil  is  supposed  to  be  due  to  a 
peculiarity  in  the  oleine,  which  is  said  not  to  be  ordinary  oleine,  but  to 
furnish  a  different  acid,  linoleic  acid,  when  saponified.  AVhen  linseed  oU  is 
exposed  for  some  time  to  a  high  temperature,  it  becomes  viscous  and  treacly, 
and  is  used  in  this  state  for  the  preparation  of  printing  ink.  If  the  viscous 
oil  be  boiled  with  dilute  nitric  acid,  it  is  converted  into  artificial  caout- 
chouc, which  is  used  in  the  manufacture  of  surgical  instruments.  This 
property  appears  to  be  connected  with  the  drying  qualities  of  the  oil. 

Castor  oil,  obtained  from  the  seeds  of  Ricinus  communis,  also  yields  a 
peculiar  acid  when  saponified,  termed  ricinoleic  (H-C^gllggOg),  containing 
one  more  atom  of  oxygen  than  oleic  acid,  which  it  much  resembles.  The 
destructive  distillation  of  castor  oil  yields  oenanthic  acid  (H.C^HjgOg)  and 
oenanthole  or  cenanthic  aldehyde  (C^-Hj^O),  and  by  distilling  it  mth  caustic 
potash,  caprylic  alcohol  (CgHjgO)  is  obtained.  As  in  the  case  of  olive  oil, 
the  cold  drawn  castor  oil,  which  is  expressed  from  the  seeds  without  the 
aid  of  heat,  is  much  less  liable  to  become  rancid.  Castor  oil  is  much 
more  soluble  in  alcohol  than  any  other  of  the  fixed  oils. 

*  During  the  oxidation,  a  volatile  compound  is  formed  which  resembles  acroleine  in 
smell,  and  colours  unsized  paper  brown.  It  has  been  suggested  that  the  brown  coloui 
and  musty  smell  of  old  books  may  be  due  to  the  oxidation  of  the  oil  in  the  printing-ink. 


584  SPERMACETI. 

The  various  fish  oils,  such  as  seal  and  whale  oil,  also  consist  chiefly  of 
oleine,  and  appear  to  owe  their  disagreeable  odour  to  the  presence  of  cer- 
tain volatile  acids,  such  as  valerianic. 

Cod-liver  oil  appears  to  contain,  in  addition  to  oleine  and  stearine,  a 
small  quantity  of  acetine  (CgH^^Og),  which  yields  acetic  acid  and  glycerine 
when  saponified.  Some  of  the  constituents  of  bile  have  also  been  traced 
in  it,  as  well  as  minute  quantities  of  iodine  and  bromine. 

Btitter  contains  about  two-thirds  of  its  weight  of  solid  fat,  which  consists 
in  great  part  of  margarine  (see  page  573),  but  contains  also  butine,  which 
yields  glycerine  and  butic  acid  (H.C20H39O2)  when  saponified.  The  liquid 
portion  consists  chiefly  of  oleine.  Butter  also  contains  small  quantities 
of  butyrine,  caproine,  and  caprine,  which  yield,  when  saponified,  glycerine 
and  butyric  {H.C4H7O2),  caproic  (H.CgHuOg),  and  capric  (H.CioH^902) 
acids,  distinguished  for  their  disagreeable  odour. 

Fresh  butter  has  very  little  odour,  being  free  from  these  volatile  acids, 
but  if  kept  for  some  time,  especially  if  the  caseine  of  the  milk  has  been 
imperfectly  separated  in  its  preparation,  spontaneous  resolution  of  these 
fats  into  glycerine  and  the  volatile  disagreeable  acids  takes  place.  By 
salting  the  butter  this  change  is  in  great  measure  prevented. 

The  fat  of  the  sheep  and  ox  (suet,  or  when  melted,  tallow)  consists 
chiefly  of  stearine,  whilst  in  that  of  the  pig  (lard)  oleine  predominates  to 
about  the  same  extent  as  in  butter.  Margarine  (or  palmitine?)  is  als5 
present  in  these  fats.  Benzoated  lard  contains  some  gum  benzoin,  which 
prevents  it  from  becoming  rancid. 

Human  fat  contains  chiefly  oleine  and  margarine  (or,  if  we  do  not 
admit  the  independent  existence  of  the  latter,  palmitine  and  stearine). 

Sperm  oil,  which  is  expressed  from  the  spermaceti  found  in  the  brain 
of  the  sperm  whale,  owes  its  peculiar  odour  to  the  presence  of  a  fat  which 
has  been  called  phocenine,  but  which  appears  to  be  valeriiie,  as  it  yields 
glycerine  and  valerianic  acid  (H.C5H9O2)  when  saponified. 

The  beautiful  solid  crystalline  fat,  known  as  spermaceti  or  cetine,  diflers 
widely  from  the  ordinary  fatty  matters,  for  when  saponified  (which  is  not 
easily  effected),  it  yields  no  glycerine,  but  in  its  stead  another  alcohol 
termed  ethal  (CigHg^O),  which  is  a  white  crystalline  solid,  capable  of  being 
distilled  without  decomposition. 

The  soap  prepared  from  spermaceti,  when  decomposed  by  an  acid, 
yields  palmitic  acid  (H-C-^qK^^O^)  (formerly  called  ethalic  acid),  to  which 
ethal  is  the  corresponding  alcohol. 

Palmitic  acid  and  ethal  are  formed  from  spermaceti  by  the  assimilation  of  the 
elements  of  water,  just  as  stearic  acid  and  glycerine  are  formed  from  stearine — 

C32H64O2  {Spermaceti)  +  HjO  =  CigHg^O  {Ethal)  +  H.  CiflHjiOa  {Palmitic  add). 

Upon  the  compound  radical  theory,  ethal  would  be  represented  as  cetylic  hydrate 
(CifiHagjHO,  and  as  the  alcohol  of  the.cetyle  series  running  paralled  with  the  ethyle 
series.     The  following  characteristic  members  of  the  series  have  been  studied  : — 


Cetyle  Series. 
Cetylene,       .     CjgHjj 
Cetylic  ether,     (0,5^33)20 
Ethal,  .         .     C,jH33.HO 
Palmitic  acid,   C18H31O2.H 
Spermaceti,       Ci6H33.CigH3i02 


Ethyle  Series. 
Ethylene,    .     C2H4 
Ether,         .     (C2H6)20 
Alcohol,      .     O2H5.HO 
Acetic  acid,      C2H3O2.  H 
Acetic  ether,   C2H5.C2H3O2 


Chinese  wax,    the  produce   of   an   insect   of  the   cochineal   tribe,    is 
analogous  in  its  chemical  constitution  to  spermaceti.     When  saponified 


WAX — VEGETABLE  ACIDS. 


585 


by  fusion  with  caustic  potash,  it  yields  cerotine  or  cerylic  alcohol 
C27H55.HO),  corresponding  to  ethal,  and  cerotic  acid  {H.C27H53O2), 
corresponding  to  palmitic  acid.  Cerotic  acid  is  also  contained  in  ordinary 
bees'  wax,  from  which  it  may  be  extracted  by  boiling  alcohol,  and 
crystallises  as  the  solution  cools.  It  forms  about  two-thirds  of  the  weight 
of  the  wax,  Cerotic  acid  is  found  among  the  products  of  oxidation  of 
paraffin  by  chromic  acid. 

Bees'  icax  also  contains  about  one-third  of  its  weight  of  myricine 
{^i^oi2^.^,  a  substance  analogous  to  spermaceti,  which  yields,  when 
saponified,  palmitic  acid  and  melissine  (CgQHg^.HO),  an  alcohol  corre- 
sponding to  ethal.  The  colour,  odour,  and  tenacity  of  bees'  wax  appear 
to  be  due  to  the  presence  of  a  greasy  substance  called  eeroleine,  which 
forms  about  o^jth  of  the  wax,  and  has  not  been  fully  examined.  The  tree 
icax  of  Japan  is  said  to  be  pure  palmitine. 

Wax  is  bleached  for  the  manufacture  of  candles,  by  exposing  it  in  thin 
strips  or  ribands  to  the  oxidising  action  of  the  atmosphere,  or  by  boiling 
it  with  nitrate  of  soda  and  sulphuric  acid.  Chlorine  also  bleaches  it,  but 
displaces  a  portion  of  the  hydrogen  in  the  wax,  taking  its  place  and  causing 
the  evolution  of  hydrochloric  acid  vapours  when  the  wax  is  burnt. 

The  following  table  includes  the  principal  fatty  bodies  and  their  corresponding 
acids,  with  their  fusing  points — 


Neutral 
Fats. 

FoiTOula. 

Chief 
Source. 

Fusing 
Point, 
Faiir. 

Fatty 
Acids. 

Formula. 

Fusing 
Point, 
Fahr. 

Stearine  * 

Palmitine 

Margarine 

Oleine 

Cetine 

Myricine 

f'67"iio06 

CsiHggOfi 

'^  54  "104^6 
C57H104O6 

^32^6402 
^46^9202 

Tallow 
Palm  oil 
Olive  oil 

»» 
Spermaceti 
Bees'  wax 

125°  to  157° 
114°  to  145° 

116° 
Below  32° 

120° 

162° 

Stearic       CigHjgOg 
Palmitic     CigHjjOj 
Margaric    C17H34O2 
Oleic          C18H34O2 
Palmitic     CigHjA^ 
>> 

159° 
144° 
140° 
40° 
144 

VEGETABLE  ACIDS. 

414.  Oxalic  acid. — This  poisonous  acid  occurs  pretty  abundantly  in 
the  vegetable  kingdom,  being  found  in  the  leaves  of  the  wood  sorrel  as 
binoxalate  of  potash  or  hydropotassic  oxalate  {salt  of  sorrel,  KHC2O4.  Aq.), 
in  the  stalks  of  rhubarb,  in  some  sea-weeds,  as  sodium  oxalate,  and  in 
lichens,  some  of  which  contain  more  than  half  their  weight  of  oxalate  of 
lime  (calcium  oxalate).  Oxalate  of  lime  has  also  been  found  in  wood. 
Free  oxalic  acid  is  present  in  many  fungi.  In  certain  unhealthy  conditions 
of  the  animal  frame,  calcium  oxalate  is  produced,  being  either  excreted 
in  the  urine,  or  forming  a  calculus  {mulberry  calcidus)  in  the  bladder. 
In  such  cases  the  oxalic  acid  appears  to  be  formed  in  consequence  of  an 
imperfection  in  that  oxidising  process  by  which  the  carbon  and  hydrogen 
of  the  various  parts  of  the  frame  are  finally  converted  into  carbon  dioxide 
(CO2)  and  water  (H2O),  the  production  of  oxalic  acid  (C2H2O4)  representing 
the  penultimate  stage  of  that  process. 

Guano  contains  a  considerable  quantity  of  oxalic  acid  in  combination 
Avith  ammonia  and  lime. 

*  Stearine  and  palmitine  are  said  to  present  three  modifications  with  different  fusing- 
points.  Some  recent  observations  appear  to  indicate  that  the  so-called  palmitine  ol  palm 
oil  really  contains  stearine,  oleine,  and  lauriue. 


586  PREPABATION  OF  OXALIC  ACID. 

With  the  exception  of  carbon  dioxide,  no  carbon  compound  is  more 
commonly  ra^t  with  than  oxalic  acid,  as  a  product  of  the  action  of 
oxidising  agents  upon  organic  substances,  especially  upon  those  which  do 
not  contain  nitrogen,  such  as  sugar  (C12H22O11),  starch  (CgH^oOj),  and 
woody  fibre. 

Oxalic  acid  is  largely  employed  in  calico-printing,  in  cleansing  leather 
and  brass,  as  a  solvent  for  Prussian  blue  in  the  preparation  of  blue  ink, 
&e.,  and  for  taking  iron-mould  out  of  linen.  It  is  manufactured  on  the 
large  scale  by  oxidising  sawdust  with  a  mixture  of  caustic  potash  and 
caustic  soda;  the  latter  would  not  produce  oxalic  acid  without  the 
potash,  and  this  alone  would  be  too  expensive.  One  molecule  of  caustic 
potash  and  2  molecules  of  caustic  soda  are  mixed  in  solution,  which 
should  have  the  sp.  gr.  1  '35,  made  into  a  thick  paste  with  sawdust,  and 
heated  ujion  iron  plates  for  several  hours;  hydrogen  is  evolved,  from  the 
decomposition  of  the  alkalies,  the  oxygen  serving  to  convert  the  wood 
into  oxalic  acid,  which  forms  more  than  one-fourth  of  the  weight  of  the 
grey  mass  finally  obtained.  On  treating  this  mass  with  cold  water,  a 
quantity  of  sodium  oxalate  is  left  undissolved;  this  is  boiled  with  lime, 
when  the  oxalic  acid  is  converted  into  the  insoluble  oxalate  of  lime,  and 
soda  is  dissolved;  the  oxalate  of  lime  is  then  decomposed  by  dilute 
sulphuric  acid,  when  the  sparingly  soluble  sulphate  of  lime  is  formed, 
and  the  solution  yields  crystals  of  oxalic  acid  (H2C204.2Aq.)  on  evapora- 
tion. The  whole  of  the  alkali  'originally  employed  is  recovered  by 
evaporating  the  liquors  to  dryness,  calcining  to  destroy  organic  matter, 
and  decomposing  the  alkaline  carbonates  with  lime.  The  sawdust  yields 
about  half  its  weight  of  crystallised  oxalic  acid. 

Before  the  introduction  of  this  process,  oxalic  acid  was  sold  at  nearly 
twice  its  present  cost,  being  then  usually  obtained  by  the  action  of  nitric 
acid  either  upon  molasses  or  upon  starch-sugar*  (page  501)  in  leaden 
vessels,  which  were  found  to  remain  unattacked  by  the  acid  as  long  as  any 
sugar  remained  unoxidised. 

For  experiment  on  the  small  scale,  oxalic  acid  may  be  prepared  by  gently  heating 
100  grains  of  starch  with  1^  measured  ounce  of  nitric  acid,  sp.  gr.  1  "38,  when  abundant 
fumes  of  N2O3  will  indicate  the  deoxidation  suffered  by  the  nitric  acid.  When  this 
has  abated,  the  solution  may  be  transferred  to  a  dish,  and  slowly  evaporated  to 
about  one-sixth  of  its  bulk  ;  on  cooling,  a  mass  of  beautiful  four-sided  prismatic 
crystals  of  oxalic  acid  will  be  obtained. 

The  crystals  of  oxalic  acid  may  be  represented  by  the  empirical  formula 
CoHgOg,  but  when  they  are  heated  to  212°  F.  they  lose  water,  melting 
first,  if  the  heat  be  suddenly  applied,  but  efflorescing  without  fusion  if 
heated  gradually.  By  suddenly  heating  the  crystals  in  a  test-tube,  much 
of  the  acid  may  be  sublimed  in  long  prismatic  crystals.  The  dried  or 
effloresced  oxalic  acid  has  the  composition  CaHgO^,  showing  that  2 
molecules  of  water  of  crystallisation  have  been  expelled,  and  that  the 
crystals  would  be  more  correctly  represented  by  C2H204.2Aq.t  On 
neutralising  oxalic  acid  with  potash  and  soda,  salts  are  obtained  which, 
when  dried  at  212°  F.,  have  the  composition  K2C2O4  and  NagCgO^,  and 
if  solutions  of  these  salts  be  precipitated  by  nitrate  of  lead  or  of  silver, 
the  oxalates  of  lead  (PbCgO^)  and  of  silver  (Ag2C204)  are  obtained.     If 

*  Hence  the  comnion  name,  acid  of  sugar. 

+  Villiers  has  obtained  large  rhombic  octahedra  of  H.2C2O4  by  dissolving  crystallised 
oxalic  acid  in  12  parts  of  warm  oil  of  vitriol  and  setting  aside. 


PROPERTIES  OF  OXALIC  ACID.  587 

the  dried  acid  be  heated  to  about  320°  F.,  it  sublimes  in  crystals,  but 
above  that  temperature  it  is  decomposed  into  water,  carbon  dioxide, 
carbonic  oxide,  and  some  formic  acid  (see  page  568).  When  heated  with 
dehydrating  agents,  such  as  sulphuric  acid,  it  is  also  decomposed  into 
carbon  dioxide  and  carbonic  oxide  (page  90). 

Oxalic  acid  is  rather  sparingly  soluble  in  cold  water,  requiring  about 
nine  times  its  weight;  hot  water  dissolves  it  more  abundantly,  and  it  is 
moderately  soluble  in  alcohol.  The  aqueous  solution  is  intensely  acid, 
more  nearly  resembling  the  strong  mineral  acids  than  one  of  vegetable 
origin,  and  is  exceedingly  poisonous,  a  property  which  is  the  more 
dangerous  on  account  of  the  resemblance  of  the  crystallised  oxalic  acid  to 
Epsom  salts  (sulphate  of  magnesia),  from  which,  however,  it  may  be 
readily  distinguished  by  its  sour  taste  and  by  the  action  of  heat,  which 
entirely  dissipates  the  oxalic  acid,  but  only  expels  water  from  Epsom 
salts.  Fortunately,  a  considerable  quantity  of  the  acid  is  required  to 
cause  death;  in  ordinary  cases,  100  grains  or  more.  The  chemical 
antidote  employed  to  counteract  its  effect  is  chalk  suspended  in  water, 
the  lime  of  the  chalk  combining  with  the  acid  to  form  the  insoluble  and 
harmless  calcium  oxalate  (CaC.204).  The  insolubility  of  this  oxalate 
renders  the  oxalic  acid  one  of  the  most  delicate  tests  for  lime,  which  may 
be  detected,  for  example,  in  common  water,  by  adding  oxalic  acid  and  a 
slight  excess  of  ammonia,  when  a  white  cloud  of  oxalate  of  lime  is  pro- 
duced. Conversely,  of  course,  salts  containing  calcium  (calcium  chloride, 
for  instance)  may  be  employed  to  detect  oxalic  acid,  the  precipitated 
calcium  oxalate  being  distinguished  from  other  similar  precipitates  by  its 
insolubility  in  acetic  acid. 

As  might  be  expected  from  its  composition  (C.2H2OJ,  oxalic  acid  is 
easily  converted  into  carbon  dioxide  and  water  by  oxidising  agents;  thus, 
if  a  hot  solution  of  oxalic  acid  be  poured  upon  powdered  manganese 
dioxide,  violent  efferv^escence  takes  place  from  the  rapid  evolution  of 
carbonic  acid  gas. 

Hydropotcuisic  oxalate,  or  binoxalate  of  potash  (KHCgO^.HgO),  is  sold 
under  the  names  of  salt  of  sorrel  and  essential  salt  of  lemons,  and  is  employed 
for  the  same  purposes  as  oxalic  acid.  It  is  a  sparingly  soluble  salt, 
requiring  40  parts  of  cold  water  to  dissolve  it,  and  has  occasionally  caused 
accidents  by  being  mistaken  for  cream  of  tartar  (hydropotassic  tartrate), 
from  which  it  is  readily  distinguished  by  the  action  of  heat,  which  chars 
tartrate,  but  not  the  oxalate,  an  alkaline  mass  containing  potassium 
carbonate  being  left  in  both  cases. 

Trihydropotassic  oxalate,  or  quadroxalate  of  potash  (KH32C2O4.2H.2O), 
is  also  sometimes  sold  as  salts  of  lemon;  it  is  even  less  soluble  than  the 
binoxalate. 

Ammonium  oxalate  (XH4).2C204.H20,  so  much  used  in  chemical 
analysis  as  a  precipitant  for  lime,  is  obtained  by  mixing  solution  of 
oxalic  acid  with  a  slight  excess  of  ammonia,  and  evaporating  the  solution, 
from  which  the  oxalate  crystallises,  on  cooling,  in  fine  prismatic  needles. 

The  action  of  heat  upon  this  salt  has  been  described  at  page  550. 

Silver  oxalate  (Ag2C204)  is  obtained  as  a  white  precipitate  Avhen  nitrate 
of  silver  is  added  to  ammonium  oxalate.  It  is  remarkable  for  being  de- 
composed, with  a  slight  explosion,  when  heated  in  the  dry  state,  metallic 
silver  being  left,  Ag2C204  =  Ago  +  2CO2. 

Potassium-ferrous  oxalate,  prepared  by  adding  potassium   oxalate   in 


588  PREPARATION  OF  TARTARIC  ACID. 

excess  to  ferrous  sulphate,  is  a  very  powerful  reducing  agent,  useful  in 
photography. 

415.  Tartaric  acid. — The  most  important  of  the  vegetable  acids  is 
tartaric  acid  (C4HgOg),  which  occurs  in  many  fruits,  but  more  especially  in 
the  grape,  the  juice  of  which  deposits  it,  during  fermentation,  in  the  form 
of  hydropotassic  tartrate  or  bitartrate  of  potash,  which  is  known  in 
commerce  as  tartar  or  argol.  This  salt  dissolves  with  difficulty  in  cold 
water,  but  may  be  dissolved  in  boiling  water,  from  which  it  crystallises  in 
prisms  on  cooling.  When  thus  purified,  it  is  known  as  cream  of  tartar, 
and  has  the  composition  KHC4H40g,  representing  tartaric  acid  in  which 
1  atom  of  hydrogen  has  been  replaced  by  potassium.  The  solution  of  this 
salt  is  acid  to  test-papers,  and  if  it  be  neutralised  with  potash  and  evapo- 
rated, it  yields  crystals  of  a  very  soluble  salt,  having  the  composition 
'K.Ju^^O^.  This  is  the  normal  potassium  tartrate,  cream  of  tartar  being 
the  acid  tartrate.     The  crystallised  tartaric  acid  is  therefore  regarded  as 

In  order  to  prepare  tartaric  acid,  which  is  largely  used  in  dyeing  and 
calico-printing,  the  impure  bitartrate  of  potash  is  boiled  with  water,  and 
calcium  carbonate  (chalk)  is  added  as  long  as  it  causes  effervescence  from 
the  escape  of  carbonic  acid  gas;  the  result  of  this  change  is  the  formation 
of  calcium  tartrate,  which  is  insoluble,  and  potassium  tartrate,  which 
dissolves  in  water — 

2(KHC4H406)  +  2CaC03  =  KgC^H^Og  +  CaC^H^Og  4-  HgO  +  2CO2. 

Calcium  chloride  is  then  added  to  the  mixture,  which  converts  the  whole 
of  the  tartaric  acid  into  the  insoluble  calcium  tartrate — 

KaC^H^O^  +  CaClg  =  2KC1  -h  CaC^H^Oo. 

The  calcium  tartrate  is  strained  off,  washed,  and  boiled  with  diluted  sul- 
phuric acid,  when  calcium  sulphate  remains  undissolved,  and  tartaric  acid 
may  be  obtained  in  crystals  by  evaporating  the  filtered  solution — 

CaC^H^Og  +  H2SO4  =  H2C4H4O6  +  CaSO^. 

Large  transparent  prisms  are  thus  obtained,  which  are  soluble  in  about  three- 
fourths  of  their  weight  of  hot  water.  When  kept,  the  solution,  unless 
very  strong,  deposits  a  curious  fungoid  growth,*  and  acetic  acid  is  found 
in  it.  When  heated  to  about  340°  F.,  the  crystals  fuse  without  loss  of 
weight ;  but  on  examining  the  fused  mass,  it  is  found  to  be  no  longer 
tartaric  acid,  but  a  mixture  of  two  new  acids.  One  of  these,  metatartaric 
acid,  has  the  same  formula  as  tartaric  acid  (Yi.cfl>^^0^,  but  cannot  be 
crystallised.  Its  salts  are  more  soluble  in  water  than  the  tartrates,  and 
are  converted  into  the  latter  when  boiled  with  water.  The  other  acid, 
isotaHaric,  is  also  uncrystallisable,  but  has  the  formula  (HC4H50g).  The 
potassium  isotartrate  (KC^HgOg)  has  the  same  composition  as  the  bitar- 
trate (KHC^H^Og),  but  is  far  more  soluble.  It  is  converted  into  that 
salt  by  boiling  with  water. 

At  374°  F.  tartaric  acid  loses  water,  and  is  converted  into  tartaric 
anhydride  (CgHgOig),  which  is  a  white  insoluble  substance,  convertible 
into  tartaric  acid  by  prolonged  contact  with  water. 

Tartar-emetic. — One  of  the  commonest  salts  of  tartaric  acid  is  tartar- 
emetic,  the  double  tartrate  of  antimony  and  potassium,  which  is  prepared 

•  This  fungus  has  been  found  to  contain  3  5  per  cent,  of  nitrogen. 


TARTAR-EMETIC.  589 

"by  boiling  antimony  with  sulphuric  acid,  driving  oflF  the  excess  of  acid  by 
heat,  and  digesting  the  residual  antimonious  oxide  with  cream  of  tartar 
and  a  little  water  for  some  hours.  The  changes  involved  in  the  process 
are  thus  represented — 

Sh,  +  3H2SO4  =  S\0.^  +  3H2O  +  3SO2 

SbgOg  +  2KHC4H4O6  =  2(K.SbO.C,H,Oe)  +  H^O. 

Bitai-trate  of  potash.  Tai  tar-emetic. 

On  boiling  the  mixture  with  water,  and  filtering,  the  cooled  solution 
deposits  octahedral  crystals,  of  the  formula  2(K.SbO.C4H40g).Aq.'- 

The  water  of  crystallisation  may  be  expelled  at  212°  F. ;  and  if  the  salt 
be  heated  to  400°  F.  it  loses  an  additional  molecule  of  water,  and  becomes 
K.Sb.C^H^Og,  which  is  reconverted  into  tartar-emetic  when  dissolved  in 
water. 

When  a  little  liydrochloric  acid  is  added  to  a  solution  of  tartar-emetic,  a  precipi- 
tate of  antimonious  oxide  is  formed,  which  dissolves  easily  in  an  excess  of  the  acid. 
If  kept  for  a  length  of  time  in  solution,  tartar-emetic  is  decomposed,  octahedral 
crystals  of  antimonious  oxide  being  deposited,  and  the  solution  ceases  to  be  preci- 
pitated by  hydrochloric  acid.  The  reaction  to  test-paper,  which  was  slightly  acid, 
is  now  slightly  alkaline. 

Compounds  perfectly  analogous  to  tartar-emetic  have  been  obtained,  in  which  the 
antimony  is  replaced  by  boron  or  by  arsenic,  and  the  potassium  by  silver,  lead,  or 
sodium. 

It  will  be  observed  that  tartar-emetic  presents  an  anomaly  in  its  composition,  for 
it  might  be  expected  to  be  KSb"'(C4H40Bi2-  The  composition  of  the  tartar-emetic, 
dried  at  400°  F.,  might  be  reconciled  with  that  of  crystallised  tartaric  acid  by  repre- 
senting it  thus,  C4(H.,KSb"'  )0g,  that  is,  crystallised  tartaric  acid  (C4HgOfi),  in  which 
1  atom  of  hydrogen  has  been  replaced  by  potassium,  and  3  atoms  by  the  trialomic 
antimony.  The  relation  existing  between  tartaric  acid,  its  potassium  salts,  and  the 
emetics,  will  be  seen  in  the  following  formulae  - 

Tartaric  acid,      ....  H,C4H406 

Potassium  tartrate,      .         .         .  K2C4H4OS 

Cream  of  tartar,  ,         .         .  KHC4H40g 

Tartar-emetic,  .         .         .  KHC4HSb06. 

The  beautiful  prismatic  crystals  known  as  Rochelle  salt  consist  of  a 
double  tartrate  of  potassium  and  sodium  (KXaC^H^Og.iAq.),  prepared  by 
neutralising  cream  of  tartar  \v\i\\  sodium  carbonate. 

Tartaric  acid  has  been  obtained  artificially  by  the  action  of  nitric  acid 
on  sugar  of  milk  and  on  gum,  which  supplies  a  link  of  connexion  between 
this  acid  and  the  members  of  the  sugar  group  which  accompany  it  in 
plants. 

Tartaric  acid  is  easily  conyertible  into  succinic  and  malic  acids,  as  might 
be  anticipated  from  an  inspection  of  their  formulae — 

Tartaric    acid,    HgC^H^Og;    malic    acid,    H9C4H4O.;    succinic    acid, 

When  tartaric  acid  is  heated  with  phosphorus  and  iodine  in  the  presence 
of  water  (or,  which  amounts  to  the  same  thing,  when  it  is  heated  with 
hydriodic  acid),  the  acid  is  deoxidised,  and  malic  and  succinic  acids  are 
produced,  thus,  H.C^H^Og  +  4HI  =  H.^C^H.O^  +  l,  +  2B.p. 

Tartaric  acid.  Succinic  acid. 

Tartaric  and  malic  acids  are  frequently  associated  in  fruits,  and  succinic 
acid  is  found  among  the  products  of  fermentation  of  grape-juice. 

Succinic  acid  may  be  reconverted  into  tartaric  acid  by  heating  it  with 
bromine  and  water,  when  it  is   converted   into   bibromosuccinic   acid, 


590  RACEMIC  ACID. 

H  C4(H2Br,)04,  which  furnishes  tartaric  acid  when  decomposed   with 
silver  oxide";  H2C4(H2Br2)04  +  AgP  +  H^O  =  HgC^H^Og 4- 2AgBr. 

When  bromosuccinic  acid,  H2C4(H3Br)04,  is  decomposed  with  silver 
oxide,  malic  acid  is  formed — 

2H2C4(H3Br)04  +  3Ag20  =  2Ag2C4H405  +  2AgBr  +  H^O. 

Bromosuccinic  acid.  Silver  mulate. 

The  synthesis  of  succinic  acid  has  been  eflFected  by  the  following  series  of  re- 
actions : — 

Cj  +  Ha  =  CjHj  (acetylene);  C2H2+  H2  =  C2H4  (ethene);  C2H4  +  Br^  =  CjH^Br, 
(ethene  dibromide);  C2H4Br2  +  2KCN  =  2KBr  +  C2H4(CN2)  (ethene  dicyanide); 
C2H4(CN)2  +  2KHO  +  2H20  =  2NH3  +  K2C4H404  (potassium  succinate). 

416.  The  tartaric  acid  found  in  grapes  is  accompanied,  particularly  in  tho.se  of 
certain  vintages  and  districts,  by  another  acid  called  racemic  or  paratartaric  acid, 
which  has  the  same  composition  as  tartaric  acid,  but  crystallises  with  a  molecule 
of  water  (H2C4H40g.Aq.).  The  crystalline  forms  of  these  acids  are  the  same,  but 
the  crystals  of  racemic  acid  effloresce,  from  loss  of  water  when  exposed  to  the  air. 
Solution  of  racemic  acid  is  precipitated  by  the  salts  of  calcium,  which  do  not  precipitate 
tartaric  acid  unless  it  be  previously  neutralised.  Moreover,  although  racemic  acid 
forms,  with  potash  and  antimonious  oxide,  a  salt  corresponding  in  composition  to 
tartar-emetic,  this  does  not  crystallise  in  octahedra,  but  in  tufts  of  needles. 

There  is  a  marked  difference  in  the  action  of  these  two  acids  and  their  salts  upon 
polarised  light,  for  solutions  of  racemic  acid  and  the  racemates  do  not  alter  the  plane 
of  polarisation,  whilst  tartaric  acid  and  the  tartrates  rotate  it  to  the  right. 

On  carefully  examining  the  crystalline  forms  of  the  tartrates,  Pasteur  observed 
that  they  generally  presented  an  exception  to  that  law  of  crystalline  symmetry,  which 
requires  that  a  modification  existing  on  an  edge  or  face  of  a  crystal  should  be 
repeated  on  all  its  other  similar  edges  or  faces,  whereas  in  the  crystals  of  the  tartrates, 
certain  of  the  edges  are  truncated  without  any  corresponding  modification  of  the 
others,  and  hemihedral  forms  are  thus  produced.  Now,  in  general,  it  is  found  that 
if  a  substance  forms  hemihedral  crystals,  their  hemihedrism  is  of  such  a  character 
that  they  can  be  superposed  upon  each  other,  so  that  the  united  crystals  shall  exhibit 
a  perfect  symmetry  upon  each  side  of  the  plane  of  junction;  but  the  hemihedrism  of 
the  tartrates  is  such,  that  the  crystals  do  not  exhibit  this  symmetry  when  superposed 
upon  each  other,  but  when  one  is  superposed  upon  the  reflection  of  the  other  in  a 
mirror,  so  that  instead  of  presenting  crystals  which  are,  as  u.sual,  partly  right  and 
jiartly  left-handed  in  their  want  of  symmetry,  the  crystals  of  the  tartrates  are  either 
all  right-handed  or -all  left-handed  hemihedral  crystals. 

"When  the  action  of  solutions  of  these  salts  upon  polarised  light  came  to  be 
examined,  it  was  found  that  the  right-handed  crystals  always  rotated  the  plane  of 
polarisation  to  the  right,  whilst  the  left-handed  crystals  produced  a  left-handed 
rotation. 

On  separating  the  acids  from  these  salts,  they  resembled  each  other  precisely  in 
all  their  chemical  properties,  but  the  acid  from  the  right-handed  salts  furnished 
cry-stals  which  were  hemihedral  right-handedly,  whilst  that  of  the  left-handed  .salts 
furni.shed  left-handed  hemihedral  crystals  ;  moreover,  the  solution  of  the  right- 
handed  acid  exerted  a  right-handed  rotation  upon  the  plane  of  polarisation,  which 
was  turned  in  the  opposite  direction  by  a  solution  of  the  left-handed  acid. 

The  former  acid  has  been  named  dextro-tartaric  acid,  and  is  the  usual  form  in 
which  this  acid  is  met  with  ;  the  other  acid  has  been  called  laevo-tartaric  acid.  In 
their  chemical  relations  these  acids  are  perfectly  identical ;  for  the  chemist  they  ar<i 
both  the  same  tartaric  acid,  equally  well  adapted  for  all  the  uses  to  which  this  acid 
is  applied. 

I'asteur  found  that  the  double  racemate  of  sodium  and  ammonium  furnished  a  crop 
of  crystals  containing  both  right-handed  and  left-handed  hemihedral  forms,  and  on 
separating  them  by  hand,  he  found  that  the  action  of  their  solutions  on  polarised 
light  corresponded  with  their  hemihedrism,  and  on  isolating  the  acids,  the  right- 
handed  crystals  furnished  dextro-tartaric,  the  left-handed,  Isevo-tartaric  acid. 

This  analysis  of  racemic  acid  was  soon  confirmed  by  its  synthesis.  On  mixing 
concentrated  solutions  of  equal  parts  of  dextro-tartaric  and  Isevo-tartaric  acids,  a 
considerable  rise  of  temperature  was  observed,  showing  that  combination  had  taken 
])lace,  and  the  solution,  which  had  no  longer  the  power  of  rotating  the  plane  of 
polarisation,  furnished  crystals  of  racemic  acid. 


CITRIC  ACID — MALIC  ACID,  591 

This  remarkable  instance  of  chemical  combination  between  two  acids  which  are 
in  their  clieraical  properties,  perfectly  identical,  to  furnish  a  new  acid  differin<^  from 
both,  affords,  by  analogy,  some  support  to  the  theory  of  the  duplex  constitution  of 
many  elementary  and  compound  bodies. 

417.  Citric  acid  (CgHgO-)  occurs  in  lemons,  oranges,  and  most  acidulous 
fruits.  It  is  prepared  from  lemon-juice,  which  contains  the  acid  in  a  free 
state,  by  neutralising  it  with  chalk,  when  calcium  citrate  (Ca32CgH507) 
is  obtained,  which  is  decomposed  by  dilute  sulphuric  acid;  the  filtered 
solution,  when  evaporated,  yields  prismatic  crystals  of  citric  acid,  which 
contain  CgHgO^.Aq.  They  fuse  at  212°  F.,  and  lose  the  water  of  crystal- 
lisation. From  the  formula  of  calcium  citrate,  it  will  be  seen  that  citric 
acid  is  tribasic,  and  should  be  written  HgCgHgO^ ;  hence,  like  ordinary 
phosphoric  acid,  it  forms  three  series  of  salts.  The  citrates  of  sodium,  for 
example,  have  the  composition,  2(]S'a3CeH507),llAq.,  iS'a^HCgHjOy.Aq., 
NaHgCgHgO^.Aq.  When  citric  acid  is  heated  above  300°  F.,  it  is  con- 
verted into  aconitic  acid  (HgCgHgOg),  another  vegetable  acid  found  in  the 
diflferent  varieties  of  monkshood  (aconitum). 

Citric  acid  is  employed  in  dyeing  and  calico-printing,  as  well  as  in 
medicine. 

By  fermentation  in  contact  with  yeast,  calcium  citrate  is  converted  into  acetate 
and  butyrate  of  calcium,  with  evolution  of  carbonic  acid  gas  and  hydrogen.  The 
crude  calcium  citrate  prepared  in  Sicily,  and  imported  for  the  preparation ;of  the  acid, 
is  found  sometimes  to  undergo  this  change  spontaneously,  so  that  it  has  been  recom- 
mended to  neutralise  the  hot  lemon-juice  with  magnesium  carbonate  (which  is 
abundant  in  Italy),  when  the  tribasic  magnesium  citrate  is  precipitated  in  minute 
crystals.  By  dissolving  this  precipitate  in  a  fresh  quantity  of  hot  lemon-juice,  and 
evaporating,  the  bihasic  magnesium  citrate  is  obtained  in  crystals,  which  is  recom- 
mended as  the  best  form  in  which  to  import  the  acid  into  this  country. 

418.  Malic  acid  (R^f^^^O^  is  &  crystalline  acid  found,  as  its  name 
implies,  in  apples  and  many  other  fruits.  It  is  present,  together  with 
oxalic  acid,  in  rhubarb.  Tobacco  leaves  also  contain  it  in  the  form  of 
calcium  bimalate,  CaH22C4lI^05. 

In  order  to  extract  the  malic  acid  from  rhubarb  stalks,  it  is  converted  into  calcium 
malate,  the  solubility  of  which  enables  it  to  be  separated  from  the  insoluble  citrate 
and  tartrate  of  calcium.  The  juice  is  squeezed  out  of  the  stalks  by  a  press,  nearly 
neutralised  with  slaked  lime  suspended  in  water,  and  calcium  chloride  is  added. 
The  precipitate  containing  tartrate,  citrate,  phosphate,  and  oxalate  of  calcium,  is 
filtered  ofl",  and  the  liquid  boiled  down,  when  calcium  malate  (CaC4H405)  is  sepa- 
rated, together  with  some  calcium  citrate.  This  is  washed  and  added  to  hot  nitric 
acid,  diluted  with  ten  measures  of  water,  as  long  as  it  continues  to  be  dissolved.  On 
cooling,  bimalate  of  calcium  is  deposited,  which  is  dissolved  in  water  and  decomposed 
by  lead  acetate,  when  it  gives  a  curious  precipitate  of  lead  malate  (PbC4H405.3Aq.), 
which  becomes  crystalline  on  standing,  and  fuses  in  the  liquid  below  the  tempera- 
ture of  boiling  water.  By  suspending  the  lead  malate  in  water,  and  decomposing 
it  with  hydrosulphuric  acid,  the  lead  is  separated  as  sulphide,  and  a  solution  of 
malic  acid  is  obtained,  which  gives  deliquescent  prismatic  crystals  of  the  acid  when 
evaporated  to  a  syrup  and  set  aside.  Malic  acid  is  decomposed  by  heat  into  two 
isomeric  acids,  the  malccic  and  fumaric  H2C4H2O4  ;  the  latter  is  found  in  the  plant 
known  diS  fumitory  {Fumaria  officinalis). 

An  excellent  source  of  malic  acid  is  the  juice  of  the  unripe  berries  of 
the  mountain  ash,  in  which  it  is  accompanied  by  a  volatile  oily  acid  of 
pungent  aromatic  odour ;  this  has  been  called  parasorbic  acid,  and  has 
the  formula  HCgH-O.,.  AVhen  fused  with  potash,  or  boiled  with  a  strong 
mineral  acid,  it  suffers  a  remarkable  conversion  into  a  crystalline  solid 
acid,  having  precisely  the  same  composition,  called  sorbic  acid. 


592  TANNIC  ACID. 

Under  the  influence  of  yeast  in  the  presence  of  water,  calcium  malate 
is  converted  into  succinate  and  acetate  of  calcium — 

3(H2C,H,05)  =  2(H2C4H,04)  +  HC^HgO^  +  2CO2  +  H^O. 

Malic  acid.  Succinic  acid.  Acetic  add. 

The  amide  of  malic  acid,  malamide,  C4HgN203,  ammonium  malate 
(NH4)2C4H405  minus  2H2O,  has  attracted  some  attention,  because  it  has 
the  same  composition  as  mpmxigine,  a  crystalline  substance  extracted 
from  the  juice  of  the  asparagus,  marsh-mallow  root,  and  some  other  plants  ; 
but  it  is  not  identical  with  it,  though  asparagine,  when  acted  on  by 
nitrous  anhydride,  yields  malic  acid — 

C4H8N2O3  +  N2O3  =  ii,c,-a,i\  +  H2O  +  N,. 

Asparagine.  Malic  acid. 

i^sparagine  is  really  the  amide  of  another  acid,  the  aspartic,  into  the 
ammonium-salt  of  which  it  becomes  converted  when  heated  for  some  time 
with  water;  C^HgNgOg  +  H2O  =  (NHJC.HgNO,. 

Asparagine.  Ammonium  aspartate. 

419.  Tannic  acid  or  tannin  [C^'jH^^^]*;),  the  astringent  principle  of 
gall-nuts,  from  which  it  may  be  extracted  by  water,  is  characterised  by 
two  very  useful  properties,  viz.,  by  yielding  a  black  precipitate  with 
the  salts  of  peroxide  of  iron,  and  by  forming  a  tough  insoluble  compound 
with  gelatine  and  gelatinous  membrane,  the  first  being  turned  to  account 
in  the  preparation  of  ink,  and  the  second  in  that  of  leather. 

For  the  preparation  of  ink,  three  quarters  of  a  pound  of  bruised  nut- 
galls  are  digested  in  a  gallon  of  cold  water,  and  6  ounces  of  green  vitriol 
(sulphate  of  iron)  are  added,  together  with  6  ounces  of  gum,  and  a  few 
drops  of  kreasote.  The  mixture  is  set  aside  for  two  or  three  weeks,  being 
occasionally  agitated,  and  the  ink  afterwards  poured  off  from  the  undis- 
solved part  of  the  nut-gall. 

Pure  ferrous  sulphate  (FeS04)  ^^^  tannic  acid  might  be  mixed  without 
change  ;  but  when  the  mixture  is  exposed  to  the  air,  oxygen  is  absorbed, 
converting  the  ferrous  into  a  ferric  salt  which  forms  a  black  precipitate  of 
ferric  tannate,  the  exact  composition  of  which  is  not  known.  The  gum 
is  added  to  render  the  liquid  viscous,  so  as  to  prevent  the  subsidence  of 
the  black  precipitate,  and  the  kreasote  prevents  the  ink  from  becoming 
mouldy.  The  brown  colour  of  the  ink  in  old  manuscripts  is  due  to  the 
tannic  acid  having  been  partly  removed  by  oxidation,  leaving  the  brown 
ferric  oxide ;  the  stain  of  iron-mould  left  by  ink  on  linen  after  washing  is 
due  to  the  entire  removal  of  the  tannic  acid  by  the  alkali  in  the  soap. 

Tanning. — When  infusion  of  nut-galls  is  added  to  a  solution  of  gelatine, 
the  latter  combines  with  the  tannic  acid,  and  a  bulky  precipitate  is 
obtained.  If  a  piece  of  skin,  which  has  the  same  composition  as  gelatine, 
be  placed  in  the  infusion  of  nut-galls,  it  will  absorb  the  whole  of  the 
tannic  acid,  and  become  converted  into  leather,  which  is  much  tougher 
than  the  raw  skin,  less  permeable  by  water,  and  not  liable  to  putrefaction. 

The  first  operation  in  the  conversion  of  hides  into  leather,  after  they 
have  been  cleansed,  consists  in  soaking  them  for  three  or  four  weeks  in 
pits  containing  lime  and  water,  which  saponifies  the  fat,  and  loosens  the 
hair.  The  same  object  is  sometimes  attained  by  allowing  the  hides  to 
enter  into  putrefaction,  when  the  resulting  ammonia  has  the  same  effect  as 
the  lime.  The  loosened  hair  having  been  scraped  off,  the  hides  are  soaked 
for  twelve  hours  in  water  containing  ydV^^^  ^f   sulphuric  acid,  which 


TANNING.  593 

removes  adhering  lime,  and  opens  the  pores  of  the  skin,  so  as  to  fit  it  to 
receive  the  tanning  liquid. 

The  tanning  material  generally  employed  for  hides  is  the  infusion  of 
oak  bark,  Avhich  contains  qiierci-tannic  acid,  very  similar  in  properties  to 
tannic  acid.  The  hides  are  soaked  in  an  infusion  of  oak  bark  for  about 
six  weeks,  being  passed  in  succession  through  several  pits  in  which  the 
strength  of  the  infusion  is  gradually  increased.  They  are  then  packed  in 
another  pit  with  alternate  layers  of  coarsely-ground  oak  bark ;  the  pit  is 
filled  with  water  and  left  at  rest  for  three  months,  when  the  hides  are 
transferred  to  another  pit,  and  treated  in  the  same  way ;  but,  of  course,  the 
position  of  the  hides  will  be  now  reversed —  that  which  was  uppermost, 
and  in  contact  with  the  weakest  part  of  the  tanning  liquor,  will  now  be 
at  the  bottom.  After  the  lapse  of  another  three  months  the  hide  is  gene- 
rally found  to  be  tanned  throughout,  a  section  appearing  of  a  uniform 
brown  colour.  It  has  now  increased  in  weight  from  30  to  40  per  cent. 
The  chemical  part  of  the  process  being  now  completed,  the  leather  is  sub- 
jected to  certain  mechanical  operations  to  give  it  the  desired  texture.  For 
tanning  the  thinner  kinds  of  leather,  such  as  morocco,  a  substance  called 
stimach  is  used,  which  consists  of  the  ground  shoots  of  the  Rhus  Curiaria, 
and  contains  a  large  proportion  of  tannic  acid. 

Morocco  leather  is  made  from  goat  and  sheep  skins,  which  are  denuded 
of  hair  by  liming  in  the  usual  way,  but  the  adhering  lime  is  afterwards 
removed  by  means  of  a  bath  of  sour  bran  or  flour.  In  order  to  tan  the 
skin  so  prepared,  it  is  sewn  up  in  the  form  of  a  bag,  which  is  filled  with 
infusion  of  sumach,  and  allowed  to  soak  in  a  vat  of  the  infusion  for 
some  hours.  A  repetition  of  the  process,  with  a  stronger  infusion,  is 
necessary  ;  but  the  whole  operation  is  completed  in  twenty-four  hours. 
The  skins  are  now  washed  and  dyed,  except  in  the  case  of  red  morocco, 
which  is  d^'ed  before  tanning,  by  steeping  it  first  in  alum  or  chloride  of 
tin,  as  a  mordant,  and  afterwards  in  infusion  of  cochineal.  Black 
morocco  is  dyed  with  acetate  of  iron,  which  acts  upon  the  tannic  acid. 
The  aniline  dyes  are  now  much  employed  for  dyeing  morocco. 

The  kid  of  which  gloves  are  made  is  not  actually  tanned,  but  sub- 
mitted to  an  elaborate  operation  called  taicing,  the  chief  chemical  features 
of  which  are  the  removal  of  the  excess  of  lime,*  and  opening  the  pores  of 
the  skin  by  means  of  a  sour  mixture  of  bran  and  water,  in  which  lactic 
acid  is  the  agent;  and  the  subsequent  impregnation  of  the  porous  skin 
with  aluminium  chloride,  by  steeping  it  in  a  hot  bath  containing  alum 
and  common  salt.  The  skins  are  afterwards  softened  by  kneading  in  a 
mixture  containing  alum,  flour,  and  the  yolks  of  eggs.  The  putrefaction 
of  the  skin  is  as  efiectually  prevented  by  the  aluminium  chloride  as  by 
tanning. 

Wash-leather  and  hiicJcskin  are  not  tanned,  but  shamoijed,  which  con- 
sists in  sprinkling  the  prepared  skins  with  oil,  folding  them  up,  and 
stocTiing  them  under  heavy  wooden  hammers  for  two  or  three  hours. 
When  the  grease  has  been  well  forced  in,  they  are  exposed  in  a  warm 
atmosphere,  to  promote  the  drying  of  the  oil  by  absorption  of  oxygen 
(page  583),  These  processes  having  been  repeated  the  requisite  number  of 
times,  the  excess  of  oil  is  removed  by  a  weak  alkaline  bath,  and  the  skins 
are  dried  and  rolled.  The  buff  colour  of  wash-leather  is  imparted  by  a 
Aveak  infusion  of  sumach. 

*  Polysulpliides  of  sodium  and  calcium  are  sometimes  employed  for  remftving  the  hair, 

2  P 


594  GALLIC  ACID. 

ParcJiment  is  made  by  stretching  lamb  or  goat  skin  upon  a  frame,  re- 
moving the  hair  by  lime  and  scraping,  as  usual,  and  afterwards  rubbing 
with  pumice  stone,  until  the  proper  thickness  is  acquired. 

Tannic  acid,  like  many  other  proximate  constituents  of  vegetables 
(see  page  482),  when  boiled  with  diluted  sulphuric  acid,  yields  glucose, 
whilst  a  new  acid  may  be  obtained  from  the  solution,  which  is  known  as 
gallic  acid;*  C,^,,0,.,   +   AR^O   =   d{C^B.,0,)   +   C^Hj^Oe 

Tannic  acid.  Gallic  add.  Glucose. 

The  addition  of  dilute  sulphuric  acid  to  the  infusion  of  gall-nuts  pro- 
duces a  precipitate  composed  of  tannic  and  sulphuric  acid,  but  this 
dissolves  when  boiled  with  excess  of  sulphuric  acid,  suffering  the  above 
change. 

According  to  Schiff,  pure  tannic  acid  does  not  yield  glucose  when  boiled  with 
sulphuric  acid.     He  regards  tannic  acid  as  digallic  acid  (C7H504).20,  of  which  natural 
taunin  is  a  glucoside,  its  decomposition  under  the  action  of  sulphuric  acid  being 
represented  by  Cj^HjgOa,  +  2H2O  =  CgHioOg  +  2C14H10O9 
Tannin.     "  Glucose.        Digallic  acid. 

The  digallic  acid  is  monobasic,  its  salts  being  formed  upon  the  type  HC]4Hj,0g. 

420.  Gallic  acid  (H3C-H3O5)  is  also  formed  from  tannic  acid  when 
exposed  to  the  air,  particularly  in  the  presence  of  the  matters  associated 
with  it  in  the  gall-nut.  The  method  generally  practised  for  obtaining 
gallic  acid  consists  in  exposing  powdered  nut-galls  in  a  moist  state  to  the 
action  of  the  air  for  some  weeks,  in  a  warm  place,  when  oxygen  is  absorbed, 
and  carbon  dioxide  evolved,  the  powder  becoming  covered  with  crystals  of 
gallic  acid  (tannic  acid  does  not  crystallise).  By  boiling  the  mass  with 
water,  the  gallic  acid  is  extracted,  and  since,  unlike  tannic  acid,  it  is  very 
sparingly  soluble  in  cold  water,  the  greater  portion  crystallises  out  as  the 
solution  cools,  in  long  silky  needles,  containing  C^HgOg.Aq. 

In  this  process  another  acid  is  obtained  in  small  quantity,  which  is 
insoluble  in  water,  and  has  been  called  ellagic  acid  (HCyHgO^) ;  it 
possesses  some  interest,  because  it  is  found  as  a  product  of  animal  life  in 
certain  intestinal  concretions  or  hezoars,  occurring  in  the  antelopes  of 
Central  Asia.  It  may  be  extracted  by  alcohol  from  the  tanning  material 
called  divi-divl  (the  pods  of  Catsalpina  coriaria). 

According  to  Schiff,  gallic  acid  is  C7H5O4.OH,  and  may  be  converted  into  tannic 
(digallic)  acid  by  boiling  its  alcoholic  solution  with  arseuic  acid,  which  undergoes  no 
change  in  the  process;  2(C,H504. OH)  =   (C7H504).0   +   HjO  . 
Gallic  acid.        Digallic  or  tannic  acid. 

He  regards  ellagic  acid  as  HjO.CjjHgOfl.     By  heating  gallic  and  arsenic  acids  together 
in  solution  for  some  time,  ellagic  acid  is  obtained  as  a  crystalline  precipitate — 

4C.Hb05  +  As-A  =  2Ci4HjoO,o  +  AsjOj  +  2Yi.fi . 
Gallic  iicid.  Ellagic  acid. 

It  may  also  be  obtained  by  heating  tannic  acid  with  arsenic  anhydride  — 

2CuHi„09  +  As^Oj  =  2C14H10O10  =  AsjOg- 
Tannic  acid. 

"When  an  alkaline  solution  of  gallic  acid  is  exposed  to  air,  it  absorbs  oxygen  and 
aei|uircs  a  dark  colour  due  to  tanncmiclanic  acid,  CgH403,  which  appears  also  to  be 
ptoduced  by  the  action  of  nitrous  acid  on  gallic  acid. 

In  most  astringent  substances  a  small  quantity  of  gallic  acid  accom- 
panies the  tannic. 

*  It  will  be  perceived  that  tannic  acid  is  analogous  in  constitution  to  the  gluco-tartaric 
.acid  mentioned  at  p  579,  which  splits  into  glucose  and  tartaric  acid  when  boiled  with 
diluted  sulplmric  acid,  exactly  as  tannic  acid  splits  into  glucose  and  gallic  acid. 


GALLIC  ACID.  595 

Gallic  acid  dissolves  in  oil  of  vitriol  with  a  red  colour,  and  when  the 
solution  is  poured  into  water,  a  red-brown  precipitate  is  obtained,  called 
rufigalUc  acid  (Cj4Hg08),  which  is  interesting  from  its  property  of  dyeing 
calico  red,  if  previously  mordanted  with  alum. 

When  powdered  nut-galls  are  heated  in  an  iron  pan  surmounted  with 
a  cone  of  paper  (see  benzoic  acid,  page  479)  to  about  420°,  a  quantity  of 
crystals  sublime  into  the  cone,  which  are  pyrogaUic  acid  (CgHgOg),  or 
more  properly,  pyrogallin  or  pyrogallol,  for  it  is  doubtful  whether  it  is 
really  an  acid  substance. 

Its  formation  from  the  tannic  acid  of  the  galls  is  explained  by  the 
equation,  C27H22O1V  {Tannic  acid)  +  H^O  =  4(C6H603)  {PyrogaUin)  +  SCOg.* 
As  its  name  implies,  this  acid  may  also  be  obtained  by  the  action  of  heat 
upon  gallic  acid,  which  suffers  a  similar  decomposition.! 

This  substance  is  extensively  prepared  for  use  in  photography,  in  which 
art  its  great  tendency  to  absorb  oxygen  is  called  into  play,  rendering  it 
capable  of  decomposing  the  salts  of  silver  with  immediate  separation  of 
the  metal  To  prepare  solution  of  pyrogallol  as  a  developer,  Thorpe  heats 
10  grammes  of  gallic  acid  with  30  c.c.  of  glycerine  to  195°  C.  as  long  as 
CO2  is  evolved,  and  makes  up  to  a  litre  with  water. 

The  solution  of  pyrogallin  soon  becomes  brown  when  exposed  to  the 
air,  from,  absorption  of  oxygen,  and  if  it  be  mixed  with  an  alkali,  it 
absorbs  oxygen  almost  instantaneously,  acquiring  a  very  dark  brown  colour. 
This  property  renders  pyrogallin  very  useful  in  the  analysis  of  air 
and  of  other  gases  containing  uncombined  oxygen;  a  portion  of  air 
confined  in  a  graduated  tube  over  mercury  (see  fig.  82)  is  shaken  with 
a  strong  solution  of  potash  to  absorb  carbonic  acid  gas,  and  the  diminution 
of  volume  having  been  noted,  some  solution  of  pyrogallin  in  4  parts  of 
water  is  introduced;  on  shaking  for  a  few  seconds,  the  oxygen  is 
entirely  absorbed,  when  the  volume  of  the  nitrogen  may  be  observed. 

The  salts  of  tannic  and  gallic  acids  are  not  very  well  known.  The 
latter  appears  to  be  a  tribasic  acid,  so  that  its  true  formula  would  be 
H3C-H3O5,  the  H3  being  replaceable  by  a  metal.  The  acid  character  of 
pyrogallic  acid  is  very  feeble. 

The  three  acids  are  distinguished  by  their  action  upon  the  salts  of  iron. 
"With  pure  ferrous  sulphate  (I'eSO^)  neither  tannic  or  gallic  acid  gives 
any  reaction,  but  pyrogallic  acid  gives  a  deep  indigo  blue  solution;  whilst 
Avith  ferric  sulphate  (Fe23S04)  or  chloride  (Fe2C]g),  the  two  former  give  a 
bluish-black  precipitate,  and  pyrogallic  acid  gives  a  bright  red  solution. 

The  presence  of  tannic  acid  in  a  vegetable  infusion  is  easily  recognised 
by  the  addition  of  ferric  chloride,  but  the  hue  which  is  produced  is  not 
the  same  in  all  astringent  substances,  becau-^e  they  contain  different 
varieties  of  tannin.  All  these  varieties,  however,  differ  from  tannic  acid 
properly  so  called,  in  not  furnishing  pyrogallin  when  heated.  The 
astringent  principle  of  catechu  (terra  japonica  or  ctitch)  and  Mno,  which 
are  used  by  tanners  and  dyers,  is  called  mim-otannic  acid. 

Phloro-gliicol,  CpHfiOg,  which  is  isomeric  with  ]iyrogallol,  is  formed  when  gamboge, 
dragon's  blood,  and  similar  gum-resins  are  fused  with  potassium  hydrate.     It  forms 

*  Or,  adopting  Schiff  s  formula  for  tannic  acid — 

2Ci4H,o09  -f  2H2O  =  4C6H«03  -f  4CO2. 
Tannic  acid.  Pyrogallin. 

+  Bj'  heating  gallic  acid  under  pressure  with  two  or  three  parts  of  water  to  410'  F.  for 
half  an  hour,  and  evajtorating  the  solution,  it  is  said  that  the  theoretical  quantity  of  pyro- 
gallic acid  may  be  obtained.     It  may  be  decolorised  with  animal  charcoal. 


596  COMPOSITION  OF  OPIUM. 

prismatic  crystals,  0^11^03.2112^,  which  dissolve  in  water,  alcohol,  and  ether.     Its 
solution  gives  a  deep  violet  colour  with  ferric  salts. 

VEGETABLE  ALKALOIDS. 

42 L  In  some  plants  the  vegetable  acids  are  combined  with  vegetable 
alkalies  or  alkaloids;  thus  in  opium,  the  morphine  is  combined  with 
meconic  acid;  in  cinchona  bark,  the  quinine  is  combined  with  kinic  acid. 
The  methods  adopted  for  the  separation  of  these  alkaloids  from  the  acids 
and  other  substances  associated  with  them  are  among  the  most  important 
processes  of  practical  chemistry. 

Extraction  of  the  alkaloids  from  opium. — Opium  is  the  concrete  milky 
juice  which  exudes  on  incising  the  unripe  capsules  of  the  Papaver  somni- 
ferum,  and  is  imported  into  this  country  from  Persia,  Turkey,  Bengal,  and 
Egypt,  in  the  form  of  round  masses  or  cakes  enveloped  in  leaves;  it  has  a 
dark  colour,  a  soft  waxy  consistence,  and  a  peculiar  characteristic  odour. 
Different  samples  vary  much  in  composition,  but  the  following  result  of 
an  analysis  of  Smyrna  opium  will  give  an  idea  of  the  nature  of  this  com- 
j)lex  drug  : — 

100  parts  of  Smyrna  Opium  contained — • 

6-7 
0-8 
0-7 

19-1 

9-9 

The  medicinal  value  of  opium  appears  to  be  due  chiefly  to  the  morphine 
(C^yH^gl^Og),  which  is  present,  for  the  most  part,  in  the  state  of  meconate ; 
in  order  to  obtain  it  in  the  separate  state,  the  opium  is  cut  into  slices  and 
digested  with  water  at  a  moderate  heat  for  two  or  three  hours;  the  liquor 
is  then  strained  and  evaporated,  a  little  chalk  being  added  to  neutralise 
the  free  acid.  The  concentrated  solution,  containing  chiefly  morphine 
and  codeine,  in  combination  with  meconic  and  sulphuric  acids,  is  mixed 
with  solution  of  calcium  chloride,  when  the  meconic  acid  is  precipitated  as 
calcium  meconate,  carrying  with  it  a  great  part  of  the  colouring  matter, 
and  leaving  in  solution  the  hydrochlorates  of  morphine  and  codeine, 
which  may  be  obtained  in  crystals  by  evaporation.  The  hydrochlorates 
are  decolorised  with  animal  charcoal  and  recrystallised.  On  adding  am- 
monia to  the  solution  containing  these  salts,  the  morphine  only  is  pre- 
pitated,  and  may  be  purified  by  crystallisation  from  alcohol,  whif  h  deposits 
it  in  white  rectangular  prisms,  having  the  formula  CjyHigNOg.Aq. 

The  solution  from  which  the  morphine  has  been  precipitated  still  con- 
tains the  codeine  hydrochlorate,  and  on  decomposing  it  with  potash,  the 
codeine  is  precipitated  in  crystals,  of  the  composition  CigHg^ISrOg.Aq. 

The  mother-liquor  from  the  hydrochlorates  of  morphine  and  codeine 
contains  narcotine,  narceine,  meconine,  thebaine,  papaverine,  and  some 
other  alkaloids,  together  with  resin  and  colouring  matter.* 

The  leading  features  of  morphine  are  its  sparing  solubility  in  cold  water, 
its  bitter  taste  and  alkaline  reaction,  and  narcotic  poisonous  properties. 
It  is  generally  identified  by  its  giving  an  inky  blue  colour  with  ferric 

*  Ka>o6»a,  apop2>}/  head  ;  vapKt},  torpor  ;  (iHkudv,  a  poppy. 


Gum, 

26-2 

Narceine,     .         .         .         . 

Caoutchouc, 

6-0 

Meconine,    .         .         .         . 

Kesin, 

3-6 

Codeine 

Oily  matter, 

2-2 

Colouring  and  other  organic 

Meconic  acid, 

5-0 

matters, 

Morphine, 

10-8 

Water 

Narcotine, 

6-8 

EXTRACTION  OF  QUININE.  597 

chloride,  and  a  golden  yellow  ivitli  nitric  acid.  The  yellow  colour 
appears  to  be  due  to  an  acid  having  the  composition  C^oH^XOg,  which 
yields  picric  acid  when  heated  with  water  to  100°  C.  in  a  sealed  tube. 

The  morphine  hydrocMorate  (CiyHjgXOg.HCl),  or  muriate  of  morphia^ 
is  the  chief  form  in  which  this  alkaloid  is  used  medicinally. 

"When  morphine  hydrochlorate  is  heated  with  hydrochloric  acid  to  150°  C.  for  some 
hours,  it  loses  the  elements  of  water,  and  is  converted  into  the  hydrochlorate  of 
apomorphine  Ci-HiyNOj,  which  is  remarkable  for  its  emetic  properties.  Morphine 
has  been  converted  into  codeine  Ci7Hj8(CH3)N03  by  heating  it  with  sodium  hydrate 
and  methyle  iodide  in  alcoholic  solution. 

Narcotine  (CggH^gNO-)  possesses  some  interest  as  having  been  the  first 
base  extracted  from  opium,  whence  it  may  be  obtained  by  simply  treating 
the  drug  with  ether,  in  which  the  morphine  is  insoluble.  The  greater 
part  of  the  narcotine  is  left  in  the  residue  after  exhausting  the  opium 
with  water,  from  which  it  is  extracted  by  digestion  with  acetic  acid ;  on 
neutralising  the  solution  with  ammonia,  narcotine  is  precipitated.  It  is 
a  weak  base,  and  has  no  alkaline  reaction. 

The  meconic  acid  which  exists  in  opium  is  a  tribasic  acid,  having  the 
formula  H3C7HO7 ;  it  is  soluble  in  hot  water,  and  crystallises  on  cooling 
in  plates  which  contain  3  molecules  of  water  of  crystallisation.  It 
gives  a  blood-red  colour  with  solution  of  ferric  chloride. 

422.  Extraction  of  quinine. — The  cinchona  or  Peruvian  hark,  so  highly 
prized  for  its  medicinal  qualities,  is  obtained  chiefly  from  the  districts 
around  the  Andes,  and  is  imported  in  three  varieties,  of  which  the  yellow 
cinchona  is  richest  in  quinine,  the  pale  or  grey  bark  in  cinchonine,  Avhilst 
the  red  bark  contains  both  these  bases  in  considerable  quantity.  The 
alkaloids  are  combined  with  kinic  acid,  and  with  a  variety  of  tannin 
known  as  quinotannic  acid. 

In  order  to  extract  them,  the  bruised  bark  is  boiled  with  diluted 
hydrochloric  acid,  and  the  filtered  solution,  containing  the  hydrochlorates 
of  quinine  and  cinchonine,  is  mixed  with  enough  lime  diffused  through 
Avater  to  render  it  alkahne.  The  quinine  and  cinchonine,  which  are  very 
sparingly  soluble  in  cold  water  (requiring  about  400  times  their  weight  to 
dissolve  ihem),  are  precipitated  together  with  some  of  the  colouring  matter 
of  the  bark. 

The  precipitate  having  been  collected  upon  a  linen  strainer  and  strongly 
pressed,  is  treated  with  boiling  alcohol,  which  dissolves  both  the  alkaloids, 
leaving  any  excess  of  lime  undissolved.  A  part  of  the  alcohol  is  then 
recovered  by  distillation,  and  the  solution  containing  the  quinine  and 
cinchonine  is  neutralised  with  sulphuric  acid,  so  as  to  convert  the  alkaloids 
into  sulphates,  and  is  then  decolorised  with  animal  charcoal,  and  allowed  to 
crystallise.  Quinine  sulphate,  being  much  less  soluble  in  water  than 
cinchonine  sulphate,  crystallises  oiit  first,  leaving  the  latter  in  solution. 
The  quinine  sulphate  is  dissolved  in  water  and  decomposed  by  ammonia, 
when  the  quinine  is  separated  as  a  white  powder,  which  may  be  dissolved 
in  alcohol  and  crystallised. 

The  liquid  from  which  the  quinine  sulphate  has  been  deposited  con- 
tains, in  addition  to  cinchonine  sulphate,  another  base  having  the  same 
composition  as  quinine,  but  distinguished  from  it  by  the  indisposition  of 
its  sulphate  to  crystallise.  This  base  is  termed  quinidine,  and  is  produced 
from  quinine  under  the  influence  of  an  excess  of  acid;  it  is  the  most 


598  THEINE  OR  CAFFEINE. 

important  constituent  of  the  substance  called  quinoidine  or  amorphous 
quinine,  which  is  prepared  for  sale  from  the  mother-liquors  of  iiuiniue 
sulphate,  and  forms  a  cheap  substitute  for  quinine  in  medicine. 

Quinamine,  C^^^^^O.2,  is  also  found  in  the  quinine  mother-liquors. 

Quinine  crystallises  in  small  prisms,  which  have  the  composition 
C.,oH24X202.3Aq.  or  Q.3Aq.,'and  altliough  sparingly  soluble,  even  in  boiling 
water,  it  has  an  extremely  bitter  taste,  which  is  also  possessed  by  its  salts. 
It  is  used  in  medicine  in  the  form  of  basic  sulphate,  Q.2H.2S04.7Aq., 
which  requires  as  much  as  700  parts  of  cold  water  to  dissolve  it,  but  is 
readily  dissolved  in  water  acidulated  with  sulphuric  acid,  when  it  is 
converted  into  the  normal  sulphate  of  quinine  (Q.H2SO4)  (or,  with 
another  atom  of  acid,  into  the  acid  sulphate).  The  solution  is  remarkable 
for  its  action  upon  light,  for  although  it  is  perfectly  colourless  when  held 
directly  in  front  of  the  eye,  if  seen  obliquely  it  appears  to  have,  especially 
at  the  edge,  a  beautiful  pale  blue  colour.  This  phenomenon,  which  is 
termed  fluorescence,  has  been  already  referred  to  in  the  case  of  other 
substances  (page  485). 

Quinic  or  kinic  acid. — By  evaporating  the  infusion  of  cinchona  bark 
from  which  the  quinine  and  cinchonine  have  been  separated  by  lime, 
crystals  of  calcium  quinate  are  obtained,  and  on  decomposing  these  with 
sulphuric  acid,  the  quinic  acid  (HC^H^jOg)  passes  into  solution,  whence  it 
may  be  obtained  in  prismatic  crystals. 

This  acid  is  chiefly  interesting  on  account  of  the  peculiar  properties 
of  some  of  its  derivatives.  When  distilled  with  sulphuric  acid  and 
manganese  dioxide,  the  oxygen  evolved  from  the  mixture  converts  the 
quinic  acid  into  a  new  substance,  which  condenses  in  beautiful  yellow 
needles  called  kinone  or  quinone;  HC-H,  ^Og  +  03  =  CgH^Og  +  COg  +  ^HgO. 

Quinic  acid.  Quiiione. 

The  same  substance  is  obtained  in  a  similar  manner  from  one  of  the 
constituents  of  the  coffee-berry  (caff'eic  or  caffeotannic  acid).  By  dissolving 
quinone  in  water  containing  sulphurous  acid,  and  evaporating  the  solution, 
colourless  crystals  of  hydroquinone  are  obtained — 

CgH^Oj  +  H2O  +  H2SO3  =  CgHgOg  +  H2SO4 . 

Quinone.  Hydroquinone. 

"When  a  solution  of  quinone  is  mixed  with  one  of  hydroquinone,  beauti- 
ful green  crystals  are  deposited,  which  are  known  as  green  hydroq^dnone 
(C^jH402.CgHg02),  and  may  also  be  obtained  by  the  action  of  oxidising 
agents,  such  as  ferric  chloride,  upon  hydroquinone.  When  quinone  is 
acted  on  with  hydrochloric  acid  and  potassium  chlorate,  it  is  converted  into 
a  yellow  crystalline  body,  known  SLsperchlorokinone  or  chlomnile  (CgCl402), 
which  is  also  obtained  in  a  similar  way  from  aniline,  salicine,  and  isatine. 
Potash  dissolves  it  when  heated,  giving  a  purple  solution. 

423.  Theme  or  Caffeine — Tea — Coffee. — A  very  remarkable  instance  of 
the  application  of  chemistry  to  explain  the  use  of  widely  different  articles 
of  diet  by  different  nations,  with  a  view  to  the  production  of  certain 
analogoiis  effects  upon  the  system,  is  seen  in  the  case  of  coffee,  tea,  Para- 
guay tea,  and  the  kola  nut  (of  Central  Africa),  which  are  very  dissimilar 
in  their  sensible  properties,  and  afford  little  or  no  gratification  to  the 
palate,  owing  what  attractions  they  possess  chiefly  to  the  presence,  in 
each,  of  one  and  the  same  active  principle  or  alkaloid,  which  has  a 
special  effect  upon  the  animal  economy.  This  alkaloid  is  known  as 
caff"eiiie  or  theine,  and  is  associated  in  the  three  articles  of  diet  men- 


COFFEE — TEA.  599 

tinned  above,  with  various  substances,  M'hicli  give  rise  to  their  diversity 
in  flavour. 

The  raw  coffee-berry  presents,  on  the  average,  the  following  composi- 
tion:— 

100  parts  of  Raw  Coffee  contain — 

Woody  fibre,     .         . 34-0 

Water, 12-0 

Fat, 12  0 

Cane-sugar  and  gum, 15 '5      . 

Legumine,  or  some  allied  substance,  .         .         .         .  13-0 

Caffeine, I'o 

Caffeic  acid, 4"0 

Mineral  substances,  .         .         .         .         .         ,         .         .  7'0 

"When  the  raw  berry  is  treated  with  hot  water,  the  infusion,  which  con- 
tains the  sugar  and  gum,  the  legumine,  caffeine,  and  caffeic  acid  (CgtlgO^), 
has  none  of  the  peculiar  fragrance  which  distinguishes  the  ordinary 
beverage,  and  is  due  to  an  aromatic  volatile  oily  substance  termed  caff'eol 
(CgHjoOg)  formed  during  the  roasting  to  which  the  berry  is  subjected 
before  use.  This  volatile  oil,  which  is  present  in  very  minute  quantity, 
is  produced  from  one  of  the  soluble  constituents  of  the  berry  (probably 
from  the  caffeic  acid),  for  if  the  infusion  of  raw  coffee  be  evaporated  to 
dryness,  the  residue,  when  heated,  acquires  the  characteristic  odour  of 
roasted  coffee. 

Acetic  and  palmitic  acids  are  also  found  among  the  products  of  coffee- 
roasting. 

The  roasting  is  effected  in  ovens  at  a  temperature  rather  below  400°  F., 
when  the  berry  swells  greatly,  and  loses  about  |th  of  its  weight,  becoming 
brittle,  and  easily  ground  to  powder.  It  also  becomes  very  much  darker 
in  colour,  from  the  convei-sion  of  the  greater  part  of  its  sugar  into  caramel 
(page  505),  Avhich  imparts  the  dark  brown  colour  to  the  infusion  of  coffee. 
If  the  roasting  be  carried  too  far,  a  very  disagreeable  flavour  is  imparted 
to  the  coffee  by  the  action  of  heat  upon  the  legumine  and  other  nitro- 
genised  substances  contained  in  the  berry. 

From  100  parts  of  the  roasted  coffee,  boiling  water  extracts  about  20 
parts,  consisting  of  caffeine,  caffeic  acid,  caramel,  legumine,  a  little  sus- 
pended fatty  matter,  fragrant  volatile  oil  (caffeone),  and  salts  of  potassium 
(especially  the  phosphate).  The  undissolved  portion  of  the  cofiee  contains, 
beside  the  woody  fibre,  a  considerable  quantity  of  nitrogenised  (and  nutri- 
tious) matter,  and  hence  the  custom,  in  some  countries,  of  taking  this 
residue  together  Avith  the  infusion. 

In  order  to  e.\tract  the  caffeine  from  the  infusion  of  coffee,  it  is  mixed 
with  solution  of  tribasic  lead  acetate,  to  precipitate  the  caffeic  acid  and 
a  part  of  the  colouring  matter.  Through  the  filtered  solution  sulphuretted 
hydrogen  is  passed  to  remove  the  lead  as  sulphide,  and  the  liquid  filtered 
from  this  is  evaporated  to  a  small  bulk,  when  the  caffeine  crystallises  out 
in  white  silky  needles,  which  have  a  bitter  taste,  and  the  composition 
C8HJ0X4O.2.H2O.     Its  basic  properties  are  very  feeble. 

The  constituents  of  the  leaves  of  the  tea-plant  (Then  nnensis)  exhibit  a 
general  similarity  to  those  of  the  coffee-berry.  In  the  fresh  leaf  we  find, 
in  addition  to  the  woody  fibre,  a  large  quantity  of  a  substance  containing 
nitrogen,  similar  to  legumine,  an  astringent  acid  similar  to  tannic  acid,  a 
small  quantity  of  caffeine,  and  some  mineral  constituents. 

The  aroma  of  tea  does  not  belong  to  the  fresh  leaf,  but  is  produced,  like 


600  COCOA— STRYCHNINE. 

that  of  coffee,  during  the  process  of  drying  by  heat,  which  develops  a 
small  quantity  of  a  peculiar  volatile  oil,  having  powerful  stimulating  pro- 
perties. The  freshly  dried  leaf  is  comparatively  so  rich  in  this  oil  that 
it  is  not  deemed  advisable  to  use  it  until  it  has  been  kept  for  some  time. 

Green  and  black  tea  are  the  produce  of  the  same  plant,  the  difference 
being  caused  by  the  mode  of  preparation.  For  green  tea  the  leaves  are 
dried  over  a  fire  as  soon  as  they  are  gathered,  whilst  those  intended  for 
black  tea  are  allowed  to  remain  exposed  to  the  air  in  heaps  for  several 
hours,  and  are  then  rolled  with  the  hands  and  partially  dried  over  a  fire, 
these  processes  being  repeated  three  or  four  times  to  develop  the  desired 
flavour.  The  black  colour  appears  to  be  due  to  the  action  of  the  air  upon 
the  tannin  present  in  the  leaf. 

Boiling  water  extracts  about  30  parts  of  soluble  matter  from  100  of 
black  tea,  and  36  from  100  of  green  tea.  The  principal  constituents  of 
the  infusion  of  tea  are  tannin,  aromatic  oil,  of  which  green  tea  contains 
about  0"8  and  black  tea  0'6  per  cent.,  and  caffeine,  the  proportion  of 
which,  in  the  dried  leaf,  varies  from  2*2  to  4"1  per  cent.,  being  present  in 
larger  quantity  in  green  tea. 

The  spent  leaves  contain  the  greater  part  of  the  legumine  and  a  con- 
siderable quantity  of  caffeine,  which  may  be  extracted  by  boiling  them 
with  water,  and  treating  the  decoction  as  above  recommended  in  the  case 
of  coffee. 

If  tea  be  boiled  with  water,  the  solution  precipitated  with  tribasic 
lead  acetate,  the  filtered  liquid  evaporated  to  dryness,  and  the  residue 
cautiously  heated,  the  caffeine  sublimes  in  beautiful  crystals. 

Cocoa  and  chocolate  are  prepared  from  the  cacao-nut,  which  is  the 
seed  of  Theohroma  Cacao,  and  is  characterised  by  the  presence  of  more 
than  half  of  its  weight  {minus  the  husk)  of  a  fatty  substance  kiaown  as 
cacao-hutter,  and  consisting  of  oleine  and  stearine,  which  does  not  become 
rancid  like  the  natural  fats  generally.  The  cacao-nut  also  contains  a 
large  quantity  of  starch,  a  nitrogenised  substance  resembling  gluten,  to- 
gether with  gum,  sugar,  and  theobromine,  a  feeble  base  very  similar  to 
caffeine,  but  having  the  composition  C^HgN^Og. 

The  seeds  are  allowed  to  ferment  in  heaps  for  a  short  time,  which 
improves  their  flavour,  dried  in  the  sun  and  roasted  like  coffee,  which 
develops  the  peculiar  aroma  of  cocoa.  The  roasted  beans  having  been 
crushed  and  winnowed  to  separate  the  husks,  are  ground  in  warm  mills, 
in  which  the  fatty  matter  melts  and  unites  with  the  ground  beans  to  a 
paste,  which  is  mixed  with  sugar  and  pressed  into  moulds.  In  the  pre- 
paration of  chocolate,  vanilla  and  spices  are  also  added. 

From  the  composition  of  cocoa  and  chocolate  it  is  seen  that  when  con- 
sumed, as  is  usual,  in  the  form  of  a  paste,  they  would  prove  far  more 
nutritious  than  mere  infusions  of  tea  and  coffee. 

Caffeine  appears  to  be  a  methylated  derivative  from  theobromine,  for  when  it  is 
boiled  with  potash,  methylamine  is  evolved,  and  by  acting  with  methyle  iodide 
(CH.jI)  npon  a  silver  compound  obtained  from  theobromine,  C-(H-Ag)N40.„  the 
silver  and  methyle  change  places,  yielding  Agl  and  caffeine,  C7H7(CH3)N4b2  or 
nietliyle-thcobromine. 

424.  The  vegetable  alkah  strychnine  (C^^E^^f)^),  only  too  Avell  known 
for  its  activity  as  a  poison,  is  contained"  in  crow-Jig  or  Nux-vomica,  the 
seed  of  the  poison  nut  tree  of  the  East  Indies,  and  in  several  other  plants 
of  the  same  family.     The  strychnine  appears  to  be  combined,  in  the  nux- 


TOBACCO.  601 

vbmicca,  with  lactic  acid,  and  is  accompanied  by  a  second  alkaloid,  hnicme 
(C23H26X2O4).  In  order  to  extract  it,  the  bruised  seeds  are  boiled  with 
water  acidulated  with  hydrochloric  acid,  the  solution  is  strained,  and  ren- 
dered alkaline  by  adding  lime,  which  displaces  the  strychnine  and  brucine 
from  their  combination  with  the  acid,  and  separates  them  in  the  form  of 
a  precipitate.  When  this  is  boiled  with  alcohol,  the  excess  of  lime  re- 
mains undissolved,  whilst  the  strychnine  and  brucine  are  carried  into 
solution ;  and  since  the  former  is  less  soluble  in  alcohol  than  the  latter, 
it  is  deposited,  before  the  brucine,  on  evaporating  the  liquid,  in  the 
form  either  of  octahedral  or  prismatic  crystals,  which  have  an  intensely 
bitter  taste.  This  remarkable  bitterness  is  one  of  the  most  prominent 
characters  of  strychnine  ;  for  although  7000  parts  of  water  are  required 
to  dissolve  one  part  of  the  alkaloid,  the  solution  possesses  an  intolerably 
bitter  flavour,  even  when  further  diluted  with  100  times  its  weight  of 
water.  Chloroform  and  benzene  both  dissolve  strychnine  with  great  ease  ; 
and  since  these  liquids  refuse  to  mix  with  water,  they  are  often  employed 
to  extract  the  poison  from  a  large  bulk  of  aqueous  liquid  by  agitatinw  it 
with  a  small  quantity  of  one  of  them,  which  is  then  separated  from  the 
water  and  evaporated,  in  order  to  obtain  the  strychnine  in  the  solid  foim. 
Very  minute  quantities  may  then  be  identified  by  moistening  with  strong 
sulphuric  acid,  and  adding  a  minute  quantity  of  potassium  chromate,  when 
the  chromic  acid  acts  upon  the  strychnine,  giving  rise  to  products  of  oxida- 
tion, which  pervade  the  liquid  in  the  form  of  beautiful  purple  streaks. 

Curarine,  C^qHj.X,  is  a  crystalline  alkaloid  which  has  been  extracted 
from  the  woorari  or  curara  poison  employed  by  the  American  Indians 
for  poisoning  arrows.  It  dissolves  easily  in  water  and  alcohol,  but  not  in 
ether.     Strong  sulphuric  acid  gives  it  a  fine  blue  colour. 

425.  Tobacco  owes  its  active  character  chiefly  to  the  presence  of  a  vege- 
table alkali  which  is  not  found  in  any  other  plant  than  the  Nicotiana  taba- 
cum,  from  the  leaf  of  which  the  various  forms  of  tobacco  are  manufactured. 
This  alkali,  nicotine  (CjoHj^Ng),  is  distinguished  from  most  others  by  the 
absence  of  oxygen,  and  by  its  liquid  condition  at  the  ordinary  temperature. 

In  order  to  extract  the  nicotine  from  tobacco,  the  leaves  are  boiled  with 
water,  which  dissolves  the  alkaloid,  in  combination  with  malic  and  citric 
acids.  The  liquid,  having  been  strained,  is  evaporated  to  a  syrup  and 
mixed  with  alcohol,  when  it  separates  into  two  layers,  of  which  the 
upper  contains  the  salts  of  nicotine  dissolved  in  alcohol,  the  lower  aqueous 
layer  retaining  the  greater  part  of  the  extraneous  vegetable  matters.  The 
alcoholic  layer  having  been  drawn  off,  is  next  shaken  with  potash,  to 
combine  with  the  acids,  and  with  ether  to  dissolve  the  nicotine  then  set 
free.  On  decanting  the  ethereal  solution  of  nicotine  which  rises  to  the 
surface,  and  evaporating  the  ether,  the  nicotine  is  left  in  the  form  of  an 
oily  liquid,  which  is  colourless  when  perfectly  pure,  but  soon  acquires  a 
dark  brown  colour  when  exposed  to  the  air.  It  is  very  readily  distin- 
guished by  its  very  pungent,  irritating  odour,  recalling  that  of  tobacco, 
and  which  is  \qvj  perceptible  at  the  common  temperature,  although  the 
boiling-point  of  nicotine  is  so  high  as  480°  F.  Water,  alcohol,  and  ether 
dissolve  nicotine  with  facilit}-.  The  poisonous  action  of  this  alkaloid  upon 
animals  is  very  powerful,  death  almost  immediately  following  its  adminis- 
tration. The  Virginian  tobacco  contains  more  nicotine  than  other  varieties, 
the  alkaloid  amounting  to  nearly  7  per  cent,  of  the  weight  of  the  leaf 


602  COLOURING.  MATTEK  OF  PLANTS. 

dried  at  212°  R,  whilst  the  ^Maryland  and  Havaiinah  varieties  contain 
only  2  or  3  per  cent,  of  nicotine.  Tobacco  is  remarkable  for  the  very 
large  amount  of  ash  which  it  leaves  when  burnt,  amounting  to  about  one- 
fifth  of  the  weight  of  the  dried  leaf,  and  containing  about  one-third  of  potas- 
sium carbonate,  resulting  from  the  decomposition  of  the  malate,  citrate, 
and  nitrate  of  potassium,  during  the  combustion.  The  presence  of  tliis 
latter  salt  in  large  quantity  (3  or  4  parts  in  100  of  the  dried  leaf)  distin- 
guishes tobacco  from  most  other  plants,  and  accounts  for  the  peculiar 
smouldering  combustion  of  the  dried  leaves. 

Ci(jars  are  made  directly  from  the  tobacco  leaves,  which  are  only  mois- 
tened with  a  weak  solution  of  salt  in  order  to  impart  the  requisite  sup- 
pleness ;  but  snuff,  after  being  thus  moistened,  is  subjected,  in  large 
heaps,  to  a  fermentation  extending  over  eighteen  or  twenty  months,  which 
results  in  its  becoming  alkaline  from  the  development  of  ammonium 
carbonate  (b}"^  the  putrefaction  of  the  vegetable  albumen  in  the  leaf)  and 
of  a  minute  quantity  of  free  nicotine,  which  imparts  the  peculiar  pungency 
to  this  form  of  tobacco.  The  aroma  of  the  snuff  appears  to  be  due  to 
the  production  of  a  peculiar  volatile  oil  during  the  fermentation.  The 
proportion  of  nicotine  in  snuff  is  only  about  2  per  cent.,  being  one-third 
of  that  found  in  the  unfermented  tobacco;  and  a  great  part  of  this  exists 
in  the  snuff  in  combination  with  acetic  acid,  which  is  also  a  result  of  the 
fermentation.  It  is  also  not  improbable  that  a  little  acetic  ether  is  pro- 
duced, and  perhaps  some  other  acids  and  ethers  of  the  acetic  series  {e.g., 
butyric  and  valerianic),  of  which  extremely  minute  quantities  would  give 
rise  to  great  difterences  in  the  aroma  of  the  snufF. 

VEGETABLE  COLOURING  MATTERS. 

426.  Notwithstanding  the  great  variety  and  beauty  of  the  tints  ex- 
hibited by  plants,  comparatively  few  yield  colouring  matters  which  are 
sufficiently  permanent  to  be  employed  in  the  arts ;  the  greater  number  of 
them  fading  rapidly  as  soon  as  the  plant  dies,  since  they  are  nnable  to 
resist  the  decomposing  action  of  light,  oxygen,  and  moisture,  unless  sup- 
ported by  the  vital  influence  in  the  plant;  some  of  them  even  fading  during 
the  life  of  the  plant,  as  may  be  seen  in  some  varieties  of  the  rose,  which 
are  only  fully  coloured  in  those  parts  which  have  been  partly  obscured. 

The  green  colouring  matter  of  plants  has  been  termed  chlorophyll,*  and 
is  a  resinous  substance  containing  carbon,  hydrogen,  nitrogen,  and  oxygen, 
which  has  never  yet  been  obtained  in  so  pure  a  condition  that  its  composi- 
tion could  be  accurately  determined,  since  it  cannot  be  crystallised  or 
distilled,  and  is  therefore  not  amenable  to  the  usual  methods  by  which 
organic  substances  are  obtained  in  a  pure  state. 

When  green  leaves  are  boiled  with  alcohol,  the  latter  acquires  a  fine 
green  colour,  and,  when  evaporated,  deposits  the  chlorophyll.  "When  the 
alcoholic  solution  of  chlorophyll  is  boiled  with  alcoholic  solution  of 
potash,  and  hydrochloric  acid  afterwards  added,  a  yellow  precipitate  {phyl- 
loxanthine)  is  obtained,  and  a  fine  blue  colouring  matter  (j)h yllocyanine) 
remains  in  solution.  The  blue  matter  contains  nitrogen,  and  both  are 
insoluble  in  water.  The  autumnal  colour  of  leaves  may  possibly  be  due 
to  the  dissappearance  of  the  phyllocyanine.  On  immersing  green  leaves 
in  chlorine  they  assume  an  autumnal  tint 

*  XXupoi,  green;  <pu\Kov,  a  leaf. 


COLOURING  MATTER  OF  PLANTS.  G03 

The  blue  colouring  matter'  contained  in  many  flowers,  such  as  the  violet, 
has  been  named  cyanine.  Acids  change  its  blue  colour  to  red,  and  hence 
the  blue  colour  is  exhibited  only  by  flowers  the  juice  of  which  is  neutral, 
whilst  red  flowers  yield  an  acid  juice.  The  colouring  matter  of  grapes 
and  of  red  wine  appears  to  be  identical  with  cyanine. 

Saffron  is  a  yellow  colouring  matter  obtained  from  the  flowers  of  the 
CrociMs  sativus,  which  are  themselves  of  a  blue  colour,  but  have  yellow 
anthers.  When  these  are  dried  and  pressed  into  cakes,  they  form  the 
saff'ron  of  commerce,  which  is  characterised  t)j  its  very  remarkable  and 
somewhat  agreeable  odour.  The  yellow  colouring  matter  is  readily  dis- 
solved by  water  and  alcohol,  and  has  been  found  to  be  a  glucoside,  which 
yields,  when  treated  with  sulphuric  acid,  beside  glucose,  crocitie,  CigH^gOg, 
and  an  essential  oil  having  the  formula  CjqHj^O. 

Safflower  consists  of  the  petals  of  the  Carthamus  iinctorius,  a  plant 
cultivated  in  Egypt.  It  furnishes  a  red  colouring  matter  called  cartlia- 
mine  (Cj^H^gO^),  which  is  used  in  dyeing,  although  it  fades  easily  when 
exposed  to  light.  It  exhibits  the  characters  of  an  acid,  being  dissolved 
by  alkalies  and  reprecipitated  by  acids,  a  circumstance  which  is  taken 
advantage  of  when  extracting  it  from  the  safflower. 

The  orange-yellow  colouring  matter  known  as  annatto  is  extracted  from 
the  seeds  of  the  Bixa  Orellana,  a  native  of  the  West  Indies.  The  colouring 
principle  has  been  called  bixine,  and  is  dissolved  by  alkalies,  but  precipi- 
tated again  by  acids.     Annatto  is  used  for  colouring  butter  and  cheese. 

A  valuable  jellow  colour  is  obtained  from  the  tceld,  or  Reseda  luteola, 
by  boiling  the  dried  leaves  with  water.  This  colouring  matter  is  termed 
luteoUne  (CgoHj^Og),  and  may  be  sublimed  in  yellow  needles. 

The  woods  of  various  trees,  when  boiled  with  water,  furnish  colouring 
matters  of  considerable  importance  ;  thus,  the  wood  of  Morus  tindona, 
or  fustic,  a  West  Indian  tree,  yields  a  crystalline  yellow  colour  called 
moritanuic  acid  (Cj3HjgOy.H20). 

Logwood  is  the  wood  of  the  Hcematoxylon  campechianum,  which  grows 
at  Campeachy,  in  the  Bay  of  Honduras.  Its  most  important  constitutent 
is  a  yellow  colouring  matter  called  hmmatoxyline,  Avhich  may  be  obtained 
in  needle-like  crystals  having  the  composition  (C^gHj^Og.SAq.).  It  becomes 
intensely  red  in  contact  with  alkalies  and  oxygen,  from  the  formation  of 
hcematein  (CigH-^,,Og).  Potassium  chromate  gives  an  intense  black  colour 
with  infusion  of  logwood,  which  has  been  used  as  an  ink,  but  is  not 
permanent. 

Brazil  icood,  which  is  employed  in  the  preparation  of  red  ink,  contains 
hrazilein  (CigHjgOg),  a  colouring  matter  somewhat  resembling  that  of 
logwood. 

The  well-known  Turkey  red  colour  is  obtained  from  madder,  the  root 
of  the  Ruhia  tinctorum,  imported  from  the  south  of  France  and  the 
Levant.  This  root  does  not  contain  any  red  colouring  matter  during  the 
life  of  the  plant,  but  a  yellow  substance  [ruhian,  CggHg^Oij),  from  the 
decomposition  of  which  the  madder  red  is  obtained.  There  are  several 
methods  in  use  for  obtaining  the  red  colour  from  madder.  If  the  root  be 
steeped  in  water  for  some  time,  so  that  some  of  the  nitrogenised  con- 
stituents begin  to  undergo  decomposition,  a  peculiar  fermentation  is  excited 
in  the  rubian,  resulting  in  its  decomposition  into  several  new  bodies,  the 
chief  of  which  are  a  red  crystalline  colouring  matter  alizarine  (C14H8O4), 
and  an  uncrystallisable  sugar.     The  alizarine  may  be  dissolved  out  either 


604  PRODUCTION  OF  ARTIFICIAL  ALIZARINE. 

by  water  or  alcohol,  and  may  be  obtained  in  beautiful  plates  having  a 
golden  lustre. 

If  the  madder  root  be  boiled  with  water  the  rubian  is  dissolved,  and 
when  this  solution  is  boiled  with  dilute  sulphuric  acid,  the  rubian  under- 
goes a  decomposition  similiar  to  that  mentioned  above,  and  the  alizarine, 
being  insoluble  in  the  dilute  acid,  is  precipitated. 

Madder  which  has  been  treated  with  hot  sulphuric  acid,  so  as  to  decom- 
pose the  rubian,  is  used  in  print-works  under  the  name  of  garancine,  and 
yields  a  red  solution  containing  alizarine  when  boiled  with  water. 

Artificial  alizarine. — The  discovery  of  a  process  for  the  artificial  pro- 
duction of  the  colouring  matter  of  madder  from  anthracene,  one  of  the 
constituents  of  coal-tar,  is  one  of  the  most  important  services  which 
chemistry  has,  of  late  years,  rendered  to  the  useful  arts,  and  affords  an 
excellent  illustration  of  the  practical  importance  of  the  minute  study  of 
the  constitutron  of  organic  substances.  When  alizarine,  C^^^O^,  was 
heated  with  powdered  zinc,  it  was  found  to  be  converted  into  anthracene, 
Cj^HjQ,  a  substance  obtained  among  the  last  products  of  the  distillation 
of  coal-tar,  for  which  no  useful  application.had  hitherto  been  discovered.* 
It  somewhat  resembles  naphthalene  in  properties,  but  may  be  dis- 
tinguished from  it  by  its  sparing  solubility  in  alcohol.  When  treated 
with  oxidising  agents,  such  as  a  mixture  of  acetic  and  chromic  acids,  it 
yields  a  crystalline  compound  known  as  oxanthracene,  Cj4Hg02,  which 
bears  the  same  relation  to  anthracene  as  quinone  (page  598)  (CgH^Og) 
bears  to  benzene  (CgH^),  and  has  therefore  been  called  anthraquinone. 
When  acted  upon  by  bromine,  this  is  converted  into  dihromanthraquinone, 
C^Ji^TjT.fi.^  By  heating  this  to  about  350°  F.  with  caustic  potash, 
Cj^HgBr^O^  +  4KH0  =  C^JIeK^O^  (potassic  alizarate)  +  2KBr  +  2H2O. 
Alizarine  is  precipitated  by  decomposing  the  potassic  alizarate  with  hvdro- 
chloric  acid,  Ci4HeK204  -1-  2HC1  =  Ci^HgO^  {alizarine)  +  2KCI. 

This  reaction  shows  that  alizarine  is  really  dioxyanthraquinone,  or  anthraquinone 
in  which  2  atoms  of  hydrogen  are  replaced  by  hydroxyle — 

Anthraquinone,  Ci4Hg02  ;  Alizarine,  Ci4Hg(HO)202 . 

Another  colouring  matter  exists  in  madder,  named  purpurine,  having  the  formula 
C,4H5(HO)302,  or  anthraquinone  in  which  3  atoms  of  hydrogen  have  been  replaced 
by  hydroxyle.  In  the  process  of  preparing  alizarine  from  anthracene,  a  red  colouring 
matter  is  formed  which  has  the  same  composition  as  the  purpurine  of  madder,  but 
differs  from  it  in  some  of  its  properties ;  this  body  has  been  called  anthrapurpurine, 
and  its  presence  in  artificial  alizarine  greatly  enhances  the  brilliancy  of  the  reds 
obtained  with  this  dye. 

Alizarine-orange,  'Cifi^{'^02)04,  is  obtained  by  the  action  of  nitrous  acid  vapours 
upon  dry  alizarine. 

Within  the  last  few  years,  the  production  of  artificial  alizarine  has  been  conducted 
on  a  very  large  scale,  and  has  materially  reduced  the  importation  of  madder.  The 
anthracene  which  crystallises  out  from  the  last  runnings  of  the  tar  stills  is  purified  by 
pressure  and  treatment  with  petroleum  spirit.  It  is  then  distilled  with  a  mixture  of 
potashes  with  a  little  lime,  by  which  certain  impurities  are  decomposed,  and  the 
anthracene  condenses  in  primrose-yellow  crystalline  cakes. 

Production  of  artificial  alizarine  from  anthracene  tvithout  previous  convers-ion  into 
anthraquinone.— The  anthracene  is  exposed  in  leaden  chambers  to  the  action  of 
clilorine  gas,  which  converts  it  into  a  bright  yellow  crystalline  mass  of  dichlor- 
anthracene  ;  C,4Hio  +  CI4  =  C,4H8Cl2  +  2HC1.  The  dichloranthracene  is  heated  to  260° 
C.  with  strong  sulphuric  acid,in  an  iron  pot,  until  a  sample  dissolves  in  water  without 
fluorescence,  when  the  following  changes  take  place— 

*  CuHgOi  +  H2O  +  Zus  +  5ZnO  =  CuH^o .  ■ 


CONVERSION  OF  ANTHRACENE  INTO  ALIZARINE.  605 

(1)  Ci^HgCla  +  2H,S0^=    C,4H«(S0:,H),C]2  +  2H2O. 
Disulphodichlofun- 
tliracenic  acid. 

Ci4H6(S03H)2Cl2    +    H2SO4  =  C,4H6(S03H)202      +   SO^   +   2HC1. 

Disulphanthra- 
qulnonic  acid. 

C14H8CI2  +   H.SO4  =  Ci^HsOa  +  SO2     +    2HC1. 
Anthraquinone. 

(4)  CuHaOa    +   H^SO^  =  C,4H,(S03H)02     +  H2O . 
Sulplianthra- 
quinonic  acid. 

The  mixture  of  sulpho-acids  is  neutralised  with  slaked  lime,  and  the  calcium 
salts  are  converted  into  sodium  salts  by  treatment  with  sodium  carbonate.  The 
concentrated  solution  of  the  sodium  salts  is  heated  with  caustic  soda  (and  a  little 
jwtassium  chlorate),  in  a  closed  iron  boiler,  to  about  180°  C.  for  twenty-four  hours, 
when  a  purple  solution  is  obtained,  containing  the  ali2arate  and  anthrapurpurate  of 
sodium — 

Ci4H,(HS03)02  +  4XaH0  -  Ci4H6(NaO)A  +  Na-^SOs  +  2HjO  +  H^ 
Sodium  ali Karate. 

Ci4H6(HS03)202  +  7NaH0  =  Ci4H5(NaO)302  +  2Na2S03  +  4li.fi  +  H, . 

Sodium  antlira- 
purpurate. 

The  solution  is  run  into  dilute  sulphuric  acid  in  leaden  tanks,  when  the  artificial 
alizarine  separates  as  a  yellow  precipitate  consisting  of  a  mixture  of  alizarine  aud 
authrapurpurine,  which  is  washed  and  pressed — 

CuHgCNaOjoOa  +  2H2SO4  =  Cj4Hs{HO)202  +  2NaHS04 
Alizarine. 

Ci4H6(NaO)302  +  3H2SO4  =  Ci4H5(HO)302  +  3XaHS04 . 
Anttirapui-purine. 

The  potassium  chlorate  is  added  in  order  to  oxidise  some  sodium  oxanthraquinonate 
resulting  from  a  secondarj'^  reaction^ 

C,4H7(NaO)0,  +  NaHO  +  0  =  Ci4H6(NaO)202  +  HgO. 

^'^„",!?nnn^|p''™"  Sodium  alizarate. 

qumonate. 

Conversion  of  anthracene  into  anthraquinmic  and  alizarine. — Anthracene  is  treated 
in  leaden  tanks  with  potassium  dichromate  and  diluted  sulphuric  acid,  the  reaction 
being  completed  by  boiling.  The  dichromate  is  converted  into  chrome  alum,  and  the 
liberated  oxygen  changes  ths  anthracene  into  anthraquinone,  Ci4Hj0  +  O3=Ci4H8O, 
+  H2O. 

Tlie  anthraquinone  is  dissolved  in  strong  sulphuric  acid  and  reprecipitated  b}"- 
water,  which  retains  the  impurities  in  solution.  After  being  washed  and  dried,  it  is 
heated  for  eight  or  ten  hours  to  180°  C.  with  fuming  sulphuric  acid  in  an  iron  |iot, 
being  constantly  stirred ;  on  diluting  with  water,  any  unaltered  anthraquinone  is 
precipitated,  and  snlphanthraquinonic  acid  remains  in  solution;  C]4H802  +  H2SO4 
=  Ci4H7(HS03)Oo  +  H20. 

By  neutralising  this  ^^dth  caustic  soda,  the  sparingly  soluble  sodium  salt  is  obtained, 
which  is  converted  into  alizarine  by  heating  with  caustic  soda  and  some  potassium 
chlorate. 

The  scientific  interest  of  this  production  of  alizarine  from  anthracene  is 
enhanced  by  the  circumstance  that  anthracene  has  itself  been  produced 
by  synthesis ;  for  carbon  and  hydrogen  combine,  at  a  high  temperature, 
to  produce  acetylene  (C^H.,),  3  molecules  of  which  coalesce  at  a  high 
temperature  to  form  benzene  (C^H^),  and  by  acting  upon  2  molecules  of 
benzene  with  1  molecule  of  ethylene,  anthracene  has  been   produced ; 

Turmenc  is  the  root  of  an  East  Indian  plant,  the  Curcuma  longa  ;  its 
yellow  colouring  matter,  called  curcumine  {C-,^iii^O_^),  is  nearly  insoluble  in 
water,  but  dissolves  in  alcohol.  It  is  an  acid  body,  forming  red  salts  with 
the  alkali  metals,  and  is  used  in  the  laboratory  as  a  test  of  alkalinity. 


606  COLOURING  MATTERS  PREPARED  FROM  LICHENS. 

427.  Litmus,  archil,  and  cudbear  are  brilliant,  though  not  very  per- 
manent purple  and  violet  colours,  prepared  from  various  lichens,  such  as 
Roccdla  tinctoria  (litmus),  and  Lecanora  tartarea  (cudbear).*  ; 

Archil  and  cudbear  owe  their  colour  chiefly  to  the  presence  of  orceine 
(C7H7XO3),  which  does  not  exist  ready  formed  in  any  of  the  lichens,  but 
is  developed  during  the  preparation  which  they  undergo. 

If  cither  of  the  above  lichens  be  digested  for  some  hours  with  lime  and 
water  and  the  filtered  solution  be  neutralised  with  hydrochloric  acid,  a 
Avliite  gelatinous  precipitate  is  obtained,  which  dissolves  in  hot  alcohol, 
and  is  deposited  in  crystals  on  cooling.  This  substance  may  consist, 
according  to  the  particular  lichen  employed,  of  one  or  more  acids,  the  chief 
of  which  have  been  named  eri/thric]  (C2oH220jq),  eve)7iic  (Cj^HigO^),  and 
lecanoric  (Cj^Hj^Oy)  acids.  These  acids  are  remarkable  for  the  facility 
Avith  Avhich  they  furnish  compound  ethers  when  boiled  with  alcohol. 

When  either  of  these  acids  is  boiled  with  an  excess  of  lime  or  baryta,  it 
is  decomposed,  and  if  the  excess  of  base  be  removed  by  carbonic  acid,  the 
filtered  liquid  evaporated  to  a  syrup,  and  extracted  with  boiling  alcohol, 
the  latter  deposits  prismatic  crystals  oi  orcine  (C^HgOg.  Aq.).  The  forma- 
tion of  this  body  will  be  understood  from  the  following  equations — 

C20H22O10  +  2Ca(HO)2  =  2CaC03  +  2C7H8O2  +  C^HjA ; 

[  Krythric  acid.  Orcine.  Ejythrite. 

Ci^H^gOy    +  Ca(H0)2    =  CaCOg    -J-  CgHjoO^   +  C.HgOg 

Evei-nic  acid.  Evernesic  acid.  Orcine. 

Pure  orcine  is  a  colourless  substance,  but  when  exposed  to  the  joint  action 
of  ammonia  and  air,  it  is  converted  into  a  beautiful  red  colouring  matter, 
orceine  ;  CyHgO  +  NH3  +03  =  C7H-NO3  +  2H2O. 

Orcine.  Orceine. 

Orceine  does  not  crystallise,  and  dissolves  to  a  slight  extent  only  in  water, 
but  readily  in  alcohol  and  in  alkaline  liquids,  yielding,  in  the  latter 
case,  a  beautiful  purple  solution,  which  becomes  red  when  mixed  with 
acids,  and  deposits  red  flakes  of  orceine. 

The  chemistry  of  the  processes  by  which  archil  and  cudbear  are  prepared 
will  now  be  easily  understood.  The  powdered  lichen  is  mixed  with  urine 
(to  furnish  ammonia)  and  lime,  and  exposed  to  the  air  for  some  weeks, 
when  the  lime  decomposes  the  erythric  and  other  acids,  with  formation  of 
orcine,  which  then  passes  into  orceine  under  the  influence  of  the  ammonia 
and  atmospheric  oxygen. 

The  preparation  of  litmus  from  the  Rocella  tinctoria  is  similar  to  that 
just  described,  but  a  mixture  of  carbonates  of  ammonium  and  potassium 
is  employed  instead  of  the  urine  and  lime.  The  chemical  change  which 
takes  place,  although  similar  in  principle,  is  not  precisely  identical 
with  the  foregoing,  for  the  principal  colouring  matter  developed  appears 
to  be  a  red  substance  called  azolitmine  (CpHj^^NOg),  which  differs  from 
orceine  by  its  insolubility  in  alcohol.  It  dissolves  in  alkaline  solutions 
with  a  beautiful  blue  colour,  which  is  immediately  reddened  by  acids,  a 
]>roiierty  frequently  turned  to  account  by  the  chemist  for  detecting  the  acid 
reaction.  Litmus  occurs  in  commerce  in  small  cakes,  which  are  made  up 
with  chalk. 

Erijthrite  {G^^^O^  is  a  crystalline  substance  extracted  from  various 
lichens  and  fungi,  which  forms  combinations  with  the  fatty  acids  similar 

*  Said  to  have  been  named  after  Cuthbert,  a  manufacturer  of  the  dye. 


BLUE  INDIGO.  607 

to  those  formed  by  glycerine.     It  is  sometimes  represented  as  a  tetratomic 
alcohol  (page  565),  (C4H6)'^(HO)4. 

428.  Indigo  blue  {C^^-^^^0^*  is  prepared  from  various  species  of 
Indigofera,  grown  in  China,  India,  and  America.  The  plants  are  covered 
with  cold  water,  and  allowed  to  ferment ;  as  soon  as  a  blue  scum  appears 
upon  the  surface,  a  little  lime  is  added  and  the  mixture  stirred  briskly  for 
some  time,  when  the  indigo  is  deposited  in  a  pulverulent  form;  it  is 
collected  on  calico  strainers,  pressed,  and  cut  up  into  cakes. 

The  theory  of  the  process  is  not  yet  clearly  explained;  it  is  certain  that 
the  indigo  blue  does  not  pre-exist  in  the  plant,  but  is  a  product  of  the 
fermentation.  Eecent  observations  have  shown  that  the  indigo  plants 
probably  contain  a  substance  called  indican  (C26H33NOi8),  which  stands 
in  a  similar  relation  to  indigo  blue  to  that  in  which  rubian  stands  to 
alizarine  (in  the  case  of  madder)  ;  it  is  soluble  in  water,  and  when  heated 
with  an  acid,  splits  up  into  indigo  blue,  indigo  red,  and  a  peculiar  uncrystal- 
lisable  sugar.  The  indigo  red  may  be  extracted  from  commercial  indigo 
by  boiling  with  alcohol,  in  which  the  indigo  blue  is  insoluble.  Since 
indigo  blue  is  insoluble  in  all  ordinary  solvents,  it  is  necessary,  in  order  to 
use  it  for  dyeing,  to  reduce  it  to  the  condition  of  white  indigo,  which  is 
soluble  in  alkalies. 

If  2  pai'ts  of  ferrous  sulphate  (copperas)  be  dissolved  in  200  parts  of 
water,  and  well  shaken  in  a  stoppered  bottle  with  1  part  of  powdered 
indigo  and  3  of  slaked  lime,  the  indigo  will  disappear,  and  on  allowing 
the  precipitate  to  subside,  a  yellow  fluid  will  be  obtained,  which  becomes 
blue  at  the  surface  as  soon  as  it  is  exposed  to  air.  If  this  solution  be 
mixed  with  hydrochloric  acid,  out  of  contact  with  air,  a  flocculent  pre- 
cipitate of  white  indigo  is  obtained.  The  composition  of  this  substance 
is  CjgHjgXgOg,  and  it  is  formed  from  blue  indigo  (CigH^oNgOg)  by  the 
addition  of  2  atoms  of  hydrogen  derived  from  water,  the  oxygen  of 
which  has  converted  the  ferrous  hydrate  into  ferric  hydrate  ;  one  por- 
tion of  the  lime  combines  with  the  sulphuric  acid  of  the  ferrous  sulphate, 
whilst  another  serves  to  dissolve  the  white  indigo,  which  is  soluble  in 
alkaline  liquids ;  FeSO^  +  Ca(0H)2  =  CaSO^  -I-  re(OH)., ;  2Fe(0H)., 
+  2H,0 -F  CieHj^X  A  =  C,6H,2^V)2  +  re2(OH)6. 

The  solution  of  white  indigo  prepared  by  this  process  is  employed  for 
dyeing  linen  and  cotton,  which  are  immersed  in  the  vat,  and  then  exposed 
to  the  air,  the  oxygen  of  which  removes  two  atoms  of  hydrogen  from  the 
white  indigo,  and  the  blue  indigo  thus  formed  is  precipitated  upon  the 
fibre. 

Other  reducing  agents  are  sometimes  substituted  for  the  ferrous  sul- 
phate. Even  decaying  vegetable  matter  effects  the  conversion  of  blue 
into  white  indigo  in  an  alkaline  liquid.  Thu^,  for  some  purposes,  the  vat 
is  prepared  by  fermenting  a  mixture  of  indigo,  madder,  carbonate  of 
potash,  and  lime,  when  the  hydrogen  extricated  in  the  fermentation  of  the 
vegetable  matter  converts  the  blue  into  white  indigo,  which  is  then  dis- 
solved by  the  potash  liberated  from  the  carbonate  by  the  lime.f 

When  cloth  is  dyed  with  indigo  (Saxony  blue)  the  colour  is  dissolved 

*  This  formula,  which  is  double  that  formerly  employed,  agrees  with  the  vapour-density 
of  indigo,  which  has  been  found  to  be  9  ■■45  (air  =1). 

f  Sodium  hydrosulphite  may  be  employed  for  the  reduction  of  indigo.  To  prepare  it, 
solution  of  bisulphite  of  soda  is  placed  in  "contact  with  zinc  for  an  hour  in  a  closed  vessel. 
The  solution  is  mixed  with  the  indigo  and  milk  of  lime  (see  p.  214). 


608  DYEING  AND  CALICO-PRINTING. 

by  means  of  sulphuric  acid.  Fuming  sulphuric  acid  dissolves  indigo  blue 
very  readily,  but  oil  of  vitriol  does  not  act  quite  so  weU.  The  solution 
thus  obtained  is  commonly  caXled  sulphiiidi.gotic  acid,  but  it  really  contains 
two  acids,  the  sulj^hindylic  (HCgH^NO.SOg)  and  hyposuljMndigotic.  The 
blue  solution  becomes  colourless  when  shaken  with  powdered  zinc,  and 
resumes  its  blue  colour  when  shaken  with  air. 

On  heating  indigo,  it  evolves  purple  vapours,  which  condense  in  pris- 
matic crystals  of  a  coppery  lustre,  consisting  of  pure  indigotine  or  indigo 
blue,  which  may  be  obtained  in  larger  quantity  by  digesting  indigo  with 
grape-sugar,  caustic  soda,  and  weak  alcohol,  when  a  solution  of  white 
indigo  is  obtained  which  deposits  the  crystallised  indigotine  on  exposure 
to  air. 

Artificial  Indigo. — This  colouring  matter  has  been  obtained  from  the  toluene  of 
coal-tar,  but  the  process  is  at  present  too  expensive  to  be  commercially  successful. 
The  steps  of  the  conversion  are  the  following  : — 

(1)  CfiH,.CH3  {toluene)  +Cl4  =  2HCl  +  CfiH5.CHCl2  {henzylcnc  dichloride) ;  (2)  CgHj, 
CHClj  -1-  2KH0  =  2KC]  +  B..fi  H-CgHg.CHO  {bcnzaldchyde) ;  (3)  CgHj.CHO  -f-  CH3. 
COCl  {acetylc  chloride)  -  CgHs.CgHo.COaH  {cinnamic  acid)  -f  HCl;  (4)  CgHg-CaHj. 
CO3HI+  HNO3  =  CgH4NO2.C2H2.CO2H  (nitrocinnamic  acid) -f-HjO  ;  (5)  CgH4N02. 
CoH^.COjH  +  Bcg  =  CgH4NO2.C2H2Bro.CO2H  (dibrmnnitrophenyl  propionic  acid)  ; 
(O")  CgH4N02. C2H2Br2. CO2H  +  2NaOH  =  CgH4N02.  C2CO2H  (nitrophenyl  propiolic  add) 
+  2NaBr  +  2H20;  (7)  By  heating  this  last  acid  with  a  reducing  agent,  such  as  an 
alkaline  solution  of  grape-sugar,  the  latter  is  made  to  appropriate  the  oxygen  of  two 
molecules  of  water,  the  hj'drogen  of  which  acts  upon  the  acid,  converting  it  into  in- 
digo blue;  2C9H5NO4  [nitrophenyl propiolic  acid)  -t-2H2=2C02-t-2H20-h'Ci6HioN202 
(indigo). 

429.  Animal  colouring  matters. — From  the  animal  kingdom  only  two 
colouring  matters  of  any  great  importance  are  derived,  viz.,  cochineal  and 
lac,  both  which  are  obtained  from  insects  of  the  coccus  tribe.  The  colour- 
ing matter  of  cochineal  is  known  as  carmine,  and  may  be  extracted  from 
the  insects  by  water  or  alcohol.  It  has  acid  properties,  and  has  been 
named  carminic  acid  (C^^H^gO^o).  Carmine-lake  is  a  combination  of  this 
acid  with  alumina,  precipitated  when  a  solution  of  alum  and  an  alkaline 
carbonate  are  added  to  one  of  cochineaL 

Dyeing  and  Calico-Printinc. 

430.  The  object  of  the  dyer  being  to  fix  certain  colouring  matters 
permanently  in  the  fabric,  his  processes  would  be  expected  to  vary  with 
the  nature  of  the  latter  and  of  the  colour  to  be  applied  to  it.  In  order 
that  uniformity  of  colour  and  its  perfect  penetration  into  the  fibre  may  be 
attained,  it  is  evident  that  the  colouring  matter  must  always  be  employed 
in  a  state  of  solution ;  and  it  must  be  rendered  fast,  or  not  removable  by 
washing,  by  assuming  an  insoluble  condition  in  the  fibre. 

The  simplest  form  of  dyeing  is  that  in  which  the  fibre  itself  forms  an 
insoluble  compound  with  the  colouring  matter.  Thus,  if  a  skein  of  silk 
be  immersed  in  a  solution  of  indigo  in  sulphuric  acid,  it  removes  the  whole 
of  the  colouring  matter  from  the  liquid,  and  may  then  be  washed  with 
water  without  losing  colour ;  but  if  the  same  experiment  be  tried  with 
cotton,  the  indigo  will  not  be  withdrawn  from  the  solution,  and  when  the 
cotton  has  been  well  squeezed  and  rinsed  with  water,  it  will  become  white 
again.  It  may  be  stated  generally,  that  the  animal  fabrics  (silk  and  wool) 
will  absorb  and  retain  colouring  matters  with  much  greater  facility  than 
vegetable  fabrics  (cotton  and  linen).    In  the  absence  of  so  powerful  an 


DYEING  AND  CALICO-PEINTING.  609 

attraction  between  the  fibre  and  the  colouring  matter,  it  is  usual  to  impreg- 
nate the  fabric  with  a  mordant  or  substance  having  an  attraction  for  the 
colour,  and  capable  of  forming  an  insoluble  combination  with  it,  so  as  to 
retain  it  permanently  attached  to  the  fabric.  Thus,  if  a  piece  of  cotton 
be  boiled  in  a  solution  of  acetate  of  alumina,  the  alumina  will  be  precipi- 
tated in  tha  fibre ;  and  if  the  cotton  be  then  soaked  in  solution  of 
cochineal  or  of  logwood,  the  red  colouring  matter  will  form  an  insoluble 
compound  (or  lake)  with  the  alumina,  and  the  cotton  will  be  dyed  of  a 
fast  red  colour. 

Another  method  of  fixing  the  colour  in  the  fabric  consists  in  impregnat- 
ing the  latter  with  two  or  more  liquids  in  successiun,  by  the  admixture  of 
which  the  colour  may  be  produced  in  an  insoluble  state.  If  a  piece  of 
any  stuff  be  soaked  in  solution  of  ferric  chloride,  and  afterwards  in 
j)otassium  ferrocyanide,  the  Prussian  blue  which  is  precipitated  in  the 
fibre  will  impart  a  fast  blue  tint. 

An  indispensable  preliminary  step  to  the  dyeing  of  any  fabric  is  the 
removal  of  all  natural  grease  or  colouring  matter,  which  is  effected  by 
processes  varying  with  the  nature  of  the  fibre,  and  is  preceded,  in  the 
cases  of  cotton  and  woollen  materials  which  are  to  receive  a  pattern,  by 
certain  operations  of  shaving  and  singeing  for  removing  the  short  hairs 
from  the  surface. 

From  linen  and  cotton,  the  extraneous  matters  (such  as  grease  and  resin) 
are  generaUy  removed  by  weak  solutions  of  carbonate  of  potassium  or  of 
sodium,  and  the  fabrics  are  afterwards  bleached  by  treatment  with  chloride 
of  lime  (page  155).  But  since  the  fibres  of  silk  and  wool  are  much  more 
easily  injured  by  alkalies  and  by  chlorine,  greater  care  is  requisite  in 
cleansing  them.  Silk  is  boiled  with  a  solution  of  white  soap  to  remove 
the  gum,  as  it  is  technically  termed ;  but  the  natural  grease  is  extracted 
from  Avool  by  soaking  at  a  moderate  temperature  in  a  weak  bath  either  of 
soap  or  of  ammoniacal  (putrefied)  urine.  Both  silk  and  wool  are  bleached 
by  sulphurous  acid  (page  200). 

Among  the  red  dyes  the  most  important  are  madder,  alizarine,  Brazil 
wood,  cochineal,  lac,  and  the  colours  derived  from  aniline. 

In  dyeing  red  with  madder  or  Brazil  wood,  the  linen,  cotton,  or  wool 
is  first  mordanted  by  boiling  in  a  solution  containing  alum  and  bitartrate 
of  potash,  when  it  combines  with  a  part  of  the  alumina,  and  on  plunging 
the  stuff  into  a  hot  infusion  of  madder,  the  colouring  matter  forms  an 
insoluble  combination  Avith  that  earth. 

To  dye  Turkey-red,  the  stuff  is  also  mordanted  with  alum,  but  has  pre- 
viously to  undergo  several  processes  of  treatment  with  oil  and.  with  galls, 
the  necessity  of  Avhich  is  satisfactorily  established  in  practice,  though  it 
is  not  easy  to  explain  their  action.  The  colour  is  finally  brightened  by 
boiling  the  stuff  with  chloride  of  tin. 

Woollen  cloth  is  dyed  scarlet  with  lac  or  cochineal,  having  been  first 
mordanted  by  boiling  in  a  mixture  of  perchloride  of  tin  and  bitartrate  of 
potash. 

The  aniline  colours  (see  page  460)  are  employed  for  dyeing  silk  and 
wool,  either  without  any  mordant  or  with  the  help  of  albumen. 

Blues  are  generally  dyed  with  indigo  (p.  607),  or  with  Prussian  blue; 
in  the  latter  case  the  stuff  is  steeped  successively  in  solutions  of  a  salt  of 
peroxide  of  iron  and  of  potassium  ferrocyanide.  Aniline  blue  is  also 
much  employed  for  silk  and  wooUen  fabrics. 

2  Q 


610  PATTERNS  IN  CALICO -FEINTING. 

The  principal  yellow  dyes  are  Aveld,  quercitron,  fustic,  annatto,  clirys- 
aniline,  and  lead  chromate.  For  the  four  first  colouring  matters  aluminous 
mordants  are  generally  applied.  Lead  chromate  is  produced  in  the  fibre 
of  the  stuff,  which  is  soaked  for  that  purpose,  first  in  a  solution  of  acetate 
or  nitrate  of  lead,  and  then  in  potassium  chromate.  Carbazotic  or  picric 
acid  (page  465)  is  also  sometimes  employed  as  a  yellow  dye. 

In  dyeing  blacks  and  browns,  the  stuffs  are  steeped  first  in  a  bath  con- 
taining some  form  of  tannin  (page  592),  such  as  infusion  of  galls,  sumach, 
or  catechu,  and  afterwards  in  a  solution  of  a  salt  of  iron,  different  shades 
being  produced  by  the  addition  of  indigo,  of  copper  sulphate,  &c. 

431.  The  art  of  calico-printing  differs  from  that  of  dyeing,  in  that  the 
colour  is  required  to  be  applied  only  to  certain  parts  of  the  fabric  so  as  to 
produce  a  pattern  or  design  either  of  one  or  of  several  colours. 

A  common  method  of  printing  a  coloured  pattern  upon  a  white  ground 
consists  in  impressing  the  pattern  by  passing  the  stuff  under  a  roller,  to 
which  an  appropriate  mordant  thickened  with  British  gum  (page  492)  is 
applied.  The  stuff  is  then  dunged,  i.e.,  drawn  through  a  mixture  of  cow- 
dung  and  water,  which  appears  to  act  by  removing  the  excess  of  the 
mordant,  and  afterwards  immersed  in  the  hot  dye-bath,  when  the  colour 
becomes  permanently  fixed  to  the  mordanted  device,  but  may  be  removed 
from  the  rest  of  the  stuff  by  washing. 

If  the  pattern  be  printed  with  a  solution  of  acetate  of  iron,  and  the  stuff 
immersed  in  a  madder-bath,  a  lilac  or  black  pattern  will  be  obtained 
according  to  the  strength  of  the  mordant  employed.  By  using  acetate  of 
alumina  as  a  mordant,  the  madder-bath  would  give  a  red  pattern. 

A  process  which  is  the  reverse  of  this  is  sometimes  employed,  the 
pattern  being  impressed  with  a  resist,  that  is,  a  substance  which  will  pre- 
vent the  stuff  from  taking  the  colour'  in  those  parts  which  have  been 
impregnated  with  it.  For  example,  if  a  pattern  be  printed  with  thickened 
tartaric  or  citric  acid,  and  the  stuff  be  then  passed  through  an  aluminous 
mordant,  the  pattern  will  refuse  to  take  up  the  alumina,  and  subsequently 
the  colour  from  the  dye-bath.  Or  a  pattern  may  be  printed  with  nitrate 
of  copper,  and  the  stuff  passed  through  a  bath  of  reduced  indigo  (page  607), 
when  the  nitrate  of  copper  will  oxidise  the  indigo,  and  by  converting  it 
into  the  blue  insoluble  form,  will  prevent  it  from  sinking  into  the  fibre  of 
those  parts  to  which  the  nitrate  has  been  applied,  whilst  elsewhere,  the 
fibre,  having  become  impregnated  with  the  white  indigo,  acquires  a  fast 
blue  tint  when  exposed  to  the  air. 

Sometimes  the  stuff  is  uniformly  dyed,  and  the  colour  discharged  in 
order  to  form  the  pattern.  A  white  pattern  is  produced  upon  a  red 
(madder)  or  blue  (indigo)  ground  by  printing  with  a  thickened  acid  dis- 
charge, and  passing  the  stuff  through  a  weak  bath  of  chloride  of  lime, 
which  removes  the  colour  from  those  parts  only  which  were  impregnated 
witli  the  acid  (page  156).  By  adding  lead  nitrate  to  the  acid  discharge, 
and  finally  passing  the  stuff  through  solution  of  potassium  chromate,  a 
yellow  pattern  (lead  chromate)  may  be  obtained  upon  the  madder  red 
<,aound.  By  applying  nitric  acid  as  a  discharge,  a  yellow  pattern  may  be 
obtained  upon  an  indigo  ground  (page  136). 

Very  brilliant  designs  are  produced  by  mordanting  the  stuff  in  a  solu- 
tion of  stannate  of  potassium  or  sodium  (page  348),  and  immersing  it  in 
dilute  sulphuric  acid,  which  precipitates   the   stannic  acid  in  the  fibre. 


DIFFICtTLTIES  OF  ANIMAL  CHEMISTRY.  611 

When  the  thickened  colouring  matters  are  printed  on  in  patterns,  and 
exposed  to  the  action  of  steam,  an  insohible  compound  is  formed  between 
the  colour  and  the  stannic  acid,  which  usually  exhibits  a  very  fine  and 
permanent  colour. 

It  is  evident  that  by  combining  the  principles  of  which  an  outline  has 
just  been  given,  the  most  varied  parti-coloured  patterns  may  be  printed. 

AXIMAL  CHEMISTRY. 

432.  Our  acquaintance  with  the  chemistry  of  the  substances  composing 
the  bodies  of  animals  is  still  very  limited,  although  the  attention  of  many 
accomplished  investigators  has  been  directed  to  this  branch  of  the  science. 
The  reasons  for  this  are  to  be  found,  firstly,  in  the  susceptibility  to  change 
exhibited  by  animal  substances,  when  removed  from  the  influence  of  life  ; 
and  secondly,  in  the  absence,  in  such  substances,  of  certain  physical  pro- 
perties by  which  we  might  be  enabled  to  separate  them  from  other  bodies 
with  which  they  are  associated,  and  to  verify  their  purity  when  obtained 
in  a  separate  state.  Two  of  the  most  important  of  these  properties  are 
volatility  and  the  tendency  to  crystallise.  When  a  substance  can  suffer 
distillation  without  change,  it  will  be  remembered  that  its  boiling-point 
affords  a  criterion  of  its  purity ;  or  if  it  be  capable  of  crystallising,  this 
may  be  taken  advantage  of  in  separating  it  from  other  substances  which 
crystallise  more  or  less  easily  than  itself,  and  its  purity  may  be  ascertained 
from  the  absence  of  crystals  of  any  other  form  than  that  belonging  to  the 
substance.  But  the  greater  number  of  the  components  of  animal  frames 
can  neither  be  crystallised  nor  distilled,  so  that  many  of  the  analyses  which 
have  been  made  of  such  substances  differ  widely  from  each  other,  because 
the  analyst  could  never  be  sure  of  the  perfect  purity  of  his  material ;  and 
even  when  concordant  results  have  been  obtained  as  to  the  percentage  com- 
position of  the  substance,  the  atomic  formula  deduced  from  it  has  been  of 
so  singular  and  exceptional  a  character  as  to  cast  very  strong  suspicion 
upon  the  purity  of  the  substance. 

Accordingly,  the  chemical  formulae  of  a  great  many  animal  substances 
are  perfectly  unintelligible,  conveying  not  the  least  information  as  to  the 
position  in  which  the  compound  stands  with  respect  to  other  substances, 
or  the  changes  which  it  might  undergo  under  given  circumstances. 

It  has  been  shown  in  the  previous  chapters  of  this  work  that  we  are 
gradually  learning  to  class  all  compound  bodies  under  a  few  typical  forms, 
so  that  the  chemical  properties  of  any  substance  may  in  many  cases  be 
predicted  from  its  composition  as  indicating  the  type  to  which  it  belongs. 
Take,  for  example,  the  class  of  alcohols  C„H2„+20),  or  of  volatile  acids 
(CjiHgnOg),  or  of  ammonias  (XYg),  and  it  will  be  seen  that  even  those 
formula3  which  are  apparently  the  most  complex  are  perfectly  intelligible 
when  referred  to  their  proper  type  (page  545).  But  the  extraordinary 
formulae,  for  example,  deduced  from  the  ultimate  analysis  of  albumen, 
C7-2Hn2^'^i8S022'  ^^^  caselne,  C^^^^o^^t^^^^,  cannot  be  referred  to  any 
known"  type,  and  refuse  to  be  classed  with  other  substances,  even  if  a 
type  were  invented  expressly  for  them. 

Animal  chemistry  is  for  the  above  reasons  in  a  very  backward  condition, 
as  compared  with  vegetable  and  mineral  chemistry,  though  an  observation 
of  the  progress  of  research  affords  us  the  consolation,  that  a  steady  advance 
is  bein"  made  towards  a  generalisation  of  the  facts  which  have  been  dis- 


612  MILK. 

covered,  especially  by  analogical  reasoning  from  those  two  other  depart- 
mentsifof  the  scieace. 

Milk. — The  chemistry  of  milk  is  well  adapted  to  introduce  the  study  of 
animal  chemistry,  because  that  liquid  contains  representatives  of  all  the 
substances  which  make  up  the  animal  frame ;  and  it  is  on  this  account  that 
it  occupies  so  high  a  position  among  articles  of  food. 

Although,  to  the  unaided  eye,  milk  appears  to  be  a  perfectly  homo- 
geneous fluid,  the  microscope  reveals  the  presence  of  innumerable  globules 
floating  in  a  transparent  liquid,  which  is  thus  rendered  opaque.  If  milk 
be  very  violently  agitated  for  several  hours,  masses  of  an  oily  fat  (butter, 
p.  584)  are  separated  froni  it,  and  leave  the  liquid  transparent.  This  fat 
was  originally  distributed  throughout  the  milk,  in  minute  globules  enclosed 
in  very  thin  membranes  which  were  torn  by  the  violent  agitation,  and  the 
fatty  globules  then  cohered  into  larger  masses. 

For  the  preparation  of  butter,  it  is  usual  to  allow  the  milk  to  stand  for 
some  hours,  when  a  layer  of  cream  collects  upon  the  surface,  the  proportion 
of  which  is  very  variable,  but  is  generally  about  yV*'^  ^^  *^^  volume  of  the 
milk.  The  skimmed  milk  retains  about  half  of  the  fatty  matter.  This 
cream  contains  about  5  per  cent,  (by  weight)  of  fat,  3  per  cent,  of  caseine, 
and  water.  When  the  cream  is  churned,  the  enclosing  membranes  of  the 
fat  globules  are  broken,  and  the  fat  unites  into  a  semi-solid  mass  of  butter, 
from  which  the  butter-milk  containing  the  caseine  may  be  separated.  If 
this  be  not  done  effectually,  the  caseine  which  is  left  in  the  butter,  being  a 
nitrogenised  substance,  will  soon  begin  to  decompose,  and  will  induce  a 
decomposition  in  the  butter  (page  584),  resulting  in  the  formation  of 
certain  volatile  acids,  which  impart  to  it  a  rancid  and  offensive  taste  and 
odour.  To  prevent  this,  salt  is  generally  added  to  butter  which  has  been 
less  carefully  prepared,  in  order  to  preserve  the  caseine  from  decomposition. 
Butter-milk  contains  about  one-fourth  of  the  fatty  matter  of  the  milk. 

Pure  butter  is  essentially  a  mixture  of  margarine  and  oleine  with  smaller 
quantities  of  other  fats,  such  as  butyrine,  caprine,  and  caproine  (page  584). 

Fresh  milk  is  slightly  alkaline  to  test-papers,  but  after  a  short  time  it 
acquires  an  acid  reaction ;  and  if  it  be  then  heated,  it  coagulates  from  the 
separation  of  the  caseine.  This  spontaneous  acidification  of  milk  is  caused 
by  the  fermentation  of  the  surjar  of  milk,  which  results  in  the  produc- 
tion of  lactic  acid,  according  to  the  equation,  C12H24O12  {Sugar  of  milk) 
=  4HC3H5O3  {Lactic  acid)' 

The  caseine,  being  insoluble  in  the  acid  fluid,  separates  in  the  form  of 
curd.  This  development  of  lactic  acid  is  spoken  of  as  the  lactic  fermenta- 
tion, and  may  be  excited  not  only  in  milk-sugar,  but  in  other  substances 
analogous  to  it.  This  is  taken  advantage  of  in  the  preparation  of  lactic 
acid,  for  which  purpose  8  parts  of  cane-sugar  are  dissolved  in  50  parts  of 
water,  and  1  part  of  poor  cheese  with  3  parts  of  chalk  are  added  to  the 
mixture,  wliich  is  then  allowed  to  remain  for  some  weeks  at  about  80°  F. 
The  lactic  acid  formed  from  the  cane-sugar  (C12H22O11)  under  the 
influence  of  the  changing  caseine  in  the  cheese,  decomposes  the  chalk, 
fonning  crystals  of  calcium  lactate,  Ca(C3H503).^.  This  is  dissolved  in 
boiling  water,  recrystallised  in  order  to  purify  it,  and  digested  with  one- 
third  of  its  weight  of  sulphuric  acid,  which  converts  the  lime  into  sulphate, 
liberating  the  lactic  acid;  by  adding  alcohol,  the  whole  of  the  sulphate 
of  lime  is  precipitated,  and  the  lactic  acid  is  dissolved  by  the  alcohol, 
which  leaves  it  on  evaporation  as  a  colourless,  syrupy,  very  acid  liquid, 


LACTIC  ACID — CHEESE.  613' 

which  may  be  distilled,  though  with  some  loss  from  decomposition,  if 
heated  out  of  contact  with  air. 

By  heating  lactic  acid  to  about  270°  F.  for  a  considerable  length  of  time, 
a  molecule  of  water  is  expelled,  and  the  lactic  anhydride  (CgH^oOg)  is  left 
as  a  brownish  glassy  substance,  which  is  reconverted  into  the  acid  by 
boiling  with  water.  At  a  temperature  of  500°  F.  lactic  acid  undergoes  a 
destructive  distillation,  the  most  interesting  product  of  which  is  a  trans- 
parent crystalline  substance  called  lactide  (CgH^Oo),  differing  from  lactic 
acid  by  the  elements  of  water,  which  it  resumes  when  dissolved  in  that 
liquid,  being  converted  into  lactic  acid  (CgHgOg).  When  lactic  acid  is 
hieated  with  hydriodic  acid  in  a  sealed  tube,  it  is  converted  into  propionic 
acid ;  HC3H5O3  {Lactic  add)  +  2HI  =  HCgHjOg  {Propionic  add)  +  H2O  + 1^. 

When  lactic  acid  is  heated  in  contact  with  diluted  sulphuric  acid  it 
yields  aldehyde  and  formic  acid. 

Lactic  acid  is  an  important  constituent  of  the  animal  body,  being  found 
in  the  juice  of  muscular  flesh,  in  the  gastric  juice,  &c. 

If  milk  be  maintained  at  a  temperature  of  about  90''  F.,  the  fermentation 
results  in  the  production  of  alcohol  and  carbonic  acid,  for  although  milk- 
sugar  is  not  fermented  like  ordinary  sugar  by  contact  with  yeast,  it  appears, 
under  the  influence  of  the  changing  caselne  at  a  favourable  temperature, 
to  be  converted  first  into  grape-sugar  (page  496),  and  afterwards  into 
alcohol  and  carbonic  acid.  The  Tartars  prepare  an  intoxicating  liquid 
which  they  call  koumiss,  by  the  fermentation  of  milk. 

When  an  acid  is  added  to  milk,  the  caseine  is  separated  in  the  form  of 
curd,  in  consequence  of  the  neutralisation  of  the  soda  which  retains  it 
dissolved  in  fresh  milk,  and  this  curd  carries  with  it,  mechanically,  the 
fat  globules  of  the  milk,  leaving  a  clear  yellow  whey. 

In  the  preparation  of  cheese,  the  milk  is  coagulated  by  means  of  rennet, 
which  is  prepared  from  the  lining  membrane  of  a  calf's  stomach.  This  is 
left  in  contact  with  the  warm  milk  for  some  hours,  until  the  coagulation 
is  completed.  This  action  of  rennet  upon  milk  depends  upon  the  presence 
of  certain  microscopic  organisms.  The  curd  is  collected  and  pressed  into 
cheeses,  Avhich  are  allowed  to  ripen  in  a  cool  place,  where  they  are 
occasionally  sprinked  with  salt.  The  peculiar  flavour  which  the  cheese 
thus  acquires  is  due  to  the  decomposition  of  the  caseine,  giving  rise  to  the 
production  of  certain  volatile  acids,  such  as  butyric,  valerianic,  and 
caproic,  which  have  very  powerful  and  characteristic  'odours.  If  this 
ripening  be  allowed  to  proceed  very  far,  ammonia  is  developed  by  the 
putrefaction  of  the  caseine,  and  in  some  cases  the  ethers  of  the  above- 
mentioned  acids  are  produced,  at  the  expense  probably  of  a  little  sugar  of 
milk  left  in  the  cheese,  conferring  the  peculiar  aroma  perceptible  in  some 
varieties  of  it. 

The  different  kinds  of  cheese  are  dependent  upon  the  kind  of  milk  used 
in  their  preparation,  the  richer  cheeses  being,  of  course,  obtained  from 
milk  containing  a  large  proportion  of  cream;  such  cheese  fuses  at  a 
moderate  heat,  and  makes  good  toasted  cheese,  whilst  that  which  contains 
little  butter  never  fuses  completely,  but  dries  and  shrivels  like  leather. 
Double  Gloucester  and  Stilton  are  made  from  a  mixture  of  new  milk  and 
cream;  Chedder  cheese  is  made  from  new  milk  alone.  Cheshire  and 
American  cheeses,  from  milk  robbed  of  about  one-eighth  of  its  cream. 
Dutch  cheese  and  the  Skim  Dick  of  the  midland  counties,  from  skimmed 
milk. 


614  CASEINE — SUGAR  OF  MILK. 

Caserne. — The  pure  curd  of  milk  is  known  as  caseine,  and  consists 
essentially  of  carbon,  hydrogen,  nitrogen,  oxygen,  and  a  small  proportion 
(one  per  cent.)  of  sulphur.  The  simplest  expression  of  the  result  of  the 
analysis  of  caseine  Avoiild  be  Ci44H22gNgg045S,  but  the  anomalous  com- 
plexity of  this  formula  conveys  a  suspicion  that  the  composition  of  pure 
caseine  has  yet  to  be  fixed.  By  whatever  process  it  has  been  purified, 
hitherto  it  has  always  been  found  to  retain  saline  matters.  The  com- 
plexity of  its  composition  accounts  for  its  liability  to  undergo  putrefactive 
decomposition. 

Coagulated  caseine  is  characterised  by  the  facility  with  which  it  is  dis- 
solved by  alkaline  solutions,  such  as  sodium  carbonate,  yielding  a  liquid 
upon  the  surface  of  which,  when  boiled,  an  insoluble  pellicle  forms,  exactly 
similar  to  that  which  forms  upon  the  surface  of  boiled  milk.  Coagulated 
caseine  may  also  be  dissolved  by  acetic  or  oxalic  acid,  but  the  addition  of 
sulphuric  or  hydrochloric  acid  reprecipitates  it,  these  acids  apparently 
forming  insoluble  compounds  with  caseine. 

If  skimmed  milk  be  carefully  evaporated  to  dryness  and  the  fat  extracted 
from  the  residue  by  ether,  the  caseine  is  left  in  the  soluble  form  mixed 
with  milk-sugar,  and  is  capable  of  dissolving  in  water  or  in  weak  alcohol. 

Caseine  appears  to  possess  the  properties  of  a  weak  acid,  since  it  com- 
bines both  with  the  alkalies  and  alkaline  earths,  and  is  even  said  to  be 
capable  of  partially  neutralising  the  former.  A  mixture  of  cheese  and 
slaked  lime  is  sometimes  used  as  a  cement  for  earthenware,  the  caseine 
combining  with  the  lime  to  form  a  hard  insoluble  mass.  The  curd  of 
milk,  washed  and  dried,  is  used  by  calico-printers,  under  the  name  of 
ladarine,  for  fixing  colours.  If  it  be  dissolved  in  weak  ammonia,  mixed 
with  one  of  the  aniline  dyes,  printed  on  calico,  and  steamed^  the  ammonia 
is  expelled,  and  the  colour  is  left  behind  as  an  insoluble  compound  with 
the  caseine. 

Caseine,  or  a  substance  so  closely  resembling  it  as  to  be  easily  con- 
founded with  it,  is  found  in  peas,  beans,  and  most  leguminous  seeds.  If 
dried  peas  be  crushed  and  digested  for  some  time  in  tej)id  water,  a  turbid 
]i(][uid  is  obtained,  holding  starch  in  suspension.  If  this  be  allowed  to 
settle,  the  clear  liquid  is  an  impure  aqueous  solution  of  le(jumme,  or  vege- 
table caseine,  which  constitutes  about  one-fourth  of  the  weight  of  the 
peas. 

This  solution  is  not  coagulated  by  heat,  but  becomes  covered  with  a 
pellicle  similar  to  that  which  forms  upon  the  surface  of  boiled  milk.  It 
is  coagulated  by  acetic  acid  and  by  rennet,  just  as  is  the  case  with  the 
caseine  of  milk. 

Sugar  of  milk. — When  whey  is  evaporated  to  a  small  bulk  and  allowed 
to  cocl,  it  deposits  hard  white  prismatic  crystals  of  sugar  of  milk,  or  lactine 
(Cj2H24r)j2),  which  is  much  less  soluble,  and  therefore  less  sweet  than 
cane-sugar.  Like  this,  it  is  converted  into  glucose  {CgHjgO^),  when  boiled 
with  dilute  acids.  Milk-sugar  resembles  the  other  sugars  in  its  capability 
of  combining  with  some  bases,  such  as  the  alkalies,  alkaline  earths,  and 
oxide  of  lead  ;  with  the  latter  it  forms  two  insoluble  compounds. 

At  about  280°  F.  the  crystals  of  milk-sugar  lose  a  molecule  of  water 
and  become  C^J1.220^y  At  400°  F.  the  sugar  fuses,  and  2  molecules 
lose  5  molecules  of  water. 

It  will  be  seen  that  the  characteristic  constituents  of  milk  are  the  caseine 
and  milk-sugar,  but  the  proportions  in  which  these  are  present  vary  widely, 


CONSTITUTION  OF  BLOOD.  615 

not  only  with  the  animal  from  which  the  milk  is  obtained,  but  with  the 
food  and  condition  of  the  animal.  A  general  notion  of  their  relative 
quantities,  however,  may  be  gathered  from  the  following  table,  exhibiting 
the  results  of  the  analyses  made  by  Boussingault : — 


Cow. 

Ass. 

Goat. 

Woman. 

Water, 

87-4 

90-5 

82  0 

88-4 

Butter, 

4-0 

1-4 

4-5 

2-5 

Milk-sugar,         .  > 
Soluble  salts,         > 

5-0 

6-4 

4-5 

4-8 

Caseine,      .         .  ) 
Insoluble  salts,      ) 

3-6 

17 

9  0 

3-8 

The  soluble  salts  present  in  milk  include  the  phosphates  and  chlorides 
of  potassium  and  sodium,  whilst  the  insoluble  salts  are  the  phosphates  of 
calcium,  magnesium,  and  iron.  All  these  salts  are  in  great  request  for 
the  nourishment  of  the  animal  frame. 

The  milk  supplied  to  consumers  living  in  towns  is  subject  to  consider- 
able adulteration  ;  but  in  most  cases  this  is  effected  by  simply  removing 
the  cream  and  diluting  the  skimmed  milk  with  water,  a  fraud  which  is 
not  easily  detected,  as  might  be  supposed,  by  determining  the  specific 
gravity  of  the  milk,  for  since  milk  is  heavier  than  water  (1-032  sp.  gr.), 
and  the  fatty  matter  composing  cream  is  lighter  than  water,  a  certain 
quantity  of  cream  might  be  removed,  and  water  added,  without  altering 
the  specific  gravity  of  the  milk. 

The  simplest  method  of  ascertaining  the  quality  of  the  milk  consists 
in  setting  it  aside  for  twenty- four  hours  in  a  tall  narrow  tube  (lactometer), 
divided  into  100  equal  parts,  and  measuring  the  proportion  of  cream  which 
separates,  this  averaging,  in  pure  milk,  from  eleven  to  thirteen  divisions. 
By  shaking  milk  with  a  little  potash  (to  dissolve  the  membrane  which 
envelops  the  fat  globules)  and  ether,  the  butter  may  be  dissolved  in  the 
ether  which  rises  to  the  surface,  and  if  this  be  poured  off  and  allowed  to 
evaporate,  the  weight  of  the  butter  may  be  ascertained ;  or  the  milk  may 
be  evai^orated  by  a  steam  heat,  and  the  fat  dissolved  by  treating  the 
residue  with  ether.  One  thousand  grains  of  milk  should  give,  at  least, 
27  or  28  grains  of  butter.  Since,  however,  the  milk  of  the  same  cow  gives 
very  different  quantities  of  cream  at  different  times,  it  is  difficult  to  state 
confidently  that  adulteration  has  been  practised.  The  standard  usually 
adopted  by  analysts  is  25  grains  of  fat  or  butter  and  90  grains  of  **  solids 
not  fat  "  in  1000  grains  of  milk. 

433.  Blood. — The  blood  from  which  the  various  organs  of  the  body 
directly  receive  their  nourishment  is  the  most  important,  as  well  as  the 
most  complex  of  the  animal  fluids.  Its  chemical  examination  is  attended 
with  much  difficulty,  on  account  of  the  rapidity  with  which  it  changes 
after  removal  from  the  body  of  the  animal. 

On  examining  freshly-drawn  blood  under  the  microscope,  it  is  observed 
to  present  some  resemblance  to  milk  in  its  physical  constitution,  consisting 
of  opaque  flattened  globules  floating  in  a  transparent  liquid ;  the  globules, 
in  the  case  of  blood,  having  a  Avell-marked  red  colour. 

In  a  few  minutes  after  the  blood  has  been  drawn,  it  begins  to  assume  a 
gelatinous  appearance,  and  the  semi-solid  mass  thus  formed  separates  into 
a  red  solid  portion  or  clot,  which  continues  to  shrink  for  ten  or  twelve 


616  COMPOSITION  OF  BLOOD  GLOBULES, 

hours,  and  a  clear  yellow  liquid  or  scrum.  It  might  be  supposed  that  this 
coagulation  is  due  to  the  cooling  of  the  blood,  but  it  is  found  by  experi- 
ment to  take  place  even  more  rapidly  when  the  temperature  of  the  blood 
is  raised  one  or  two  deg  rees  after  it  has  been  drawn ;  and  on  the  other 
hand,  if  it  be  artificially  cooled,  its  coagulation  is  retarded.  Indeed,  the 
reason  for  this  remarka  ble  behaviour  of  the  blood  is  not  yet  understood. 

If  the  coagulum  or  clot  of  blood  be  cut  into  slices,  tied  in  a  cloth,  and 
well  washed  in  a  stream  of  water,  the  latter  runs  off  with  a  bright  red 
colour,  and  a  tough  yellovv  filamentous  substance  is  left  upon  the  cloth  ; 
this  substance  is  called  fih'ine,  and  its  presence  is  the  proximate  cause  of 
the  coagulation  of  the  blood,  for  if  the  fresh  blood  be  well  whipped  with 
a  bundle  of  twigs  or  glass  rods,  the  tibrine  will  adhere  to  them  in  yellow 
strings,  and  the  dejibrinated  blood  will  no  longer  coagulate  on  standing. 
If  this  blood,  from  which  the  fibrine  has  been  extracted,  be  mixed  with 
a  large  quantity  of  a  saline  solution  (for  example,  8  times  its  bulk  of  a 
saturated  solution  of  sodium  sulphate),  and  allowed  to  stand,  the  red 
globules  subside  to  the  bottom  of  the  vessel. 

These  globules  are  minute  bags  of  red  fluid,  enclosed  in  a  very  thin 
membrane  or  cell-ivall,  and  if  water  were  mixed  with  the  defibrinated 
blood,  since  its  specific  gravity  is  lower  than  that  of  the  fluid  in  the 
globules,  it  would  pass  through  the  membrane  (by  endosmose),  and  so 
swell  the  latter  as  to  break  it  and  disperse  the  contents  through  the  liquid. 

The  red  fluid  contained  in  these  blood  globules  consists  of  an  aqueous 
solution,  containing  as  its  principal  constituents  a  substance  known  as 
f/lobidine,  which  very  nearly  resembles  albumen,  aud  the  peculiar  colouring 
matter  of  the  blood,  which  is  called  hcematine. 

Beside  these,  the  globules  contain  a  little  fatty  matter  and  certain 
mineral  constituents,  especially  the  iron  (which  is  associated  in  some 
unknDwn  form  with  the  colouring  matter),  the  chlorides  of  sodium  and 
potassium,  and  the  phosphates  of  potassium,  sodium,  calcium,  and 
magnesium. 

Though  the  quantities  of  these  constituents  are  not  invariable,  even  in 
the  same  individual,  the  following  numbers  may  be  taken  as  representing 
the  average  composition  of  these  globules  : — 


1000  parts  of  Mood  Globules  contain — 

Water 688-00 

Globuline,  .  .  .  282-22 
Hsematine,  .  .  .16-75 
Fat,  ....       2-31 


Organic  substances  of )  „  .^„ 

unknown  nature,      ) 
Mineral  substances,*  .  .     8-12 


Potassium,        .         .         .  3-328 

Phosphoric  oxide  (PgOg),  .  1-134 

Sodium,   ....  1-052 

Chlorine,  .         .         .  1-686 


The  mineral  sxLbstances  consist  of — 

Oxygen,      ....  0667 

Calcium  phosphate,     .         .  0-114 

Magnesium  phosphate,        .  0  -073 

Sulphuric  oxide  (SO3),         .  0-066 

Glohidine  is  a  substance  very  similar  in  its  character  and  composition 
to  albumen ;  it  is  found  also  in  large  proportion  in  the  matter  composing 
the  crystalline  lens  of  the  eye. 

Nudeine  is  another  albuminoid  body  found  in  the  blood  globules  of 
snakes  and  birds ;  it  is  remarkable  for  its  insolubility  in  water,  alcohol, 
ether,  and  dilute  acids  or  alkalies.  It  a))pears  to  be  the  chief  component 
of  the  cell-nucleus  or  cytoblast, 

*  Exclusive  of  the  iron  which  is  associated  with  the  haematine. 


COMPOSITION  OF  BLOOD  GLOBULES.  617 

The  hcemattne  or  hcematosine  must  be  accounted  the  most  important 
constituent  of  the  blood  globules,  since  it  appears  to  be  more  intimately 
connected  than  any  other  with  the  functions  discharged  by  the  blood  in 
nutrition  and  respiration. 

In  order  to  obtain  it  in  the  separate  state,  the  blood  globules  are  boiled 
with  alcohol  acidulated  with  sulphuric  acid,  and  the  red  solution  mixed 
with  ammonium  carbonate,  which  separates  the  greater  part  of  the  globu- 
line  ;  the  filtered  liquid  is  evaporated  to  dryness,  and  all  soluble  matters 
are  extracted  by  successive  treatments  with  water,  alcohol,  and  ether.  By 
again  dissolving  the  brown  residue  in  alcohol  containing  ammonia,  filter- 
ing, evaporating  to  dryness,  and  removing  any  soluble  matter  by  water,  a 
dark  brown  substance  is  obtained,  which  is  supposed  to  be  pure  haematine, 
though  no  longer  in  the  soluble  state  in  which  it  existed  in  the  blood.  It 
is  now  dissolved  only  by  alkalies  or  by  acidulated  alcohol. 

In  its  chemical  composition  hcematine  is  remarkable  for  the  presence  of 
iron,  associated  in  a  very  intimate  manner  with  carbon,  hydrogen,  nitrogen, 
and  oxygen,  so  that  it  cannot  be  recognised  by  the  ordinary  tests.  The 
formula  which  has  been  assigned  to  it  is  C34H3gIs'405re,  but  it  is  very 
doubtful  Avhether  it  has  been  analysed  in  a  perfectly  pure  state. 

The  most  important  chemical  property  of  hsematine  is  its  behaviour  with 
oxygen.  It  is  well  known  that  the  blood  issuing  from  an  artery  has  a  much 
brighter  red  colour  than  that  drawn  from  a  vein,  and  that  when  the  latter 
is  allowed  to  coagulate,  the  upper  part  of  the  clot,  which  is  in  contact  with 
the  air,  is  brighter  than  the  lower  part. 

When  the  dark  red  blood  drawn  from  a  vein  is  shaken  up  with  air  or 
oxygen,  a  quantity  of  the  latter  is  absorbed,  and  a  nearly  equal  volume  of 
carbonic  acid  gas  is  disengaged,  the  dark  red  colour  being  at  the  same 
time  changed  to  the  bright  red  characteristic  of  arterial  blood.  The 
carbonic  acid  gas  exists  already  formed  in  the  venous  blood,  and  is  given 
off  if  the  blood  is  exposed  under  an  exhausted  receiver.  The  condition 
assumed  by  the  oxygen  when  absorbed  by  the  blood  is  not  yet  clearly 
understood,  but  it  is  generally  allowed  that  the  conversion  of  venous  into 
arterial  blood  is  due  to  the  displacement  of  carbonic  acid  gas  by  oxygen. 

Eecent  experiments  indicate  that  hajmatine  is  really  a  product  of  the 
alteration  of  another  body  existing  in  the  blood  globules,  which  has  been 
named  hcemaglobine.  This  substance  is  obtained  by  treating  the  blood- 
globules  with  water,  adding  alcohol,  and  cooling  in  a  mixture  of  ice  and 
salt,  when  the  hsemaglobine  crystallises  out  in  shapes  differing  in  different 
animals.  By  treating  haemaglobine  with  common  salt  and  glacial  acetic 
acid,  the  so-called  blood-crystals  are  obtained,  which  appear  to  be  composed 
of  haematine  and  hydrochloric  acid. 

Hsemaglobine  contains  carbon  54-2  per  cent.,  hydrogen  7*2,  nitrogen 
16,  oxygen  21-5,  sulphur  07,  iron  O'i.  Its  solution  absorbs  oxygen, 
acquiring  a  bright  red  colour,  and  if  daylight  be  transmitted  through  this 
solution,  and  afterwards  through  the  prism  of  a  spectroscope  (p.  272),  the 
green  portion  of  the  spectrum  is  seen  to  be  crossed  by  two  broad  black 
bands,  which  are  also  seen  when  arterial  blood  is  employed.  When 
venous  blood  is  examined  in  the  same  Avay,  it  exhibits  only  one  broad 
black  band,  not  coincident  with  either  of  those  furnished  by  arterial 
blood ;  but  on  shaking  the  venous  blood  with  air  till  it  has  become  red, 
the  two  black  absorption  bands  are  seen  in  its  spectrum.  Arterial  blood 
which  has  been  shaken  with  carbonic  acid  gas  gives  the  single  broad  band 


618  COMPOSITION  OF  LIQUOR  SANGUINIS. 

characteristic  of  venous  blood.     These  optical  properties  are  found  useful 
for  the  identification  of  blood-stains. 

The  liquid  in  which  the  blood  globules  float  is  an  alkaline  solution  con- 
taining albumen,  fibrine,  and  saline  matters  in  about  the  proportions  here 
indicated. 

1000  parts  q/"  Liquor  Sanguinis  contain — 

3-94 
8-55 


Water,      . 
Albumen, 
Fibrine,    . 
Fat, 

.     902-90 

.       78-84 

4-05 

1-72 

Organic  substances  of  un- 
known nature, 
Mineral  substances,   . 

The  mineral  substances  consist  of — 

Sodium,  . 
Chlorine, . 
Potassium, 
Oxygen,  . 

.       3-341 
.       3-644 
.       0-323 
..      0-403 

Phosphoric  oxide  (P2O5), 
Sulphuric  oxide  (SO3), 
Calcium  phosphate,  . 
Magnesium  phosphate, 

0-191 
0-115 
0-311 
0-222 

The  alkaline  character  of  this  liquid  appears  to  be  due  to  the  presence 
of  carbonate  and  phosphate  of  sodium. 

The  albumen  present  in  the  serum  of  blood  causes  it  to  coagulate  to  a 
gelatinous  mass  when  heated,  this  property  being  the  distinctive  feature 
of  albumen.  This  substance  may  be  obtained  as  a  transparent  yellow 
mass,  resembling  gum,  and  dissolving  slowly  in  water,  by  evaporating 
either  serum  of  blood  or  white  of  egg  below  120°  F. ;  but  if  the  tempera- 
ture be  raised  above  that  point,  the  albumen  is  coagulated,  and  cannot  be 
redissolved  in  water  unless  heated  with  it  under  pressure. 

Albumen,  like  caseine,  has  never  been  obtained  perfectly  free  from 
saline  matters,  particularly  the  alkaline  and  earthy  phosphates,  and  much 
difficulty  attends  the  exact  determination  of  its  composition.  The 
analysis,  by  G.  S.  Johnson,  of  some  remarkable  compounds  of  albumen 
with  the  acids,  confirms  the  formula  originally  proposed  by  Lieberkiihn, 
viz.,  C7oHj^2NjgS022  (Journal  of  the  Chemical  Society,  August  1874). 

It  will  be  remembered  that  a  substance  identical  with,  or  very  closely 
resembling  albumen,  and  known  as  vegetable  albumen,  is  found  in  those 
vegetable  juices  which  are  coagulated  by  heat. 

Fibrine,  as  existing  in  blood,  differs  from  all  other  animal  substances 
by  its  tendency  to  spontaneous  coagulation.  "When  coagulated  it  exhibits 
characters  very  similar  to  those  of  coagulated  albumen;  but  when  sepa- 
rated from  the  freshly-drawn  blood  by  violent  stirring,  it  forms  elastic 
strings  which  dry  into  a  yellow  horny  mass.  Fibrine  is  one  of  the  most 
important  constituents  of  the  animal  frame,  for  all  muscular  flesh  consists 
of  this  substance.  The  gluten  found  in  the  seeds  of  the  cerealia  bears  a 
very  close  resemblance  to  fibrine,  and  is  often  called  vegetable  fibrine. 

The  same  formula  has  been  often  assigned  to  fibrine  as  to  albumen,  and 
its  complexity  Avould  explain  its  disposition  to  putrefy  when  removed 
from  the  influence  of  life.  It  does  not  appear  quite  certain  that  the 
fibrine  dissolved  in  the  blood  is  identical  in  composition  with  that  of 
muscular  fibre.  Some  analyses  have  shown  that  the  muscular  fibrine 
contains  more  oxygen  than  blood-fibrine,  and  this  latter  more  than  albumen, 
atlording  some  ground  for  the  belief  that  the  blood-fibrine  represents  the 
transition  state  between  the  albumen  of  the  serum  and  the  muscular  flesh 
into  which  it  is  eventually  converted. 

Albumen,  fibrine,  and  caseine  have  been  regarded  by  some  chemists 
as  compounds  of  the  same  primary  substance  (proteine)  combined  with 


EGGS — JUICE  OF  FLESH.  619 

different  proportions  of  sulpliur  and  phosphorus,  the  proteine  being 
isolated  by  boiling  the  albuminous  body  with  potash  and  precipitating  the 
solution  by  an  acid.  The  composition  usually  assigned  to  this  substance 
is  CigH27X40g ;  but  since  it  is  neither  crystallisable  nor  capable  of  conver- 
sion into  vapour,  there  is  no  proof  of  its  purity ;  and  the  great  use  vt^hich 
has  been  made  of  this  substance  by  writers  on  animal  chemistry  is  du3  to 
the  apparent  simplicity  which  it  confers  upon  the  relations  existing 
between  the  numerous  modifications  of  albumen,  fibrine,  and  caseine,  the 
ultimate  formula?  of  which  present  so  high  a  degree  of  complexity. 

In  the  substance  of  the  brain  there  has  been  found  a  very  remarkable 
crystalline  substance,  Avhich  has  been  termed  protagon,  and  is  a  complex 
compound  of  carbon,  hydrogen,  nitrogen,  oxygen,  and  perhaps  phosphorus, 
to  which  no  probable  formula  has  yet  been  assigned.  It  is  very  easily 
decomposed,  even  below  212°.  Protagon  is  insoluble  in  water,  but  dis- 
solves in  hot  alcohol  and  in  acetic  acid.  When  boiled  with  solution  of 
bai'yta,  it  yields  phosphoglyceric  acid,  and  a  strongly  alkaline  base^  neurine. 

Eggs. — The  shell  of  the  egg  contains  about  nine-tenths  of  its  weight 
of  calcium  carbonate,  associated  with  animal  matter.  The  white  of  egg 
consists  of  albumen  (about  12  per  cent.),  water  (about  86  per  cent.),  and 
small  quantities  of  soluble  salts.  It  is  alkaline,  from  the  presence  of  a 
little  soda.  Raw  white  of  egg  has  no  smell  of  sulphuretted  hydrogen, 
and  does  not  blacken  silver ;  but  after  boiling,  both  these  properties  are 
manifested,  showing  that  it  suffers  some  decomposition  during  coagula- 
tion. 

Yolk  of  egg  contains  a  modification  of  albumen  termed  vitelline,  and 
owes  its  colour  to  a  yellow  oil  which  may  be  extracted  with  ether,  and 
contains  phosphoric  acid.  The  yolk  of  hens'  eggs  has  about  half  the 
weight  of  the  white,  and  commonly  contains  about  half  its  weight  of 
water,  1 6  per  cent,  of  vitelline,  30  per  cent,  of  fat,  and  1  "5  per  cent,  of 
saline  matters. 

434.  Flesh. — The  fibrine  composing  muscular  flesh  contains  about 
three-fourths  of  its  weight  of  water,  a  part  of  which  is  due  to  the  blood 
contained  in  the  vessels  traversing  it,  and  another  part  to  the  juice  of  flesh, 
w^hich  may  be  squeezed  out  of  the  chopped  flesh.  In  this  juice  of  flesh 
there  are  certain  substances  which  appear  to  play  a  very  important  part 
in  nutrition.  The  liquid  is  distinctly  acid,  which  is  remarkable  when 
the  alkaline  character  of  the  blood  is  considered,  and  contains  phosphoric, 
lactic,  and  butyric  acid,  together  with  kreatine,  inosite,  and  saline  matters. 
By  soaking  minced  flesh  in  cold  water  and  well  squeezing  it  in  a  cloth, 
a  red  fluid  is  obtained  containing  the  juice  of  flesh  mixed  with  a  little 
blood.  "When  the  liquid  is  gently  heated,  the  albumen  of  the  blood  and 
of  the  juice  is  coagulated  in  flakes  stained  with  the  colouring  matter ; 
the  liquid  filtered  from  these  may  be  mixed  with  baryta  water  to  precipi- 
tate the  phosphoric  acid ;  and  after  a  second  filtration,  evaporated  to  a 
syrupy  consistence  and  set  aside,  when  beautiful  colourless  prismatic 
crystals  are  obtained,  consisting  of  a  feeble  organic  base  called  kreatine,* 
the  composition  of  which  is  represented  by  the  formula  C^HgNgOaAq. 

The  quantity  of  this  substance  obtained  from  the  flesh  of  different 
animals  varies  very  considerably,  that  of  fowls  having  been  found  hitherto 
most  productive,  and  next,  that  of  fish.     One  thousand  parts  of  the  flesh 

*  From  Kpeai,  flesh. 


fi20  COOKING  OF  MEAT.     " 

of  fowl  furnished  3-2  parts  of  kreatine,  1000  parts  of  cod,  1-71  of  kreatine, 
and  1000  of  beef,  0*70  parts.  Human  flesh  is  said  to  contain  a  large  pro- 
portion of  kreatine. 

When  boiled  with  acids,  kreatine  loses  the  elements  of  Avater,  and  is 
converted  into  a  powerful  base  called  kreatinine  (C^H^NgO),  which  is  also 
found  in  minute  proportion,  accompanied  by  kreatine,  in  the  urine. 

Boiled  with  alkalies,  kreatine  gains  the  elements  of  water,  and  furnishes 
two  organic  bases,  urea  (also  found  in  urine),  and  sarcosine  (crdpi,  Jlesh) — * 

C4H9N3O2   +   HgO   =   CH4N2O   +    C3H.NO2 

Kreatine.  Urea.  Sarcosiue. 

From  the  concentrated  flesh-extract  which  has  deposited  the  kreatine, 
there  may  be  obtained,  by  careful  treatment,  crystals  of  a  sweet  substance 
called  inosite  or  sugar  of  flesh,  and  having  the  composition  CgHj20g.2Aq. 
At  a  temperature  below  212°  F.  it  loses  water,  and  has  then  the  same 
composition  as  dry  grape-sugar,  CgHjgOg,  with  which,  however,  it  is 
certainly  not  identical. 

Inosite  has  been  obtained  in  very  minute  proportion  from  flesh,  but 
unripe  beans  are  said  to  yield  as  much  as  0*75  rer  cent,  of  this  interesting 
sugar.  It  has  also  been  obtained  from  the  leaves  of  the  walnut-tree, 
which  contained,  in  August,  0'3  per  cent,  of  the  dried  leaves. 

The  saline  constituents  of  the  juice  of  flesh  are  chiefly  phosphates  of 
potassium,  magnesium,  with  a  little  chloride  of  sodium.  It  is  worthy 
of  notice  that  potassium  is  the  predominant  alkali-metal  in  the  juice  of 
flesh,  whilst  sodium  predominates  in  the  blood,  especially  in  the  serum. 

According  to  Liebig,  the  acidity  of  the  juice  of'  flesh  is  chiefly  due  to 
the  acid  phosphate  of  potassium,  KHgPO^,  whilst  the  alkalinity  of 
the  blood  is  caused  by  sodium  phosphate,  NagHPO^ ;  and  it  has  been 
suggested  that  the  electric  currents  which  have  been  traced  in  the 
muscular  fibres  are  due  to  the  mutual  action  between  the  acid  juice  of 
flesh  and  the  alkaline  blood,  separated  only  by  thin  membranes  from  each 
other,  and  from  the  substance  of  the  muscles  and  nerves. 

The  average  composition  of  flesh  may  be  represented  as  follows  : — 

AVater 78 

Fibrine,  vessels,  nerves,  cells,  &c.,  .  17 

Albumen, 2*5 

Other  constituents  of  the  juice  of  flesh,  .  2*5 

100-0 
Liehig's  extract  of  meat  is  prepared  by  exhausting  all  the  soluble  matters 
from  the  flesh  with  cold  water,  separating  the  albumen  by  coagulation, 
and  evaporating  the  liquid  at  a  steam  heat  to  a  soft  extract.  It  contains 
about  half  its  weight  of  water,  40  per  cent,  of  the  organic  constituents  of 
the  juice  of  flesh  (albumen  excepted),  and  10  per  cent,  of  saline  matter. 

Myosine  (from  fxixi,  a  muscle)  is  a  constituent  of  flesh  wbich  is  liquid 
during  life,  and  coagulates  after  death.  It  may  be  extracted  from  the 
chopped  flesh  by  water  containing  ^^^th  of  salt,  and  is  precipitated  from 
the  solution  by  saturating  it  with  salt. 

Cool-ing  of  meat. — A  knowledge  of  the  composition  of  the  juice  of  flesh 
explains  the  practice  adopted  in  boiling  meat,  of  immersing  it  at  once  in 

*  Sarcosine  has  been  obtained  artificially  by  the  action  of  chloracetic  acid  on  methyl- 
amine — 

CjHsClOa    -f-    NHj^CHs)   =    C3H7NO2   +    HCl. 
Chloracetic  acid.    Metliylamine.  Sai-cosine. 


GELATINE,  621 

boiling  water,  instead  of  placing  it  in  cold  water,  which  is  afterwards 
raised  to  the  boiling-point.  In  the  latter  case,  the  water  would  soak  into 
the  meat,  and  remove  the  impoi;tant  nutritive  matter  contained  in  the 
juice  ;  whilst^  in  the  former,  the  albumen  in  the  external  layer  of  flesh  is 
at  once  coagulated,  and  the  water  is  prevented  from  penetrating  to  the 
interior.  In  making  soup,  of  course,  the  opposite  method  should  be  fol- 
lowed, the  meat  being  placed  in  cold  water,  the  temperature  of  which  is 
gradually  raised,  so  that  all  the  juice  of  flesh  may  be  extracted  and  the 
muscular  fibre  and  vessels  alone  left. 

The  object  to  be  attained  in  the  preparation  of  heef-tea,  is  the  extraction 
of  the  whole  of  the  soluble  matters  from  the  flesh,  to  effect  which  the 
meat  should  be  minced  as  finely  as  possible,  soaked  for  a  short  time  in  an 
equal  weight  of  cold  water,  and  slowly  raised  to  the  boiling-point,  at 
which  it  is  maintained  for  a  few  minutes.  The  liquid  strained  from  the 
residual  fibrine  contains  all  the  constituents  of  the  juice  except  the  albu- 
men, which  has  been  coagulated. 

When  meat  is  roasted,  the  internal  portions  do  not  generally  attain  a 
sufficiently  high  temperature  to  coagulate  the  albumen  of  the  juice,  but 
the  outside  is  heated  far  above  212°  F.;  so  that  the  meat  becomes 
impregnated  to  a  greater  extent  with  the  melted  fat,  and  some  of  the 
constituents  of  the  juice  in  this  part  suffer  a  change,  which  gives  rise  to 
the  peculiar  flavour  of  roast  meat.  The  brown  sapid  substance  thus  pro- 
duced has  been  called  osmazome*  but  nothing  is  really  known  of  its  true 
nature.  In  salting  meat  for  the  purpose  of  preserving  it,  a  great  deal  of  the 
juice  of  flesh  oozes  out,  and  a  proportionate  loss  of  nutritive  matter  is  sus- 
tained. 

435.  Gelatine. — "When  portions  of  meat,  containing  cartilages  (gristle) 
or  tendons,  are  boiled  for  some  time  with  water,  the  liquid  so  obtained 
sets  to  a  jelly  on  cooling.  This  is  due  to  the  presence  of  gelatine  or 
cliondrine,  or  both — substances  so  nearly  resembling  each  other,  that  they 
were  long  confounded  under  the  name  of  gelatine.  The  difference  in  their 
origin  is  that  gelatine  is  obtained  by  the  action  of  water  at  a  high  tem- 
perature on  skin,  membrane,  and  bone,t  Avhilst  chondrine  is  obtained  in 
the  same  way  from  the  cartilages.  In  their  properties  there  is  very  little 
difference,  the  most  important  being  that  a  solution  of  chondrine  is  pre- 
cipitated by  acetic  acid,  by  alum,  and  by  lead  acetate,  Avhich  do  not  pre- 
cipitate gelatine. 

Gelatine  mixed  with  chromate  or  dichromate  of  potassium  and  exposed 
to  light,  yields  an  insoluble  compound  which  is  turned  to  account  in  the 
"  carbon  process  "  and  some  other  methods  of  photography. 

In  composition  there  is  a  considerable  difference  between  gelatine  and 
chondrine,  the  latter  containing  considerably  more  oxygen  and  less  nitro- 
gen.    The  simplest  forraulte  which  have  been  assigned  to  them  are — 

Gelatine,         .         .         .         C^jHg-N'jgOjg 
Chondrine,      .         .         .         CggHgXgO^g ; 

but  they  both  contain  phosphates  of  calcium  and  magnesium  in  a  very 
intimate  state  of  association. 

The  characteristic  properties  of  gelatine  are  the  tendency  of  its  solution 
to  gelatinise  on  cooling,  and  the  formation  of  an  insoluble  compound  with 

*  From  o<r/ixj},  odour  ;  ^wfio's,  sovp. 

t  The  animal  matter  of  bone  appears  to  be  insomeric  with  gelatine,  and  is  called  osseine. 


622  ISINGLASS — SIZE — URINE. 

tannic  acid.  The  latter  is  the  foundation  of  the  art  of  tanning  (page  592), 
and  the  former  is  turned  to  account  in  the  preparation  of  jelly,  size,  and 
glue.  A  solution  containing  only  1  per  cent,  of  gelatine  will  set  on 
cooling,  though  if  it  be  repeatedly  boiled  it  loses  this  property. 

Islwjlass  is  a  very  pure  variety  of  gelatine  prepared  from  the  air-bladder 
of  fishes,  especially  of  the  sturgeon. 

For  the  manufacture  of  glue,  the  refuse  and  parings  of  hides  are  gene- 
rally employed,  after  being  cleansed  from  the  hair  and  blood  by  steeping 
in  lime  water,  and  thoroughly  exposed  to  the  air  for  some  days,  so  as  to 
convert  the  lime  into  carbonate,  and  prevent  the  injurious  effect  of  its 
alkaline  character  upon  the  gelatine.  They  are  then  boiled  with  water 
till  the  solution  is  found  to  gelatinise  firmly  on  cooling,  when  it  is  run 
off  into  another  vessel,  where  it  is  kept  warm  to  allow  the  impurities  to 
settle  down,  after  which  it  is  allowed  to  gelatinise  in  shallow  wooden 
coolers.  The  jelly  is  cut  up  into  slices,  and  dried  upon  nets  hung  up  in 
a  free  current  of  air.  Spring  and  autumn  are  usually  selected  for  drying 
glue,  since  the  summer  heat  would  liquefy  it,  and  frost  would,  of  course, 
split  it,  and  render  it  unfit  for  the  market. 

Size  is  made  in  a  similar  manner,  but  finer  skins  are  employed,  and 
the  drying  is  omitted,  the  size  being  used  in  the  gelatinous  state.  The 
best  size  is  made  from  parchment  cuttings. 

By  the  action  of  acids  or  alkalies  upon  gelatine,  two  crystalline  organic 
bases  may  be  obtained,  known  by  the  names  of  glycocoU,  glycocine,  or 
sugar  of  gelatine  (C2H5XO2),  and  leucine  (CgH^gNOj). 

It  will  be  seen  that  glycocine  is  isomeric  with  nitrous  ether  (CgH^.JiTOg),* 
and  leucine  witl\  the  (at  present  unknown)  nitrous  ether  of  the  caproic 
series.     Leucine  has  been  found  in  bullock's  lungs  and  in  calf's  liver. 

A  large  number  of  animal  substances  very  nearly  resemble  gelatine  in 
their  composition;  among  these  are  hair,  wool,  nails,  horns,  and  hoofs. 

Hair  contains,  iti  addition  to  carbon,  hydrogen,  nitrogen,  and  oxygen, 
from  3  to  5  per  cent,  of  sulphur.  Wool  has  sometimes  to  be  separated 
from  the  cotton  in  worn-out  mixed  fabrics.  The  mixture  is  plunged  into 
diluted  hydrochloric  aci<l,.-dried  at  220°  F.,  and  submitted  to  the  action 
of  a  machine  {devil),  which  removes  the  cotton,  rendered  brittle  by  the 
action  of  the  acid,  in  the  form  of  dust,  and  leaves  the  wool  fibres 
untouched.  When  the  object  is  to  save  the  cotton  fibre,  the  fabric  is 
exposed  to  high-pressure  steam,  which  has  no  action  upon  cotton,  but 
converts  the  wool  into  a  brown  matter  easily  removed  by  a  beating 
machine,  and  sold  for  manure  as  ulmate  of  ammonia. 

Silk  is  said  to  consist  of  three  layers,  the  outermost  consisting  of  gela^ 
tine,  and  soluble  in  water ;  the  next  of  albumen,  soluble  in  acetic  acid  on 
boiling  ;  and  the  third  of  a  nitrogenised  substance  called  sericine,  which  is 
insoluble  in  water  and  acetic  acid.  Spider's  threads  appear  to  consist  of 
this  substance.  » 

Sponge  consists  of  a  similar  material,  Avhich  has  been  called  fibroine. 

436.  Urine. — The  urine  of  animals  is  characterised  by  the  presence  of 
certain  substances  which  are  only  met  with  in  very  minute  quantities,  if 
at  all,  in  a  state  of  health,  in  the  other  fluids  of  the  body.     The  most  im- 

*  tJlvcocine  has  been  formed  by  passing  cyanogen  through  a  boiling  saturated  aqueous 
solution  of  hydriodic  acid  ;  "iCN  -I-  5HI  +  2H2O  =  C2H5NO2  -f-  NHJ  +  I^.  Tri-methyl- 
<jlijcocine,  C2H._;(CH3)3NOj  or  betaine,  is  found  inbeet-root. 


CONSTITUTION  OF  UREA.  623 

portant  of  these  are  an  organic  base  called  urea,  uric  acid,  and  Jiippuric 
acid. 

Urea, — When  human  urine  is  evaporated  to  about  an  eighth  of  its 
original  bulk,  and  mixed  with  an  equal  volume  of  nitric  acid,  a  semi- 
solid mass  is  formed,  consisting  of  pearly  scales  of  urea  nitrate  (CH^NgO. 
HXO3).  If  these  be  washed  with  cold  water,  afterwards  dissolved  in 
boiling  water,  and  treated  with  barium  carbonate,  the  urea  is  liberated ; 
2(CH^X20.HX03)  +  EaO.CO^  =  2CH4X2O  +  Ba2X03  +  H^O  +  CO^ . 

After  filtering  from  the  excess  of  barium  carbonate,  the  liquid  is 
evaporated  on  a  water-bath,  when  a  mixture  of  urea  and  barium  nitrate 
is  obtained,  from  which  the  urea  may  be  extracted  by  hot  alcohol  On 
evaporating  the  alcohol,  beautiful  prismatic  crystals  of  urea  are  deposited. 
These  crystals,  when  once  separated  from  the  urine  in  a  pure  state,  may 
be  preserved  indefinitely,  even  if  dissolved  in  water ;  but  the  urea  occur- 
ring in  the  urine  is  very  soon  decomposed,  a  putrefactive  decomposition 
being  excited  by  the  mucus,  a  changeable  substance  somewhat  resembling 
albumen,  which  collects  in  feathery  clouds  in  the  urine.  The  change 
which  is  thus  induced  in  the  urea  results  in  its  conversion  into  ammonium 
carbonate ;  CH4X2O  +  2H2O  =  (NHJgCOg. 

It  is  in  consequence  of  this  change  that  the  urine  so  soon  exhales  an 
ammoniacal  odour.  In  order  to  effect  the  same  change  in  pure  urea,  it 
is  necessary  to  heat  it  with  water  under  high  pressure.  "When  urea  is 
combined  with  hydrochloric  acid,  and  the  hydrochlorate  is  heated,  it 
furnishes  ammonium  chloride  and  cyanuric  acid,  according  to  the 
equation;  3(CH4X20.HC1)  --  SXH^Cl  +  H3C3X3O3. 

Hydrochlorate  of  urea.  Cyanuric  acid. 

When  cyanuric  acid  is  distilled,  it  yields  3  molecules  of  cyanic  acid 
(HCXO),  and  the  connexion  thus  established  between  urea  and  the 
cyanogen  series  becomes  intelligible  when  we  see  that  this  base  is  isomeric 
with  ammonium  cyanate  (XH3.HCXO).  In  fact,  by  combining  cyanic 
acid  with  ammonia,  and  evaporating  the  solution,  no  ammonium  cyanate, 
but  simply  urea,  is  obtained. 

Upon  this  has  been  founded  a  process  for  obtaining  urea  artificially, 
which  has  attracted  a  great  deal  of  attention  as  one  of  the  earliest  examples 
of  the  production,  in  the  laboratory,  of  a  complex  substance  formed  in  the 
animal  body.  For  the  artificial  production  of  urea,  56  parts  of  well-dried 
potassium  ferrocyanide  are  intimately  mixed  with  28  parts  of  dried  man- 
ganese dioxide,  and  the  mixture  heated  to  dull  redness  in  an  iron  dish, 
and  stirred  until  it  ceases  to  smoulder  (see  p.  444).  The  oxygen  supplied 
by  the  oxide  of  manganese  converts  the  potassium  and  part  of  the  cyano- 
gen of  the.  ferrocyanide  into  potassium  cyanate,  the  remainder  of  the 
cyanogen  being  burnt,  and  the  iron  converted  into  oxide — 

K4(CX)eFe  -^09  =  4KCX0  +  2CO2  -f-  Xg-l-FeO. 

Potassium  Potassium 

feiToeyanide.  cyanate. 

On  treating  the  residue  with  cold  water,  the  potassium  cyanate  is 
dissolved  out,  and  after  the  insoluble  portion  has  subsided,  the  liquid 
may  be  poured  ofi",  and  41  parts  of  ammonium  sulphate  dissolved  in  it. 
Potassium  sulphate  and  ammonium  cyanate  are  thus  formed — 

2KCX0  +  (XH^).2.S0^  =  K2SO4  +  2XH^CX0; 

and  if  the  solution  be  evaporated  to  dryness  (on  a  water-bath)  the  latter 


624  COMPOUND  UREAS. 

salt  is  transformed  into  urea,  which  may  be  separated  from  the  potassium 
sulphate  by  alcohol,  Avhich  dissolves  the  urea  only.* 

If  strong  solutions  of  potassium  cyanate  and  ammonium  sulphate  be  mixed  in  a 
test-tube  and  placed  in  a  freezing  mixture,  potassium  sulphate  soon  crystallises  out. 
Tlie  solution  of  ammonium  cyanate  is  poured  off  and  divided  into  two  parts  ;  one  of 
these  is  boiled  for  a  minute  or  two  to  convert  the  cyanate  into  urea,  which  may  be 
preci])itated  by  nitric  acid. 

By  fusing  urea  with  sodium,  Fenton  has  converted  it  into  ajanamide ;  CON2H4 
+  Na  =  NaOH-l-H  +  NH2.CN  (cyanamide)  ;  this  is  obtained  in  the  pure  state  by  dis- 
solving the  mass  in  water,  adding  ammonia  in  excess,  and  silver  nitrate,  which  gives 
a  yellow  precipitate ;  this  is  washed,  dried,  covered  with  ether,  and  decomposed  by 
HjS,  when  Ag^S  is  separated,  and  the  cyanamide  dissolves  in  the  ether,  from  which  it 
may  be  crystallised. 

437.  The  true  constitution  of  urea  has  been  the  subject  of  much  discussion  among 
chemists.  The  circumstance  that,  under  certain  conditions,  this  base  assimilates  the 
elements  of  water  and  is  converted  into  ammonium  carbonate,  has  led  to  the  opinion 
that  urea  should  be  classed  among  the  amides  (page  550),  when  it  would  be  repre- 
sented as  derived  from  ammonium  carbonate  (NH4)2C03  by  the  loss  of  water,  just 
as  oxamide  is  derived  from  ammonium  oxalate — 

(NH4).,C03  -  2H,0  =  CH4N„0  ;  (NH4).,C204  -  2H„0  =  C2H4N20.^ . 
Ammonium  ^rea.  Ammonium  Oxamlde. 

carbonate.  oxalate.  • 

When  ammonium  carbonate  is  heated  to  140°  C.  in  a  sealed  tube,  it  is  converted 
into  urea. 

The  question  naturally  presents  itself  whether  the  various  bases  formed  by  substi- 
tution from  ammonia  (page  541)  would  furnish  corresponding  ureas  when  acted  upon 
by  cyanic  acid.  This  has  been  actually  found  to  be  the  case  ;  ethylamine  NH2(C2Hb), 
lor  example,  acting  ujion  cyanic  acid,  yields  ethyl-urea,  which  is  isomeric  with 
ethylamine  cyanate,  just  as  urea  is  isomeric  with  ammonium  cj'anate — 

NH.3(C2H5).HCNO  =  CH3(C2H6)N20 
Ethylamine  cyanate.  Etliyl-urea. 

It  is  evident  that  if  urea  be  derived  from  a  double  molecule  of  ammonia  by  the 
substitution  of  CO  for  H,,  then  ethyl-urea  will  be  derived  in  a  similar  manner  from  a 
double  molecule  of  ethylamine  ;  N,H4(C2H5)2;  N'2H3(C2H5)(CO)". 

Ethylamine.  Ethj-l-urea. 

In  this  case  it  will  be  observed  that  the  diatomic  group  CO  is  substituted  for  one 
atom  of  the  hydrogen,  and  for  one  of  its  representative,  ethyle. 

It  will  be  remembered  that  the  amides  can  be  obtained  by  the  action  of  ammonia 
u  j)on  the  corresponding  ethers  ;  thus  oxalic  ether  treated  with  ammonia  gives  oxamide, 
and  the  conversion  may  be  intelligibly  represented  thus — 

icor)         "')         (0,0,)")  „    1 

Oxalic  ether.        Ammonia.  Oxamide.  Alcohol. 

In  a  similar  manner,  carbonic  ether,  when  heated  in  a  sealed  tube  with  an 
alcoliolic  solution  of  ammonia,  yields  urea  and  alcohol — 

Carbonic  ether.        Ammonia.  Urea.  Alcohol. 

When  cyanic  ether  (CjHg.CNO)  is  acted  on  by  ammonia,  it  yields  ethyle-urea,  the 
action  being  precisely  parallel  to  that  of  ammonia  upon  cyanic  acid — 

H.CXO  +  NH3  =  NH3.H.CNO  ;     (C2H5).CNO  +  NH3  =  NH3.(C2Hs).CNO 
C\  iiiiic  acid.  Urea.  Cyanic  ether.  Ethyl-urea. 

*  Urea  has  been  artificially  obtained  by  Herroun,  by  passing  a  mixture  of  benzene 
vajiour,  ammonia,  and  air  over  red  hot  platinum  wire.  Mixter  has  also  produced  it  by 
passing  ammonia  and  carbon  dioxide  together  through  a  red  hot  tube. 


URIC  OR  LITHIC  ACID.  625 

Many  other  compound  ureas  of  this  description  have  been  obtained,  in  which  the 
hydrogen  is  partly  or  entirely  replaced  by  the  alcohol  radicals.  The  relation  existing 
between  those  and  their  prototype,  urea,  will  be  seen  in  the  following  examples  :  — 

Urea,  CH^K.O  ;  ethyl-methyl-urea,  C(C2H5)(CH3)H2N20  ;  tetrethyl-urea,  C(C2H5)4 
N2O  ;  diphenyi-urea,  C(C6H5)2H2N20. 

The  supposition  that  urea  is  really  constituted  upon  the  ammonia  type  derives 
some  confirmation  from  the  circumstance,  that  a  number  of  substances  have  been 
obtained  which  bear  the  same  relation  to  urea  as  the  amides  do  to  ammonia.  They 
are,  therefore,  sometimes  styled  ureides,  and  sometimes  compound  ureas,  in  which  a 
negative  or  acid  radical  occupies  the  place  of  a  part  of  the  hydrogen.  In  illustration 
of  the  mode  of  formation  of  the  bodies  of  this  class,  the  production  of  benzureide  or 
benzoyl-urea  may  be  referred  to. 

When  ammonia  acts  upon  benzoyl  chloride,  it  yields  benzamide  and  hydrochloric 
acid  ;  C7H5O. CI  +  NH3=  C.H5O.  NH2  +  HCl. 

If  urea  be  substituted  for  the  ammonia,  benzureide  and  hydrochloric  acid  are 
formed  ;  C7H5O.  CI  -I-  CH4N0O  =  C7H5O.  CH3N2O  -t-  HCl.  Both  reactions  become  much 
more  intelligible  if  urea  and  its  derivatives  be  allowed  to  be  composed  upon  the 
ammonia  type — 

NH3  +  (C7H50)C1  =  NHaiCyHgO)  +  HCl 
Ammonia.         chloridp  Benzamide. 

N"2H4(C0)"  +  (C7H50)C1  =  N2H3(C7H50)(CO)"  +  HCl . 
^^'•«*-  fhloridi?  Benzureide. 

By  similar  processes  there  have  been  obtained  acetyl-urea,  N2H3(CoH30)(CO)", 
butyryl-urea,  N2H3(C4H70)(CO)",  &c. 

438.  Uric  acid. — When  human  urine  is  acidified  with  hydrochloric 
acid  and  allowed  to  stand  for  some  time,  it  deposits  minute  hard  red 
grains,  consisting  of  iiric  acid  (0511^^X^03)  tinged  with  the  urinary  colour- 
ing matter.  In  urine  the  acid  is  present  as  urate  of  sodium  and  urate  of 
ammonium,  which  are  often  deposited  from  urine  in  slight  derangements 
of  the  system,  when  they  are  present  in  excess,  these  salts  being  very 
much  more  soluble  in  warm  water  than  in  cold.  Since  uric  acid  and  its 
salts  are  very  common  ingredients  of  calculi,  the  acid  is  sometimes  called 
lithic  acid  (A.i9os,  a  stone). 

As  the  quantity  of  uric  acid  in  human  urine  does  not  exceed  1  grain 
in  1000,  recourse  is  had  to  other  sources  for  the  preparation  of  this  acid, 
which  was,  at  one  time,  extensively  used  for  the  preparation  of  the 
murexide  employed  in  calico-printing. 

The  excrements  of  the  boa-constrictor  and  of  birds,  Avhich  consist  almost 
entirely  of  acid  ammonium  urate,  and  guano,  which  has  been  formed  by 
the  partial  decomposition  of  the  excrements  of  sea-birds,  are  excellent 
sources  of  uric  acid.  The  separation  of  the  uric  acid  from  acid  am- 
monium urate  is  easily  effected  by  dissolving  it  in  solution  of  potash, 
filtering,  and  adding  hydrochloric  acid,  when  the  uric  acid,  which  requires 
10,000  parts  of  cold  water  to  dissolve  it,  is  precipitated  as  a  white 
crystalline  powder. 

When  a  solution  of  potash  is  saturated  with  uric  acid  in  the  cold,  and 
boiled  down  out  of  contact  with  air,  small  needle-like  crystals  are  de- 
posited, having  the  composition  .KgCaHoX^Og,  and  if  this  be  dissolved  in 
water,  and  carbonic  acid  gas  be  passed  through  the  solution,  half  the  potas- 
sium is  removed  as  carbonate,  and  a  granular  precipitate  of  acid  potassium 
urate,  KHCgHoX^Og  is  deposited.  Uric  acid,  therefore,  is  a  dibasic  acid, 
and  the  formida  of  the  acid  itseK  (C-H^X^Oo)  should  be  written 
H,C,H2X403. 

When  uric  acid  is  added  by  degrees  to  strong  nitric  acid,  it  dis3olve3 

2  R 


626  HIPPURIC  ACID. 

■with  effervescence  and  evolution  of  heat ;  th^  solution,  on  cooling,  deposits 
octahedral  crystals  of  a  substance  called  alloxan  (C^^^O^,  which  may 
be  represented  as  formed  by  the  oxidation  of  the  uric  acid  according  to 
the  following  equation  : — 

C5H4N4O3  +  0  +  H2O  =  C^HgNgO^  +  CH4N2O 

Uric  acid.  Alloxan.  Urea. 

Alloxan  has  the  curious  property  of  staining  the  fingers  of  a  beautiful 
pink  colour,  and  its  solution  gives  an  intense  purple  colour  with  ferrous 
sulphate.  A  connexion  is  established,  by  means  of  alloxan,  between  uric 
acid  and  urea,  which  becomes  important,  because  these  two  bodies,  accom- 
panied by  a  small  quantity  of  alloxan,  are  always  found  together  in  the 
urine.  Alloxan  appears  to  be  the  intermediate  stage  in  the  conversion  of 
uric  acid  into  urea  by  oxidation,  for  if  a  solution  of  alloxan  be  boiled  with 
peroxide  of  lead  (PbOg)  carbonic  acid  gas  is  evolved,  and  the  alloxan  is 
converted  into  urea  by  oxidation — 

C4H2N2O4  +  2Pb02  +  H2O  =  CH4:N'20  +  3CO2  +  2PbO. 

Alloxan.  Urea. 

When  sulphuretted  hydrogen  is  passed  through  a  solution  of  alloxan, 
the  liquid  is  troubled  by  the  separation  of  sulphur,  and  deposits  prismatic 
crystals  of  alloxantine  (CgH^N^Oy) — 

2C4H2N2O4  +  H2S  =  CgH.N^O-  +  H2O  +  S. 

Alloxan.  Alloxnntine. 

If  4  grains  of  alloxantine  and  7  grains  of  crystallised  alloxan  be  dissolved 
in  hot  water,  and  80  grains  of  a  cold  saturated  solution  of  ammonium 
carbonate  added,  carbonic  acid  gas  is  disengaged  with  effervescence,  and 
the  liquid  assumes  a  brilliant  purple  colour,  depositing  as  it  cools  splendid 
crystals,  which  have  a  red  colour  by  transmitted  light,  and  reflect  a  play 
of  green  and  gold,  like  the  wing  of  the  sun- beetle.  This  magnificent  sub- 
stance is  known  as  murexide,  and  has  the  formula  CgHgN^Og.  The  beau- 
tiful colour  of  murexide  has  been  applied  to  dyeing  and  calico-printing, 
being  prepared  for  that  purpose  from  the  uric  acid  furnished  by  guano. 

By  acting  upon  lead  urate  with  methyl  e  iodide,  meihyluric  acid^ 
C^^{G}i.^'S  fi^,  has  been  obtained  as  a  sparingly  soluble  crystalline  body 
which  yields  methylamine,  glycocine,  ammonia,  and  carbon  dioxide  wheu 
distilled. 

439.  Hippuric  acid. — Another  acid  peculiar  to  the  urine,  and  found 
in  very  minute  quantity  in  human  urine,  is  hippuric  acid  (C9H9NO3),  so 
named  because  it  occurs  in  far  larger  quantity  in  the  urine  of  horses  (iTnros, 
a  horse)  and  cows,  the  cow's  urine  yielding  more  than  1  per  cent,  of  the 
acid.  It  is  generally  prepared  from  cow's  urine  by  evaporating  it  to  about 
an  eighth  of  its  bulk,  and  adding  an  excess  of  hydrochloric  acid.  On 
standing,  long  prismatic  needles  of  hippuric  acid  are  deposited.  It  is 
remarkable  that  this  acid  can  be  obtained  only  from  the  urine  of  stall-fed 
cows  or  of  horses  kept  at  rest,  for  if  the  animals  are  actively  exercised, 
the  above  treatment  educes  benzoic  acid  (CyHgOa)  in  place  of  hippuric. 
Again,  only  the  fresh  urine  yields  hippuric  acid,  for  after  putrefaction,  only 
benzoic  acid  can  be  obtained  from  it.  Conversely,  if  benzoic  acid  be  admin- 
istered to  an  animal,  it  makes  its  appearance  as  hippuric  acid  in  the  urine. 

The  relation  between  these  two  acids  becomes  evident  when  hippuric 
acid  is  boiled  for  some  time  with  strong  hydrochloric  acid ;  on  cooling, 
the  solution  deposits  crystals  of  benzoic  acid,  and  if  the  liquid  separated 


ULTIMATE  ELEMENTS  OF  PLANTS.  627 

from  these  be  evaporated,  neutralised  with  ammonia,  and  mixed  with 
alcohol,  crystals  of  glycocine  (page  622)  are  obtained — 

Hipporic  acid.  Benzoic  add,  Glycocine. 

This  result  has  been  confirmed  synthetically  by  acting  upon  the  com- 
pound resulting  from  the  action  of  glycocine  on  zinc  oxide,  with  benzoyl- 
chloride  (page  481),  when  hippuric  acid  is  reproduced — 

Zn.2C.^H,N02   +   2(C;H50.C1)   =   ZnClg   +   2C9H9XO3 

Zlnc-(jlycoclne,  Benzoyle  chloride.  Hippuric  acid. 

Hippuric  acid,  therefore,  may  be  represented  as  benzoyle-glycocine, 
C2H^(C;H50)N02.  A  very  interesting  illustration  of  the  doctrine  of 
substitution  is  connected  with  these  acids.  By  acting  upon  hippuric  acid 
with  nitric  and  sulphuric  acids,  it  is  converted  into  nitro-hippuric  acid  by 
the  substitution  of  ^02  for  1  atom  of  its  hydrogen,  and  if  this  acid  be 
boiled  with  hydrochloric  acid,  it  yields  nitrobenzoic  acid,  just  as  hippuric 
yields  benzoic  acid — 

Nitro-hippuric  acid.  Nitro-benzoic  acid.  Glycocine. 

In  contact  with  bases,  hippuric  acid  forms  salts  of  the  general  formula 
MjC^HgNOg,  so  that  the  acid  itself  should  be  written  as  HCgHgNOg. 

In  addition  to  the  organic  substances  which  have  been  already  men- 
tioned as  occurring  in  the  urine  (urea,  uric  acid,  mucus,  hippuric  acid, 
kreatine),  it  always  contains  a  large  proportion  of  alkaline  and  earthy 
salts,  especially  of  sodium  chloride,  phosphate  and  sulphate  of  potassium, 
and  phosphates  of  calcium,  magnesium,  and  ammonium. 

The  average  composition  of  human  urine  may  be  thus  stated — 

Water, 956-80 

Urea, 14-23 

Uric  acid, 0-37 

Mucus 0-16 

Hippuric  acid,  kreatinine,  ammonia,  colouring  )  i  r  -o^ 

matter,  and  unknown  organic  matters,    .        \ 

Chloride  of  sodium,    .         .         .         .         .         .  7  "22 

Phosphoric  acid  (strictly,  PjOj),          .         .         .  2 '12 

Potash, 1-93 

Sulphuric  acid  (strictly,  SO3)      .         .         .         .  1-70 

Lime 021 

Magnesia, 0-12 

Soda, 005 

999-94 

CHEMISTRY  OF  VEGETATION. 

440.  The  ultimate  elements  of  plants,  that  is,  the  substances  with  which 
plants  must  be  supplied  in  one  form  or  other,  to  sustain  their  growth,  are 
carbon,  hydrogen,  nitrogen,  oxygen,  sulphur,  phosphorus,  chlorine,  silicon, 
potassium,  sodium,  calcium,  magnesium,  iron,  manganese. 

Of  these,  the  carbon,  hydrogen,  nitrogen,  oxygen,  sulphur,  and  phos- 
phorus are  grouped  together  to  form  the  various  organic  compounds 
furnished  by  pl-ants,  the  remaining  elements  being  arranged  generally  in 
the  following  forms  : — 


628  MINERAL  SUBSTANCES  OF  THE  SOIL. 

Chlorides  and  silicates  of  potassium  and  sodium,  calcium  sulphate, 
phosphates  of  iron  (manganese?),  calcium,  magnesium,  and  ammonium, 
salts  of  potassium,  sodium,  and  calcium,  with  vegetable  acids. 

Plants  are  capable  of  receiving  food,  either  in  the  form  of  gas  through 
the  instrumentality  of  their  leaves,  or  in  solution  by  their  roots. 

The  carbon,  which  is  their  most  important  constituent  as  regards  quan- 
tity is  taken  up  in  the  form  of  carbonic  acid  gas  by  both  these  organs  of 
the  plant.  This  carbonic  acid  is  derived  either  from  the  surrounding 
atmosphere,  or  from  the  decay  of  the  organic  matters  contained  in  the  soil 
which  surrounds  the  roots  of  the  plant. 

The  hydrogen  is  derived,  partly  from  water,  and  partly  from  the  am- 
monia which  is  carried  down  to  the  roots  of  the  plant  by  rain,  or  is 
evolved  in  the  putrefaction  and  decay  of  the  nitrogenised  oiganic  matters 
of  the  soiL  The  ammonia  also  forms  one  great  source  of  the  nitrogen  in 
plants,  another  being  the  nitric  or  nitrous  acid,  which  is  either  brought 
down  by  the  rain,  or  formed  within  the  soil  by  the  nitrification  of  the 
ammonia  (page  133).  As  to  the  oxygen,  it  is  obtained  both  from  the 
carbonic  acid  and  water,  which  contain  this  element  in  larger  propor- 
tion than  is  ever  present  in  any  vegetable  product.  The  sulphur  and 
phosphorus  contained  in  the  organic  parts  of  the  plant  appear  to  be 
chiefly  derived  from  the  sulphates  and  phosphates  of  the  soil.  The 
chlorine,  silicon,  and  the  metals  are  derived  from  the  mineral  constituents 
of  the  soil. 

It  is  not  difficult  to  imagine  the  course  of  formation  of  a  fertile  soil  from 
a  primary  rock  (of  granite,  for  example)  under  the  influence  of  the 
atmosphere  and  rain,  exerted  through  a  very  long  period. 

It  will  be  remembered  that  granite  consists  essentially  of  quartz  (silica), 
felspar  (silicate  of  aluminium  and  potassium  or  sodium),  and  mica  (silicates 
of  aluminium,  iron,  potassium,  and  magnesium)  ;  in  addition  to  these, 
there  may  always  be  found  in  granite  minute  quantities  of  calcium  phos- 
phate, of  sulphates,  of  chlorides,  and  of  manganese. 

By  the  disintegration  of  such  rock  under  the  action  of  air  and  moisture 
(page  290),  a  soil  will  be  formed  containing  the  various  mineral  substances 
required  for  the  food  of  the  plant.  If  now,  upon  the  thin  layer  of  soil 
thus  formed  over  the  face  of  the  rock,  some  seeds  of  the  lower  orders  of 
plants,  the  lichens,  for  instance,  be  deposited,  they  will  grow  and  fructify, 
deriving  their  carbon,  hydrogen,  nitrogen,  and  oxygen  from  the  air  and 
rain,  and  their  mineral  constituents  from  the  soil.  The  death  of  these 
lichens  would  add  new  elements  of  fertility  to  the  soil,  in  the  shape  of  the 
food  which  they  had  condensed  from  the  air,  and  of  the  saline  ingredients 
which  had  been  converted  within  their  organisations  into  forms  better 
suited  to  sustain  the  higher  orders  of  plants.  Given,  then,  the  seeds  of  a 
higher  vegetation,  a  similar  process  may  be  supposed  to  take  place,  and  at 
length  animals  would  be  attracted  to  the  spot  by  the  prospect  of  vegetable 
food,  and  by  transporting  to  it  elements  which  they  had  derived  from 
other  sources,  would  eventually  confer  upon  it  the  highest  fertility.  The 
soil  then  coming  under  tillage,  the  crops  raised  upon  it  are  consumed  by 
animals  and  removed  to  a  distance,  so  that  the  mineral  food  contained  in 
the  soil  is  by  degrees  exhausted,  and  unless  it  is  restored  the  soil  becomes 
barren. 

To  restore  its  fertility  is  the  object  of  manuring,  which  consists  in  add- 
ing to  the  soil  some  substance  which  shall  itself  serve  directly  as  food  for 


FOOD  FOR  PLANTS.  629 

the  plant,  or  shall  so  modify,  by  chemical  action,  some  material  already 
present  in  the  soil,  as  to  convert  it  into  a  state  in  which  the  plant  may 
take  advantage  of  it. 

As  examples  of  substances  which  are  added  as  direct  food  for  plants, 
may  be  enumerated  : — 

(1)  The  ashes  of  peat,  turf,  coal,  &c.,  which  furnish  the  mineral  sub- 
stances originally  obtained  from  the  soil  by  the  vegetables  from  which 
these  materials  were  formed. 

(2)  Gypsum,  or  calcium  sulphate,  and  magnesium  sulphate,  which 
appear  to  be  valuable  not  only  as  sources  of  sulphur,  calcium,  and  mag- 
nesium, but  because  they  are  capable  of  decomposing  the  ammonium 
carbonate,  which  is  either  brought  down  by  rain  or  evolved  by  putrefaction 
in  the  soil,  and  of  converting  it  into  ammonium  sulphate  which  is  retained 
in  the  soil,  Avhereas  the  carbonate,  being  a  volatile  salt,  would  be  again 
exhaled  into  the  air  and  lost  to  the  plants. 

(3)  Phosphate  of  lime  (calcium  phosphate),  or  bone-ash,  which  is  most 
commonly  converted  into  the  soluble  superphosphate  (page  222),  by  treat- 
ment with  sulphuric  acid,  before  being  employed  as  a  manure. 

(4)  Sodium  chloride,  or  common  salt,  serves  as  a  source  of  sodium, 
for  in  contact  with  the  calcium  carbonate,  which  is  found  in  all  fertile 
soils,  it  is  partly  converted  into  sodium  carbonate,  which  may  in  turn  be 
converted  into  sodium  silicate,  or  any  other  salt  of  sodium  necessary  to 
the  growth  of  the  plant. 

(5)  Sodium  nitrate  (Peruvian  nitre)  is  held  to  be  of  great  service  in 
some  cases,  as  yielding  both  sodium  and  nitrogen  in  a  form  serviceable  to 
the  plant. 

(6)  The  silicates  of  potassium  and  sodium,  which  are  especially  useful 
to  crops  containing,  like  the  cereals,  a  considerable  proportion  of  silica  in 
their  stems  ;  since,  although  that  substance  is  contained  in  abundance  in 
all  soils,  it  is  not  available  for  the  plant  unless  converted  into  a  soluble 
state  by  combination  with  an  alkali. 

(7)  Sulphate  of  ammonia  (derived  from  the  gas-works)  is,  of  course, 
useful  both  for  its  sulphuric  acid  and  ammonia. 

(8)  Plants,  or  parts  of  plants,  ploughed  into  a  soil,  would  obviously 
furnish  food  for  other  plants  by  their  gradual  putrefaction  and  decay. 

(9)  Bones,  which  furnish  carbonic  acid  and  ammonia  by  the  putrefac- 
tion of  their  gelatinous  matter,  as  well  as  a  large  supply  of  phosphate  of 
lime. 

(10)  Urine,  yielding  much  ammonium  carbonate  by  the  decomposition 
of  the  urea  and  uric  acid,  arid  an  abundance  of  the  phosphates  and  other 
saline  matters  required  by  the  plant. 

(11)  Solid  excrements  of  various  animals,  containing  the  insoluble  salts 
(especially  phosphates)  of  the  animal's  food,  as  well  as  easily  putrescible 
organic  matters  yielding  much  ammonia  and  sulphuretted  hydrogen. 

(12)  Guano,  the  dung  of  carnivorous  sea-birds,  which  owes  its  very  high 
value  partly  to  the  large  proportion  of  urate  of  ammonia  and  other  nitro- 
genised  organic  substances  which  it  contains,  and  partly  to  the  presence 
of  phosphates  and  salts  of  the  alkalies. 

(13)  Soot,  which  appears  to  act  chiefly  by  virtue  of  the  salts  of 
ammonia  derived  from  the  destructive  distillation  of  the  coal. 

The  chief  substance  employed  for  acting  chemically  upon  the  consti- 
tuents of  the  soil,  so  as  to  render  them  more  serviceable  to  the  plant,  is 


630  KOTATION  OF  CROPS. 

lime,  which  modifies  in  a  very  important  manner  both  the  organic  and 
mineral  portions  of  the  soil.  Its  action  upon  the  former  consists  in  pro- 
moting its  decay,  and  the  conversion  of  its  elements  into  those  forms,  viz., 
carbonic  aciti,  water,  ammonia,  and  nitric  acid,  in  which  they  may  be  of 
service  to  the  plant.  Upon  the  inorganic  constituents  of  the  soil,  lime 
acts  by  assisting  the  decomposition  of  minerals,  particularly  of  those  which 
furnish  the  alkalies  (such  as  felspar),  and  thus  converting  them  into 
soluble  forms. 

In  some  cases  fertility  is  restored  to  an  apparently  exhausted  soil,  with- 
out the  addition  of  manure,  by  allowing  it  to  lie  fallow  for  a  time,  so  that 
under  the  influence  of  the  air  and  moisture,  such  chemical  changes  may 
take  place  in  it  as  will  again  replenish  it  with  food  available  for  the  crops. 
It  is  not  even  necessary  in  all  cases  that  the  soil  should  be  altogether 
released  from  cultivation;  for  even  though  it  may  refuse  to  feed  any  longer 
one  particular  crop,  it  may  furnish  an  excellent  crop  of  a  different  descrip- 
tion, and,  which  is  more  remarkable,  it  may,  after  growing  two  or  three 
different  crops,  be  found  to  have  regained  its  power  of  nourishing  the  very 
crop  for  which  it  was  before  exhausted.  Experience  of  this  has  led  to  the 
adoption  of  the  system  of  rotation  of  crops,  by  which  a  soil  is  made  to 
yield,  for  example,  a  crop  of  barley,  and  then  successive  crops  of  grass, 
beans,  turnips,  and  barley  again. 

The  possibility  of  this  rotation  is  partly  accounted  for  by  the  difference 
in  the  mineral  food  removed  from  the  soil  by  different  crops;  thus  turnips 
require  much  of  the  alkalies  and  lime ;  wheat,  much  alkali  and  silica ; 
barley,  much  lime  and  silica;  and  clover,  much  lime,  so  that  the  soil  which 
had  been  exhausted  for  wheat,  because  it  no  longer  contained  enough 
soluble  silica,  might  still  yield  sufficient  alkali  and  lime  to  a  crop  of  turnips, 
and  when  the  alkali  was  exhausted,  might  furnish  enough  lime  to  a  crop 
of  clover,  after  which,  in  consequence  of  the  chemical  changes  allowed  by 
lapse  of  time  in  the  soil,  more  of  the  original  minerals  composing  it  might 
have  been  decomposed  and  rendered  available  for  a  fresh  wheat  crop. 

Another  explanation  of  the  benefit  of  systems  of  rotation  may  be  given 
in  those  cases  in  which  the  refuse  of  the  preceding  crop  is  allowed  to 
remain  on  the  land.  Some  plants  extending  their  roots  more  deeply  into 
the  soil,  avail  themselves  of  mineral  food  which  is  beyond  the  reach  of 
plants  furnished  with  shorter  roots,  and  when  the  refuse  of  the  former 
plants  is  ploughed  into  the  land,  the  surface  is  enriched  with  the  food 
collected  from  the  subsoil. 

Our  knowledge  of  the  chemical  operations  taking  place  in  the  plant,  and 
resulting  in  the  elaboration  of  the  great  variety  of  vegetable  products,  is 
very  slight  indeed.  We  appear  to  have  sufficient  evidence  that  sugar  and 
starch,  for  example,  are  constructed  in  the  plant  from  carbonic  acid  and 
water,  that  gluten  results  from  the  mutual  action  of  the  same  compounds, 
together  with  ammonia,  or  nitric  acid,  and  certain  sulphates,  and  phos- 
phates, but  the  intermediate  steps  in  this  conversion  are  as  yet  unknown. 

All  seeds  contain  starch,  gluten,  or  some  similar  nitrogenised  substance 
(legumine,  for  example),  together  with  mineral  matters,  these  being  pro- 
vided for  the  nourishment  of  the  young  plant  until  its  organs  are  suffi- 
ciently developed  to  enable  it  to  procure  its  own  food  from  the  air  or  from 
the  soil.  During  the  process  of  germination,  the  seed  absorbs  oxygen  and 
evolves  carbonic  acid  gas,  and  since  the  albuminous  constituent  is  the 
most  mutable  substance  present,  it  is  probably  this  which  undergoes  oxi- 


GROWTH  OF  PLANTS.  361 

dation,  and  excites  the  conversion  of  the  insoluble  starch  into  soluble  sugar. 
At  this  state  the  seed  requires,  as  is  well  known,  a  fair  supply  of  water,  the 
elements  of  which  are  required  for  the  conversion  of  the  starch  (CgH^oOj) 
into  sugar  (CgH^gC^e)  >  """^.ter  is  also  required  to  dissolve  the  sugar  as  well 
as  the  altered  albuminous  matter  and  the  mineral  salts,  in  order  to  form  the 
sap  of  the  embryo  plant.  These  constituents  of  the  sap,  directed  by  the 
mysterious  vital  energy  in  the  seed,  build  up  the  root,  which  extends  itself 
in  search  of  nourishment  down  into  the  soil,  and  the  leaves,  which  dis- 
charge a  similar  function  with  respect  to  the  air.  As  soon  as  the  leaves 
are  developed,  the  plant  becomes  able  to  decompose  carbonic  acid,  water, 
and  ammonia,  to  provide  the  organic  components  of  its  sap.  Some  part 
of  these  changes,  at  least,  appears  to  take  place  in  the  leaves  of  the  plant, 
from  which,  during  the  day-time,  oxygen  (together  with  a  little  nitrogen) 
is  continually  evolved.  The  leaves  have  been  compared  to  the  lungs  of 
animals,  the  functions  of  which  they  reciprocate,  for  whilst,  in  the  lungs 
of  animals,  an  absorption  of  oxygen  and  an  evolution  of  carbonic  acid  gas 
is  observed,  in  the  leaves  of  plants  it  is  the  carbonic  acid  gas  which  is 
absorbed  and  oxygen  is  disengaged.  In  the  dark,  plants  exhale  carbonic 
acid  gas,  but  in  much  smaller  quantity  than  they  decompose  in  the  light. 

That  oxygen  must  be  evolved,  if  plants  construct  their  carbonaceous 
compounds  from  carbonic  acid  gas  and  water,  is  obvious  on  reflecting  that 
all  these  compounds  contain  less  oxygen,  in  proportion  to  their  carbon 
and  hydrogen,  than  is  contained  in  carbonic  acid  gas  and  water. 

Thus,  we  may  conceive  the  formation  of  all  the  compounds  of  carbon 
and  hydrogen,  or  of  those  elements  with  oxygen,  which  are  met  with  in 
plants,  by  the  concurrence,  in  various  proportions,  of  carbonic  acid  gas 
and  water,  and  the  separation  of  the  whole  or  a  part  of  their  oxygen. 

To  take  an  example :  cellulose  (CgHj^Og)  would  result  from  the  coalition 
of  6  molecules  of  carbonic  acid  gas  and  5  molecules  of  water,  with  separa- 
tion of  1 2  atoms  of  oxygen.  Again,  malic  acid,  C^HgO^,  w^ould  require  4 
molecules  of  carbonic  acid  gas  and  3  molecules  of  water,  whilst  6  atoms 
of  oxygen  would  be  set  free. 

It  is  equally  easy  to  represent  the  formation  of  nitrogenised  compounds 
from  carbonic  acid  gas,  water,  and  ammonia,  with  separation  of  oxygen, 
for  the  nitrogen  in  all  such  compounds  is  present  in  so  small  a  number  of 
atoms  relatively  to  the  carbon  and  hydrogen,  that  the  amount  of  oxygen 
separated  from  the  carbonic  acid  gas  and  water,  would  always  far  more 
than  suffice  to  convert  the  whole  of  the  hydrogen  of  the  ammonia  into 
water,  even  if  this  hydrogen  did  not  itself  take  part  in  the  formation  of 
the  compound.  Suppose,  for  instance,  that  the  formation  of  quinine  is 
to  be  accounted  for — 

2OCO2   -t-    9H2O    +    2NH3   =    C20H24X2O2   +    0,7. 

Quinine. 

If  sulphur  be  a  constituent  of  the  vegetable  compound  to  be  formed,  it 
is  conceivable  that  the  sulphuric  oxide  derived  from  the  sulphates  present 
in  the  soil  should  co-operate  with  the  carbonic  acid  gas,  water,  and 
ammonia. 

If  the  composition,  of  gluten  be  correctly  represented  by  the  formula 
CiogHjggXg^Og^S,  the  equation  explaining  its  formation  from  the  above 
constituents  of  the  food  of  the  plant  would  be  written — 

IO8CO2   +    UB..P    +    27:SR^    +    SO3    =    Cio8Hi69^^27034S    -I-    O229. 


632  RIPENING  OF  FRUITS. 

The  chemical  tendency  of  vegetables,  therefore,  is  to  reduce  to  a  lower 
state  of  oxidation  the  substances  presented  in  their  food,  whilst  animals 
exhibit  a  reciprocal  tendency  to  oxidise  the  materials  on  which  they  feed. 

"With  respect  to  the  last  stage  in  the  existence  of  the  plant,  the  ripening 
of  the  fruit,  we  know  a  little  more  concerning  the  chemical  changes  which 
it  involves.  Most  fruits,  in  their  unripe  condition,  contain  cellulose, 
starch,  and  some  one  or  more  vegetable  acids,  such  as  malic,  citric,  tartaric, 
and  tannic,  the  latter  being  almost  invariably  present,  and  causing  the 
peculiar  roughness  and  astringency  of  the  unripe  fruit.  The  characteristic 
constituent  of  unripe  fruits,  however,  is  pectose,  a  compound  of  carbon, 
hydrogen,  and  oxygen,  the  composition  of  which  has  not  been  exactly 
determined.  Pectose  is  quite  insoluble  in  water,  but  during  the  ripening 
of  the  fruit  it  undergoes  a  change  induced  by  the  vegetable  acids,  and  is 
converted  into  pectine  (CgaH^oOgg),  which  is  capable  of  dissolving  in  water, 
and  yields  a  viscous  solution.  As  the  maturation  proceeds,  the  pectine 
itself  is  transformed  into  pectic  acid  {^i^^i^ib)^  ^^^  pectosic  acid 
(CggH^gOg  J,  which  are  soluble  in  boiling  water,  yielding  solutions  which 
gelatinise  on  cooling.  It  is  from  the  presence  of  these  acids,  therefore, 
that  many  ripe  fruits  are  so  easily  convertible  into  jellies. 

Whilst  the  fruit  remains  green,  its  relation  to  the  atmosphere  appears 
to  be  the  same  as  that  of  the  leaves,  for  it  absorbs  carbonic  acid  gas,  and 
evolves  oxygen ;  but  when  it  fairly  begins  to  ripen,  oxygen  is  absorbed 
from  the  air,  and  carbonic  acid  gas  is  evolved,  whilst  the  starch  and 
cellulose  are  converted  into  sugar,  under  the  influence  of  the  vegetable 
acids  (page  501),  and  the  fruit  becomes  sweet.  It  has  been  already  seen 
that  the  conversion  of  starch  and  cellulose  (CgHjoOj)  into  sugar  (CgH^gOg) 
Avould  simply  require  the  assimilation  of  the  elements  of  water,  so  that 
the  absorption  of  oxygen  and  evolution  of  carbonic  acid  gas  are  probably 
necessary  for  the  conversion  of  the  tannic  and  other  acids  into  sugar.  For 
example — 


Tannic  acid. 

+     0^4     = 

SCfiHigOe    +    I5CO2; 

Fruit-sugar. 

SC^HgOe   +    03   = 

Tartai-jc  acid. 

'   CgHjgOg 

4-     3H2O     +     6CO2. 

When  the  sugar  has  reached  the  maximum,  the  ripening  is  completed; 
and  if  the  fruit  be  kept  longer,  the  oxidation  takes  the  form  of  ordinary 
decay. 

The  scheme  of  natural  chemistry  would  not  be  complete  unless  provi- 
sion were  made  for  the  restoration  of  the  constituents  of  plants,  after  death, 
to  the  atmosphere  and  soil,  where  they  might  aiford  food  to  new  genera- 
tions of  plants.  Accordingly,  very  shortly  after  the  death  of  a  plant,  if 
sufficient  moisture  be  present,  the  changeable  nitrogenised  (albuminous) 
constituents  begin  to  putrefy,  and  chemical  motion  being  thus  excited,  is 
communicated  to  the  other  parts  of  the  plant,  under  the  form  of  decay,  so 
that  the  plant  is  slowly  consumed  by  the  atmospheric  oxygen,  its  carbon 
being  reconverted  into  carbonic  acid,  its  hydrogen  into  water,  and  its 
nitrogen  into  ammonia,  these  substances  being  then  transported  in  the 
atmosphere  to  living  plants  which  need  them,  while  the  mineral  con- 
stituents of  the  dead  plants  are  washed  into  the  soil  by  rain. 

Moist  wood  is  slowly  converted  by  decay  into  a  brown  substance,  which 
lias  been  called  hurmis,  and  forms  the  chief  part  of  the  organic  matter  in 
soils.     Alkalies  dissolve  this  substance,  and  on  the  addition  of  an  acid  to 


NUTRITION  OF  ANIMALS.  ■  633 

the  bro-vvn  solution,  a  brown  precipitate  is  obtained,  whicb  is  said  to  con- 
tain Jiumic,  ulmic,  and  geic  acids,  but  these  substances  do  not  crystallise, 
and  their  existence  as  definite  acids  appears  to  be  somewhat  doubtful. 
Two  other  acids  of  a  similar  kind,  crenic  and  ajyrocrenic  acids  (^Kp-^vrj,  a 
well),  have  been  obtained  from  the  same  source,  and  are  also  found 
occasionally  in  mineral  waters. 

When  it  is  desired  to  preserve  wood  from  decay,  it  is  impregnated  with 
some  substance  which  shall  form  an  unchangeable  compound  with  the 
albuminous  constituents  of  the  sap.  Kreasote  (page  464)  and  corrosive 
sublimate  {kyanising)  are  occasionally  used  for  this  purpose,  the  wood 
being  made  to  imbibe  a  diluted  solution  of  the  preservative,  either  by 
being  soaked  in  it  or  under  pressure. 

In  Boucherie's  process  for  preserving  wood,  the  natural  ascending  force 
of  the  sap  is  ingeniously  turned  to  account  in  drawing  up  the  preservative 
solution.  A  large  incision  being  made  around  the  lower  part  of  the  trunk 
of  the  growing  tree,  a  trough  of  clay  is  built  up  around  it,  and  filled  with 
a  weak  solution  of  sulphate  of  copper,  peracetate  of  iron,  or  calcium 
chloride.  Even  after  the  tree  has  been  felled,  it  may  be  made  to  imbibe 
the  preserving  solution,  whilst  in  a  horizontal  position,  by  enclosing  the 
base  of  the  trunk  in  an  impermeable  bag  supplied  with  the  liquid  from  a 
reservoir.  The  impregnation  of  the  wood  with  such  solutions  not  only 
prevents  chemical  decay,  but  renders  it  less  liable  to  the  attacks  of  insects 
and  the  growth  of  fungi. 

NUTRITION  OF  ANIMALS. 

441.  Between  the  chemistry  of  vegetable  and  that  of  animal  life  there 
is  this  fundamental  distinction,  that  the  former  is  eminently  constructive 
and  the  latter  destructive.  The  plant,  supplied  with  compounds  of  the 
simplest  kind — ^carbonic  acid,  water,  and  ammonia — constructs  such  com- 
plex substances  as  albumen  and  sugar;  whilst  the  animal,  incapable  of 
deriving  sustenance  from  the  simpler  compounds,  being  fed  with  those  of 
a  more  complex  character,  converts  them  eventually,  for  the  most  part, 
into  the  very  materials  with  which  the  constructive  work  of  the  plant  com- 
menced. It  is  indeed  true,  that  some  of  the  substances  deposited  in  the 
animal  frame,  such  as  fibrine  and  gelatinous  matter,  rival  in  complexity 
many  of  the  products  of  vegetable  life ;  but  for  the  elaboration  of  these 
substances,  the  animal  must  receive  food  somewhat  approaching  them  in 
chemical  composition.  It  is  to  this  nearer  resemblance  between  the  food 
of  animals  and  the  proximate  constituents  of  their  frames,  that  we  may 
partly  ascribe  the  greater  extent  of  our  knowledge  on  the  subject  of  the 
nutrition  of  animals,  which  is,  however,  far  from  being  complete. 

The  ultimate  elements  contained  in  the  animal  body  are  the  same  as 
those  of  the  vegetable,  but  the  proximate  constituents  are  far  more 
numerous  and  varied. 

The  bones  containing  the  phosphates  and  carbonates  of  calcium  and 
magnesium,  together  with  gelatinous  matter,  require  that  the  animal  should 
be  supplied  with  food  Avhich,  like  bread,  contains  abundance  of  phosphates, 
as  well  as  the  nitrogenised  matter  (gluten)  from  which  the  gelatinous 
substance  may  be  formed.  In  milk,  the  food  of  the  young  animal,  we 
have  also  the  necessary  phosphates,  whilst  the  caseine  affords  the  supply 
of  nitrogenous  matters. 


634  CHEMISTRY  OF  DIGESTION. 

Muscular  flesh  finds,  in  the  gluten  of  bread  and  the  caseine  of  milk,  the 
nitrogenised  constituent  from  which  its  fibrine  might  be  formed  with  even 
less  transformation  than  is  required  for  the  gelatinous  matter  of  bone,  since 
the  composition  of  fibrine,  gluten,  and  caseine  is  very  similar.  The 
albumen  and  fibrine  of  the  blood  have  also  their  counterparts  in  the 
ghiten  and  caseine  of  bread  and  milk,  whilst  all  the  salts  of  the  blood  may 
be  found  in  either  of  these  articles  of  food. 

Bread  and  milk,  therefore,  may  be  taken  as  excellent  representatives  of 
the  food  necessary  for  animals,  and  the  same  constituents  are  received  in 
their  flesh  diet  by  animals  which  are  purely  carnivorous,  but  the  flesh 
contains  them  in  a  more  advanced  stage  of  preparation. 

It  is  natural  to  suppose  that  those  parts  of  the  frame  which  contain  no 
nitrogen  should  be  supplied  by  those  constituents  of  the  food  which  are 
free  from  that  element,  such  as  the  starch  in  bread  and.  the  sugar  and  fat 
in  milk. 

Before  the  food  can  be  turned  to  account  for  the  sustenance  of  the  body, 
it  must  undergo  digestion,  that  is,  it  must  be  either  dissolved  or  otherwise 
reduced  to  such  a  form  that  it  can  be  absorbed  by  the  blood,  which  it 
accompanies  into  the  lungs  to  undergo  the  process  of  respiration,  and  thus 
to  become  fitted  to  serve  for  the  nutrition  of  the  various  organs  of  the 
body,  since  these  have  to  be  continually  repaired  at  the  expense  of  the 
constituents  of  the  blood. 

The  first  step  towards  the  digestion  of  the  food  is  its  disintegration, 
eff"ected  by  the  teeth  with  the  aid  of  the  saliva,  by  which  it  should  be 
reduced  to  a  pulpy  mass.  The  saliva  is  an  alkaline  fluid  characterised  by 
the  presence  of  a  peculiar  albuminous  substance  called  ptyaline  (tttuw,  to 
spit),  which  easily  putrefies.  The  action  of  saliva  in  mastication  is  doubt- 
less in  great  part  a  mechanical  one,  but  it  is  possible  that  its  alkalinity 
assists  the  process  chemically,  by  partly  emulsifying  the  fatty  portions  of 
the  food.  The  liability  of  ptyaline  to  putrefaction  favours  the  supposition 
that  it  may  act  in  some  way  as  a  ferment  in  promoting  the  digestion.  This 
disintegration  of  the  food  is  of  course  materially  assisted  by  the  cooking 
to  which  it  has  been  previously  subjected,  the  hard  and  fibrous  portions 
having  been  thereby  softened. 

The  food  now  passes  to  the  stomach,  in  which  it  remains  for  some  time, 
at  the  temperature  of  the  body  (98°  F.),  in  contact  with  the  gastric  juice, 
the  chief  chemical  agent  in  the  digestive  process.  The  gastric  juice, 
which  is  secreted  by  the  lining  membrane  of  the  stomach,  is  an  acid 
liquid,  containing  hydrochloric  and  lactic  acids.  It  is  characterised  by 
the  i)resence  of  a  peculiar  substance  belonging  to  the  albuminous  class 
of  bodies,  which  is  called  pepsine  (TreVrw,  to  digest),  and  possesses  the 
remarkable  power  of  enabling  dilute  acids,  by  its  mere  presence,  to 
dissolve  such  substances  as  fibrine  and  coagulated  albumen,  which  would 
resist  the  action  of  the  acid  alone  for  a  great  length  of  time. 

An  imitation  of  the  gastric  juice  may  be  made  by  digesting  the  mucous 
membrane  of  the  stomach  for  some  hours  in  warm  very  dilute  hydrochloric 
acid.  The  acid  liquid  thus  obtained  is  capable  of  dissolving  meat,  curd, 
&c.,  if  it  be  maintained  at  the  temperature  of  the  body.  The  pepsine 
prepared  from  the  stomach  of  the  pig  and  other  animals  is  sometimes 
administered  medicinally  in  order  to  assist  digestion. 

The  principal  change  which  the  food  suffers  by  the  action  of  the  gastric 
juice  is  the  conversion  of  the  fibrinous  and  albuminous  constituents  into 


BILE.  635 

soluble  forms  {peptones) ;  the  starch  js  also  partly  converted  into  dextrine 
aud  sugar,  but  the  fatty  constituents  are  unchanged. 

The  food  which  has  thus  been  partially  digested  in  the  stomach  is  called 
by  physiologists  chyme,  and  passes  thence  into  the  commencement  of  the 
intestines  (the  dttodenum),  where  it  is  subjected  to  the  action  of  two  more 
chemical  agents,  the  hile  and  \h&  pancreatic  juice. 

Bile  consists  essentially  of  a  solution  of  two  salts  known  as  glycocholate 
and  taurocholate  of  sodium.  Both  glycochoUc  and  taurocholic  acids  are 
resinous,  and  do  not  neutralise  the  alkali,  so  that  the  bile  has  a  strong 
alkaline  character.  Another  characteristic  feature  of  this  secretion  is  the 
large  portion  of  carbon  which  it  contains.  GlycochoUc  acid  has  the 
composition  HC26H42^"Og,  and  contains  therefore  67  per  cent,  of  carbon, 
whilst  laiirocholic  acid,  ^C2QHni^0>;S,  contains  61  per  cent.  The  names 
of  these  acids  have  reference  to  the  circumstance  that  they  furnish  respec- 
tively glycocine  and  taurine,  together  with  two  new  acids  free  from  nitro- 
gen, when  they  are  boiled  with  dilute  hydrochloric  acid — 

2HC,,H,2XOe  +  H^O  =  C,,n,fi,      +  2C2H,I^02 

Glycoholic  acid.  Choloidic  acid.  Glycocine. 

Taurocholic  acid.  Taurine.  Cholic  acid. 

Taunne  forms  colourless  crystals  of  great  beauty,  and  is  remarkable  for 
the  large  proportion  (above  25  per  cent.)  of  sulphur  which  it  contains. 
It  also  presents  an  interesting  example  of  a  complex  animal  derivative 
which  may  be  artificially  prepared  in  a  very  simple  manner. 

When  olefiant  gas  is  passed  over  sulphuric  anhydride,  it  is  absorbed, 
and  if  the  product  be  dissolved  in  water,  neutralised  with  ammonia,  and 
evaporated,  crystals  of  ammonium  isethionate  are  obtained — 

CoH^  +  SO3  +  XH3  +  H2O  =  XH8.H2O.C2H4SO3 

Amuionium  isethionate. 

If  the  corresponding  potassium  salt  be  distilled  with  PCI5,  it  yields 
isethionic  chloride,  C2H4SO2CI2,  which,  when  decomposed  by  water,  gives 
chlorethyh-ulphurous  or  chlorethylsulphonic  acid,  C2H4S02C1(H0),  aud 
wlien  the  silver-salt  of  this  acid  is  treated  with  ammonia,  it  yields  taurine — 

C2H,S02Cl(AgO)  +  NH3  =  C2H7NO3S  -f-  AgCl. 

Taurine  is  also  known  as  amido-ethyl-sidphonic  acid,  and  is  monobasic. 

Another  characteristic  ingredient  of  the  bile  is  cholesterine  *  (CjeH^^O), 
a  crystalline  substance  somewhat  resembling  the  fats,  and  often  deposited 
in  large  quantity  in  the  form  of  biliary  calculi.  It  has  also  been  found  in 
pease,  "wheat,  and  some  vegetable  oils. 

The  colouring  matter  of  the  bile  has  never  been  obtained  in  a  pure  state. 

A  peculiar  substance  called  glycogen,  or  animcd  starch  (CgHjoOj),  has 
been  found  in  the  liver,  and  becomes  speedily  converted  into  sugar  after 
death,  by  assimilating  the  elements  of  water. 

The  special  function  of  the  bile  in  the  digestion  of  the  food  has  not  been 
explained,  but  from  its  strongly  alkaline  reaction  it  does  not  appear  im- 
probable that  its  assists  in  the  digestion  of  fatty  substances. 

The  pancreatic  juice  is  another  alkaline  secretion  which  differs  from  the 
bile  in  containing  a  considerable  quantity  of  albumen,  and  is  very  putres- 
cible.     Its  particular  office  in  digestion  appears  to  consist  in  promoting 

*  From  xo^^,  bile;  <rTeap,fat. 


636  CHEMISTRY.  OF  NUTRITION. 

the  conversion  of  the  starchy  portions  of  the  food  into  sugar  (page  501  )j 
though  it  also  has  a  powerful  action  upon  the  fats,  causing  them  to  form 
an  intimate  mixture,  or  emulsion,  with  water,  and  partly  saponifying 
them.  The  digestion  of  the  starch  and  sugar  is  completed  by  the  action 
of  the  intestinal  fluid  in  the  further  passage  of  the  food  through  the 
intestines,  so  that  when  it  arrives  in  the  small  intestines,  aU  the  soluble 
matters  have  become  converted  into  a  thin  milky  liquid  called  chyle,  which 
has  next  to  be  separated  mechanically  from  the  insoluble  portions,  such  as 
woody  fibre,  &c.,  which  are  excreted  from  the  body. 

This  separation  is  effected  in  the  small  intestines  by  means  of  two  dis- 
tinct sets  of  vessels,  one  of  which  (the  mesenteric  veins)  absorbs  the 
dissolved  starchy  portions  of  the  food,  and  conveys  them  to  the  liver, 
whence  they  are  afterwards  transferred  to  the  right  auricle  of  the  heart. 
The  other  set  of  vessels  (lacteals)  absorbs  the  digested  fatty  matters,  and 
conveys  them,  through  the  thoracic  duct,  into  the  subclavian  vein,  and 
thence  at  once  into  the  right  auricle  of  the  heart. 

From  the  right  auricle  this  imperfect  blood  passes  into  the  right  ventricle 
of  the  heart,  and  is  there  mixed  with  the  blood  returned  from  the  body  by 
the  veins,  after  having  fulfilled  its  various  functions  in  the  system.  The 
mixture,  which  has  the  usual  dark  brown  colour  of  venous  blood,  is  next 
forced,  by  the  contraction  of  the  heart,  into  the  lungs,  where  it  is  distri- 
buted through  an  immense  number  of  extremely  fine  vessels  traversing  the 
lungs,  in  contact  with  the  minute  tubes  containing  the  inspired  air,  so  that 
the  venous  blood  is  only  separated  from  the  air  by  very  thin  and  moist 
membranes.  Through  these  membranes  the  dark  venous  blood  gives  up 
the  carbonic  acid  gas  with  which  it  had  become  charged  by  the  oxidation 
of  the  carbon  of  the  organs  in  its  passage  through  the  body,  and  acquires,  in 
return,  about  an  equal  volume  of  oxygen,  which  converts  it  into  the  bright 
crimson  arterial  blood.  In  this  state  it  returns  to  the  left  side  of  the  heart, 
whence  it  is  conveyed,  by  the  arteries,  to  the  different  organs  of  the  body. 
The  chemistry  of  the  changes  effected  and  suffered  by  the  blood  in  its 
circulation  through  the  body  is  very  imperfectly  understood.  One  of  its 
great  offices  is  the  supply  of  the  oxygen  necessary  to  oxidise  the  com- 
ponents of  the  various  organs,  and  thus  to  evolve  the  heat  which  maintains 
the  body  at  its  high  temperature.  The  results  of  the  oxidation  of  these 
organs  are  undoubtedly  very  numerous  ;  among  them  we  may  trace 
carbonic,  sulphuric,  phosphoric,  lactic,  butyric,  and  uric  acids,  as  well  as 
urea  and  some  other  substances.  The  destroyed  tissues  must  at  the  same 
time  be  replaced  by  the  deposition,  from  the  blood,  of  fresh  particles 
similar  to  those  which  have  been  oxidised.  In  the  course  of  the  blood 
through  the  circulation,  the  above  products  of  oxidation  have  to  be  removed 
from  it — the  carbonic  acid  by  the  lungs  and  skin — the  sulphuric,  phos- 
phoric, and  uric  acids,  and  the  urea,  by  the  kidneys. 

The  various  liquid  secretions  of  the  body,  such  as  the  bile,  the  saliva, 
the  gastric  juice,  &c.,  have  also  to  be  elaborated  from  the  blood  during  its 
circulation  through  the  arteries,  after  which  it  returns,  by  the  veins,  to 
the  heart,  to  have  its  composition  restored  by  the  matters  derived  from 
the  food,  and  to  be  reconverted  into  arterial  blood  in  the  lungs. 

AVhen  it  is  remembered  that  the  body  is  exposed  to  very  considerable 
variations  of  external  heat  and  cold,  a  question  occurs  as  to  the  provision 
made  for  maintaining  it  at  its  uniform  temperature.  This  is  effected 
through  the  agency  of  the  fat  which  is  deposited  in  all  the  organs  of  the 


,    CHEMISTRY  OF  FOOD.  637 

body.  Since  fatty  substances  in  general  are  particularly  rich  in  carbon 
and  hydrogen,  their  oxidation  within  the  body  would  be  attended  with 
the  production  of  more  heat  than  that  of  those  parts  of  the  organs  which 
contain  much  nitrogen  and  oxygen.  Accordingly,  when  the  body  is 
exposed  to  a  low  temperature,  a  larger  quantity  of  its  fat  is  consumed  by 
the  oxidising  action  of  the  blood,  and  a  corresponding  increase  takes 
place  in  the  amount  of  heat  evolved,  thus  compensating  for  the  greater 
loss  of  heat  suffered  by  the  body  in  the  cooler  atmosphere.  Of  course, 
in  cold  weather,  when  more  oxygen  is  required  to  maintain  the  heat  of 
the  frame,  a  larger  quantity  of  that  gas  is  inhaled  at  each  breath,  on 
account  of  the  higher  specific  gravity  of  the  air,  in  addition  to  which, 
we  have  the  quickened  respiration  which  always  attends  exposure  to 
cold.  To  supply  this  extra  demand  for  carbon  and  hydrogen  in  cold 
weather,  we  instinctively  have  recourse  to  such  substances  as  fat,  starch, 
sugar,  &c.,  which  contain  them  in  large  proportion,  and  these  aliments, 
free  from  nitrogen,  are  often  spoken  of  as  the  respiratory  constituents  of 
food;  whilst  flesh,  gluten,  albumen,  &c.,  which  contain  nitrogen,  are  styled 
i\iQ  plastic  elements  of  nutrition  {wXaa-a-oi,  to  form). 

Bearing  in  mind  that  the  food  has  a  twofold  office — to  nourish  the 
frame  and  to  maintain  the  animal  heat — it  will  be  evident  that  a  judiciously 
regulated  diet  will  contain  due  proportions  of  these  nitrogenous  consti- 
tuents, such  as  albumen,  fibrine,  and  caseine,  which  serve  to  supply  the 
waste  of  the  organs,  and  of  such  non-nitrogenised  bodies  as  starch  and 
sugar,  from  which  fat  may  be  elaborated  to  sustain  the  bodily  warmth. 

The  proportion  which  these  two  parts  of  the  food  should  bear  to  each 
other  will,  of  course,  depend  upon  the  particular  condition  of  existence 
of  the  animal  Thus,  for  a  growing  animal,  a  larger  proportion  of  the 
nitrogenised  or  plastic  portion  of  food  would  be  required  than  for  an 
animal  whose  growth  has  ceased;  and  animals  exposed  to  a  low  tempera- 
ture would  require  more  of  the  non-nitrogenised  or  heat-giving  portions  of 
the  food. 

Accordingly,  we  find  that  a  man  can  live  upon  a  diet  which  contains 
(as  in  the  case  of  wheaten  bread)  5  parts  of  non-nitrogenised  (starch 
and  sugar)  to  1  part  of  nitrogenised  food  (gluten) ;  whilst  an  infant, 
whose  increasing  organs  require  more  nitrogenised  material,  thrives  upon 
milk,  in  which  this  amounts  to  1  part  (caseine)  for  every  4  parts  of  the 
non-nitrogenised  portion  (milk-sugar  and  fat).  The  inhabitants  of  cold 
climates  consume,  as  is  well  known,  much  more  oil  and  fat  than  those  of 
the  temperate  and  hot  regions. 

An  examination  of  the  composition  of  different  articles  of  food  affords 
us  an  explanation  of  the  custom  which  experience  has  warranted,  of  asso- 
ciating particular  varieties  of  food.  Thus,  assuming  as  our  standard  of 
comparison  the  composition  of  bread,  which  contains  one  of  nutritive  to 
five  of  heat-giving  matter,  the  propriety  of  associating  the  following  kinds 
of  food  will  be  appreciated  : — 


Beef,   . 
Potatoes, 

Ham,  . 
Veal,  . 

Mutton, 
Kice, 


Heat-giving. 

17 
10- 

3- 
0  1 

27  \ 

12-3         ) 


638  CHANGES  AFTER  DEATH. 

All  muscular  or  mental  exertion  is  attended  with  a  corresponding 
oxidation  of  the  tissues  of  the  frame,  just  as  each  movement  of  a  steam- 
engine  may  be  traced  to  the  combustion  of  a  proportionate  quantity  of 
coal  under  the  boiler;  and  hence  such  exertion  both  creates  a  demand 
for  food,  and  quickens  the  respiration  to  obtain  an  increased  supply  of 
oxygen. 

Experiment  has  proved  that  the  proportion  which  the  oxygen  consumed 
in  respiration  bears  to  the  carbonic  acid  gas  exhaled,  depends  very  much 
upon  the  nature  of  the  food.  Thus  an  animal  fed  upon  vegetable  matters, 
such  as  starch  and  sugar  (the  oxygen  in  which  exactly  suffices  to  convert  the 
hydrogen  into  water),  will  turn  nearly  all  the  inspired  oxygen  to  account 
in  the  formation  of  carbonic  acid  gas,  the  volume  of  which  will  be  nearly 
equal  to  that  of  oxygen  which  disappears  at  each  inspiration;  but  when 
tiesh,  or  particularly  fat,  is  consumed,  much  more  of  the  inspired  oxygen 
is  required  to  convert  the  hydrogen  of  the  food  into  water,  so  that  the 
volume  of  the  carbonic  acid  gas  is  far  less  than  that  of  the  oxygen  consumed 
in  respiration.  When  an  animal  has  been  kept  for  a  length  of  time 
without  food,  the  proportion  between  the  volume  of  the  carbonic  acid  gas 
and  that  of  the  oxygen  consumed  is  the  same  as  if  the  animal  were  being 
fed  upon  a  flesh  diet,  inasmuch  as  its  own  flesh  alone  is  now  supporting 
its  respiration. 

CHANGES  IN  THE  ANIMAL  BODY  AFTEE  DEATH. 

442.  After  the  death  of  animals,  just  as  after  that  of  plants,  their  com- 
ponent parts  are  reduced  to  the  primary  forms  from  which  they  were 
derived,  so  that  they  may  begin  again  at  the  foot  of  the  ascending  scale 
of  life.  Very  soon  after  life  is  extinct,  a  change  takes  place  in  some 
of  the  nitrogenous  constituents,  and  this  change  is  soon  communicated 
to  aU  parts  of  the  body,  which  undergo  a  putrefaction  or  metamor- 
phosis, of  which  the  ultimate  results  are  the  conversion  of  the  carbon 
into  carbonic  acid,  the  hydrogen  into  water,  the  nitrogen  into  ammonia, 
nitrous  and  nitric  acids,  and  the  sulphur  into  sulphuretted  hydrogen 
and  sulphuric  acid.  The  mineral  constituents  of  the  animal  frame 
then  mingle  with  the  surrounding  soil,  and  are  ready  to  take  part  in 
the  nourishment  of  plants,  which  construct  the  organic  components  of 
their  frames  from  the  carbonic  acid  and  ammonia  furnished  by  the 
putrefaction  of  the  animal,  and  then  serve  in  their  turn  as  sustenance  for 
animals  whose  respiration  supplies  the  air  with  carbonic  acid  gas  and  takes 
in  exchange  the  oxygen  eliminated  by  the  plant. 

The  functions  of  the  two  divisions  of  animate  nature  are,  therefore, 
perfectly  reciprocal,  and  this  relationship  must  be  regarded  as  the  founda- 
tion of  economical  agriculture.  If  it  were  possible  to  prevent  the  change 
of  the  .atmosphere,  it  is  quite  conceivable  that  a  perpetual  succession  of 
plants  and  animals  could  be  raised  upon  a  given  farm  without  any  importa- 
tion of  food,  provided  that  there  was  also  no  exportation.  Or  even,  permit- 
ting an  exportation  of  food,  the  succession  of  plants  and  animals  raised  upon 
the  same  land  might  be,  at  least,  a  very  long  one,  if  the  solid  and  liquid 
excrements  of  the  animals,  to  feed  whom  this  exportation  took  place,  were 
restored  to  the  land  upon  which  this  food  was  raised.  The  explanation  of 
this  is,  that  the  solid  and  liquid  excrements  of  the  animal  contain  a  very 
large  proportion  of  the  mineral- constituents  of  the  soil,  in  the  very  state 


NATURE  OF  PUTREFACTION.  63& 

in  which  they  are  best  fitted  for  assimilation  by  the  crop,  and  as  long  as 
the  soil  contains  the  requisite  supply  of  mineral  food,  the  plant  can  derive 
its  organic  constituents  from  the  atmosphere  itself. 

Forasmuch,  however,  as  the  vegetable  and  animal  food  produced  upon 
a  farm  is  generally  exported  to  feed  the  dwellers  in  towns,  whose  excre- 
ments cannot,  without  excessive  outlay,  be  returned  to  the  soil  whence 
the  food  was  derived,  it  becomes  necessary  for  the  agriculturist  to  pur- 
chase farm-yard  manure,  guano,  &c.,  in  order  to  prevent  the  exhaustion  of 
his  soil.  A  great  inanufacturing  country,  in  which  the  majority  of  the 
inhabitants  are  congregated  in  very  large  numbers  around  a  few  centres 
of  industry,  at  a  distance  from  the  land  under  tillage,  is  thus  of  necessity 
dependent  for  a  considerable  proportion  of  its  food  upon  more  thinly 
populated  countries  where  manufactures  do  not  flourish,  to  which  it  exports 
in  return  the  produce  of  the  labour  which  it  feeds. 

The  parts  of  the  frames  of  animals  difi"er  very  considerably  in  their 
tendency  to  putrefaction.  The  blood  and  muscular  flesh  undergo  this 
change  most  readily,  as  being  the  most  complex  parts  of  the  body,  whilst 
the  fat  remains  unchanged  for  a  much  longer  period,  aud  the  bones  and 
hair  will  also  resist  putrefaction  for  a  great  length  of  time.  The  compara- 
tive stability  of  the  fat  is  observed  in  the  bodies  of  animals  which  have 
been  buried  for  some  time  in  a  very  wet  situation,  when  they  are  often 
found  converted  almost  entirely  into  a  mass  of  adipocere,  consisting  of 
the  palmitic  and  raargaric  acids  derived  from  the  fat. 

Some  evidence  has  been  brought  forward  of  the  existence  of  poisonous 
organic  bases  [ptomaines  or  cadaveric  alkaloids)  in  decomposed  human 
bodies. 

When  an  animal  body  is  thoroughly  dried,  it  may  be  preserved  un- 
changed for  any  length  of  time,  and  this  is  the  simplest  of  the  methods 
adopted  for  the  preservation  of  animal  food,  becoming  far  more  efficacious 
when  combined  with  the  use  of  some  antiseptic  substance,  such  as  salt, 
sugar,  spice,  or  kreasote.  The  preservative  effects  of  salt  and  sugar  are 
sometimes  ascribed  to  the  attraction  exerted  by  them  upon  moisture,  which 
they  withdraw  from  the  flesh,  whilst  spices  owe  their  antiseptic  power 
to  the  essential  oils,  which  appear  to  have  a  specific  action  in  arresting 
fermentative  change,  a  character  which  also  belongs  to  kreasote,  carbolic 
acid,  and  probably  to  other  substances  which  occur  in  the  smoke  of  wood, 
well  known  for  its  efficacy  in  curing  animal  matter.  Such  substances  are 
often  called  antizymotic  bodies  ;  carbolic,  salicylic,  benzoic,  and  boracic 
acids  are  classed  under  this  head, 

A  process  commonly  adopted  for  the  presentation  of  animal  and  vege- 
table food,  consists  in  heating  them  with  a  little  water  in  tin  canisters, 
which  are  sealed  air-tight  as  soon  as  the  steam  has  expelled  all  the  air, 
and  if  the  organic  matter  be  perfectly  fresh,  this  mode  of  preserving  it  is 
found  very  successful,  though,  if  putrefaction  has  once  commenced,  to  ever 
so  slight  an  extent,  it  will  continue  even  in  the  sealed  canister  quite  in- 
dependently of  the  air. 

Modern  experiments  have  disclosed  a  great  imperfection  in  our  acquaint- 
ance with  the  conditions  under  w^hich  putrefaction  takes  place,  and 
indicate  the  presence  in  the  atmosphere  of  some  minute  solid  patricles 
which  appear  to  be  minute  ova  or  germs,  and  have  the  power  of  inducing 
the  commencement  of  this  change.  It  has  been  found  that  milk,  for 
example,  may  be  kept  for  a  very  considerable  period  without  putrefying, 


640  JNATURE  OF  PUTREFACTION. 

if  it  be  boiled  in  a  flask,  the  neck  of  which  is  afterwards  loosely  stopped 
with  cotton  wool,  whilst,  if  the  plug  of  cotton  wool  be  omitted,  the  other 
conditions  being  precisely  the  same,  putrefaction  will  take  place  very 
speedily. 

Perfectly  fresh  animal  matters  have  also  been  preserved  for  a  length  of 
time  in  that  state,  in  vessels  containing  air  which  has  been  passed  through 
red  hot  tubes  with  the  view  of  destroying  any  living  germs  which  might 
be  present,  and  such  substances  have  been  found  to  putrefy  as  soon  as  the 
unpurified  air  was  allowed  access  to  them. 

The  extremes  of  the  scale  of  animated  existence  would  appear  to  meet 
here.  The  highest  forms  of  organised  matter,  immediately  after  death, 
serve  to  nourish  some  of  the  lowest  orders  of  living  germs,  these  helping 
to  resolve  the  complex  matter  into  the  simpler  forms  of  carbonic  acid, 
ammonia,  &c.,  which  are  returned  to  the  atmosphere,  the  great  receptacle 
for  the  four  chief  elements  of  living  matter. 


INDEX. 


The  nanus  of  minerals  are  printed  in  italics. 


Abel's  experiments  on  gun-cotton,  508. 
fuze-composition,  365. 
gun-cotton  pulp,  508, 
Abietene,  474. 
Acetal,  556. 
Acetamide,  551. 
Acetates,  565. 
Acetic  acid,  HC2H3O2,  471. 

artificial  formation,  536. 
formed  from  alcohol,  498. 
formed  from  citric,  591. 
glacial,  HC2HQO2,  566. 
purification,  471. 
synthesis  of,  536. 
anhydride,  CiHgOg,  567. 
ether,  527. 
oxychloride,  567. 
peroxide,  568. 
Acetification,  498. 
Acetine,  584. 
Acetone,  CsHgO,  566. 

diethylated,  570. 
dimethylated,  571. 
ethylated,  570. 
methylated,  571. 
properties,  566. 
Acetones,  566. 
Acetonitrile,  551. 
Acetyls,  558. 

chloride,  567. 
peroxide,  568. 
urea,  625. 
Acetylene,  CgH,,  92. 

copper  test  for,  93. 
detection  in  coal  gas,  112. 
formed  from  olefiant  gas,  97. 
preparation  from  coal  gas,  93. 

ether,  94. 
properties,  94. 
silver  precipitate,  94. 
synthesis,  92. 
Acetylide  of  copper,  preparation,  93. 
potassium,  94. 
sodium,  94. 
Acid,  12. 

definition,  27,  253. 
etymology  of,  12. 
of  sugar,  586. 
Acids,  acrylic  series  of,  CnH.2n  -  2O2,  578. 
aromatic,  463. 
dibasic,  constitution,  252. 
'  definition,  86,  253. 
Acids,  monobasic,  constitution,  140,  250. 
diatomic,  483. 


Acids,  monobasic,  definition,  253. 
tetrabasic,  117. 
tribasic,  121. 
of  the  acetic  series,  519. 
lactic  series,  563. 
organic,  constitution,  437,  566. 
oxalic  series  of,  582. 
polybasic,  528. 
tribasic,  constitution,  253. 

definition,  253. 
vegetable,  585. 
volatile,  separation,  571. 
water-type  view  of,  251. 
Acidulous  waters,  50. 
Aconitic  acid,  591. 
Aconitine,  540. 
Acridine,  469. 
Acroleine,  577. 
Acrylic  acid,  HC3H3O2,  578. 
Actinic  rays  of  light,  150. 
Adapter,  93. 
Additive  formulae,  87. 
Adipic  acid,  582. 
Adipocere,  639. 
Aerated  bread,  500. 
After-damp,  77. 
Ag,  silver,  378. 
AgBr,  silver  bromide,  384. 
AgCl,  silver  chloride,  383. 
Agl,  silver  iodide,  384. 
AgNOs,  silver  nitrate,  382. 
Ag20,  silver  oxide,  382. 
Agriculture,  economy  of,  628. 
AggS,  silver  sulphide,  384. 
Agate,  113. 
Aich-metal,  360. 

Air,  analysis  of,  by  eudiometer,  36. 
by  nitric  oxide,  142. 
by  phosphorus,  57. 
by  pyrogallol,  595. 
atmospheric,  57. 
benzoJised,  for  illuminating,  108. 
burnt  in  coal  gas,  106. 
candle  test  applied  to,  77. 
effect  of  combustion  on,  76. 
effect  of  electric  sparks  on,  134. 
eudiometric  analysis,  36. 
exact  analysis  by  copper,  58. 
germs  of  life  in,  639. 
proportion  of  ammonia  in,  123. 
tested  for  impurity,  77. 
Al,  aluminium,  290. 
AI0O3,  alumina,  293. 
Alabaster,  278. 

2s 


642 


INDEX. 


Alabaster,  oriental,  47. 
Albite,  295. 

Albumen  of  blood,  618. 
Alcarsin,  532. 
Alcohol,  G-HfiO,  521. 
absolute,  522. 
allylic,  486. 
aluminium,  5.30. 
amylic,  C5H12O,  518. 
anisic,  561. 
benzoic,  500. 
caprylic,  583. 
cerylic,  585. 
chemical  constitution,  530. 

definition,  437. 
cuminic,  560. 
flame,  109. 
from  milk,  613. 
methylated,  479. 
methylic,  CH4O,  471. 
radicals,  C„Hi„+i,  524. 

doubled  formulae,  525. 
synthesis,  530. 
water-type  view,  530. 
Alcoholic  fermentation,  496. 
Alcohols  and  their  derivatives,  517. 
boiling-points,  518. 
diatomic,  .06I. 
general  properties,  518. 
iso-,  517. 
monatomic,  517. 
normal,  517. 

table  of,  518. 
polyatomic,  561. 
primary,  517. 
secondary,  517. 
tertiary,  517. 
triatomic,  564. 
vapour-densities,  518. 
Aldehyde,  acetic  or  vinic,  C.2H4O,  556. 
ammonia,  NH3,CjiH40,  556. 
benzoic,  560. 
but3rric,  558. 
caprj'lic,  558. 

chemical  constitution,  557. 
cinnaraic,  560. 
cuminic,  560. 
euodic,  558. 

formation  in  vinegar-making,  499. 
lauric,  558. 
cenanthic,  558. 
preparation,  556. 
properties,  557. 
propionic,  558. 
pyromucic,  569. 
resin,  557. 
rutic,  558. 
salicylic,  560. 
valeric,  558. 
Aldehydes,  437,  556. 

action  on  amines,  558. 
derivation  from  aJcohoIs,  519. 
Aldol,  557. 

Ale,  composition,  497. 
Algaroth,  powder  of,  341. 
Alizarine,  artificial,  604. 

orange,  604. 
Alkali,  definition,  12. 

manufacture,  262. 
metals,  group  of,  254. 
works,  fumes  from,  158. 


Alkaline  earth  metals,  general  review,  280. 
Alkaloids,  constitution,  540. 
Alkaloids,  constitution  determined,  545. 
organic,  540. 

vegetable,  extraction  of,  596. 
AUotropy,  192. 
Alloxan,  C^HoNjO.,  626. 
Alloxantine,  C8H4N4O7,  626. 
Allyle,  C3H5,  485. 
iodide,  486. 
series,  486. 
sulphide,  486. 
sulphocyanide,  486. 
terbromide,  578. 
Allylene,  487. 
Allylic  alcohol,  486. 

aldehyde,  578. 
Almond  cake,  480. 

oil,  583. 
Almonds,  480. 
Aloes,  487. 
Aludels,  885. 
Alum,  291. 

basic,  292. 
concentrated,  291. 
in  bread,  501. 
shale,  291. 
uses,  292. 
Alumina,  AlgOj,  293. 
Aluminium,  Al,  290. 

acetate,  565. 
action  on  water,  13. 
and  copper,  295. 
bronze,  360. 
chloride,  AlgCle,  293. 
ethide,  537. 
extraction,  294. 
hydrate,  293. 
methide,  537. 
phosphates,  296. 
properties,  294. 
silicates,  295. 
silicide,  118. 
sulphates,  291. 
Alums,  211. 
Alunogen,  291. 

Amalgam,  for  electrical  machines,  386. 
of  ammonium,  130. 
of  sodium,  130. 
Amalgamating  zinc  plates,  386. 
Amalgamation  of  gold  ores,  401. 

of  silver  ores,  379. 
Amalgams,  386. 
A  marine,  569. 
Amber,  478. 
Attiethj/st,  113. 
Amides,  constitution,  550. 
formation,  551. 
of  phosphoric  acid,  236. 
Amidide  of  potassium,  553. 
Amido-diphenylimide,  463. 

ethyl-sulphonic  acid,  635. 
Amidogen,  NHj,  551. 
Ammonia,  NH3,  123. 

absorbed  by  charcoal,  66. 

absorption  by  water,  125. 

action  of  iodine  on,  180. 

-alum,  292. 

and  chlorine,  152. 

arsenite,  240. 

as  food  for  plant?,  124. 


INDEX. 


64J 


Ammonia,  bicarbonate,  269. 

bi-hydrosulpliate,  271. 
burnt  in  oxygen,  129. 
carbonate,  (NH4)2C03,  269. 
combination  with  acids,  130. 
common  carbonate,  268. 
composition,  129. 
decomposed  by  the  spark,  129. 
delicate  test  for,  390. 
derivatives,  438. 
explosion  with  oxygen,  133. 
formation  from  nitric  acid,  138. 
gas,  dried,  128. 

preparation,  124. 
group  of  hydrogen  compounds, 

243. 
hydriodate,  271. 
hydrobromate,  271. 
hydrochlorate,  NH3.HCI,  130. 
properties,  270. 
hydrosulphate,  NH3.H2S,  270. 
hyposulphite,  271. 
identified,  125. 

in  waters,  examination  for,  390. 
isethionate,  635. 
liquefied,  127. 
molybdate,  334. 
muriate,  269. 
Nessler's  test  for,  390. 
nitrate,  140. 

decomposed  by  heat,  140. 
preparation,  140. 
nitrification  of,  132. 
oxalate,  (NH4)2C204,  587. 
properties,  125. 
proportion  in  air,  123. 
salts,  268. 

sesquicarbonate,  268. 
soda-process,  264. 
solution,        determination        of 

strength^  126. 
solution,  specific  gravity,  126. 
sources  of,  123. 
sulphate,  (NHJoSO^,  268. 
urate,  625. 
volcanic,  266. 
Ammoniacal  liquor,  453. 

extraction  of  ammonia 
from,  124. 
Ammoniacum,  487. 
Ammonia-meter,  126. 
Ammonias,  complex,  541. 

ethylated,  541. 
Ammoniated  chloride  of  silver,  127. 
Ammonide,  sulphuric,  (NH3)2S03,  268. 
Ammonium,  NH4,  268. 
alum,  292. 
amalgam,  130. 
arsenite,  240. 
bisulphide,  271. 
bromide,  271. 
carbonate,  269. 
chloride,  269. 

properties,  270. 
heptasulphide,  271. 
iodide,  271. 
molybdate,  334. 
nitrate,  140. 
oxalate,  587. 
pentasulphide,  271. 
salts,  268. 


Ammonium,  sulphate,  268.  -     ■ 

sulphide,  (NH4)2Si  270. 

yellow,  271. 
sulphocyanide,  prepared,  217. 
Ammonium  theory,  130. 

tri-iodide,  181. 
Amorces,  228. 
Amorphous,  62. 
Amorphous  phosphorus,  224. 
Amygdaline,  480. 
Amylacetic  (oenanthic)  acid,  570. 
Amylamine,  543. 
Amyle,  C5H11,  526. 

acetate,  556.  ■  _ 

valerianate,  556. 
Amylene,  521. 
Amylene-glycol,  564. 
Amylethylic  ether,  531. 
Amylic  alcohol,  CsHijO,  518. 
Araylic  iodide,  525. 
Analysis  of  gaseous  hydrocarbons,  110. 
of  marsh  gas,  111. 
organic,  84. 

calculation  of,  85. 
Anatase,  350. 
Ancaster  stone,  412. 
Anchoic  acid,  582. 
Angelic  acid,  578. 
Anylesite,  PbO.SOs,  366. 
Anhydride,  acetic,  566. 

beuzoacetic,  567. 
benzoic,  481 . 
carbonic,  86. 
defined,  25. 
lactic,  613. 
nitric,  139. 
phosphoric,  230. 
sulphuric,  210. 
sulphurous,  198. 
tartaric,  588. 
Anhydrides  of  organic  acids,  566. 
Anhydrite,  279. 
Anhydrous,  40. 
Aniline,  CgHyN,  4.'^.9. 
black,  462. 
blue,  461. 

constitution,  547. 
colours,  460. 
constitution,  547. 
-green,  462. 
-purple,  460. 
-red,  460. 

constitution,  547. 
salts,  462. 
test  for,  460. 
-violet,  462. 

constitution,  548. 
-yellow,  461. 
Animal  charcoal,  67. 

chemistry,  611. 
heat,  637. 
Animals  and  plants,  reciprocity  of,  633. 
changes  after  death,  638. 
destructive  functions  of,  633. 
nutrition  of,  633. 
oxidising  functions  of,  636. 
ultimate  elements  of,  633. 
Animi  resin,  478. 

Aniseed,  essential  oil  of,  482,  560. 
Anisic  acid,  482,  561. 
alcohol,  561. 


644 


INDEX. 


Anisyle  hydride,  482,  560. 
Annatto,  603. 

Ansell's  fire-damp  indicator,  99. 
Anthracene,  469. 
Anthracite,  70,  433. 

composition,  71,  433. 

production  of  flame  from,  88. 
Anthrapurpurine,  604. 
Anthra<niinone,  604. 
Anticlilore,  201,  212. 
Anticorrosive  caps,  16f>. 
Antimonic  oxide,  SbaO.,,  339. 
Antimonietted  hydrogen,  340. 
Antimony,  Sb,  337. 

action  on  water,  13. 

amorphous,  338. 

antimoniate,  339. 

butter  of,  341. 

chlorosnlphide,  341. 

crocus,  338. 

crude,  SbjSg,  338. 

detected,  197,  340. 

extraction    in    the    laboratory, 
338. 

glass  of,  342. 

grey  ore  of,  SbgSs,  337. 

ore,  red,  SbgOs,  2Sb2S3,  342. 
white,  Sb.Oj,  339. 

oxide,  SbjOs,  339. 

oxychloride,  341. 

oxysulphide,  342. 

pentachloride,  SbClg,  341. 

pentasulphide,  SbjSg,  342. 

potassio-tartrate,  588. 

regulus,  338. 

sulphide,  SbjSj,  341. 

sulphide  identified,  341. 

sulphides,  341. 

tested  for  lead  and  iron,  342. 

trichloride,  SbCla,  341. 

uses,  338. 

vermilion,  214,  342. 
Antiseptic  properties  of  boracic  acid,  121. 
carbolic  acid,  465. 
kresylic  acid,  466. 
sulphurous       acid, 
201. 
AntizjTT.otics,  639. 
Ants,  acid  of,  568. 

oil  of,  569. 
Apatite,  222. 
Apocrenic  acid,  633. 
Apomorphine,  597. 
Apple  oil,  556. 

Aq.,  water  of  crystallisation,  42. 
Aqua  fortis,  136. 
regia,  172. 
Arabine,  489. 

Arachiilic  (butic)  acid,  520. 
Arbor  Dianas,  387. 
Archil,  606. 
Argand  lamp,  107. 
Argent-ethenyle,  chloride  of,  94. 

oxide  of,  94. 
Argent-allylene,  487. 
-ethenyle,  94. 
Argillaceous  iron  ores,  300. 
Argol,  257,  588. 
Aromatic  nucleus,  459. 

series,  459. 
AiTack,  516. 


Arragonite,  CaCOs,  277. 
Arrowroot,  492. 
Arsenite.s,  240. 
Arsenic,  As,  236. 

combining  volume,  236. 

detection,  242. 

di-iodide,  244. 

extraction,  237. 

extraction  from    organic    matters, 

244. 
in  copper,  358. 
native,  236. 
oxides,  238. 
pentasulphide,  245. 
subsulphide,  244. 
sulphide,  identified,  245. 
sulphides,  244. 
tribromide,  244. 
chloride,  243, 
ethoxide,  536. 
fluoride,  244. 
iodide,  244. 
white,  238. 
Arsenic  acid,  H3ASO4,  241. 

action  of  hydrosulphuric  acid 
on,  245. 
Arsenical  nickel,  NiAsjj,  326. 
paper-hangings,  241. 
pyrites,  236. 
soap,  240. 
Arsenic  eating,  241. 
Arsenides,  236. 
Arsenietted  hydrogen,  AsHg,  242. 

decomposed  by  heat, 
243. 
Arsenio-diethyle,  536. 
-dimethyle,  536. 
-sulphides,  237. 
-triethyle,  536. 
-trimethyle,  536. 
Arsenious  anhydride,  AS2O3,  240. 

action  of  ammonia  on,  240. 
chlorine  on,  243. 
hydrochloric     acid 

on,  244. 
hydrosulphuric  acid 
on,  24o. 
behaviour  with  water,  239. 
composition,  240. 
crystalline,  239. 
identified,  239. 
opaque,  239. 
smallest  fatal  dose,  239. 
vitreous,  239. 
Arseniuretted  or  arsenietted  hydrogen,  242. 
As,  arsenic,  236. 
Asafoetida,  487. 

essential  oil  of,  485. 
Asbestos,  281. 

ASH3,  arsenietted  hydrogen,  242. 
Ashes  of  coal,  71. 
AS3O3,  arsenious  oxide,  238. 
AS2O5,  arsenic  oxide,  241. 
Asparagine,  592. 
Asparagus,  506. 
Aspartic  acid,  592. 
AsphcUtum,  473. 

Assay  of  gold  by  cupel  lation,  401. 
Atacamite,  363. 
Atmolysis,  21. 
Atmosphere,  composition,  57. 


INDEX. 


645 


Atmospheric  air,  57. 

Atmospheric  germs  of  putrefaction,  639. 

Atom,  definition,  2. 

Atomic  formulae,  types  of,  247. 

Atomic  heat,  280. 

Atomic  heats,  280. 

of  compound  bodies,  281. 
potassium,    sodium,     and 
lithium,  280. 
Atomicities,  classification  by,  247. 
Atomicity,  247. 

importance  in  theory,  248. 

notation  of,  249. 
Atomic  theory,  2. 
weight,  3. 

of  sulphur,  194. 
Atropine,  540. 

Attraction,  chemical,  definition,  5. 
Au,  gold,  400. 

AuCls,  gold  trichloride,  404. 
Augite,  296. 
Auric  oxide,  AujOs,  ^^ 
Aurine,  466. 

Autogenous  soldering,  204. 
Avogadro's  law,  1. 
Azobenzide,  459. 
Azodinaphthylamine,  467. 
Azolitmine,  606. 
Azote,  etymology,  123. 

B,  BORON,  119. 

Ba,  barium,  274. 

BaCl2,  barium  chloride,  275. 

BaCOs,  barium  carbonate,  275. 

Baking  powders,  80. 

Balenic  acid,  520. 

Balloons,  16. 

made,  514. 
Balsam  of  Peru,  477. 
Tolu,  477. 
Balsams,  477. 
Banca  tin,  344. 

Ba(N03)2,  barium  nitrate,  275. 
BaO,  baryta,  275. 
Barilla,  262. 
Bar-iron,  best,  312. 

composition,  312. 
crystalline,  314. 
fibrous,  314. 
manufacture,  308. 
Barium,  Ba,  274. 

action  on  water,  13. 

binoxide,  275. 

carbonate,  275. 

chlorate,  276. 

chloride,  BaClj,  275. 

hydrate,  275. 

hypophosphite,  232. 

nitrate,  Ba(N03)2,  275. 

sulphate,  274. 

sulphide,  274. 

sidphovinate,  528. 
Barley  sugar,  505. 
Baryta,  BaO,  275. 

carbonate,  275. 

preparation    from    heavy 
spar,  275. 

chlorate,  276. 

hydrate,  BaO.HoO,  275. 

in  glass,  408. 

sulphate,  274. 


Baryta,  sulphate,  decomposition,  275. 

BarytocaZcite,  277. 

Basalt,  296. 

Base,  definition,  28. 

Basicity  of  acids  determined,  251. 

Basic  oxides,  28. 

BaS04,  barium  sulphate,  274. 

Bassorine,  490. 

Basylous,  246. 

Bathgate  coal,  472. 

Bath  stone,  412. 

Baths,    photographic,    recovery    of    silver 

from,  383. 
Battery,  galvanic,  7. 
Baume's  flux,  417. 
Bauxite,    extraction    of   aluminium    from, 

294. 
Baysa'lt,  261. 
Beans,  inosite  in,  620. 
Bear,  335. 
Beef-tea,  621. 
Beehive-shelf,  11. 
Beer,  composition,  497. 
ropy,  498. 
sparkling,  80. 
Bees'  wax,  585. 
Behenic  acid,  520. 
Bell-metal,  347. 
Bengal  saltpetre,  KNO3,  413. 
Benic  acid,  520. 
Benzamide,  551. 
Benzene,  CgHg,  458. 
Benzene  sulphonic  acid,  464. 
Benzoacetic  anhj'dride,  567. 
Benzoic  acid,  HC7H5O2,  479. 

in  cow  s  urine,  626. 
alcohol,  481,  560. 
anhydride,  481. 
peroxide,  567. 
Benzoin,  gum,  479. 
Benzoine,  481. 
Benzole  or  Benzine,  CgHg,  458. 

action  of  nitric  acid  on,  139. 
chloride,  458. 
Benzoliae,  4,')6. 
Benzolised  air,  108. 
Benzone,  560. 
Benzonitiile,  551. 
Benzophenone,  560. 
Benzoyle,  C7H5O,  481. 

compounds,.  481.  • 

glycdc611,;627. 

hydride,' ^EO: 

peroxide,  567. 

salicylamide,  552. 

salicyle,  483'. 

series,  481. 
Benzoyle-urea,  625. 
Benzureide,  625. 
Benzylamine,  560. 
Benzyle,  chloride,  560. 
Bergamotte,  essential  oil  of,  476. 
Beryl,  290. 

Bessemer's  process  (iron),  313. 
Betaine,  622. 
Bezoars,  594. 

Bi,  bismuth,  335.  >' 

Bibasic  acids,  constitution,- 252. 
Biborate  of  soda,  266. 
Bibromosuccinic  acid,  589. 
Bicarbonate  of  soda,  NaHCOj,  265. 


646 


INDEX. 


Bicarbonates,  86. 
Bichloracetic  acid,  566. 
Bi-equivaleut  elements,  247. 
Bile,  635. 
Binietantimoniate  of  potash,  839. 

soda,  339. 
Binoxide  of  hydrogen,  53. 
nitrogen,  141. 
Bi.jO^,  bismuthic  oxide,  336. 
Birch,  essential  oil  of,  476. 
Bi^Ss,  bismuthic  sulphide,  337. 
Biscuit  porcelain,  410. 
Bismuth,  Bi,  335. 

action  on  water,  13. 
glance,  337. 
impurities,  336. 
nitrate,  Bi(N03)3,  337. 
ochri-,  336. 
oxides,  336. 
cxychloride,  337. 
sulphide,  337. 
telluride,  220. 
trichloride,  BiClj,  337. 
trisuitrate,  337. 
Bismuthic  acid,  336. 
Bismuthite,  337. 
Bistearine,  576. 

Bisulphate  of  potash,  KHSO4,  135. 
Bisulphide  of  carbon  in  coal  gas,  217. 
Bisulphites,  201. 
Bisulphuret  of  carbon,  215. 
Bitter  almond  oil,  CyHgO,  480. 
Bittern,  172,  261. 
Bitumen,  473.  .  , 

Bituminous  coal,  70. 
Bixine,  603. 
Black  ash,  263. 

Black  ash  liquor,  treatment,  26S. 
Blackhand,  300. 
Black  dyes,  610. 
Blacking,  vitriol  in,  208. 
Black  lead,  63. 

crucibles,  63. 
vitriol,  363. 
wash,  390. 
Blast-furnace,  302. 

chemical  changes  in,  303. 
gases,  304. 
Blasting-gelatine,  581. 
Blasting  with  gunpowder,  427. 
Bleaching  by  chloride  of  lime,  155. 
chlorine,  154. 
ozone,  55. 

sulphurous  acid,  200. 
powder,  155. 
Bleach  killed,  201. 
Blende,  ZnS,  285. 
Blistered  steel,  316. 
Block  tin,  345. 
Blood,  615. 

action  of  oxygen  on,  617. 
aeration  of,  617. 
coagulation  of,  615. 
crystals,  617. 
defibrinated,  616. 
formation  from  food,  634,  6-3G. 
globules,  616. 
venous  and  arterial,  617. 
Bloom  (iron),  311. 
RloDiiiery  forge,  320. 
Blowers  in  coal-mines,  98. 


Blowpipe,  cupellation  with,  372. 
flame,  109. 
hot-blast,  110. 
oxyhydrogen,  39. 
reduction  of  metals  by,  109. 
table,  117. 

test  for  lithium,  271. 
test  for  potassium,  259. 
sodium,  265. 
Blue  bricks,  411. 
copperas,  362. 
dyes,  609. 

fire  composition,  165. 
flowers,  colouring  matter  of,  603. 
mrdachite,  353. 
metal  (copper),  357. 
oxide  of  molybdenum,  334. 

tungsten,  351. 
pill,  386. 
pots,  63. 

Prussian,  Fe4Fcy3,  441. 
stone,  362. 
Thenard's,  325. 
Tumbull's,  446. 
verditer,  363. 
vitriol,  362. 

water  of  copper  mines,  357. 
writing  paper,  296. 
B2O3,  boracic  anhydride,  119. 
Bog-butter,  474. 
Boghead  cannel,  472. 
Boiler  fluid,  arsenical,  240. 

incrustations,  46. 
Boiling  meat,  620. 
Boiling-point,  definition,  52. 
Boiling-points  of  benzene  series,  454. 
Boiling  process  (iron),  313. 
Bolivite,  337. 
Bolsover  stone,  412. 
Bone-ash,  222. 

as  manure,  629. 
black,  67. 

earth,  as  manure,  629. 
formation  from  food,  633. 
Bones,  ammonia  furnished  by,  548. 
as  manure,  629. 
composition,  222. 
destructive  distillation,  67. 
Boracic  acid,  H3BO3,  119. 
crystals,  120. 
identified,  121. 
in  glass,  408. 
manufacture,  120. 
tribasic,  121. 
vitreous,  121. 
anhydride,  119. 
ether,  527. 
lagunes,  120. 
Boracite,  283. 
Borates,  120. 

Borax,  NagO.  26,03, 119>  266. 
glass,  267. 
identified,  267. 
manufacture,  266. 
refining,  266. 
uses,  267. 
vitrified,  267. 
Boric  ethide,  537. 

methide,  537. 
Borne^ne,  477. 
Borneo  camphor,  477. 


INDEX. 


647 


Borofluoric  acid,  186. 
Borofluorides,  186. 
Boroglyceride,  576. 
Boron,  B,  119. 

amorphous,  122. 

chloride,  BCI3,  171. 

crystallisfed,  122. 

diaiuoiid,  122. 

fluoride,  BF3,  186. 

graphitoid,  122. 

nitride,  122. 

trichloride,  171. 

trifluoride,  186. 
Botany  Bay  gum,  465. 
Boucherie's    process    for  preserving    wood, 

633. 
Bouquet  of  wines,  516. 
Boyle's  fuming  liquor,  271. 
Br,  bromine,  172. 
Brandy,  516. 
Brass,  360. 

for  engraving,  360. 
guns,  346. 
preparation,  360. 
Brassic  acid,  578. 
Braunite,  JNInoOg,  328. 
Brazil  wood,  603. 
Bread,  499. 

aerated,  500. 

new  and  stale,  501. 
Brewing,  495. 
Bricks,  411. 

efflorescence  on,  267. 
Bright  iron,  307. 
Brimstone,  188. 
Britannia  metal,  346. 
British  brandy,  516. 

gum,  492. 
Brochantite,  363, 
Bromates,  174. 
Bromic  acid,  174. 
Bromine,  Br,  172. 

action  on  potash,  173. 
chloride  of,  175. 
etymology,  173. 
hydrate,  173. 
identified,  173. 
in  waters,  172. 
useful  applications,  173. 
with  hydrogen,  174. 
Bromoform,  554. 
Bromosuecinic  acid,  590. 
Bronze,  347,  360. 

annealing  of,  347. 

coin,  347. 

powder,  349. 
Bronzing,  360. 
Brookite,  350. 
Brown  acid  (sulphuric),  207. 

blaze,  289. 

coal,  70. 

dyes,  610. 

hcemaiite,  300. 
Brucine,  540. 
Bi-ucite,  283. 
Brunolic  acid,  454. 
Brunswick  green,  363. 
Bubbles,  explosive,  34. 
Buckskin,  593. 
Bug-poison,  389. 
Building-materials,  411. 


Building  stone,  effect  of  air  of  towns  on,  412, 

preservation  of,  412. 
Bullets,  rifle,  372. 

shrapnel,  372, 
Burner,  air-gas,  107. 

Bunsen's,  107. 

gauze,  107. 

hot-air,  107. 

ring,  51. 

rosette,  51. 
Burners,  smokeless,  107. 
Burnett's  disinfecting  fluid,  289, 
Butic  acid,  520. 
Butiue,  584, 
Butter,  584. 
Butter-milk,  612. 

preparation  of,  612. 
Butylactic  acid,  563. 
Butylamine,  548. 
Butyle,  C4H9,  525. 

-amyle,  525. 

-caproyle,  525. 

-sulphocyanide,  486. 
Butylene,  521. 

-glycol,  564. 
Butylic  alcohol,  518. 
Butyramide,  551. 
Butyric  acid,  HC4H7O2,  519,  569. 

formed  from  citric,  591. 

synthesis  of,  570. 

two  rational  formulae  of,  570. 

ether,  556. 
Butyrine,  584. 
Butyrone,  559, 
Butyryle,  558, 

-urea,  625. 

C,  CARBON,  61, 
Ca,  calcium,  276. 
Cacao-butter,  600. 
CaCl.2,  calcium  chloride,  279. 
CaCOs,  calcium  carlwnate,  277, 
CaC204,  calcium  oxalate,  587, 
Cadaveric  alkaloids,  639. 
Cadet's  fuming  liquor,  532, 
Cadmia,  CdS,  289, 
Cadmium,  Cd,  289, 

carbonate,  289, 

identified,  289, 

iodide,  289. 

oxide,  289. 

sulphide,  CdS,  289. 
Caesia,  273. 

Caesium  carbonate,  273,  279. 
platinochloride,  395, 
Caen-stone,  412. 
CaFg,  calcium  fluoride,  181, 
Caffeic  acid,  599, 
CaJfeitie,  CgHtoNiOa,  599. 

chemical  constitution,  600, 
extraction  of,  599, 
formed  from  theobromine,  600. 
Caffeol,  599. 
Cairngorm  stones,  113. 
Gaking-ooal,  71. 
Calainine,  ZnCOs  285, 

electric,  285. 
Calcareous  waters,  47. 
Calcium,  Ca,  276. 

action  on  water,  11, 
bimalate,  591 


648 


INDEX. 


Cnlcium,  bisulphide,  198. 

carbonate,  Ca(X)s,  277. 

chloride,  CaCl,,  279. 

fluoride,  CaFj,  181. 

hydrate,  Ca(H0)2, 278. 

hypochlorite,  162. 

hyposulphite,  212. 

lactate,  612. 

oxalate,  CaC204,  587. 

oxychloride,  IS."),  279. 

pentasulphide,  198. 

phosphide,  235. 

sulphate,  CaS04,  278. 

sulphide,  279. 
C'alc-spar,  277. 
Calculation  of  forniulse,  85. 
("alico-priuting,  610. 
Calomel,  HgCl,  389. 
Calorific  instensitv,  431. 
Calx  chlorata,  162. 
Cameos,  113. 

Camomile,  essential  oil  of,  476. 
Camphilene,  475. 
Camphine,  475. 
Camphor,  CioHigO,  477. 
artificial,  475. 
oil  of,  477. 
Camphoric  peroxide,  475. 
Camphorimide,  552.  » 

Camphors,  477. 
Candle,  chemistry  of,  103. 
Caudles,  574. 

composite,  574. 
C^ane-sugar,  CjaHj-iOji,  503. 

action  of  yeast  on,  496. 
composition,  506. 
Cannel,  71. 

Cannel  gas,  composition,  112. 
Canton's  phosphorus,  279. 
CaO,  lime,  277. 

CaO.C02,  carbonate  of  lime,  277. 
CaO.O,  oxalate  of  lime,  587. 
CaO.SOj,  sulphate  of  lime,  278. 
Caoutchine,  488. 
Caoutchouc,  487. 

artificial,  583. 
in  plant  juices,  487. 
solvents  for,  487. 
Cap  composition,  449. 
Capric  (rutic)  acid,  519. 
Caprine,  584. 
Caproic  acid,  519. 

alcohol,  518. 
Caproine,  584. 
Caproyle,  CgHi3,  525. 
Cuproylene,  521. 
Caprylic  acid,  519. 

alcohol,  518. 
Capsicine,  540. 
Caramel,  505. 
Carbamates,  269. 
Carliamic  acid,  269. 
Carbamines,  552. 
Carbazotic  acid,  465. 
Carbinol,  521. 
Carbodianiine,  443. 
Carbolic  acid,  C'gHgO,  464. 

antiseptic  character,  465. 
tests  of  purity,  464. 
Carbon,  C,  61. 

and  hydrogen,  92. 


Carbon  and  oxygen,  72. 
atomicity,  248. 
atonnc  weight,  92 
bichloride,  CCI4,  169. 
bisulphide,  CS.2,  215. 
uses,  217. 
burnt  to  carbonic  oxide,  calorific 

value  of,  433. 
calorific  intensity  calculated,  431. 
calorific  value,  429. 
chemical  relations  of,  68. 
chlorides  of,  168. 

composition  by  volume, 
170. 
circulation  in  nature,  72. 
determination  of,  84. 
disulphide,  215. 
group  of  elements,  122,  246. 
iodide,  180. 

liquid  sesquichloride,  CCI3,  170. 
natural  sources  61. 
oxides  of,  72. 
oxychloride,  COaj,  170. 
oxysulphide,  218. 
physical  properties,  65. 
protochloride,  C2CI4,  169. 
sesquichloride,  CjClg,  168. 
subchloride,  CjC^  169. 
tetrabromide,  175. 
use  in  metallurgy,  69. 
Carbonate  of  baryta  and  lime,  277. 
lime  and  soda,  277. 
lime  in  waters,  46. 

natural  sources  of,  73. 
Carbonates,  86. 

additive  formulae,  87. 
alkaline,  274 
normal,  251.     . 
substitutive  formulae,  87. 
Carbonic  acid  gas,  CO2, 72. 

absorption  by  water,  79. 
analysis  of,  87. 
composition  by  volume, 

91. 
decomposed  bv   carbon, 
88. 
potassium,  87. 
determination  of,  83. 
evolved  by  plants,  72. 
experiments  with,  74. 
formation  of  propylic  acid 

from,  536. 
formed  in  combustion,  72. 
respiration,  72. 
in  air,  sources  of,  72. 
in  breathed  air,  77. 
injurious  eflFects  of,  76. 
liquefaction  of,  81. 
preparation,  73. 
properties,  73. 
separation    from     other 
gases,  83. 
Carbonic  acid  springs,  73. 

synthesis  of,  61. 
Carbonic  anhyibide,  86. 

ether,  528. 
Carbonic  oxide,  CO,  88. 

absorption  by  cuprous  chlo- 
ride, 249. 
action  on  heated  metallic 
oxides,  91. 


INDEX. 


649 


Carbonic  oxide,  caloriflc  value,  433. 

composition     by     volume, 

91. 
decomposition  by  heat,  91. 
formation  in  fires,  88. 
formed  from  steam,  89. 
identified,  88. 

loss  of  heat  in  furnaces  pro- 
ducing, 433. 
metallurgic      applications, 

88. 
poisonous  properties,  89. 
prepai-ation    from  carbonic 

acid,  88. 
preparation    from    ferrocy- 

anide  of  potassium,  90. 
preparation  from  oxalic  acid, 

90. 
properties,  89. 
Carbonisation,  61. 
Carbonising  fermentation,  69, 
Carbouyle,  437. 
Carbotriamine,  547. 
Carbovinate  of  potash,  528. 
Carburetted  hydrogen,  98. 
Carmine,  608. 
Carmine  lake,  608. 
Carminie  acid,  608. 
Camcdlite,  260. 
C'arnelian,  113. 
Carraway,  essential  oil  of,  476. 
Carre's  free.zing  apparatus,  127. 
Carthamine,  603. 
Cartilage,  621. 
Case-hardening,  318. 
Caseine,  614. 

vegetable,  500,  614. 
CaS04,  calcium  sulphate,  278. 
Cassia,  essential  oil,  482. 
Cassiterite,  Sn02,  347. 
Cast-iron,  composition  of,  306. 
fusing- point,  308. 
grey,  307. 
malleable,  318. 
mottled,  307. 
phosphorus  in,  307. 
silicon  in,  119. 
specific  gravity,  308. 
sulphur  in,  307.    - 
varieties  of,  307. 
white,  307. 
Castor  oil,  583. 

cold-drawn,  583. 
Cast  steel,  317. 
Catalan  process,  320. 
Catalysis,  53,  530. 
Catechu,  595. 
Cat's  eye,  113. 
Caustic  alkali,  12. 

etymologv  of,  12. 
lunar,  AgNOs,  382. 
potash,  258. 
soda,  265. 
Cd,  cadmium,  289. 
Cedar-wood,  essential  oil,  477. 
Cedrene,  477. 
Cedriret,  470,  473. 
Celery,  506. 
Velesline,  SrSOi,  276. 
Celluloid,  514. 
Cellulose,  CgHioOs,  469. 


Cellulose,  converted  into  sugar,  502. 

solvent  for,  362. 
Cement  for  earthenware,  614. 

Keene's  and  Keating's,  279. 
Portland,  413. 
Eoman,  413. 
Rust-joint,  193. 
Scott's,  413. 
Cementation  process,  315. 

theory  of,  316, 
Centrifugal  sugar  drainer,  505. 
Cerasine,  490, 
Cerine,  489. 
Cerite,  298. 
Cerium,  Ce,  298. 

oxalate,  298. 
oxides,  298. 
Ceroleine,  585. 
Cerotene,  521. 
Cerotic  acid,  520,  585. 
Cerotine,  585. 
Ceruse,  375. 

Cerylic  alcohol,  518,  585. 
Cetine,  585. 
Cetyle,  CigHja,  584. 
series,  584. 
Cetylene,  521. 
CetyUc  alcohol,  518. 

ether,  584. 
CHj,  methyle,  436. 
CH4,  marsh  gas,  98. 
CH4O,  methylic  alcohol,  471. 
C.2H2,  acetylene,  92. 
C2H4,  defiant  gas,  95. 
C.2H4CI2,  Dutch  liquid,  96. 
C2H5,  ethyle,  625. 
C2Hg,  etliane,  474. 
C4H10O,  ether,  522. 
CaHgO,  alcohol,  521. 
CfiHg,  phenyle,  465. 
C5H5,  benzene,  458. 
CgHyN,  aniline,  459. 
C7H5O,  benzoyle,  481. 
CioHg,  naphthalene,  467. 
Chalcedony,  113. 
Chalk,  CaCOs,  277. 

decomposed  by  sodium,  88. 
in  waters,  46. 
Chalybeate  waters,  50,  321. 
Chameleon  mineral,  329. 
Champagne,  515. 
Charbon  roux,  417. 
Charcoal,  absorption  of  gases  by,  66. 

action  of  steam  on,  89. 

animal,  67. 

as  fuel,  69. 

ash,  417. 

burning,  65. 

combustion  of,  68. 

decolorising  properties,  67. 

deodorising  properties,  66. 

for  gunpowder,  417. 

oxidised  by  nitric  acid,  137. 

preparation  in  the  laboratory,  428. 

prepared    at    different    tempera- 
tures, 417. 

properties  of,  65. 

retort,  65. 

sufibcation,  89. 

wood,  64. 
Charring  by  steam  418, 


650 


INDEX. 


Cheese,  613. 
Cheltenham  water,  50. 
Chemical  equivalent,  definition,  12. 
Chemistry,  definition,  1. 
Cheques,  prepared  paper  for,  493. 
Chessylite,  363. 

Chevreul's  investigations,  57*2. 
Chili  saltpetre,  NaNOj,  414. 
Chill-casting,  308. 
Chimney,  hot  air,  for  lamps,  107. 
use  of,  in  lamps,  107. 
ventilation  by,  78. 
Chimneys  on  fire  extinguished,  200. 
China  moss,  490. 
Chinese  wax,  584. 
Chinese  white,  288. 
Chlonaphthalise.  CjoClg,  169. 
Chloracetic  acid,'  HCoH.ClOa,  566. 
Chloral,  C0HCI3O,  bSo. ' 
Chloralum,  294. 
Chlorauile,  598. 
Chloraniline,  550. 
Chlorate  of  baryta,  276. 

potash,  KaOj,  163. 

action  of  heat  on,  166. 
sulphuric  acid 
on,  167. 
and  sugar  inflamed,  167. 
burnt  in  coal  gas,  165. 
preparation,  163. 
preparation    of   oxygen 
from,  32. 
Chlorates,  164. 
Chlorethyl-sulphonic  acid,  635. 

.sulphurous  acid,  635. 
Chlorhydrine,  576. 

of  glycol,  561. 
Chloric  acid,  163. 
ether,  527. 
peroxide,  CIO2, 167. 
Chloride  of  aluminium  and  sodium,  294. 
ammonium,  NH^Cl,  269. 
calcium  tube,  84. 
lime,  155. 

constitution  of,  155. 
spontaneous      decomposi- 
tion, 162. 
nitrogen,  171. 
nitrosyle,  172. 

preparation,  172. 
potassium,  solubility  of,  414. 
soda,  163. 
sodium,  260. 
sulphuryle,  201. 
thionyle,  201. 
Chlorine,  CI,  147. 

action  on  ammonia,  153. 

hydrosulphuric  acid,  196. 
leaves,  155. 
sal-ammoniac,  171. 
water,  152. 
and  hydrogen,  150. 

exploded    by    sun- 
light, 150. 
exploded  by  spark, 
151. 
atomicity  of,  248. 
bleaching  by,  154. 
chemical  relations  of,  149. 
disinfecting  properties,  156. 
etymology,  149. 


Chlorine,  (experiments  with,  149. 
group  of  elements,  186. 
hydrate,  149. 
liquefied,  149. 
occurrence  in  nature,  147. 
oxides,  161. 

composition  by  volume,  168. 
general  review,  168. 
oxidising  action,  154. 
peroxide,  167. 
preparation,  148. 
properties,  149. 
taper  in,  153. 
water,  149. 
Chlorite,  295. 
Chlorites,  168. 
Chlorobenzene,  458. 
Chlorocarbonic  acid,  COClj,  170. 

atomic      constitution, 
249. 
Chlorochromic  acid,  333. 
Chlorofomi,  CHCI3,  553. 
Chlorophosphamide,  236. 
Chlorophyll,  602. 
Chloropicrine,  CClj(NO,),  466. 
Chlorosulphuric  acid,  201. 
Chlorous  acid,  168. 
Chocolate,  600. 
Choke-damp,  77. 
Cholesterine,  C^H440,  635. 
Cholic  acid,  635/ 
Choline,  548. 
Choloidic  acid,  635. 
Chondrine,  621. 
Chromates  of  lead,  332. 

of  potash,  331. 
Chrome-alnm,  332. 
Chrome-irnn-ore,  FeO.CrjOs,  330. 
Chrome-yellow,  PbCr04,  332. 
Chromic  acid,  331. 

action  of  hydrochloric    acid 

on,  161. 
oxide,  Ci-jOg,  331. 
Chromium,  Or,  330. 

action  on  water,  13. 
chlorides,  333. 
oxides,  331. 
oxychloride,  333. 
protoxide,  331. 
sesquichloride,  333. 
sesquioxide,  CrjO^,  332. 
sesquisulphide,  333. 
sulphate,  332. 
trifluoride,  333. 
Clirysaniline,  461. 
Chrysean,  446. 
Chrysene,  469. 
Chrysoberyl,  290. 
Chrysocolla,  363. 
Churning,  612. 
Chyle,  636. 
Chyme,  635. 
Cigars,  602. 
Cinchona  bark,  597. 
Cinch  onine,  597. 

extraction  of,  597. 
Cinder,  71. 
Cinder-iron,  305. 
Cinnabar,  HgS,  391. 
Cinnameine,  477. 
Cinnamene,  478. 


INDEX. 


651 


Cinnaniic  acid,  CgHgOn,  477. 

Cinnamon,  essential  oil  of,  482. 

Cinnamyle,  liydride,  482. 

Circulation  of  blood,  chemistry  of,  636. 

Cisterns,  incrustations  in,  47. 

Citric  acid,  H3C6H5O7,  591. 

CI,  chlorine,  147. 

Clarite,  245. 

Clark's  process  for  softening  water,  49. 

Clay,  291. 

Claying  sugar,  505. 

Clay  ironstone,  average  yield,  304. 

Clay  ironstones,  300. 

CI2O,  hypochlorous  anhydride,  161. 

CI2O3,  chlorous  anhydride,  168. 

CI2O4,  chloric  peroxide,  167. 

Clot  of  blood,  615. 

Cloves,  essential  oil  of,  476. 

CN,  cyanogen,  443. 

CO,  carbonic  oxide,  88. 

CO2,  carbonic  acid  gas,  72. 

Coal,  69. 

ash  of,  71. 
Bathgate,  472. 
bituminous,  70. 

composition  of,  433. 
Boghead,  472. 
.  brasses,  71. 
brown,  70. 
caking,  71. 
cannel,  71. 
combustion  of,  70. 
composition  of,  71. 
distillation  of,  HI,  452. 
formation  of,  69. 
mines,  fire-damp  of,  98. 
products  of  combustion,  71 
distillation,  111. 
stone,  71. 
varieties  of,  70. 
Welsh,  71. 
Coal  gas.  111. 

composition  of,  112. 
manufacture,  452. 

effect  on  chemistry,  452. 
purification,  453. 

removal  of  bisulphide  of  carbon 
from,  218. 
Coal  naphtha,  treatment  of,  456. 
Coal  tar,  455. 

distillation  of,  456. 
dyes  from,  460. 
Coarse  copper,  357. 
Coarse-metal  (copper),-  CuFeS2,  354. 
Cobalt,  Co,  324. 

action  on  water,  13. 
arseniate,  237. 
bloom,  Co3(As04)2,  237. 
chloride,  325. 

commercial  oxide,  preparation,  325. 
gloMce,  C0AS2.C0S2,  324. 
oxides,  325. 
phosphate,  325. 
pyrites,  C0.2S3,  326. 
separation  from  nickel,  327. 
sul])hides,  326. 
Cocaine,  540. 
Cocculus  Indicus,  485. 
Cochineal,  608. 
Cochlearia,  oil  of,  486. 
Cocinic  acid,  520. 


Cocoa,  600. 
Cocoa-nut  oil,  574. 
Codeine,  540. 

extraction,  596 
Cod-liver  oil,  584. 
Coerulignone,  473. 
Coffee,  composition,  599. 

roasting,  599. 
Coil,  induction,  10. 
Coin-bronze,  347. 
Coke,  71. 

action  of  steam  on,  89. 
composition,  433. 
Colcothar,  202,  322. 
Cold,  greatest  artificial,  141. 
saturated  solution,  40. 
shortness  in  iron,  314. 
Collodion  balloons  maile,  514. 

cotton,  513. 
Colophene,  475. 
Colophony,  476. 
Coloured  fires,  165. 
Colouring-matters,  animal,  608. 

vegetable,  602. 
Columbite,  352. 
Columbium,  352. 
Colza  oil,  583. 
Combination  by  volume,  35. 

definition,  5. 
Combined  carbon  in  cast-iron,  306,  308. 
Combining  proportions,  5. 
Combustibles  and  supporters,  reciprocity  of, 

38,  106. 
Combustion,  acetylene  formed  in,  92. 
definition,  24. 
formation  of  carbon  dioxide  in, 

72. 
furnace,  84. 
in  air,  definition,  24. 
in  confined  air,  76. 
in  oxygen,  25. 
temperature  of,  431. 
Common  salt,  NaCl,  260. 
Composition  and  constitution,  85. 
Compound  and  mixture,  distinction,  60. 

definition,  3. 
Compressed  gases,  38. 
Concrete,  413. 
Condenser,  Liebig's,  52. 
Condurrite,  IZl. 
Condy's  disinfecting  fluid,  329. 
Coniferine,  484. 
Coniine,  540. 

constitution,  545. 
Constitution  of  salts,  249. 
Converting  furnace,  315. 
Converting  vessel,  Bessemer's,  313. 
Cooking.  620. 
Copal,  478. 
Copper,  Cu,  352. 

aceto-arsenite,  241. 

acetylide,  93. 

action  of  nitric  acid  on,  137. 

on  ammonia  and  air,  361. 
on  water,  13. 
alloys  of,  360. 
amalgam,  387. 
ammonio-sulphate,  363. 
Anglesea,  357. 
arsenite,  241. 
basic  acetate,  566. 


652 


INDEX. 


Copper,  basic  carbonates,  353,  363. 
phosphates,  863. 
best  selected,  356. 
blistered,  355. 
chlorides,  363. 
cleaned,  361. 
detected  in  lead,  372. 
dry,  356. 

effect  of  impurties  on,  357. 
phosphorus  on,  358. 
sea- water  on,  359. 
electric  conductivity  of,  358. 
electrotype,  358. 
emerald,  363. 

extraction  in  laboratory,  357. 
fusing-point,  358. 
glance,  CugS,  352. 
nydrated  oxide,  363. 
hydride,  233. 
Lake  Superior,  352. 
lead  in,  356. 
metallurgy  of,  352. 
moss,  355. 
native,  352. 
ore,  grey,  352. 
red,  353. 
variegated,  352. 
ores,  352. 

fusion  for  coarse  metal,  354. 
white  metal,  355. 
roasting,  353. 

treatment  of,  for  silver,  379. 
overpoled,  356. 
oxide,  CuO,  361. 
oxides,  361. 
oxychloride,  359,  363. 
peacock,  352. 
pentasulphide,  365. 
phosphide,  234. 
poling  or  toughening,  356. 
precipitated,  94. 
properties  of,  358. 
pyrites,  CuFeSj,  352. 
quadrant  oxide,  362. 
reduced  by  hydrogen,  38. 
refining,  355. 
rose,  357. 
sand,  352. 

.separated  from  silver,  379. 
silicates,  363. 
smelting,  composition  of  products 

from,  356. 
smelting,  summary  of,  353. 
smoke,  354. 
Spanish,  358. 
subchloride,  Cu.jClj,  363. 
suboxide,  Cu.,0,  361. 
subsulphide,  Cu.^S,  364. 
sulphate,  CUSO4,  362. 

action  of  heat  on,  211. 
in  bread,  501. 
sulphides,  364. 
tinning,  345,  359. 
tough -cake,  356. 
tough-pitch,  356. 
iinderpoled,  356. 
verdigris,  359. 
vessels  for  cooking,  359. 
with  aluminium,  295. 
( 'opper-zinc  couple,  14. 
C'opi.eras,  FeSO^,  323. 


Copperas,  blue,  362. 

Coprolite,  222,  229. 

Coquimbite,  323. 

Coral,  277. 

Corallin,  466. 

Cork,  489. 

Corn-flour,  492. 

Corpse-light  in  coal-mines,  102. 

Corrosive  sublimate,  HgClj,  388. 

antidote  to,  389. 
antiseptic     properties 
389. 
Corundum,  293. 
Cotton,  470. 

and  wool,  separation  of,  622. 

dissolved  by  ammonio-cupric  solu- 
tions, 362. 
Coumarine,  484. 
Cr,  chromium,  330. 
Crackers,  detonating,  451. 
Crampton's  furnace,  314. 
Cream,  612. 

Cream  of  tartar,  257,  588. 
Creasote,  464,  466. 
Crenic  acid,  633. 
Cress,  essential  oil  of,  560. 
Cresole,  466. 

Cresylic  acid,  CyHgO,  466. 
Critical  point,  81. 
CrOs,  chromic  anhydrde,  331. 
CrgOg,  chromic  oxide,  331. 
Crocus  of  antimony,  338. 
Crookes'  discovery  of  thallium,  377. 
Croton-chloral,  555. 
Crotonic  acid,  578. 

aldehyde,  555. 
Crow-fig,  600. 
Crucibles,  411. 

black  lead,  63. 
graphite,  63. 
Ciyohydrates,  43. 
Cryolite,  265. 
Crystalline  lens,  616. 
Crystallisation,  40. 

Crystals  from  the  leaden  chambers,  204. 
CS2,  carbon  disulphide,  215. 
Cu,  copper,  352. 
CuClj,  cupric  chloride,  363. 
CujClo,  cuprous  chloride,  363. 
Cudbear,  606. 
Cnmidine,  545. 
Cuminic  acid,  HCioHnOa,  482. 

alcohol,  560. 
Cummin,  essential  oil,  482. 
Cumyle,  482. 

hydride,  482. 
Cumylene,  547. 

diamine,  547. 
CuO,  oxide  of  copper,  361. 
CuO.SOg,  sulphate  of  copper,  362. 
Cupel-furnace,  372. 
Cupellation  on  the  large  seal",  370. 
small  scale,  372. 
Cupric  acid,  362. 

chloride,  CuCU,  363. 

oxide,  CuO,  361. 
Cupros-ethenyle  oxide,  94. 
Cuprous  acetylide,  preparation,  93. 
chloride,  CujClj,  363. 

ammoniacal,  364. 
solution,  preparation,  93. 


INDEX. 


■653 


Cuprous  oxide,  CujO,  361. 

Curarine,  601. 

Curcumine,  605. 

Curd  of  milk,  613. 

Curing  animal  matters,  639. 

Current,  electric,  8. 

CuS,  copper  sulphide,  365. 

CUSO4,  copper  sulphate,  362. 

Cyamelide,  445. 

Cyanamide,  624. 

Cyanic  acid,  445. 

ether,  624. 
Cyanide  of  phosphorus,  447. 

potassium,  KCN,  444. 

commercial,  444. 
from  blast  furnaces, 
444. 
Cyanides  of  alcohol-radicals,  551. 
Cyanine,  603. 
Cyanite,  296. 
Cyanogen,  CN,  443. 

chlorides,  447. 

compounds,  439. 

iodide,  446. 

preparation,  443. 

solution,  metamorphosis  of,  444. 
Cyanuric  acid,  447,  623. 
CygFe,  ferrocyanogen,  440. 
Cylinder-charcoal,  65,  418. 
Cymole,  C10H14,  477. 

Dadtle,  475. 

hydrochlorate,  475. 
Damaluric  acid,  578. 
Dankes'  furnace,  314. 
Daturine,  540. 
Davy-lamp,  100. 
Davyum,  400. 

Deacon's  chlorine  process,  149. 
Dead  head,  346. 
Dead  oil  of  coal-tar,  456. 
Decay,  72. 

Decolorising  by  charcoal,  67. 
Decomposing-cell,  8. 
Decomposition,  definition,  6. 
Definition  of  acid  salt,  251. 

alcohol,  517. 

atomic  heat,  281. 

basic  salt,  251. 

normal  salt,  250. 

salt,  250. 
Deflagrating  collar,  26. 

spoon,  26. 
Deflagration,  416. 
Dehydration,  42. 
Deliquescence,  43. 
Density,  absolute,  421. 
apparent,  421. 
Deodorising  by  charcoal,  66. 
chlorine,  156. 
Dephlo^isticated  muriatic  acid,  157. 
Derbyshire  spar,  181. 
Desilverising  lead,  369. 
Destructive  distillation,  definition,  64. 
Detonating  tubes,  165,  586. 
Devitrification,  408. 
Dextrine,  CgHjoOs,  492. 
Dextrose,  503. 
Dextrotartaric  acid,  590. 
Dbil  mastic,  374.  • 

Diacetine,  565. 


Diacid  diamines,  546. 
Di-allyle,  486. 
Dialysis,  114. 
Diamines,  546. 

aromatic,  547. 
Diamond,  61. 

ash  of,  63. 

black,  63. 

combustion  of,  62. 

dust,  63. 

glazier's,  63. 
Diamylamine,  543. 
Diaspore,  293. 
Diastase,  494. 
Diathermanous,  216. 
Diatomic  elements,  247. 
Diazoamido-benzene,  463. 
Diazobenzene,  463. 

nitrate,  463. 
Dibenzyle,  469. 
Dichloracetic  acid,  566. 
Dichloraniline,  550. 
Dichloranthracene,  604. 
Dichlorhydrine,  576. 
Didymium,  Di,  297. 
Diet,  regulation  of,  637. 
Diethacetic  acid,  570. 
ether,  570. 
Diethoxalic  acid,  563. 
Diethyle,  525. 

Diethylamine,  NH(C2Hs)2,  542. 
Diethyl-diethylene-diamine,  546. 
Diethylene-diamine,  N2H2{C.2H4)2,  546. 

-diammonium,  hydrate  of,  546. 

-diethyl-triamine,  547. 

-trialcohol,  565. 

-triamine,  547. 

-triammonium,  trichloride,  548. 
Diethylzincamine,  553. 
Difi'usibility  of  gases,  definition,  18. 
law  of,  18. 
measurement  of,  19. 
rate  of,  18. 
Diffusion-tube,  18. 
Digallic  acid,  594. 
Digestion,  634. 

Dimethacetic  (butyric)  ether,  570. 
Dimethoxalic  acid,  564. 
Dimethylamine,  543. 
Dimorphous,  62. 
Dinasfire-hricks,  411. 
Dinitraniline,  550. 
Dinitrobenzene,  139. 
Dinitro-diphenylamine,  5-14. 
Dicenanthylene-diamylamine,  558. 
Dioptase,  363. 
Dioxyanthraquinone,  60f. 
Diphenylamine,  544. 
Diphenyl-benzoylamine,  544. 

-diethylene-diamine,  546. 
-guanidine,  547. 
-urea,  625. 
Diphenyle,  (CgHg),,  462. 
Diphenyle  oxide,  465. 
Diplatinaniine,  396. 
Diplatosamine,  396. 

hydrate,  396, 
hydrochlorate,  396. 
sulphate,  396. 
Dipropargyle,  487. 
Discharge  in  calico  printing,  156,  610. 


654 


INDEX, 


Disinfectant,  MacDongall's,  465. 
Disinfecting  by  chloride  of  lime,  156. 
chlorine,  156. 
ferric  chloride,  324. 
manganates,  329. 
Disinfecting  tiuid,  Buniett's,  289. 

Candy's,  329. 
Disintegration  of  rocks,  80. 
Disodacetic  ether,  570. 
Displacement,  collection  of  gas  br,  21. 
Dissociation  of  sal-ammoniac,  270. 

vermilion  vapour,  391. 
Disthene,  296. 
Distillation,  51. 

definition  of,  51. 
destructive,  64. 
dry,  64. 
fractional,  456. 
Distilled  sulphur,  188. 

■water,  51. 
Diterpene,  476. 

Dithionic  (hyposulphuric)  acid,  214. 
Ditoluylamine,  544. 
Divi-divi,  594. 
Doeglic  acid,  578. 
Dolomite,  MgCa.2C03,  281. 
Dough,  499. 
Downcast  shaft,  78. 
Dragon's  blood,  478. 
Dryers,  583.  - 

Drying  gases,  38. 

in  vacuo,  209. 
oils,  583. 

over  oil  of  vitriol,  209. 
Dry  rot,  502. 
Ductility  of  copper,  358. 
Dung  as  manure,  629. 
Dung-substitute,  242. 
Dust,  60. 
Dutch  liquid,  C.2H4Cl2>  96. 

action  of  chlorine  on,  168. 
Dutch  metal  in  chlorine,  150. 
Dyad  elements,  247. 
Dyeing,  608. 
Dynamite,  .580. 

Earthenware,  411. 
Earths,  alkaline,  280. 

proper,  290. 
Ebonite,  488. 

Economico-fumace  for  lead-smelting,  368. 
Effervescence,  80. 
Efflorescence,  42. 
Eggs,  619. 
Egg  shells,  73. 
Elaene,  521. 
Elaldehyde,  557.  " 
J-J/fxi  iron  ore,  300. 
Electrical  amalgam,  386. 
Electrogilding,  404. 
Electrolysis,  definition,  9. 

of  hydrochloric  acid,  160. 

of  water,  4. 
Electro-negative  elements,  9. 
Electroplating,  380. 
Electro-positive  elements,  9. 
Element,  definition,  3. 
Elements,  non-metallic,  general  review,  246. 
Elemi  resin,  478. 
Ellagic  acid,  594. 
Embolite,  384. 


Emerald  green,  241. 

Emery,  293. 

Emetics,  588. 

Emetine,  540. 

Empirical  formulae,  85,  435. 

Empirical  and  rational  formulae,  85,  435. 

EmpjTeumatic,  476, 

Emuisine,  480. 

Enamel  glass,  409. 

Endosmose,  616. 

Eosine,  469. 

pjpsom  salts,  282. 

Equivalent,  definition,  12. 

Erbium,  297. 

Erucic  acid,  578. 

Erythric  acid,  606. 

Erythrite,  606. 

Esculetine,  485. 

Esculine,  485. 

Essence  of  almonds,  480. 

turpentine,  474. 
Essential  oils  containing  sulphur,  485. 

extraction  of,  476. 
Ethal,  C16H34O,  584. 
Ethalic  acid,  584. 
Ethane,  474. 
Ethene  dibromide,  96. 
Ethenyle-benzene,  95. 
Ether  (Q^n^hO,  522. 

chemical  constitution,  531. 
decomposition  by  heat,  94. 
water-type  view,  531. 
Etherification,  continuous,  523. 

theory  of,  529. 
Ethers,  derivation  from  alcohols,  437. 
double,  531. 

perfuming  and  flavouring,  556. 
Ethylamine,  NHgCC^jH.),  542. 
Ethylammonia  or  etnylia,  542. 
Ethyl-apiyle  ketone,  528. 
Ethylaniline,  544. 
Ethylate  of  aluminium,  530. 

potash,  530. 
Ethylate  of  soda,  530. 
zinc,  535. 
Ethyl-codyl-ammonium,  hydrate  of,  545. 
Ethyle,  C2H5,  525. 
Ethyle-amyle,  525. 
-butyle,  525. 
carbonate,  528. 
cyanide,  532. 
glucose,  506. 
hydride,  535. 
hypothesis,  525. 
iodide,  524. 
kakodyle,  536. 
orthocarbonate,  528. 
peroxide,  568. 
sulphate,  528. 
sulphide,  531. 
Ethylene,  CjH^,  95. 

diamine,  NjHilCaH^),  546. 
dibromide,  546. 
hexethyl-diphosphonimn,  hydrate 

of,  549. 
oxide,  561. 
Ethylfonniate  of  sodium,  568. 
Ethylic  alcohol,  521. 
bromide,  524. 
chloride,  524. 
ether,  522. 


INDEX. 


655 


Ethylic  iodide,  524. 
Etliylideiie  dichloride,  562. 
Ethyl-methyl-phenylamine,  544, 
-urea,  625. 
nicotyl-animonium,  hydrate  of,  545. 
Ethylo-platammonium,  hydrate  of,  550. 

toluidine,  544. 
Ethyloxamide,  551. 
Ethylsulphuric  acid,  528. 
Ethyl-urea,  625. 
Eucalyptus,  476. 
Euchlorine,  168. 
Eudiometer,  Cavendish's,  34. 

etymology,  34. 

siphou,  -36. 

Ure's,  36. 
Eudiometric  analysis  of  air,  36. 

marsh  gas,  110. 
Euodic  acid,  519. 
Euphorbium,  487. 
Eupione,  473. 
Eupittonic  acid,  473. 
Eupyrion  matches,  167. 
Evemic  acid,  606. 
Excretion,  636. 

Explosion  of  hydrogen  and  oxygen,  33. 
Explosions  in  coal-mines,  98. 

F,  FLUORINE,  181. 
Fagotting,  312. 
Fallowing,  630.      ' 
Fast  colours,  608. 
Fats,  581. 

table  of,  585. 
Fatty  acid  series,  519. 
Fatty  acids,  preparation,  574. 
Fey,  ferrocyanogen,  440. 
Fe,  iron,  299. 

FegClg,  perchloride  of  iron,  323. 
FejFcys,  Prussian  blue,  441. 
Felspar,  295. 

potash-,  295. 
soda-,  295. 
Fennel,  essential  oil  of,  482. 
FeO,  piotoxide  of  iron,  322. 
FcoOs,  peroxide  of  iron,  322. 
FcsOj,  magnetic  oxide  of  iron,  322. 
FeO.SOs,  protosulphate  of  iron,  323. 
Fermentation,  72. 

acetous,  498. 

alcoholic,  496. 

arrested  by  sulphurous  acid, 

&c.,  200. 
production  of  carbonic  acid 

in,  72. 
viscous,  506. 
Ferric  acid;  323. 

chloride,  FeaClg,  323. 

molecular  formula,  324. 
oxide,  Fe,,03,  322. 
sulphate,  323. 
Ferricum,  324. 

Ferricyanogen  (femdcyanogen),  CygFe,  447. 
Ferrocyanates,  440. 
Ferrocyauic  acid,  440. 
Ferrocyanide  of  potassium,  K4Cy6Fe,  440. 

action  of  sulphu- 
ric acid  on,  90. 
Ferrocyanogen,  CvgFe,  440. 
Ferromanganese,  319. 
Ferrosoferric  oxide,  Fe304,  322. 


Ferrosum,  324. 
Ferrous  oxide,  FeO,  322. 

sulphate,  FeS04,  323. 
Ferruretted  chyazic  acid,  440. 
FeS2,  iron  pyrites,  187. 
Fibrine,  blood-,  618. 

extracted  from  blood,  618. 
muscle-,  618. 
vegetable,  500. 
Fibroine,  622. 
Fibrous  bar-iron,  314. 
Filtration,  67. 

Finery-cinder,  2FeO.Si0.2,  309, 
Fire-bricks,  411. 
Fire-clay,  291. 
Fire-damp,  98. 

conditions  of  inflammation,  99. 
indicator,  99,  101. 
Fire,  white,  composition,  245. 
Fires,  blue  flame  in,  88. 

coloured,  165. 
Fish  oils,  573. 
shells,  73. 
Fixing  photographic  prints,  213. 
Flags,  Yorkshire,  411. 
Flake-white,  337. 
Fl.ime,  analysis  of  by  siphon,  106. 

blowpipe,  109. 

cause  of  luminosity  in,  103. 

definition  of,  102. 

efl"ect  of  atmospheric  pressure  on,  107. 
oxygen  on,  110. 
wire  gauze  on,  101. 

experimental  study  of,  104.  . 

extinction  by  gases,  75. 

extinguished  by  carbonic  acid  gas,  75. 

extinguished  by  good  conductors,  100. 

gases  in,  104. 

nature  of,  102. 

oxidising,  109. 

reducing,  109. 

relation  of  fuel  to,  108. 

separation  of  carbon  in,  105. 

structure  of,  102. 

supply  of  air  to,  107. 
Flames,  simple  and  compound,  103. 

smoky,  107. 
Flask,  to  make  a  three-necked,  106. 
Flesh,  619. 

composition  of,  619. 

juice  of,  619. 
Flint,  113.  * 

Flint  and  steel,  113. 
Flints  dissolved,  267. 
Florence  flask,  33. 
Floss-hole,  310. 

Flour,  proximate  analysis  of,  499. 
Flowers  bleached  by  sulphurous  acid,  200. 
Fluoboric  acid,  186. 
Fluocerine,  298. 
Fluocerite,  298. 
Fluoresceine,  469. 
Fluorescence,  485,  598. 
Fluoric  acid,  HF,  181. 
Fluoride  of  calcium,  181. 
silicon,  185. 
Fluorides,  184. 
Fluorine,  F,  181. 

attempts  to  isolate,  183. 
Fluor-spar,  Ca.Y.,,  181. 
Flux,  Baume's,  417. 


656 


INDEX. 


Flux  in  iron  smelting,  303,  305. 
Food,  effect  of,  upon  respiration,  638. 
exportation,  638. 
plastic  constituents  of,  637. 
preservation  of,  639. 
respiratory  constituents  of,  637. 
Forge-iron,  308. 
Formamide,  551. 
Foriuamidine,  443. 
Formic  acid,  HCHO2,  520,  568. 
Forniouitrile,  551. 
Formulae,  additive,  87. 

calculation  of,  85. 
empirical  and  rational,  85,  435. 
substitutive,  87. 
Formj'lamine,  hydriodate  of,  443. 
Formyl-diphenyl-diamine,  546. 
Formyle,  CH,  554. 

trichloride  of,  554. 
Fouling  of  guns,  428. 
Foundry-iron,  308. 
Fousel-oil,  518. 
Fowler's  solution,  241. 
Fractional  distillation,  456. 
Frankincense,  487. 
FranBinite,  ZnO.FejOj,  322. 
Free-stone,  411. 
Freezing-apparatus,  127. 

in  red  hot  crucible,  199. 
mixtures,  128,  141,  270. 
of  water,  52. 

with  carbon  disulphide,  217. 
French  chalk,  281. 
Friction-tubes,  165. 

composition  for,  165. 
Fructose,  CgHjoOg,  503. 
Fruit  essences,  556. 
Fruits,  ripening  of,  632. 
Fuel,  calculation  of  calorific  intensity,  432. 
value,  430. 
chemistry  of,  429. 
practical  applications  of,  431. 
Fuels,  composition  of,  433. 

illuminating,  composition  of,  108. 
Fuller's  earth,  291. 
Fulminic  acid,  449. 
Fulminate  of  mercury,  C2HgNj02,  448. 

action  of  hydrochloric 

acid  on,  451. 
preparation,  448. 
properties,  449. 
silver,  450. 
Fulminates,  chemical  constitution,  451. 

double,  451. 
Fulminating  gold,  405. 

platinum,  395. 
sQver,  382. 
Fumaric  acid,  591. 
Fumigating  with  chlorine,  156. 

sulphurous  acid,  201. 
Fuming  sulphuric  acid,  202. 
Fumitory,  591.  *- 

Funnel-tube,  15. 
Fur  in  kettles,  45. 
Furfural,  569. 
Furfuramide,  569. 
Furfurine,  569. 
Fui-rurol,  C5H4O.2,  569. 
Furnace,  charcoal,  117. 

regenerative,  434. 
reverberatory,  88. 


Furnace,  Sefstrttm's,  321. 
Furnaces,  theory  of,  430. 

waste  of  heat  in,  433. 
Fused  common  salt,  157. 
Fusible  alloy,  336. 
Fusing-points  of  fats,  585. 
Fusion,  114. 
Fustic,  603. 
Fuze,  Abel's,  365. 

Armstrong  percussion,  228. 

Oadolinite,  297. 

Galbanum,  487. 

Galena,  PbS,  366. 

Gallic  acid,  594. 

Gallium,  297. 

Gall-nuts,  592. 

Galvanic  battery,  7. 

Galvanised  iron,  284. 

Gamboge,  487. 

Gangue,  305. 

Garancine,  604. 

Garlic,  essence,  artificial  production,  486. 

essential  oil  of,  485. 
Garnet,  295. 
Gas,  air  vitiated  by,  77. 

-burner,  Bunsen's  rosette,  51. 
ring,  51. 
smokeless,  107. 
-carbon,  455. 
composition  of,  112. 
-cylinder,  21. 
-holder,  90. 
valuation  of,  97. 
-jar,  26. 

manufacture  of,  452. 
springs,  98. 
Gaseous  hydrocarbons,  analysis  of,  110. 
Gases,  diflFusion  of,  18. 

expansion  by  heat,  426. 
in  waters,  44. 
Gastric  juice,  634. 
Gaultheria,  oil  of,  472. 
Gauze  burner,  107. 
Gaylussite,  277. 
Gedge's  metal,  360. 
Geic  acid,  633. 
Gelatine,  621. 
Gelose,  490. 
German  silver,  360. 
Germination,  494,  630. 
Germs  of  disease,  60. 
Geysers,  114. 
Gilding,  404. 

porcelain,  410. 
Gin,  516. 

Gl,  glucinum,  289. 
Glass,  407. 

bottle,  408. 

coloured,  408. 

composition  of,  407. 

corrosion  by  hydrofluoric  acid,  183. 

crown,  408. 

decolorised,  409. 

etched,  183. 

flint,  408. 

-gall,  408. 

manufacture  of,  407. 

of  antimony,  342. 

plate,  408. 

plate  perforated,  204. 


INDEX. 


657 


Glass-pots,  411. 
silvered,  S87. 
window.  407. 
Glavberite,  267. 
Glauber's  salt  211. 
Glaze  for  earthenware,  412. 
Glazier's  diamond,  63. 
Globuline,  616. 
Glonoine,  579. 
Glucic  acid,  506. 
Glucina,  289. 

separation  from  alumina,  290. 
Glucinum,  Gl,  289. 
Glucose,  CgHioOg,  501. 
artificial,  493. 
stearic,  579. 
Glucosides,  482. 
Gluco- tartaric  acid,  579. 
Glue,  622. 
Gluten,  500. 

varieties  of,  501. 
Glutine,  500. 
Glyceric  acid,  563. 

alcohol,  577. 
aldehyde,  576. 
ether,  577. 
Glycerides,  576. 
Glycerine,  CsHgOs,  577. 

converted  into  glycol,  576. 
extraction  of,  575. 
properties,  577. 
soap,  573. 
triatomic,  564. 
Glyceryle,  C3H5,  564. 
Glycocholic  acid,  635. 
GlycocoU  (glycocine),  CoHgNOo,  622. 
Glycogen,  635. 
Glycol,  CaHfiOa,  561. 

acetobutyrate  of,  565. 
aldehyde  of,  562. 
binacetate  of,  561. 
chlorhydrine  of,  561. 
converted  into  alcohol,  564. 
monacetate  of,  565. 
Glycolic  acid,  HC0H3O3,  563. 
Glycols,  561. 
Glycvrrhizine,  507. 
Glyoxal,  562. 
Gneiss,  296. 
Gold,  Au,  400. 

and  sodium,  hyposulphite,  405. 

assay  by  cupellation,  403. 

coin,  402. 

crucible,  404. 

dissolved,  172. 

extracted  from  old  sUver,  401 . 

extraction,  400. 

fulminating,  405. 

identification  of,  137. 

in  chlorine,  150. 

lace  cleaned,  445. 

treatment  of,  403. 
leaf,  404. 
oxides  of,  404. 
physical  properties,  40.3. 
protochloride,  AuC'l,  405. 
refining,  402. 

removal  of  mercury  from,  386. 
ruby,  227,  404. 

separated  from  silver  and  copper,  209. 
standard,  402. 


Gold,  standard,  specific  gravity  of,  403. 
sulphides  of,  406. 
testing,  403. 
thread,  404. 
trichloride,  AUCI3,  404. 
Gongs,  347. 
Goulard's  extract,  566. 
Gradational  relations  of  elements,  186,  273, 

280. 
Grains,  brewers',  495. 
Granite,  290. 

disintegration  of,  290. 
Granitic  rocks,  257. 
Granulated  zinc,  14. 
Grape-husks,  515. 
juice,  515. 
sugar,  C6H14O7,  501. 

composition,  503. 
distinguished  from  cane-sugar, 
502. 
Grapes,  colouring  matter  of,  603. 
Cfraphite,  63. 

ash  of,  63. 
Graphite  crucibles,  63. 

in  cast-iron,  63,  307. 
uses  of,  63. 
Grease  removed  from  clothes,  463. 
Green,  alkali,  549. 

arsenical,  241. 

borate  of  chromium,  332. 

Brunswick,  363. 

chrome,  332. 

colour  of  plants,  603. 

fire,  composition  for,  166. 

flame  of  barium,  276. 

boracic  acid,  121. 
copper,  363. 
thallium,  377. 
malachite,  363. 
mineral,  363. 
Rinman's,  325. 
salt  of  Magnus,  396. 
vitriol,  323. 
Grey  copper  ore,  352. 
Grey  iron,  307. 

nickel  ore,  326. 
powder,  386. 
Gristle,  621. 
Grotto  del  Cane,  74. 
Grough  saltpetre,  413. 
Groups  of  non-metallic  elements,  246. 
Grove's  battery,  8. 
Guaiacum  resin,  478. 
Guanidine,  547. 
Guanite,  283. 
Guano,  625,  629. 
Guelder  rose,  57 1. 
Gum  Arabic,  489. 
British,  492. 
Senegal,  490. 
tragacanth,  490. 
Gum-resins,  487. 
Gums,  489. 

Gun-cotton,  CfiHyOoCNOs)^,  507. 
Abel's,"508. 

compared  with  gunpowder,  512. 
composition,  509. 
equation  of  explosion,  510. 
in  mining,  511. 

Karolyi's  experiments  on,  510. 
manufacture,  508. 

2  T 


658 


INDEX. 


Gun-cotton,  objections  to,  513. 

preparation,  507. 

products  of  explosion,  510. 

properties,  512. 

pulp,  Abel's,  508. 

reconversion,  509. 
Gun-metal,  346. 
Gun-paper,  507. 
Gunpowder,  413. 

calculation  of  force,  424. 

collection  of  gases  from,  423. 

composition,  variations  in,  423. 

dusting,  421. 

effect  of  pressure  on  explosion 
of,  428. 

equation  of  explosion,  424. 

examination  of,  421. 

facing,  421. 

glazing,  421. 

granulating  or  corning,  420. 

heat  of  combustion,  425. 

hygroscopic  character,  421. 

incorporation,  420. 

iniluence  of  size  of  grain,  427. 

manufacture,  419. 

mechanical  effect,  426. 

preparation  in  the  laboratory, 
428. 

pressing,  420. 

products  of  explosion,  424. 

slow     combustion, 
426. 

properties,  421. 

smoke,  424. 

speciftc  heat  of  products  from, 
425. 

temperature  of  combustion,  426. 

volume  of  gas  from,  426. 

white,  166. 
Gutta  percha,  489. 
Gujisum,  278. 

H,  HYDROGEN,  14. 

Hfemateine,  603. 
Hicmatine,  616. 
Hcematite,  brmrni,  300. 

red,  FeaOg,  300. 
Hsematosine,  617. 
Hsematoxyline,  603. 
Haemoglobine,  617. 
Hair,  622. 

Hair-dye,  215,  374,  382. 
Halogen,  definition  of,  186. 
Halogens,  general  review  of,  186. 
Haloid  salts,  186. 
Hammer-slag,  311. 
Hard  metal,  346. 
Hardness,  degrees  of,  48. 

permanent,  48. 

temporary,  48. 
Hard  water,  45. 
Hargreave's  soda-process,  264. 
Harrogate  water,  50. 
Hartshorn,  spirit  of,  127. 
Hausmannite,  Mn304,  328. 
Hay,  smell  of,  484. 
HBr,  hydrol)romic  acid,  174. 
HC'l,  hydrochloric  acid,  157. 
HCy,  hydrocyanic  acid,  442. 
Heat  and  temperature,  431. 
atomic  280. 


Heat  rays  separated  from  light,  177,  216, 
relation  to  chemical  attraction,  30. 
specific,  431. 
Heath's  patent  (steel),  317. 
Heating  of  hayricks,  69. 
Heat  of  combustion  of  hydrocarbons,  430. 
Heat-units,  429. 
Heuvy-lead  ore,  PbOj,  375. 

spar,  BaS04,  274. 
Hemihedral  crystals,  590. 
Hemming's  jet,  101. 
Hepatic  waters,  50. 
Heptane,  474. 
Heptylene,  472. 
Hesperetine,  485. 
Hesperidine,  485. 
HF,  hydrofluoric  acid,  181. 
2HF.SiF4,  hydrofluo-silicic  acid,  185. 
Hg,  mercury,  384. 
HgClg,  mercuric  chloride,  388. 
HgCl,  mercurous  chloride,  389. 
Hg(N03).,,  mercuric  nitrate,  388. 
Hg2(N03)2,  mercurous  nitrate,  387. 
HgO,  mercuric  oxide,  387. 
HggO,  mercurous  oxide,  387. 
HgS,  mercuric  sulphide,  391. 
HggS,  mercurous  sulphide,  390. 
HI,  hydriodic  acid,  179. 
Hippuric  acid,  HCBH8NO3,  626. 

artificial  formation,  627. 
extraction  from  cow's  urine, 
626. 
H2O,  water,  33. 
H2O2,  hydric  peroxide,  53. 
Holl way's  process,  357. 
Homologous  series,  438. 
Homology  explained,  438,  578. 
Honey,  503. 
Hoofs,  622. 
Hopeite,  289. 
Hops,  496. 

essential  oil  of,  476. 
Hornblende,  296. 
Horn-lead,  376. 

-silver,  383. 
Horns,  622. 
Horse-chestnut  bark,  485. 

-hair  inflamed  by  nitric  acid,  138. 
-radish,  essential  oil  of,  485. 
Hot  blast,  theory  of,  432. 
blast  iron,  304. 
saturated  solution,  40. 
H2S,  hydrosulphuric  acid,  194. 
H.2SiFg,  hydrofluo-silicic  acid,  185. 
H2SO4,  sulphuric  acid,  202. 
Humic  acid,  633. 
Humus,  632. 
Hyacinth,  297. 
Hysenic  acid,  520. 
Hydrargyrum  cum  creta,  386. 
Hydrated  bases,  43. 
Hydrate  of  lime,  CaHoOg,  43. 
potash,  KHO,  43. 
Hydriites,  43. 
Hydraulic  cements,  413. 

main,  453. 
Hydric  phosphides,  233. 

sulphides,  194. 
Hydrides  of  alcohol-radicals,  526. 
Hydriodate  of  potash,  180. 
Hydriodic  acid,  HI,  179. 


INDEX. 


659 


Hj'driodic  acid  gas,  preparation,  179. 

reducing  properties,  179. 
solution,  preparation,  179. 
ether,  524. 
Hydroboracite,  283. 
Hydrobromic  acid,  HBr,  174. 

ether,  524. 
Hydrocarbons,  92.  438. 

heat  of  combustion  of,  430. 
turpentine-series,  476. 
Hydrocellulose,  502. 
Hydrochloric  acid,  HCl,  157. 

absorption  by  water,  158. 
action  of  heat  on,  159. 
action  on  metallic  oxides, 

160. 
action  on  metals,  159. 

nitric  acid,  172. 
plants,  159. 
analysis  of,  160. 
composition  by  volume, 
160.  ^ 

•     decomposed  by  the  bat- 
tery, 160. 
from  alkali-works,  158. 
gas,  preparation  of,  157. 
liquid,  158. 
properties,  157. 
pure,  preparation  of,  158. 
synthesis  of,  150. 
valuation  of,  158. 
yellow,  158. 
Hydrochloric  ether,  524. 

gas,  dry,  preparation,  159. 
Hydrocyanic  acid,  HCN,  442. 

anhydrous,  442. 
Liebig's  test  for,  446. 
sjTithesis,  95. 
ether,  532. 
Hydrocyan-rosaniliue,  462. 
Hydroferricyanic  acid,  HjCygFe,  447. 
Hydroferrocyanic  acid,  H4Cy6Fe,  442. 
Hydrofluoboric  acid,  186. 
Hydrofluoric  acid,  HF,  181. 

action  on  metals,  183. 
silica,  183. 
Hydrofluo-silicic  acid,  185. 

decomposed  by  heat, 
185. 
Hydrogen,  H,  14. 

and  arsenic,  242. 
carbon,  92. 
sulphur,  194. 
binoxide,  53. 
calorific  intensity  calculated,  432. 

value,  430. 
chemical  properties,  20. 

relations,  40. 
displaced  by  sodium,  13. 
etymology  of,  20. 
experiments  with,  16. 
flame,  22. 
identification  of,  9. 
peroxide,  53. 
persulphide,  198. 
phosphides,  233. 
physical  properties,  16. 
poured  up  through  air,  16. 
preparation  with  iron,  14. 
zinc,  14. 
purification,  38. 


Hydrogen,  selenietted,  220. 

sulphuretted,  194. 
Hydrogenium,  40. 
Hydrokinone,  598. 
Hydronitroprussic  acid,  447. 
Hydroselenic  acid,  H.iSe,  220. 
Hydrosulphocarbonic  acid,  217. 
Hydrosulphocyanic  acid,  HCj'S,  446. 
Hydrosulphuric  acid,  HjS,  194. 

disposal  of,  195. 

liquefied,  198. 

preparation,  194. 

production  in  waters, 
212. 

solution  of,  195. 

test  for,  196. 

use  in  analysis,  197. 
ether,  531. 
Hydrosulphurous  acid,  214. 
HydroteUuric  acid,  HgTe,  221. 
Hydroxides,  43. 
Hydroxyle,  437. 
Hydroxyle  theory  of  acids,  253. 
Hydroxylamine,  NH3O,  138,  526. 
Hyoscyamine,  540. 
Hypobromous  acid,  174. 
Hypochlorite  of  lime,  162. 
Hypochlorous  acid,  161. 

action  on  sal-ammoniac,  172. 
Hypogeic  acid,  578. 
Hyponitric  acid,  145. 
Hyponitrites,  144. 
Hypophosphites,  232. 
Hypophosphoric  acid,  232. 
Hypophosphorous  acid,  232. 
Hyposidphates,  214. 
Hyposulphindigotic  acid,  608. 
Hyposulphite  of  soda,  NagSjOs,  212. 
Hyposulphites,  213. 

constitution  of,  214. 
Hyposulphuric  (dithionic)  acid,  214. 
Hyposulphurous  acid,  212. 

I,  IODINE,  175. 

Ice,  52. 

Iceland  spar,  CaCOs,  277. 

Idrialene,  469. 

Illuminating  gas  from  water,  89. 

Imides,  .552. 

constitution  of,  552. 
Imidogen,  NH,  552. 
Incorporating  mill,  420. 
Incrustation  on  charcoal,  109. 
Incrustations  in  boilers,  46. 
Indian  fire,  245. 
Indian  ink,  478. 
Indican,  607. 
Indiiferent  oxides,  29. 
Indigo,  action  of  chlorine  on,  154. 

artificial,  608. 

blue,  Ci6H,oN.^O.i,  607. 

copper,  CuS,  365. 

red,  607. 

reduced,  607. 

vat,  preparation,  607. 

white,  607. 
Indigotine,  608. 
Indium,  298. 

oxide,  298. 
Induction-coil,  10. 

tube,  Siemens',  54. 


6G0 


INDEX. 


Ink,  592. 

blue,  441. 
from  logwood,  603. 
red,  603. 

stains  removed,  162. 
vanadium,  335. 
Inorganic  substances,  definition,  6. 
Inosite,  CgHisOj,,  620. 
Instantaneous  light,  393. 
Introduction,  1. 
Intumescence,  267. 
lodammonium  iodide,  180. 
lodates,  178. 
Iodic  acid,  HIO3,  178. 
Iodide  of  ethyle,  524. 
nitrogen,  180. 
potassium,  180. 
silver,  Agl,  384. 
Iodine,  I,  175. 

action  on  ammonia,  180. 

potash,  176. 
and  starch,  177. 
bromides,  180. 
chloride,  ICl,  180. 
etymology  of,  175. 
extraction  from  sea- weed,  175. 
identified,  176. 
oxides,  178. 
test  for,  177. 
tincture  of,  177. 
trichloride,  ICI3, 180. 
Iodised  starch  paper,  55. 
Iodoform,  554. 
Iridium,  Ir,  399. 

ammoniochloride,  399. 
black,  399. 
chlorides,  399. 
oxides,  399. 
Iron,  Fe,  299. 

action  of  acids  on,  321. 

air  of  towns  on,  284. 
hydrochloric  acid  on,  160. 
on  water,  13. 
amalgam,  387. 
and  carbon,  306. 
and  oxygen,  28. 

and  potassium,  ferrocyanide,  441. 
atomic  weight,  324. 
bar-,  312. 

basic  persulphate,  202. 
bisulphide,  301. 
black  oxide,  322. 
bright,  307. 
carbonate,  300. 
cast,  306. 

chemical  properties,  321. 
chlorides,  323. 
cold  short,  314. 
diatomic,  324. 

extraction  in  the  laboratory,  321. 
ferricyanide,  446. 
fibre  in,  314. 
galvanised,  284. 
glance,  300. 
grey,  307. 

group  of  metals,  general  review,  334. 
in  blood,  617. 
in  zinc,  287. 
iodide,  181. 

magnetic  oxide,  Fe304,  322. 
metallurgy,  301. 


Iron,  mottled,  307. 

-mould,  321,  586. 

occurrence  in  nature,  299. 

of  antiquity,  319. 

ores,  300. 

British,  composition,  300. 
calcining  or  roasting,  302. 

oxides,  322. 

passive  state  of,  321. 

perchloride,  FcjClg,  o23. 

peroxide,  FegOa,  322. 

persulphate,  Fe.23S04,  323. 

phosphates,  323. 

phosphorus  in,  314. 

plates  cleansed,  345. 

proto-chloride,  323. 

proto-sesquioxide,  322. 

proto-sulphate,  323. 

uses,  323. 

protoxide,  FeO,  29,  322. 

prussiate,  440. 

pure,  preparation  of,  321. 

purification,  309. 

pyrites,  FeSg,  301. 

pyrophoric,  29,  91. 

red  oxide,  322. 

red  short,  314. 

refining,  309. 

rust,  ammonia  in,  132. 

rusting  of,  321. 

sand,  301. 

scales,  311. 

scurf,  411. 

separation  from  manganese,  330. 

sesquichloride,  323. 

sesquiferrocyanide,  441. 

sesqui-iodide,  181. 

sesquioxide,  29. 

sesquisulphate,  323. 

smelting,  English  method,  302. 

specular,  300. 

steely,  321. 

sulphate,  action  of  heat  on,  211. 

nitric  acid  on,  142. 

sulphide,  preparation,  194. 

sulphuret,  194. 

sulphur  in,  314. 

tincture  of,  324. 

tinned,  345. 

triatomic,  324. 

nseful  properties  of,  301. 

variation  in  strength  of,  314. 

white,  307. 

wire,  composition,  312. 

works  of  the  Pyrenees,  320. 

wrought  or  bar,  composition,  314. 
direct  extraction,  319. 
manufacture,  308. 
Iserine,  350. 
Isethionic  acid,  635. 

chloride,  636. 
Isinglass,  622. 
Iso-alcohols,  517. 
Isocumole,  454. 
Isodimorphism,  339. 

of  antimonious  oxide  and 
arsenious  oxide,  246. 
Isologons  series,  438. 
Isomeric,  439. 
Isomerism,  439. 

explanation  of,  439. 


INDEX. 


661 


Isomorphism,  363. 
Isoprene,  488. 
Isopurpurates,  466. 
Isotartaric  acid,  588. 
Isoterebeuthene,  475. 
Ivory,  artificial,  514. 
Ivory-black,  67. 

Japan,  473. 

Jasper,  113. 

Jatrophine,  492. 

Jellies,  fruit,  632. 

Jellv,  621. 

Jet,  71. 

Jet  for  burning  gases,  22. 

Jeweller's  rouge,  322. 

Juice  of  sugar-cane,  503. 

Juniper,  essential  oil  of,  476. 

K,  POTASSIUM,  257. 
Kainite,  283. 
Kakodyle,  CgHgAs,  632. 

chemical  constitution  of,  532. 

chloride,  532. 

cyanide,  533. 

oxide,  532. 

series,  533. 
Kakodylic  acid,  533. 
Kaolin,  291. 
Kapnomor,  473. 
KCl,  potassium  chloride,  260. 
2KC],PtCl4,  potassium  platino-chloride,  395. 
KCIO3,  „         chlorate,  163. 

K2CO3,  ,,  carbonate,  257. 

KCy,  „         cyanide,  444 

KCyO,  „         cyanate,  445. 

KCyS,  ,,         sulphocyanide,  445. 

Kekiile's  chain,  459. 
Kelp,  175. 
Kentledge,  305. 
Kermes  mineral,  342. 
Kernel  roasting,  364. 
Kerosene,  474. 

shale,  472. 
Kerosoline,  474. 
Ketones,  437,  558. 

K4Fcy,  potassium  ferrocyanide,  440. 
KgFdcy,  potassium  ferricyanide,  447. 
KHCO3,  bicarbonate  of  potash,  260. 
KHO,  caustic  potash,  258. 
KHSO4,  bisulphate  of  potash,  211. 
KI,  potassium  iodide,  180. 
Kid,  593. 
Kieselguhr,  580. 
Kieserite,  283. 
King's  yellow,  245. 
Kinic  acid,  598. 
Kino,  595. 

Kiuone,  CgHiOo,  598. 
Kirschwasser,  516. 
Kish,  63. 
Klumene,  92. 

KMn04,  potassium  permanganate,  329. 
KNO3,  saltpetre  or  nitre,  413. 
K.jO,  dipotassium  oxide,  259. 
KoO.CrOg,  chromate  of  potash,  331. 
Ko0.2Cr03,  bichromate  of  potash,  331. 
Kola  nut,  598. 

K.20.Sb.205,  antimoniate  of  potash,  339. 
Koumiss,  613. 
Kreasote,  464,  466. 


Kreatine,  C4H9N3O2,  619. 

extraction  from  tlesh,  619. 
Kreatinine,  C4H7N3O,  620. 
Kresole,  466. 
Kresyle,  466. 

Kresylic  acid,  C7H8O,  466. 
Krupp's  steel,  319. 
Kryolite,  Na3AlF6,  265. 
K.jS,  potassium  sulphide,  422. 
Kupfemickel,  NiAs,  326. 
Kyanising  wood,  633. 
Kyanite,  296. 

Lac,  478,  608. 
seed,  478. 
shell,  478. 
stick,  478. 
Lacquer,  478. 
Lacquering,  360. 
Lactai'ine,  614. 
Lactic  acid,  HC3H:g03,  486,  563,  612. 

converted  into  butyric,  569. 

propionic,  613. 
preparation,  612. 

anhydride,  613. 

fermentation,  612. 

series  of  acids,  563. 
Lactide,  613. 
Lactine,  G^^^fii^  614. 
Lactometer,  615. 
Lajvotartaric  acid,  590. 
Lagunes,  boracic,  120. 
Lakes  alumina,  608. 
Lamp,  action  explained,  104. 

-black,  64. 

without  flame,  393. 
Lanarkite,  376. 
Lanthanium,  La,  297. 
Lapis  Lazuli,  296. 
Lard,  584. 
Laughing  gas,  140. 
Laurel  water,  442,  481. 
Laurent's  doctrine  of  substitution,  467. 

nomenclature,  467. 
Laurie  acid,  519. 

alcohol,  518. 
Laurite,  398. 
Lava,  296. 

Law  of  multiple  proportions,  146. 
Lead,  Pb,  365. 

acetate,  Pb(C2H30.2)2,  565. 

action  of  acids  on,  373. 

suli^huric  acid  on,  207,  373. 
on  water,  13,  50. 

amalgam,  387. 

argentiferous,  369. 

basic  carbonate,  375. 
chix)mate,  332. 

binoxide,  375. 

calcining,  368. 

carbonate,  native,  376. 

chloride,  PbClg,  376. 

chlorobromide,  377. 

chlorosulphide,  377. 

chromate,  PbO.CrOj,  332. 

dichromate,  332. 

extraction  in  the  laboratory,  372. 

fusing-point  of,  365. 

-glazed  earthenware,  374,  411. 

hard,  368. 

hydrated  oxide,  374. 


62 


INDEX. 


Lead,  hyposulphite,  214. 

improving  process,  368. 

in  cider,  &c.,  373. 

in  water,  50. 

iodide,  Pbl.^  178,  377. 

malate,  591. 

metallurgic  chemistry,  366. 

molybdate,  334. 

ores,  365. 

oxide,  use  of,  in  glass,  407. 

oxides,  373. 

oxychloride,  376. 

peroxide,  PbO.^,  375. 

phosphate,  376. 

plaster,  577. 

protoxide,  PbO,  373. 

pyrophorus,  373. 

selenide,  377. 

smelting,  366. 

Spanish,  368. 

specific  gravity,  365. 

sugar  of,  565. 

sulphate,  PbSOi,  366,  376. 

sulphides,  377. 

tartrate,  preparation,  373. 

test  for,  in  water,  50. 

tribasic  acetate,  566. 

uses,  365. 

vanadiate,  335. 
Lead-vitriol,  PbS04,  376. 
Leaden  cisterns,  danger,  50. 

coffins,  corrosion,  373. 
Leadhillite,  376. 
Leather,  593. 
Leaven,  601. 

Leaves,  formation  of,  631. 
Lecanoric  acid,  606. 
Leeks,  essential  oil  of,  485. 
Legumine,  614. 
Lemery's  volcano,  193. 
Lemons,  essential  oil  of,  476. 
Lepargylic  acid,  582. 
Lepidolite,  271. 
Leucaniline,  461. 

triphenylic,  462. 
Leucic  acid,  HCgHuOa,  563. 
Leucine,  CgHigNOa,  622. 
Leucone,  119,  171. 
Levulose,  603. 
Li,  lithium,  271. 
Libethenite,  363. 

Lichens,  colouring  matter  from,  606. 
Liebig's  condenser,  52. 

extract,  620. 
Life,  its  extremes  meet,  640. 
Light,  action  on  chloride  of  silver,  213. 

rays  separated  from  heat,  177,  216. 
Light  carburetted  hydrogen,  98. 

oil  of  coal-tar,  456. 
Lign  aloes,  essence  of,  477. 
Liguine,  469. 
Li<jnUe,  70. 

composition,  71,  433. 
Ligroine,  474. 
Lime,  CaO,  277. 

action  on  soils,  630. 

agricultural  uses,  630. 

bi  malate,  591. 

burning,  277. 

carbonate,  CaO.CO^,  277. 
in  waters,  46. 


Lime,  fat,  278. 

hydrate,  CaO.H,0,  278. 
hypochlorite,  162. 
hyposulphite,  212. 
kilns,  278. 
-light,  39. 
lactate,  612. 
overburnt,  278. 
oxalate,  CaC204,  587. 
platinate,  394. 
poor,  278. 
purifier,  454. 
-stone,  CaO.COo,  277. 
sulphate,  CaO.SOj,  278. 
superphosphate,  ^2. 
test  for,  587. 
water,  278. 
Linen,  470. 
Linoleic  acid,  583. 
Linseed,  490. 

oil,  683. 

boiled,  683. 
Lipic  acid,  582. 

Liquation  of  argentiferous  copper,  379. 
Liquor  ammonias,  124. 
chlori,  149. 
iodi,  177. 

sanguinis,  composition,  618. 
Liquorice  root,  607. 
Litharge,  PbO,  374. 
Lithia,  271. 

carbonate,  271. 
-mica,  271. 
phosphate,  271. 
Lithic  (uric)  acid,  625. 
Lithium,  Li,  271. 

blowpipe  test  for,  271. 
Litmus,  606. 

commercial,  606. 
Loadstone,  Y^zOi,  29,  301. 
Loam,  291. 
Logwood,  603. 

Looking-glasses  silvered,  386. 
Lucifer  matches,  165,  227. 

tipped  with  sulphur,  227. 
Lugol's  solution,  1^7. 
Luraiuosity  of  flames,  103. 
Lunar  caustic,  382. 
Lupuliue,  496. 
Luteoline,  603. 
Luting  for  crucibles,  286. 

iron  joints,  193. 
Lycopodium,  102. 

Madder,  603. 
Magenta,  460. 
Magic  lantern,  oil  for,  477. 
Magnesia,  MgO,  283. 

calcined,  283. 

citrate,  591. 

hydrate,  283. 

hydraulic,  283. 

medicinal,  283. 

silicates,  283. 

sulphate,  MgO.SOs,  282. 
Magnesian  limestone,  281. 

for  building,  412. 
Magnesite,  281. 
Magnesium,  Mg,  281. 

action  on  water,  13. 
ammouiophosphate,  283. 


INDEX. 


663 


Magnesium  arsenite,  240. 
borate,  283. 
carbonate,  283. 
chloride,  118,  283. 

extraction    from    sea- 
water,  261. 
extraction,  281. 
fluoride,  184. 
hydrate,  283. 
nitride,  282. 
phosphate,  283. 
properties,  281. 
silicates,  283. 
silicide,  118. 
sulphate,  MgSOi,  282. 
Magnet-fuze  composition,  365. 
Magnetic  iron  ore,  Fe304,  322. 
Magnus'  green  salt,  396. 
Malachite,  353. 
Malaeic  acid,  591. 
Malamide,  592. 
Malic  acid,  H2C4H40g,  591. 

converted  into  acetic,  592. 

succinic,  592. 
extracted  from  rhubarb,  591. 
formed  from  succinic,  590. 
tartaric,  589. 
Malleability  of  copper,  358. 
Malleable  cast-iron,  318. 
Malonic  acid,  582. 
Malt  dust,  495. 

high  dried,  498. 
Malting,  494. 
Maltose,  503. 
Manganate  of  potash,  328. 

soda  for  preparing  oxygen,  31. 
Manganese,  Mn,  327. 

action  on  water,  13. 

alum,  328. 

binoxide,    action    of   sulphuric 

acid  on,  211. 
llack,  327. 
carbonate,  328, 
chlorides,  330. 
dioxide  MnOg,  327. 
hydrated  peroxide,  327. 
oxides,  327. 
peroxide,  327. 
protoxide,  MnO,  328. 
recovery  from  chlorine  residues, 

330. 
red  oxide,  328. 
separation  from  iron,  330. 
sesquioxide,  Mn.203,  328. 
spar,  MnCOg,  328. 
sulphate,  MnS04,  327. 
test  for,  328. 
Manganic  acid,  328. 
Manganite,  M.n^O^.YL<fi,  328. 
Manna,  506. 
Mannitane,  579. 
Maunite,  CgHi40g,  506. 
glycerides,  579. 
glycerine,  579. 
steariue,  579. 
Mantle  of  flame,  106. 
Manures,  629. 
Manuring,  628. 
Maraschino.  516. 
Marble,  279. 
Marcasite,  301. 


Margaric  acid,  520,  582. 
Margarine,  582. 
Marine  glue,  488. 
Marking-ink,  382. 
Marl,  291. 
Marsh  gas,  CH4,  98. 

and  chlorine,  154. 
composition  by  volume,  110. 
eudiometric  analysis,  110. 
identified,  98. 
preparation,  98. 
series,  CiH^n+o,  526. 
Marsh-mallow,  490. 
Marsh's  test  for  arsenic,  242. 
Mascagnine,  268. 
Massicot,  PbO,  374. 
Matches,  165. 

eupyrion,  167. 
lucifer,  227. 
safety,  227. 
silent,  227. 
Vesta,  167. 

without  phosphorus,  228. 
Matt,  354. 

Matter,  definition  of,  1. 
Mauve,  460. 
Mauveine,  460. 
Meadow-sweet,  oil  of,  482. 
Meal  powder,  420. 
Meconic  acid,  H3C7HO7,  597. 
Meerschaum,  281. 
Melaniline,  547. 
Melissene,  521. 
Melissic  acid,  520. 

alcohol,  518. 
Melissine,  585. 
Menaccanite,  350. 
Mendelejeff  s  law,  256. 
Mendipite,  PbCl2.2PbO,  377. 
Menthene,  477. 
Menthole,  477, 
Mercaptan,  531. 
Mercaptide  of  mercury,  531. 
Merchant  bar  iron,  312. 
Mercuramine,  387. 
Mercuric  ethide,  Hg(C3Hg)2,  537. 
fulminate,  448. 
iodide,  Hglg,  390. 
methide,  537. 
nitrate,  H£(NO.,).„  388. 
sulphate,  HgSOi,  388. 
Mercurous  chloride,  HgCl,  389. 
iodide,  Hgl,  390. 
nitrate,  HgoCNOj),,  388. 
sulphate,  HgaO.SOj,  388. 
Mercuiy,  Hg,  384. 

action  of  hydrosulphuric  acid  on 

196. 
amido-chloride,  389. 
ammoniated  oxide,  387. 
bichloride  or  perchloride,  388. 
black  oxide,  HgoO,  387. 
chloride,  HgCl2,"388. 
chlorosulphide,  391. 
cyanide,  Hg(CN).2,  442. 
extraction  irom  its  ores,  384. 
frozen  by  liquid  sulphurous  acid, 

199. 
fulminate,  HgCaNgOo,  448. 
iodide,  390. 
metallurgy  of,  384. 


664 


INDEX. 


Mercury,  nitrate,  HgCNOgU,  388. 
nitric  oxide  of,  387. 
nitride,  387. 
oxides,  387. 

protochloride,  BgCl,  389. 
protonitrate,  HgailNOa)^,  388. 
prussiate,  440. 
red  oxide,  HgO,  387. 
stains  removed  from  gold,  387. 
subsulphide,  390. 
sulphate,  388. 
sulphide,  390. 
uses  of,  386. 
volatility  of,  386. 
yellow  oxide,  HgO,  387. 
Metacetone,  559. 
Metacetonic  (propylic)  acid,  519. 
Metal,  definition,  29. 
Metalaniides,  553. 
Jletaldehyde,  557. 
Metallic  oxides,  action  of  hydrochloric  acid 

on,  160. 
Metallurgy  of  copper,  352. 
iron,  301. 
lead,  342. 
tin,  342. 
zinc,  285. 
Metals,  action  of  hydrochloric  acid  on,  159. 
hydrosulphiyric     acid    on, 

196. 
sulphuric  acid  on,  209. 
on  water,  12. 
burnt  in  sulphur  vapour,  19-3. 
chemistry  of,  254. 
classification  of,  254. 
iron  group,  general  review,  334. 
noble,  13. 

of  the  alkalies,  general  review,  273. 
of  the  alkaline  earths,  280. 
platinum  group,  399. 
relations  to  oxygen,  27. 
i\Ietal-slag  (copper),  355. 
Metameric,  439. 
Metantimonic  acid,  340. 
Jletaphosphates,  232. 
Metaphosphoric  acid,  HPO3,  232. 
Metastannic  acid,  348. 
Metastyrole,  478. 
Metatartaric  acid,  588. 
Metaterebenthene,  475. 
Meteoric  iron,  299. 
Methylamine,  543,  548. 
Methylauiline,  544. 
^Methylated  spirits,  479. 
Methyle,  CH3,  436. 

-caproyle,  525. 

chloride,  548. 

-phenylamine,  544. 

prepared  from  acetic  anhydride, 

567. 
salicylate,  472. 
series,  436. 
-theobromine,  600. 
toluene,  459. 
Methylethylamine,  543. 
M  I'thyl-amylo-phenylium,  hydrate,  544. 
Mi'thylethylaniline,  544. 
Mitlivl-ethyl-amylo-phenyl-ammonium,  hv- 

ilrate.  544. 
Methylethylic  ether,  531. 
JU'thyl-hexyl  ketone,  528. 


Methylmorphylammonium,  hydrate,  545. 
Methylation,  438. 
Methylic  acetate,  471. 

alcohol,  CH4O,  471,  517. 

formiate,  471. 

hydrate,  471. 
Methyluric  acid,  626. 
Mg,  magnesium,  281. 
MgO,  magnesia,  283. 
MgO.SOs,  sulphate  of  magnesia,  282. 
Mica,  290. 

Microcosmic  salt,  232. 
Mildew,  60. 
Milk,  612. 

adulteration,  615. 
coagulation  of,  612. 
composition  of,  615. 
Mill-cake,  420. 

furnace,  312. 
Millstone  grit,  411. 
Mimotannic  acid,  595. 
Mine  iron,  305. 
Mineral  cotton,  306. 
green,  363. 
silicates,  295. 
waters,  50. 
yellow,  377. 
Mines,  ventilation,  78. 
Minium,  PbjOi,  374. 
Mirbane,  essence  of,  139. 
Mirrors,  manufacture,  386. 
Mispickel,  FeSa,  FeAS,,  236. 
Mixture  and  compound,  distinction,  60. 
Mn,  manganese,  327. 
MnOo,  peroxide  of  manganese,  327. 
Moire  metallique,  347. 
Molasses,  503. 
Molecular  compounds,  270. 

formula,  435. 

weight,  3,  436. 
Molecule,  definition,  1,  2. 

of  a  base  determined,  132. 

of  an  acid  determined,  85. 

of  water,  2. 
Molecules,  1,  2. 
Molybdate  of  lead,  334. 
Molybdena,  M0S2,  334. 
Molybdenum,  Mo,  334. 

bisulphide,  334. 
blue  oxide,  334. 
chlorides,  334. 
metallic,  334. 
oxides,  334. 
Molybdenum  sulphides,  334. 
Molybdic  acid,  MoO,,  334. 

dialysed,  334. 

ochre,  335. 
Monacetine,  565. 
Mona  copper,  357. 
Monad  elements,  247. 
Monamines,  545. 
Monatomic  elements,  247. 
Monkshood,  591. 

Monobasic  acids,  constitution  of,  250. 
Monophosphaniide,  236. 
Monostearine,  576. 
Mordants,  609. 
Moringic  acid,  578. 
Moritannic  acid,  603. 
Morocco  leather,  593. 
Morphine,  Ci7Hi9NOa,  596. 


INDEX. 


665 


Morphine,  characters  of,  596. 

extraction,  596. 

hydrochlorate,  597. 
Mortar  for  building,  412. 
Mould,  60. 
Mosaic  gold,  350. 
Mountain  ash  berries,  591. 
Mucic  acid,  490. 
Mucilage,  490. 
Mucus,  623. 
Muffle,  372. 

MulbeiTy  calculus,  585. 
Multiple  proportions,  law  of,  146. 
Mundic,  FeSg,  301. 
Muntz  metal,  360. 
Murexide,  626. 
Muriate  of  morphia,  597. 
Muriatic  acid,  158. 
Muscle  formed  from  food,  634. 
Mushrooms,  506. 
Muslin,  uninflammable,  268,  351. 
Mustard,  essential  oil  of,  485. 

artificial  production,  486. 
Myosine,  620. 
Myricine,  585. 
Myristic  acid,  520. 
Myronic  acid,  485. 
MjTOsine,  485. 
Myrrh,  487. 

N,  NITROGEN,  122. 

Na,  sodium,  260. 

NaCl,  common  salt,  260. 

Nails,  622. 

Na.20,  disodium  oxide,  265. 

NaoO.BoOs,  borax,  119,  266. 

NaaCOs,  sodium  carbonate,  262. 

NaHO,  caustic  soda,  265. 

NaHCOs,  bicarbonate  of  soda,  264. 

Na.2HP04,  sodium  phosphate,  267. 

NaNOj,  „     nitrate,  414. 

Na,S04,  ,,     sulphate,  267. 

Na-jSaOg,  ,,     hyposulphite,  212. 

Naphtha,  coal,  455. 
wood,  471. 

Naphthalic  acid,  468. 

Naphthalene,  C'loHg,  467. 

chlorides,  468. 

chlorine  substitution-products 

from,  467. 
nitro  -  substitution    products 
from,  468. 

Naphthalising,  105. 

Naples  yellow,  377. 

Narcotiue,  540. 

extraction,  597. 

Nardic  acid,  520. 

Nasturtium,  oil  of,  560. 

Negative  pole,  8. 

Nessler's  test  for  ammonia,  390. 

Nettles,  acid  of,  568. 

Neurine,  548. 

Neutralisation,  12. 

Neutrality  of  constitution,  250. 

NHj,  ammonia,  123. 

NH4,  ammonium,  130. 

NH4CI,  ammonium  chloride  or  sal-ammoniac, 
124. 

2NH4Cl,PtCl4,    ammonio-chloride   of  plati- 
num, 395. 

NH3,HC1,  sal-ammoniac,  124. 


(NH4)2COj,  ammonium  carbonate,  268. 
(NH4).,C204,         „         oxalate,  587. 
(NH4)2S04,  „  sulphate,  268. 

(NH4)oS,  „         sulphide,  270. 

Ni,  nickel,  326. 
Nickel,  Ni,  326. 

action  on  water,  13. 
arsenical,  NiAs.2,  326. 
arsenio- sulphide,  326. 
glance,  NiAs.^NiSg,  326. 
oxides,  326. 
sulphate,  326. 
sulphides,  327. 
Nicotine,  C10H14N.2,  601. 
extraction,  601. 
properties,  601. 
Nil  album,  285. 
Niobic  acid,  352. 
Niobium,  Nb,  352. 
Nipper-tap,  152. 
Nitraniline,  550. 

Nitrate  of  potash,  action  of  heat  on,  140. 
solubility,  414. 
silver  prepared  from  standard  sil- 
ver, 382. 
soda,  solubility,  414. 
Nitrates,  composition,  140. 

decomposition  by  heat,  140. 
formation  in  nature,  133. 
oxidising  properties,  139. 
Nitre,  KNO3,  413. 

action  on  carbon,  416. 
artificial  production,  414. 
cable,  414. 
examination  of,  416. 
-heaps,  414. 
properties,  416. 

purified  in  the  laboratory,  429. 
refining,  415. 

relation  to  combustion,  416. 
Nitricacid,  HNO3,  134. 

action  on  benzene,  139. 
charcoal,  137. 
hydrochloric  acid,  172. 
indigo,  136. 
metals,  137. 
organic      substances, 

138. 
phosphorus,  137. 
sulphurous  acid,  205. 
turpentine,  138. 
anhydrous,  139. 
cause  of  colour,  136. 
decomposed  by  heat,  136. 
light,  136. 
distillation  of,  136. 
formed  from  air,  134. 

ammonia,  132. 
from  batteries,  145. 
fuming,  136. 

oxidising  properties,  137. 
preparation  on  the  large  scale, 

135. 
preparation  on  a  small  scale,  135. 
properties,  136. 
strongest,  preparation,  135. 
test  of  strength,  136. 
anhydride,  139. 
ether,  527. 
oxide,  NO,  141. 

analysis  of  air  by,  142. 


666 


INDEX. 


Nitric  oxide,  behaviour  with  hydrogen,  143. 
identified,  141. 
pure,  preparation,  142. 
with  carbon  disulphide,  152. 
peroxide,  NOg,  145. 

composition     by     volume, 
147. 
Nitrification,  theory  of,  133. 
Nitriles,  551. 
Nitrites,  144. 
Nitrobenzoic  acid,  627. 
Nitrobenzene,  CgH5(N02),  459. 
preparation,  139. 
Nitro-ethane,  527. 
Nitrogen,  N,  122. 

atomicity  of,  246. 
binoxide,  141. 
bromide,  174. 
bulbs,  131. 

chemical  relations,  123. 
chloride,  171. 

preparation,  171. 
circulation  in  nature,  124. 
determination,  131. 
etymology,  59. 
function  in  air,  60. 
group  of  elements,  216. 
identification  of,  123. 
iodide,  180. 
oxides,  146. 

general  review,  146. 
peroxide,  145. 
preparation,  123. 
properties,  59. 
protoxide,  140. 
sulphide,  218. 
Nitrogenised  bodies  identified,  68. 
Nitroglycerine,  579. 

use  in  blasting,  580. 
Nitrohippuric  acid,  627. 
Nitromagnite,  581. 
Nitromannite,  514. 
Nitromuriatic  acid,  172. 
Nitrophenisic  acid,  465. 
Nitroprussides,  447. 
Nitrosubstitution  products,  139. 
Nitrosyle  chloride,  172. 
sulphate,  172. 
Nitrotoluole,  464. 
Nitrous  acid,  143. 

action  on  hydrosulphuric  acid, 

196. 
action ,  on  organic  substances, 

144. 
commercial,  145. 
composition  by  volume,  146. 
formed  from  ammonia,  132. 
oxidising  and  reducing  power, 
146. 
ether,  527. 
Nitrous  oxide,  NgO,  140. 

composition  by  volume,  146. 
identified,  141. 
Nitroxylole,  464. 
X..0,  nitrous  oxide,  140. 
NO,  nitric  oxide,  141. 
N0O3,  nitrous  anhydride,  143. 
NO2,  nitric  peroxide,  145. 
NoOg,  nitric  anhydride,  134. 
Noble  metals,  13. 
Non-metallic  elements,  3. 


Nordhausen  oil  of  vitriol,  202. 
Normal  alcohols,  521. 

salt,  definition,  250. 
Normandy's  still,  52. 
Nucleine,  616. 
Nuggets,  400. 
Nutrition  of  animals,  633. 
plants,  627. 
plastic  elements  of,  637. 
Nux-vomica,  600. 

0,  OXYGEN,  23. 
Oak  bark,  593. 
Occlusion  of  hydrogen,  40. 
Ochres,  291. 
(Enanthene,  521. 
(Enanthic  acid,  519,  583. 

synthesis,  570. 
alcohol,  518. 
(Enanthole,  583. 
Oil  of  spiraea,  482. 
Oil  of  vitriol,  H2SO4,  203. 
brown,  207. 
dehydrated,     by    phosphoric 

acid,  210. 
dissociation  of,  210. 
distillation  of,  207. 
manufacture,  203. 
sulphate  of  lead  in,  208. 
Oil  of  wine,  628. 
Oils,  581. 
Olefiant  gas,  C2H4,  95. 

absorbed    by   sulphuric    acid, 

210. 
combination  with  chlorine,  96. 
converted  into  alcohol,  530. 
decomposed  by  chlorine,  97. 
heat,  97. 
the  spark,  97. 
identification  of,  95. 
preparation,  95. 
with  iodine,  180. 
Olefines,  C„H,n,521. 
Oleic  acid,  HCigHgaOj,  582. 

action  of  niti-ic  acid  on,  583. 
series  of  acids,  578. 
Oleine,  C57H104O8,  582. 

synthesis  of,  576. 
Olibanum,  487. 
Oligist  iron  ore,  300. 
Olive-oil,  581. 
Olivine,  283. 
Onions,  506. 

essential  oil  of,  485. 
Onyx,  113. 
Oolite  limestone,  111. 
Oolitic  iron  ore,  301. 
Opal,  113. 
Opium,  composition,  596. 

extraction  of  alkaloids  from,  596. 
Orange  chrome,  2PbO.Cr03,  332. 
Orange,  essential  oil  of,  476. 
Orceine,  606. 
Orcine,  606. 
Ore-furnace,  354. 
Organic  analysis,  elementary,  84. 

and  inorganic  substances,  435. 
chemistry,  435. 
compounds  classified,  435. 
matter  identified,  61. 
substances,  definition,  6. 


INDEX. 


667 


Organic  substances,  synthetical    formation, 

92. 
Organo-metallic  bodies,  532. 

table  of,  53& 
Oriental  alabaster,  47. 
Orpiment,  red,  AS.2S2,  244. 

yellow,  AS2S3,  245. 
Orthoclase,  295. 
Orthophosphates,  231. 
Orthophosphoric  acid,  H3PO4,  231. 
Osmazome,  621. 
Osmic  acid,  398. 
Osm,iridiu7)i,  398. 
Osmium,  Os,  398. 

chlorides,  398. 
oxides,  398. 
tetrasulphide,  398. 
Osseuie,  621. 
Oswego,  492. 
Oxalates,  585. 
Oxalethylic  acid,  527. 
Oxalic  acid,  H.,C204,  585. 
analysis  of,  85. 
fatal  dose,  587. 
occurrence  in  nature,  585. 
preparation,  586. 
properties,  587. 
test  for,  587. 
uses,  586. 
ether,  526. 
Oxalonitrile,  551. 
Oxalovinic  acid,  527. 
Oxamic  acid,  551. 
Oxamide,  N2H4.C2O2,  550. 
Oxanilide,  551. 
Oxatyle,  437. 
Oxidation,  definition,  24. 

of  tissue,  products,  636. 
Oxide  of  copper  reduced  by  hydrogen,  38. 
Oxides,  30. 

metallic,  action  of  hydrochloric  acid 
on,  160. 
hydrosulphuric 
acid  on,  196. 
sulphuric       acid 
on,  210. 
nomenclature  of,  30. 
Oxidising  blowpipe  flame,  109. 
Oxycalcium  light,  39. 
Oxygen,  0,  23. 

absorption  by  pyrogallic  acid,  595. 

atomicity  of,  246. 

blowpipe  flame,  110. 

burnt  in  ammonia,  129. 

combustion  in,  25. 

detected  in  mixed  gases,  141. 

determination  of,  in  gases,  36. 

eff"ect  on  flame,  110. 

electro-negative,  53. 

electro-positive,  53. 

etymology,  27. 

evolved  from  steam,  152. 

experiments  with,  25. 

extracted  from  air,  .30. 

group  of  elements,  246. 

identified,  9. 

natural  sources,  23. 

preparation,  30. 

from  air,  30. 
from     bichromate     of 
potash,  211. 


Oxygen,  preparation  from  chloride  of  lime. 
162. 
properties,  23. 

purification,  61.  . 

relation  to  metals,  27. 

non-metals,  24. 
Oxygenated  water,  53. 
Oxygenised  muriatic  acid,  157. 
Oxyhydrogen  blowpipe,  39. 
Oxymuriatic  acid,  157. 
Ozokerite,  474. 
Ozone,  54. 

electrolytic,  54. 
experiments  with,  55. 
in  the  atmosphere,  54. 
nature  of,  54. 
test  for,  55. 
Ozonisation  by  ether,  56. 

phosphorus,  55, 
Ozonised  air,  54. 

oxygen,  54. 
Ozonising  tube,  54. 

P,  PHOSPHORUS,  221. 

Paint   blackened  by  hydrosulphuric   acid, 
197. 
luminous,  279. 
removed  from  clothes,  458. 
Paintings,  effect  of  light  and  air  on,  197. 
Palladamine,  hydrochlorate,  397. 
Palladium,  Pd,"397. 

carbide,  397. 
chlorides,  397. 
cyanide,  397. 
nitrate,  397. 

occlusion  of  hydrogen  by,  40. 
oxides,  397. 
Palmitic  acid,  520. 
Palmitine,  CgiHggOg,  573. 

synthesis  of,  576. 
Palm-oil,  573,  581. 

bleaching  of,  581. 
Pancreatic  juice,  635. 
Panification,  499. 
Papaverine,  540. 
Paper,  470. 

action  of  nitric  acid  on,  507. 
dissolved   by  ammonio-cupric  solu- 
tion, 362. 
Paper  for  cheques,  &c.,  493. 

for  photographic  printing,  213. 
Paracyanogen,  443. 
Paraflin,  CigHji,  472. 

extraction,  472. 
oil,  474. 
series,  526. 
Paraguay  tea,  598. 
Paraldehyde,  557. 
Paramylene,  521. 
Paranaphthalene,  469. 
Paraniline,  547. 
Parasorbic  acid,  591. 
Paratartaric  acid,  590. 
Parchment,  594. 

size,  622. 
vegetable,  502. 
Paris  yellow,  377. 
Parsley,  essential  oil  of,  476. 
Partial  saturation,  metliod  of,  571. 
Parting  of  gold  by  sulpluiric  acid,  209. 
Passive  state  of  metals,  321. 


668 


INDEX. 


Patent  yellow,  377. 

Pattinson's  process,  369. 

Paviine,  4S6. 

Paying  stones,  411. 

Pb,  lead,  365. 

PbClij,  chloride  of  lead,  376. 

Pbl.,,  iodide  of  lead,  377. 

PbO,  i)rotoxide  of  lead,  372. 

PbO.CrOs,  chroniate  of  lead,  332. 

PbO.SOa,  sulphate  of  lead,  376. 

PbS,  sulphide  of  lead,  377. 

Pd,  palladium,  397. 

Pea  iron  ore,  300. 

Pear  flavour,  556. 

Pearlash,  257. 

Pearl  hardener,  279. 

Pearls,  73. 

Pearl-spar,  283. 

Pearl  white,  BiCi^,  BiaOg,  337. 

Peas,  614. 

Peat-bog,  70. 

composition,  433. 
Pectic  acid,  C32. 
Pectine,  632. 
Pectose,  632. 
Pectosic  acid,  632. 
Pelargonic  acid,  519. 
Pentanes,  isomeric,  439. 
Peutathionic  acid,  215. 
Pentethylene  -  tetrethyl  -  tetriammonium,  hy- 
drate, 548. 
Pepper,  essential  oil  of,  476. 
Peppermint,  essential  oil  of,  477. 
Pepsine,  634. 
Peptones,  635. 
Perchlorates,  166. 
Percliloric  acid,  166. 

hydrated,  166. 
ether,  527. 
Perchlorokinone,  598. 
Perchromic  acid,  333. 
Percussion  cap  composition,  449. 

fuze,  165. 
Perfume  ethers,  556. 
Perfumes,  extraction  of,  476. 
Periclase,  283. 
Pericllne,  295. 
Periodates,  178. 
Periodic  acid,  178. 

classification,  256. 
Permanent  ink,  382. 

white,  275. 
Permanganate  of  potash,  KMn04,  329. 
Permanganic  acid,  329. 
Perspiration  of  the  skin,  569. 
Persul})huric  acid,  215. 
Peruvian  bark,  597. 

saltpetre,  NaNOo,  414. 
Petalite,  271. 
Petinine,  548. 
Petrifying  springs,  47. 
Petroleum,  98,  473. 
Peucvle,  475. 
Pewter,  346. 
Phenanthraquinone,  469. 
Phenantlireue,  469. 
Phenic  acid,  464. 
Phenole,  CgHgO,  464. 
Phenoles,  465. 
I'henose,  459. 
Pheuylacetonitrile,  560. 


Phenylamlne,  459,  644. 
Phenylaniline,  544. 
Phenyle,  CgHs,  462. 

carbamine,  554. 
ether,  465. 
hydrate,  465. 
Phenylene-diamine,  546. 
Phenylene-ditolylene-triamine,  547. 
Phenylene-ditolylene-triethyl-triamine,  548. 
Phenylene  -  ditolylene  -  triphenyl  -  triamine. 

547. 
Phenylic  hydride,  466. 
Phenyl-toluylaniine,  544. 
Philosopher's  wool,  285. 
Phlogistic  theory,  157. 
Phlogiston,  157. 
Phloretine,  484. 
Phloridzeine,  485. 
Phloridzine,  484. 
Phloroglucol,  595. 
Phocenine,  584. 
Phosgene  gas,  COCIjj  I'O. 
Phosphamides,  236. 
Phosphates,  231. 
Phosphethylic  acid,  528. 
Phosphides,  226. 
Phosphine,  233. 
Phosphites,  232. 
Phosphodiamide,  236. 
Phosphoglyceric  acid,  576. 
Phosphomolybdate  of  ammonia,  334. 
Phosphomonamide,  236. 
Phosphor-bronze,  358. 
Phosphorescence,  224. 

prevented,  224. 
Phosphoric  acid,  231. 

anhydrou8,preparation,230. 
common,  2S1. 
dibasic,  231. 
di-hydrated,  231. 
glacial,  231. 
molybdic  test  for,  334. 
monobasic,  231. 
monohydrated,  231. 
tribasic,  231. 
trihydrated,  231. 
anhydride,  230. 
ether,  528, 
Phosphorised  oil,  224. 
Phosphorite,  222. 
Phosphorous  acid,  232. 
Pljpsphorus,  P,  221. 

action  of  potash  on,  234. 

allotropic  moditications,  225. 

amorphous,  225. 

and  oxygen,  24. 

bromides,  235. 

burnt  under  water,  167,  233. 

chemical  relations,  226. 

chlorides,  235. 

cyanide,  447. 

distUled,  225. 

fuze  composition,  228. 

iodides,  235. 

match-bottle,  224. 

occurrence  in  nature,  221. 

oxides,  228. 

oxychloride,  235. 

pentachloride,  235. 

action    of    am- 
monia on,  236., 


INDEX. 


669 


Phosphorus,  poisonous  properties,  226. 

precipitation  of  metals  by,  227. 
preparation,  222. 
properties,  223. 
red,  224. 
suboxide,  233. 
sulphides,  236. 
sulphochloride,  235. 
transformed  by  iodine,  235. 
trichloride,  235. 
vitreous,  223. 
Phosphotriamide,  236. 
Phosphovinic  acid,  528. 
Phosphurets,  226. 

Phosphuretted  hydrogen,  gaseous,  PH«,  233. 
analogy  with  am- 
monia, 234. 
composition,  233, 
liquid,  234. 
solid,  234. 
Photographic  baths,  recovery  of  silver  from, 

383. 
Photographic  printing,  213. 
Phthalic  acid,  468. 

anhydride,  469. 
Phyllocyanine,  602. 
Phylloxanthine,  602. 
Physetoleic  acid,  578. 
Picamar,  473. 
Picoline,  454. 
Picric  acid,  465. 
Picrocyamates,  466. 
Picrotoxiue,  485. 
Pig  iron,  306. 
Pilocarpine,  540. 
Pimelic  acid,  582. 
Pimple  metal  (copper),  357. 
Pine  apple  flavour,  556. 
Pinic  acid,  476. 
Pink  salt,  2NH4Cl.SnCli,  349. 
Pins  tinned,  345. 
Pipe-clay,  291. 
Piperine,  540. 
Pipette,  curved.  83. 
Pit  charcoal,  418. 
Pitch,  456,  473. 

mineral,  473. 
Pitchblende,  298. 
Pittacal,  473. 

Plants  and  animals,  reciprocity  of,  633. 
changes  after  death,  632. 
chemical  changes  in,  630. 
constructive  power  of,  633. 
food  of,  627. 
nutrition  of,  627. 
reducing  functions  of,  632. 
iiltimate  elements  of,  627. 
Plaster  of  Paris,  278. 

overbumt,  279. 
preparation,  278. 
Platammon  -  ammonium,    hydrated    oxide, 

550. 
Platammonium,  hydrated  oxide,  550. 
Platina,  muriate,  395. 
Platinamine,  396. 
Platinates.  394. 
Platinic  chloride,  PtCl4,  395. 
Platinised  asbestos,  143. 
Platinochloride  of  potassium,   2KCl.PtCl4, 

395. 
Platinoid  metals,  general  review  of,  399. 


Platinous  chloride,  PtCla-  ^95. 
Platinum,  Pt,  392. 

amalgam,  387. 

ammonio-chloride,  2NHiCl.PtCl.. 
395.  * 

and  rhodium  alloy,  397. 
attacked  by  sulphuric  acid,  209. 
bichloride,  PtCL,  395. 
black,  394. 
corroded,  394. 

by  arsenites,  240. 
by  phosphorus,  226. 
by  silicon,  117. 
crucible  heated,  115. 
extraction,  392. 
fulminating,  395. 
ores,  analysis,  399. 
oxides,  394. 

protochloride,  PtClg,  395. 
separation  from  iridium,  399. 
spongy,  .393. 

stills  for  sulphuric  acid,  207, 
sulphides,  397. 
tetrachloride,  PtCl4,  395. 
uses  of,  393. 
Platosamine,  hydrate,  396. 

hydrochlorate,  396. 
sulphate,  396. 
Plato-triethyle-arsonium,  chloride,  550. 
-phosphonium,  550. 
-stibonium,  550. 
Plumbago,  63. 
Plumbic  acid,  375. 
Pneumatic  trough,  90. 
P2O3,  phosphorous  anhydride,  232. 
P.20g,  phosphoric  anhydride,  230. 
Poison-nut,  600. 
Pole,  negative,  8. 
positive,  8. 
Pollux,  273. 
Polyammonias,  545. 
Polyatomic  alcohols,  561. 
PolyhaZite,  282. 

Polymerising  by  sulphuric  acid,  456. 
Polymerism,  439. 
Poplar,  oil  of,  476. 
Populine,  484. 
Porcelain,  410. 

English,  410. 
glazed,  410. 
painting,  410. 
Porous  cell  experiment,  19. 
Porphyry,  295. 
Porter,  composition,  498, 
Portland  cement,  413. 

stone,  412. 
Port  wine  crust,  515.   " 

effect  of  keeping,  515. 
Positive  pole,  8. 
Potash-albite,  295. 
Potash,  KHO,  259. 

bicarbonate,  KHCO3,  260. 
bichromate,  Ko0.2Cr03,  331. 
bisulphate,  KHSO4,  135,  211. 
bitartrate,  257,  588. 
bi-urate,  625. 
bulbs,  84. 
caustic,  258. 
chlorate,  KCIO3,  163. 
chromate,  KsO.CrOj,  331. 
from  wool,  257. 


670 


INDEX. 


Potash,  fused,  258. 

hydriodate,  180. 
ill  flesh,  620. 
nitrate,  413. 
periiiauganate,  329. 
pnxssiate,  K^CygFe,  440. 
quadroxalate,  587. 
red  prussiate,  446. 
sulphate,  K.,S04,  211. 
tartrate,  K2C4_H.06,  588. 
Potassamide,  NHaK,  553. 
Potassium,  K,  257. 

action  on  water,  11. 

alcohol,  530. 

amidide,  553. 

antimoniate,  KSbOj,  339. 

arsenite,  240. 

atomic  weight,  274. 

aurate,  408. 

biautimoniate,  340. 

bicarbonate,  260. 

binietantimoniate,  340. 

blowpipe  test  for,  259. 

bromate,  173. 

bromide,  173. 

carbonate,  K2CO3,  257. 

chlorate,  KCIO3, 163. 

chloride,  KCl,  260. 

solubility,  418. 

chromate,  K2Cr04,  331. 

cyanate,  KCNO,  449. 

cyanide,  KCN,  444. 

dichromate,  K2Cr207,  331. 

ethyle,  536. 

extraction,  258. 

ferricyanide,  KsCgNgFe,  446. 

ferrocyanide,  K4CgNgFe,  440. 

fulminurate,  456. 

hy.lrate,  KHO,  258. 

iodate,  176. 

iodide,  KI,  180. 

isocy  an  urate,  456. 

manganate,  328. 

mercaptan,  531. 

metantimoniate,  340. 

raetastatmate,  348. 

nitrate,  KNO3,  413. 

oleate,  573. 

osmite,  398. 

oxalates,  587. 

perchlorate,  166. 

permanganate,  329. 

peroxide,  416. 

platinochloride,  395. 

properties,  259. 

sUicofluoride,  185. 

sulpharsenite,  245. 

sulphate,  K2S0^,  211. 

sulphide,  KsS,  426. 

sulphocvanide,  KCNS,  450. 

tartrate,  588. 

test  for,  42. 

trichromate,  332. 

tri-iodide,  181. 

trithionate,  214. 

urate,  625. 
Potato,  composition,  490. 
spirit,  516. 

starch,  extraction,  490. 
Pottery.  409. 
Press  cake,  420. 


Pressure  of  gases,  18. 
Preston  salts,  268. 
Promethean  light,  167. 
Proof  spirit,  522. 
Propione,  559. 

Propionic  (propylic)  acid,  519. 
Propionitrile,  551. 
Propylamine,  548. 
Propylene,  521. 
Propylene-glycol,  564. 
Propylic  acid,  HC^HgOj,  519. 

artificial  formation,  536. 
alcohol,  518. 
Proteine,  618. 

Proximate  organic  analysis,  455. 
Prussian  blue,  Fe4Fcy3,  441. 

constitution,  441. 
decompositiou     by    alkalies, 

441. 
native,  323. 
preparation,  441. 
soluble,  441. 
Prussiate    of   potash,   action  of   sulphuric 

acid  on,  90. 
Prussic  acid,  HCy,  442. 

in  bitter  almond  oil,  481. 
of  the  PhannacopcEia,  442. 
Pseudo-carbons,  64. 
Psilomelane,  327. 
Pt,  platinum,  392. 
PtClg,  platinous  chloride,  395. 
PtCl4,  platinic  chloride,  395. 
Ptomaines,  639. 
Ptyaline,  634. 

Puddled  bar,  composition,  312. 
bars,  311, 
steel,  319. 
Puddling,  disadvantages  of,  313. 
dry,  313. 
loss  in,  312. 
mechanical,  313. 
process  of,  310. 
Pulvis  fulminans,  417. 
Pumice  stone,  291. 
Purbeck  stone,  412. 
Purple  of  Cassius,  405.         , 
Purpurine,  604. 
Putrefaction,  72. 

ammonias  furnished  by,  648. 
modem  researches  on,  639. 
Putty  powder,  348. 
Pyrene,  469. 
Pyridine,  454. 
Pyrites,  arsenical,  236. 

caviUary,  NiS,  327. 
efflorescent,  202. 
extraction  of  sulphur  from,  189. 
Fahlun,  219. 
oxidation  in  air,  202. 
white,  202. 
Pyrogallic  acid,  595. 
Pyrogalline  or  pyrogallol,  595. 
Pyi-oligneous  acid,  C2H4O2,  470. 

ether,  471. 
Pyrclusite,  Mn02,  327. 

preparation    of    oxygen    from, 
32. 
Pyromucic  acid,  569. 
Pyrophoric  iron,  91. 
PjTophorus,  lead.  373. 
Pyrophosphates,  231. 


INDEX. 


671 


Pyrophosphoric  acid,  2H2O.P2O5,  231. 
Pyroterebic  acid,  578. 
Pyroxylic  spirit,  471. 
Pyroxyline,  507. 

QUANTIVALKNCE,  247. 

Quantity  and  tension,  electric,  9. 
Quartation  of  gold,  402. 
Quartz,  113. 

artificial,  115,  528. 
Quercetiue,  485. 
Quercitannic  acid,  592. 
Qiiercitrine,  485. 
Quercitrou,  610. 
Quicklime,  CaO,  43. 
Quicksilver,  384. 
Quinamine,  598. 
Quince-seed,  490. 
Quinic  acid,  598. 
Quinidine,  597- 

extraction,  597. 
Quinine,  C00H04N.2O.,  597. 

amorphous,  597. 

extraction,  597. 

sulphate,  598. 
Quinoidine,  597. 
Quinoline,  467. 
Quinone,  598. 
Quinotannic  acid,  597. 

Racemic  acid,  590. 
Radicals,  alcohol,  524. 
Radishes,  essential  oil  of,  485. 
Railway  bars,  312. 
Rain  water,  343. 
Raisins,  503. 
Rancid  oils,  582. 
Rangoon  tar,  473. 
Rational  formulae,  85,  435. 
Realgar,  AS2S2,  244. 
Reaumur's  porcelain,  408. 
Reciprocal  combustion,  38. 
Red  copper  are,  CU2O,  361. 
Red  dyes,  609. 

fire,  composition  for,  165. 

flowers,  colouring  matter  of,  603. 

lead,  Pb304,  374. 

-ore,  PbO.CrOs,  332. 

liquor,  265. 

ochre,  300. 

orpiment,  244. 

paints,  391. 

precipitate,  387. 

-shortness,  314. 

silver-ore,  SAgjS.AsgSs,  237. 

sulphide  of  antimony,  341. 
Reduced,  30. 

Reducing  blowpipe  flame,  109. 
Reduction  of  metals  by  carbonic  oxide,  91. 

on  charcoal,  110. 
Refinery,  309. 
Refining  cast-iron,  309. 
Refraction  of  saltpetre,  413. 
Refrigerator,  Carre's,  127. 
Regulus,  354. 
Regulus  of  antimony,  338. 
Rennet,  613. 
Resins,  478. 

Resists  (calico-printing),  610. 
Resorcine,  469. 
Respiration,  72. 


Respiration,  formation  of  carbonic  acid  in, 
72. 
in  confined  air,  76. 
Retoi't,  51. 
Rhahdophane,  297. 
Rhodium,  Ro,  397. 

oxides,  398. 
sesquichloride,  398. 
sodiochloride,  398. 
sulphides,  398. 
Rice,  composition,  490. 
Ricinoleic  acid,  583. 
Rinman's  green,  325. 
Rising  of  bread,  500. 
Rivers,  self-purifying  power  of,  44. 
River-water,  44. 
Ro,  rhodium,  397. 
Roasting,  effects  on  sulphides,  198. 

meat,  621. 
RocheUe  salt,  KNaC4H406,  589. 
Rock  crystal,  113. 
ml,  473. 
salt,  260. 
disintegration,  80. 
Roman  cement,  413. 
Rosaniline,  460. 

acetate,  461. 

action  of  potassium  cyanide  on, 

triethylic,  462. 

triphenylic,  462. 
Rosette  copper,  357. 
Rosiclers,  384. 
Rosin,  476. 

soap,  476. 
Rosolic  acid,  454. 
Rotation  of  crops,  630. 
Riibian,  603. 
Rubidia,  273. 
Rubidium,  Rb,  273. 

platinochloride,  395. 

properties,  273. 

separation  from  potassium,  395. 
Rid)y,  293,  332. 

glass,  404. 
Rue,  essential  oil  of,  558. 
Rufigallic  acid,  595. 
Ruhmkorfi^'s  induction-coD,  10. 
Rum,  516. 
Rust,  2Fe203.3H20,  321. 

ammonia  in,  132. 
Rusty  deposit  in  waters,  51. 
Ruthenic  acid,  399. 
Ruthenium,  Ru,  398. 
Rutic  acid,  519. 

alcohol,  518. 
Rutile,  TiO,,  350. 
Rye  fiour,  5'01. 

S,  SULPHUR,  187. 
Saccharide,  506. 
Saccharine  matters,  501. 
Safety-lamp,  behaviour  in  mines,  101. 

Davy's,  101. 

precautions  in  using,  102. 

Stephenson's,  100. 
Safilower,  603. 
Saffron,  603. 
Sago,  492. 
Salad  oil,  581. 
Sal-alembroth,  388. 


672 


INDEX. 


Sal-ammoniac,  NH4CI,  124. 

action    on    metallic    oxides, 

270. 
composition  by  volume,  270. 
vapour-density  of,  270. 
Saleratus,  NaHCOg,  265. 
ikil  (jein,  260. 
Salicine,  482. 

derivatives,  482. 
Salicyle,  CVH5O2,  483. 
hydride,  483. 
Salicylic  acid,  HC7H5O3,  483. 
Salicylate,  potassium,  465. 
Saligenine,  482. 
Saline  waters,  50. 
Saliretine,  483. 
Saliva,  634. 
Sal-polychrest.  211. 
Sal-prunelle,  416. 
Salt-cake,  267. 
Salt  as  manure,  629. 
common,  260. 
definition,  28. 
etymologj',  249. 
extraction,  260. 
fused,  157. 

-gardens  of  Marseilles,  261. 
-glazing,  410. 
of  lemons,  587.  z 

of  sorrel,  587. 
of  tartar,  257. 
preservative  effect,  639. 
table-.  262. 

useful  applications,  262. 
Salting  of  meat,  621. 
Saltpetre,  KNO3,  413. 

as  manure,  629. 

cubical,  NaNOa,  414. 

-flour,  415. 

impurities,  416. 

prepared   from    .sodium    nitrate, 

414. 
properties,  416. 
refining,  415. 
tests  of  purity,  416. 
Salt-radicals,  186. 
Salts,  acid,  251. 
basic,  251. 
constitution  of,  249. 
definition,  249. 
double,  constitution,  251. 
haloid,  186,  250. 
mutual  decomposition  of,  414. 
neutral,  250. 
normal,  250. 
oxyacid,  250. 

water-t\7)e  theory  of,  251. 
Sal-volatile,  269.  '  * 

Samorskite,  297. 
Sand,  113. 
Siindaracli,  478. 
Sandstone,  411. 

Craigleith,  411. 
Sanitas,  476. 
Sap  of  plants,  631. 
Saponification  by  steam,  575. 

sulphuric  acid,  574. 
theory  of,  572. 
Sajwnine,  485. 
&ipph{re,  293. 
Sarcosine,  CsHyNOj,  620. 


Satin  spar,  277. 

Saturated  solution,  40. 

Savin,  essential  oil  of,  476. 

Saxon  sulphuric  acid,  202. 

Saxony  blue,  607. 

Sb,  antimony,  337. 

SbClg,  antimony  trichloride,  341. 

SbClj,  pentachloride  of  antimony,  341. 

SbjOg,  antimonious  oxide,  339. 

SbjOj,  antimonic  oxide,  339. 

Sl^Ss,  antimony  trisulphide,  341, 

Scammony,  487. 

Scarlet  dyes,  609. 

Scheele's  green,  CuHAsOj,  241. 

prussic  acid,  442. 
Scheelite,  351. 
Schlippe's  salt,  342. 
Scotch  pebbles,  113. 
Scott's  cement,  413. 
Scrubber,  453. 
Scurvy-grass,  oil  of,  486. 
Se,  selenium,  219. 
Seal-oil,  584. 
Sea- water,  51. 

extraction  of  salt  from,  261. 
Sea-weed,  175. 
Sebacic  acid,  582. 
Secretion,  636. 
Sedative  .salt,  120. 
Seeds,  composition,  630. 

germination,  494 
Sefstrom's  furnace,  321. 
Sel  d'or,  405. 
Selenic  acid,  SeOg,  220. 
Selenides,  219. 
Selenietted  hydrogen,  220. 
Selenious  acid,  SeO.2,  220. 
Selenite,  278. 
Selenium,  Se,  219. 

chlorides,  220. 
sulphides,  220. 
Sellaite,  184. 
Seltzer  water,  50. 
Separating  funnel,  96. 
Sericine,  622. 
Serpentitte,  283. 
Serum,  616. 
Shaft,  downcast,  78. 

upcast,  78. 
Shamoving,  593. 
Shear-s'teel,  317. 

Sheep-dipping  compositions,  240. 
Shell-lac,  478. 
Sherry,  516. 
Shot,  372. 
Si,  silicon,  113. 
Sicilian  sulphur,  187. 
Siemens'  induction-tube,  54. 

regenerative  furnace,  434. 
Sienna,  291. 

SiF4,  silicon  fluoride,  184. 
Signal-light  composition,  245. 
Silica,  SiOa,  113. 

amorphous,  115. 

crystalline,  115. 

dissolved  by  hydrofluoric  acid,  183. 

gelatinous,  preparation,  185. 

in  plants,  113. 

in  waters,  113. 
Silicate  of  alumina  and  soda,  295. 
soda,  114. 


INDEX. 


673 


Silicated  soap,  573. 
Silicates,  116. 
Silicic  acid,  117. 

solution  of,  115. 
ether,  528. 
Silicide  of  magnesium,  119. 
Silicium,  117. 

ethyle,  538. 
methyle,  538. 
Silicofluoric  acid,  185. 
Silicon,  Si,  lia 

action  of  hydrochloric  acid  on,  171. 
amorphous,  117. 
and  nitrogen,  118. 
chloride,  SiClj,  170. 
disulphide,  218. 
fluoride,  SiF^,  184. 
fluoride,  preparation,  184. 
fused,  118. 
graphitoid,  117. 
hydride,  118. 
Silicone,  119. 
Silk,  622. 
Silver,  Ag,  378. 

action  of  hydrochloric  acid  on,  160. 
hydrosulphuric     acid     on, 
196. 
amalgam,  387. 
arsenite,  240. 
basic  periodate,  178. 
bromide,  AgBr,  384. 
chloride,  AgCl,  383. 

action  of  light  on,  213. 
reduction  of,  383. 
cleaned,  196. 
coin,  380. 
crucibles,  382. 
detected  in  lead,  372. 
extracted  from  its  ores,  379. 
extraction  by  amalgamation,  379. 
from  copper-ores,  379. 
lead,  370. 
frosted,  380. 

fulminate,  AgaCjNjOj,  450. 
fusing- point,  381. 
fulminating,  384. 
glance,  AgoS,  384. 
hyposulphite,  213. 
in  lead,  369. 
iodide,  178. 
metaphosphate,  232. 
native,  379. 
nitrate,  AgNOj,  382. 

preparation    from    standard 
silver,  382. 
nitride,  382. 
ore,  red,  384. 
oxalate,  587. 
oxide,  Ag.>0,  382. 
oxides,  382. 
oxidised,  380. 
periodate,  178. 
plate,  380. 
l>roperties,  381. 
pure,  preparation,  381. 
pyi'ophosphate,  232. 
recovered  from  photographic  baths, 

383. 
refining,  371. 

separated  from  copper,  379. 
solder,  380. 


Silver,  stains  removed,  382. 
standard,  380. 
subchloride,  383. 
sulphide,  Ag2S,  384. 
native,  384. 
tarnished,  196. 
tree,  387. 

triphosphate,  231. 
Silvering  brass  or  copper,  381. 
dry,  381. 
glass,  381. 
Simple  solution,  40. 
SiOg,  sUica,  113. 
Siphon  eudiometer,  36. 
Size,  622. 

Slag,  blast  furnace,  composition,  305. 
iron  in,  308. 
iron-refinery,  309. 
lead-furnace,  367. 
metal  (copper),  355. 
ore-furnace,  354. 
puddling-furnace,  312. 
refinery  (copper),  356. 
roaster  (copper),  355. 
Slaked  Ume,  Ca(H0)2,  278. 
Slaking  of  lime,  43. 
Slate,  291. 
Slow  portfire,  416. 
Sraalt,  325. 
Smelling-salts,  268. 
Smoke,  cause  of,  70. 

consumption,  70. 
prevention,  70. 
Smokeless  gas-burners,  107. 
Sn,  tin,  342. 

SnCLj,  protochloride  of  tin,  348. 
SnCl4,  bichloride  of  tin,  348. 
SnO,  protoxide  of  tin,  347. 
SnOj,  binoxide  of  tin,  347. 
Snow,  52. 

SnS,  protosnlphide  of  tin,  349. 
SnS2,  bisulphide  of  tin,  249. 
Snulf,  602. 

502,  sulphurous  anhydride,  198. 

503,  sulphuric  „  202. 
Soap,  572. 

arsenical,  240. 

Castile,  573. 

glycerine,  573. 

mottled,  573. 

-nut,  485. 

palm-oil,  573. 

rosin  in,  573. 

silicated,  573. 

transparent,  573. 

-wort,  485. 

yellow,  573. 
Soaps  decomposed  by  acids,  574. 
Soda,  NaHO,  265. 

action  on  hard  waters,  48. 

arseniates,  242. 

ash,  263. 

manufacture,  263. 

biborate,  266. 

bicarbonate,  265. 

bimetantimoniate,  340. 

bitungstate,  351. 

carbonate,  Na^O.COo,  265. 

manufacture  from  common 

salt,  262. 
medicinal,  265. 

2  u 


674 


INDEX. 


Soda,  caustic,  NaHO,  265. 
chloride,  163. 
common  phosphate,  2Na2O.H2O.P2O5, 

231. 
crystals,  263. 
hydrate,  265. 
hyposulphite,  Na2S203,  212. 

use    m     photography, 
213. 
in  blood,  618. 
-lime,  131. 
-lye,  265,  572. 
manufacture  of,  history,  262. 

influence     on     useful 
arts,  263. 
nitrate,  268,  414. 

conversion     into    nitrate    of 

potash,  414. 
solubility,  414. 
obtained  from  kyrolite,  265. 
sulphate,  Na.,0.S03,  267. 

extracted   from    sea-water, 
261. 
washing,  263. 
-waste,  264. 
-water,  80. 

powders,  80. 
Sodacetic  ether,  570. 
Sodanfide,  NHLNa,  553.      - 
Sodium,  Na,  260. 

action  on  water,  13. 
alcohol,  531. 
aluminate,  294. 
amalgam,  131. 
and  oxygen,  27. 
arseniates,  242. 
arsenite,  240. 
aurochloride,  405. 
blowpipe  test  for,  265. 
borate,  266. 
carbonate,  265. 
chloride,  260. 

commercial  importance,  147. 
solubility,  414. 
equivalent  weight,  13. 
ethylate,  531. 
ethyle,  53^. 
extraction,  265. 
fluoride,  184. 
glycol,  562. 
hydrate,  NaHO,  265. 
hydrosulphite,  214. 
hypochlorite,  163. 
hypophosphite,  233. 
hyposulphite,  Na2S20o,  212. 
line  in  the  spectrum,  273. 
manganate,  328. 
metapho-spliate,  231. 
nitrate,  414. 

solubility,  414. 
nitroprusside,  447. 
oleate,  573. 
palmitate,  573. 
peutasulijhide,  214. 
periodate,  178. 
phosphate,  NajHPOi,  231. 
platiuate,  394. 
platinochloride,  395. 
pyrophosphate,  232. 
silicate,  267. 
silicortuoride,  117. 


Sodium,  stannate,  578. 

stearate,  573. 

sulphantimoniate,  197. 

sulpharseniate,  197. 

sulphate,  NagSOi,  267. 

sulphite,  201. 

sulphostannate,  197. 

sulphoxyphosphate,  235. 

tetrathionate,  214. 

tungstate,  Na.,WOj,  351. 

urate,  625. 
Soffioni,  120. 

artificial,  120. 
Softening  waters,  48. 
Soft  soap,  573. 

Soils,  formation,  80,  628. 
impoverished,  628. 
iron  in,  322. 
Solanine,  540. 
Solder,  346. 

brazier's,  360. 
coarse,  346. 
fine,  346. 

silversmith's,  380. 
Soldering,  use  of  sal-ammoniac  in,  271. 
Soluble  glass,  267. 
Solution,  40. 
Soot,  71. 

as  manure,  622. 
Sorbic  acid,  691. 
Sorbite,  507. 
Sorrel,  salt  of,  587. 
Soup,  621. 
Spanish  black,  64. 
Sparkling  wines,  80. 
Sparteine,  540. 
Spathic  iron  ore,  FeCOs,  301. 
Specific  gravity  of  gases  defined,  16,  23. 

influence    of   tem- 
perature on,  193. 
liquids,  defined,  52. 

determined,  126. 
solids,  defined,  52. 
Specific  heat  defined,  43l. 

relation    to    atomic    weights, 
283. 
Specific  heats  of  potassium,  sodium,  and 

lithium,  280. 
Spectroscope,  272. 
Spectrum  analysis,  272. 

use  of  carbon  disulphide 
in,  216. 
Specular  iron  ore,  FeoOj,  300. 
Speculum  metal,  347,  360. 
Speiss.  325. 
Spelter,  286. 
Spermaceti,  584. 
Sperm  oil,  584. 
Spheroidal  state,  199. 
Spices,  preservative  effect  of,  639. 
Spiegel-eisen,  319. 
SpineUe,  MgO.AL.Os,  293,  322. 
Spirit,  methylated,  479. 
of  salt,  148. 
of  Avine,  522, 
Spirits,  516. 

of  turpentine,  474. 
Spiritus  rectihcatuR,  522. 

tenuior,  522. 
Spirting  avoided,  116. 


INDEX. 


675 


Sponge,  622. 

ashes  of,  175. 
Spongy  platinum,  392. 
Spontaneous  combustion  of  oils,  583. 

phosphorus,  24. 
Springs,  petrifying,  47. 
Spring  water,  43,  80. 
Sprouting  of  silver,  371. 
Sr,  strontium,  276. 
SrjCOs,  strontium  carbonate,  276. 
SrO,  strontia,  279. 
Sr(N03)2,  strontium  nitrate,  276. 
SrS04,  strontium  sulphate,  276. 
Stains  of  fruit  removed,  200. 
Stalactites,  47. 
Stalagmites,  47. 
Stannates,  348. 
Stannic  acid,  348. 

dialvsed,  348. 
chloride,  SnCl4,  349. 
oxide,  SnOa,  347. 
sulphide,  SnS^,  349. 
Stannous  chloride,  SnCU,  348. 
oxide,  SnO,  347. 
sulphide,  SnS,  349. 
Star  antimony,  337. 
Starch,  CfiHioOg,  490. 

action  of  water  on,  492. 
a  gluuoside,  496. 
and  iodine,  177. 
blue,  296. 
commercial,  491. 
extraction  from  potatoes,  490. 
rice,  491. 
wheat,  491. 
from  different  plants,  distinguished, 

491. 
in  food,  492. 
iodised,  493. 
paste,  preparation,  55, 
Stassfurthite,  260,  414. 
Steam,  composition  by  volume,  36. 
decomposed  by  carbon,  89. 

chlorine,  153. 
electric  sparks,   10. 
heat,  10.- 
latent  heat  of,  432. 
specific  gravity  calculated,  53. 
Stearic  acid,  HCigHjsOa,  520,  574. 

glucose,  579. 
Stearine,  CgyHuoOg,  572. 
candles,  574. 
s\Tithesis  of,  575, 
Steatite,  281. 
Steel,  315. 

annealing,  317. 

Bessemer,  318, 

blistered,  316. 

cast,  317. 

distinguished  from  iron,  318. 

German,  319. 

hardening,  317. 

Krupp's,  319. 

made  with  coal  gas,  318. 

manufacture,  315. 

natural,  319. 

nitrogen  in,  318. 

piuldled,  319. 

shear,  317. 

temperintj,  317. 

tilted,  316. 


Steel,  titanium'in,  318. 
Stereochromy,  267. 
Sterro-metal,  360. 
Stibethyle,  Sb(C.jHg)3,  537. 
Stibiotriethyle,  537. 
Stibio-trimethyle,  537. 
Still,  51. 

Stockholm  tar,  473. 
Stone,  artificial,  267- 
-coal,  71. 
decayed,  412. 
test  of  durability,  412. 
-ware,  410. 
Storax,  477. 

Stout,  composition,  498. 
Straits  tin,  344. 
Stream-tin  ore,  342. 
Strontia,  276. 
Strontianite,  276. 
Strontium,  Sr,  276. 

carbonate,  276. 
nitrate,  SrfNOa)^,  276. 
properties,  276. 
sulphate,  276. 
sulphide,  276. 
Structural  formula,  436. 
Struvite,  283. 

Strychnine,  C21H22N2O.,,  600. 
extraction,  601. 
identified,  601. 
properties  of,  601, 
Stucco,  279. 
Styracine,  477. 
Styrole,  478. 
Styrolene,  95,  478. 
Suberic  acid,  582. 
Suberine,  489. 
Sublimate,  corrosive,  388. 
Sublimation,  124,  479. 
Sublimed  sulphur,  419. 
Substitution,  154. 

of  chlorine  for  hydrogen,  467. 
Substitutive  formulae,  87. 
Succinic  acid,  H2C4H4O4,  478,  582. 

conversion  into  tartaric,  589. 
formed  from  tartaric,  589. 
synthesis  of,  590. 
Suecussion,  207. 
Suet,  584. 

Sugar,  action  of  oil  of  vitriol  on,  208. 
adulteration,  501. 
-candy,  505. 
-cane,  composition,  503. 
extraction,  503. 
from  beet-root,  505. 
linen,  &c.,  502. 
-lime,  506. 
loaf,  505. 
maple,  505. 
of  flesh,  620. 
of  fruits,  CeHioOg,  503. 
of  gelatine,  622. 
of  manna,  506. 
of  milk,  CiaHoiOjo,  614. 
preservative  effect  of,  639. 
raw,  504. 
-refining,  504. 
starch,  501. 
uncrystallisable,  .503. 
with  lead  oxide,  506. 
with  sodium  chloride,  506. 


676 


INDEX. 


Sugars,  501. 

chemical  properties,  505. 
optical  properties,  506. 
Sulphamylic  acid,  529. 
Sulphauthraquinonic  acid,  605. 
Sulphantimoniates,  342. 
Sulphantimonites,  342. 
Sulpharseuiate,  cuprous,  245. 
Sulpliarsenic  acid,  245. 
Sulpharsenious  acid,  245. 
Sulphate  of  sotla  and  lime,  267. 

crystallisation  of,  41. 
composition,  42. 
Sulphates,  210. 

acid,  211. 

action  of  heat  on,  211. 
double,  211. 
in  common  use,  211. 
native,  187. 
normal,  211. 

reduced  to  sulphides,  212. 
Sulphethylic  acid,  C2H6HSO4,  528. 
Sulphides,  197. 

action  of  air  on,  197. 
native,  187. 

precipitated    by    hyposulphites, 
213. 
Sulphindigotic  acid,  608. 
Sulphindylic  acid,  608. 
Sulphites,  201. 
Sulphobenzolic  acid,  464. 
Sulphocarbimides,  486. 
Su'phocarbonates,  217. 
Sulpliocarbonic  acid,  217. 
Sulphochromites,  333. 
Sulphocyauide  of  ammonium,  preparation, 

217. 
Sulphocyanogen,  CyS,  445, 
Sulphoglyceric  acid,  576. 
Sulpholeic  acid,  575. 
Sulphopalmitic  acid,  575. 
Sulphophosphotrianiide,  236. 
Sulphosaccharic  acid,  506. 
Sulphostearic  acid,  575. 
Sulphovinic  acid,  C2H5HSO4.  528. 
Sulphoxyphosphoric  acid,  235. 
Sulphur,  S,  187. 

-acids,  198. 

action  of  alkalies  on,  193. 

lime  on,  198. 
allotropic  states  of,  190. 
amorphous  or  insoluble,  190. 
and  oxygen,  26. 
bases,  197. 

chemical  relations,  193, 
chloride,  SaClg,  219. 
combining  volume,  193. 
dichloride,  SOU,  218. 
dimorphous,  192. 
distilled,  188. 
ductile,  191. 
electro-negative,  191, 
electro-positive,  191. 
examination  of,  419. 
extraction,  187. 

from      copper-pyrites, 

189. 
from  iron-pyrites,  189. 
from  soda-waste,  264. 
flowers  of,  188. 
for  gunpowder,  419. 


Sulphur,  function  in  gunpowder,  419. 
group  of  elements,  221. 
nome  sources  of,  189. 
iodide,  SI2,  219. 
milk  of,  190. 

occurrence  in  nature,  187. 
octahedral,  192. 
of  coal-mines,  102, 
ores,  187. 
oxides,  198. 

o.^'idised  and  dissolved,  193. 
by  nitric  acid,  137. 
plastic,  191. 
prismatic,  192. 
properties,  190. 
refining,  188. 
roll,  188. 
rough,  188. 
-salts,  197. 
subiodide,  S2I2,  219. 
sublimed,  188.' 
test  for,  448. 
uses,  190. 

vapour  density,  193. 
washed,  419. 
Sulphureous  waters,  50. 
Sulphuretted  hydrogen,  HoS,  194. 
Sulphuric  acid,  H2SO4,  202'. 

action  on  bromides,  174. 
copper,  199. 
fats,  575. 
fluor-spar,  182. 
lead,  207. 
metallic  oxides, 

210. 
metals,  209. 
organic  matters, 

209. 
silver,  209. 
anhydrous,  210. 

preparation,  210. 
caution  in  diluting,  208. 
attraction  for  water,  208. 
combinations     with    water, 

209. 
concentrated,  208. 
concentration,  207. 
decomposition  by  heat,  210. 
diluted,  turbidity  of,  208. 
distillation  of,  207. 
formation,  203. 
from  the  chambers,  206. 
fuming,  202. 
glacial,  210. 
manufacture,  204. 

chemical  prin- 
ciples, 203. 
history  of,  203. 
illustrated, 

203. 
summary,  208. 
Nordhausen,  202. 
polymerising  by,  456. 
reduced  by  hvdriodic  aci<l, 

179. 
vapour-density  of,  210. 
anhydride,  210. 
ether,  522,  528. 
Sulphuringr  casks,  201. 
Sulphurous  acid,  H0SO3,  199. 

a  reducing  agent,  201- 


INDEX. 


677 


Sulphurous  acid,  action  on    hydrosulphuric 
acid,  215. 
nitric  acid,  203. 
nitric  peroxide, 

203. 
zinc,  214. 
propert;ies,  200. 
reduced    by   phosphorous 
acid,  232. 
anhydride,  198. 
Sulphuryle,  201. 
Sumach,  593. 

Superphosphate  of  lime,  222. 
Supersaturated  solution,  41. 
Swedish  iron  ore,  301. 
Sweet  oil,  581. 
Sweet  spirits  of  nitre,  527. 
Syenite,  296. 
Sylvic  acid,  476. 
Symbols,  4. 
Sympathetic  ink,  43. 
Synaptase,  480. 
Sjmthesis  of  acetic  acid,  536,  566. 

acids  of  the  acetic  series,  569. 
butyric  acid,  570. 
formic  acid,  568. 

fuanidine,  547. 
ippuric  acid,  627. 
hydrocyanic  acid,  95. 
leucic  acid,  563. 
natural  fats,  575. 
organic  substances,  92,  435. 
propylic  acid,  536. 
prussic  acid,  95. 
taurine,  635. 
urea,  623. 

volatile  fatty  acids,  569. 
water,  83. 

by  weight,  37. 

Tagilite,  363. 
Talc,  281. 
Tallow,  572,  584. 
Tank-waste,  212. 
Tannic  acid,  592. 
Tannin,  592. 
Tanning,  592. 
Taunomelanic  acid,  594. 
Tantalic  acid,  352. 
Tantalite,  352. 
Tantalum,  Ta,  352. 
Tap-cinder,  composition,  312. 
Tapioca,  492. 
Tar-charcoal,  419. 
Tar,  coal,  453. 

wood,  471. 
Tarragon,  essential  oil  of,  482. 
Tartar,  588. 

salt  of,  257. 
-emetic,  589. 
Tartaric  acid,  H2C4H4O6,  588. 

artificial  formation,  589. 
conversion    into    malic   acid, 

589. 
conversion  into  succinic  acid, 

589. 
formed   from    succinic    acid, 
589. 
anhydride,  588. 
Tartrate  of  potash  and  soda,  589. 
Taurine,  C2H-NO3S,  635. 


Taurine,  artificial  formation,  635. 
Taurocholic  acid,  635. 
Tawing,  593. 
Te,  tellurium,  220. 
Tea,  composition,  599. 
Telluretted  hydrogen,  221. 
Telluric  acid,  221. 
Telluride  of  bismuth,  220. 
Telluride  of  potassium,  220. 
Tellurium,  Te,  220. 

characterised,  221. 
foliated,  220. 
graphic,  220. 
sulphides,  221. 
Tellurous  acid,  221. 
Temper  spoilt,  318. 
Tempering,  colours  in,  318. 
Tenacity  of  copper,  301. 

iron,  301. 
Tendons,  621. 
Tennantite,  237. 
Terbia,  300. 
Terebene,  475. 
Terebilene,  475. 
Terne-plate,  345. 
Terpenes,  476. 
Terpinole,  475. 
Terstearine,  576. 
Test  tube,  32. 
Tetrad  elements,  248. 
Tetramethylium,  hydrate,  543. 
Telramines,  548. 
Tetramylium,  hydrate,  543. 
Tetrathionic  acid,  214. 
Tetratomic  elements,  248. 
Tetrethylarsoniura,  hydrate,  549. 
Tetrethylium,  hydrate,  NCCaHsJ^HO,  543. 

iodide,  542. 
Tetrethylphosphonium,  hydrate,  549. 
Tetrethylstibonium,  hydrate,  549. 
Tetrethyl-urea,  625. 
Thallium,  Tl,  377. 

alcohol,  531. 

extracted  from  flue-dust,  377. 
for  green  fire,  378. 
salts,  378. 
Theine,  C8H,oN402,  598. 
Thenardite,  267. 
Theobromine,  C7H8N4O2,  600. 

converted  into  caffeine,  600. 
Thiocarbonates,  217. 
Thionyle,  201. 
Thiosinnamine,  540. 
Thorina,  297. 
Thorinum,  Th,  297. 
Thorite,  297. 

Thyme,  essential  oil  of,  476. 
Tile  copper,  357. 
Tiles,  411. 
Tin,  Sn,  342. 

action  of  acids  on,  347. 

nitric  acid  on,  347. 

on  hydrosulphuric  acid,  196. 

water,  13. 

alloys  of,  346. 

amalgam,  387. 

bichloride,  Sna4,  349. 

biuoxide,  SnOo,  347. 

bisulphide,  Sn'S...,  349. 

boiling,  344. 

crystals,  348. 


678 


INDEX. 


Tin,  dichloride,  349. 
disulphide,  349. 
dropped,  344. 

extraction  in  the  laboratory,  344. 
foil,  345. 
grain,  344. 
identified,  344. 
impurities,  347. 
metallurgy  of,  342. 
nitromuriate,  SnCl4,  349. 
Tin-ore  of  Moniebras,  352. 
Tin-ores,  mechanical  treatment  of,  343. 
oxychloride,  349. 
plate,  345. 
properties  of,  344. 
protochloride,  SnGj,  348. 
protosulphide,  SnS,  349. 
protoxide,  SnO,  347. 
pure,  preparation,  347. 
pyrites,  SnS,  349. 
refining  bv  liquation,  344. 
salts,  348." 
sesquioxide,  348. 
stannate,  348. 
-stone,  SnOj,  342. 
tetrachloride,  349. 
Tin  tree,  349. 
Tincal,  119.  ^ 

refining  of,  266. 
Tinned  iron,  345. 
Tinning  brass,  345. 

copper,  345. 
Tin-iohite  cobalt,  CoAso,  324. 
Titanic  acid,  350. 

dialysed,  350. 

extracted  from  iron-sand,  350. 
hydrated,  350. 
properties,  350. 
Titanic  iron,  301. 
Titanium,  Ti,  350. 

bichloride,  350. 
bisulphide,  351. 
cvanonitride,  350. 
metallic,  350. 
nitride,  350. 
protoxide,  351. 
sesquichloride,  351. 
sesquioxide,  351. 
Tl,  thallium,  377. 
Toast,  492. 
Tobacco,  601. 
Tokay,  516. 
Tolu  balsam,  477. 

essential  oil,  476. 
Toluene-sulphonic  acid,  464. 
Toluidine,  461,  544. 
Toluene,  CyHg,  454. 
Tolylene,  547. 

diamine,  547. 
Tonka  bean,  484. 
Tojxiz,  184,  293. 
Touch-paper,  416. 
Touchstone,  137. 
Toughening  steel,  317. 
Translation,  rate  of,  18. 
Trap-rock,  296. 
Treacle,  503. 
Tree-wax  of  Japan,  585 
Triacetine,  565. 
Triacid  triamines,  547. 
Triad  elements,  248. 


Triamines,  547. 
Triamylamine,  543. 
Triatomic  elements,  248. 
Tribasic  formic  ether,  554. 
Tribasic  phosphates,  231. 

phosphoric  acid,  231. 
Tribenzoyl-phosphide,  552. 
Tribenzylamine,  560. 
Triborethyle,  B(C2H.)3,  537. 
Tribromo-phenoie,  465. 
Tricetylamine,  643. 
Trichloracetic  acid,  HC2CI3O2,  566. 
Trichloraniline,  550. 
Trichlorhydrine,  576. 

of  phenose,  459. 
Triethylamine,  N(C2H5)3,  542. 
Triethylarsine,  As(C.2H5)3,  536,  549. 
Triethylene  -  octethyl  -  tetrammonium,    hy- 
drate, 549. 
Triethylene-tetralcohol,  565. 
Triethylene-tetramine,  548. 
Triethylene-trianiine,  N3H3(C2H.)3,  547. 
Triethylphosphine,  PCCaHsk  549. 
Triethylstibine,  Sb(C2H5)3,  649. 
Trimethylamine,  548. 
Trimethylarsine,  536. 

glycocine,  622. 
Trinitro-cellulose,  509. 
Trinitrocresylic  acid,  466. 
Trinitrophenic  acid,  465. 
Triphane,  271. 
Triple  phosphate,  283. 
Tripotassamide,  NK3,  553. 
Trithionic  acid,  214. 
Tungsten,  W,  351. 

binoxide,  351. 

blue  oxide,  351. 

chlorides,  352. 

metallic,  352. 

separated  from  tin  ores,  344. 

steel,  352. 

sulphides,  352. 

test  for,  351. 
Tnngstic  acid,  351. 

dialysed,  351. 
Tungstoborates,  351. 
Turbith  or  turpeth  mineral,  388. 
Turkey  red,  603, 
Turmeric,  605. 

action  of  boracic  acid  on,  121. 
Tumbull's  blue,  Fe3Fdcy,  446. 
Turner's  yellow,  377. 
Turpentine,  CjoHi^,  474. 

action  of  nitric  acid  on,  138. 
hydrates,  475. 
hydrocarbons,  476. 
in  chlorine,  153. 
Turquoise,  296. 
Tuyere  pipes,  302. 
Type  furniture  alloy,  369. 
Type-metal,  336,  372. 
Types,  chemical,  247. 

Ulmate  of  ammonia  as  manure,  622. 
Ulmic  acid,  633. 
Ultramarine,  artificial,  296. 

green,  296. 
Umher,  291. 
Upcast  shaft,  78. 
Uranium,  U,  298. 

oxides,  298. 


INDEX. 


679 


Urea,  CH4N2O,  623. 
analysis  of,  131. 
artificial  formation,  623. 
chemical  constitution,  624. 
extraction  from  urine,  623. 
isomeric  with  ammonium  cyanate,  623. 
nitrate,  623. 
Ureides,  625. 
Uric  acid,  H2CgHoN403,  625. 

action  of  nitric  acid  on,  625. 
dibasic,  625. 
extraction,  625. 
Urine,  622. 

as  manure,  629. 
composition,  627. 
putrefaction  of,  623. 

Vacuum-pans,  504. 

VaUntinite,  339. 

Valerian,  essential  oil  of,  476. 

Valerianic  acid,  HCgHgOj,  519,  571. 

Valerian  root,  571. 

Valerine,  584. 

Valerolactic  acid,  563. 

Vanadic  acid,  335. 

Vanadium,  V,  335. 

chlorides,  335. 
ink,  335. 
metallic,  335. 
oxide,  335. 
Vauilline,  484. 
Vapour-densities,  influence  of  temperature 

on,  193. 
Vapour  densities  of  the  oleflnes,  521. 
Varnishes,  479. 
Vasculose,  469. 
Vaseline,  474. 
Vegetable  parchment,  209. 
Vegetation,  chemistry  of,  627. 
Venetian  red,  322. 
Venice  turpentine,  474. 
Ventilation,  illustrations  of,  78. 

necessity  for,  77. 
Veratrine,  540. 
Verdigris,  566. 
Verditer,  363. 
Vermilion,  HgS,  391. 
Vert  de  Guignet,  332. 
Vesta  matches,  167. 
Vinegar,  composition,  499. 

French,  499. 

malt,  499. 

manufacture,  498. 

mother  of,  499. 

sulphuric  acid  in,  499. 

white  wine,  499. 
Vinic  acids,  528. 
Viridine,  544. 
Vitelline,  619. 
Vitriol-chambers,  204. 

corrosive  properties  of,  208. 
Vivianite,  323. 
Volcanic  ammonia,  266. 
Volcano,  artificial,  193. 
Voltameter,  35. 

Volume  of  gas,  calculation  of,  16. 
Vulcanised  caoutchouc,  488. 
Vulcanite,  488. 

W,  TUNGSTEN,  351. 

Wad,  327. 


Walls,  efflorescence  on,  267. 
Washing  precipitates,  116. 
Wash-leather,  593. 

Watch-spring  for  burning  in  oxygen,  29. 
Water,  H2O,  7. 

action  upon  metals,  11. 
analysis,  7. 

chemical  relations  of,  40. 
crystallisation  of,  52. 
decomposed  by  battery,  7. 

heat,  10. 
distilled,  51. 
electrolysis  of,  7. 
from  natural  sources,  43. 
-gas,  89. 
hard,  45. 

of  constitution,  42. 
of  crystallisation,  Aq.,  42. 
oxygenated,  53. 
purification,  51, 
soft,  45. 
synthesis,  33. 
tested  for  impurity,  49. 
Waterproof  cloth,  487. 

felt,  488. 
Waters,  ammonia  detected  in,  390. 

mineral,  50. 
Water- type  theory  of  acids  and  salts,  251 . 
Watery  vapour,  52. 
WaveUite,  296. 
Wax,  bees',  585. 

bleaching,  585. 
Chinese,  584. 
Weld,  603. 
Welding,  315. 

Weldon's  chlorine  process,  148. 
Well-water,  44. 
Welsh  coal,  71. 
Whale-oU,  584. 
Wheat,  composition,  490. 

sprouted,  494. 
Wheaten  flour,  499. 
Whey,  614. 
Whisky,  516. 
White  gunpowder,  166. 
iron,  307. 
lead,  375. 

manufacture,  375. 
ore,  PbO.COa,  366. 
metal,  CugS,  355. 
precipitate,  NHoHgCl,  389. 

fusible,  389. 
vitriol,  288. 
Willow-bark,  bitter  principle,  482. 
Windows,  crystals  on,  268. 
Wine,  514. 
Wines,  dry,  515. 

fruity,  515. 

proportion  of  alcohol  in,  514. 
red,  515. 
ropy,  498. 
white,  515. 
Winter-green  oil,  472. 
Wire  iron,  312. 
Witherite,  BaO.CO«,  274. 
Wolfram,  342,  451." 
Wood,  carbonisation,  64. 
-charcoal,  64. 
combustion,  64. 
composition,  469. 
destructive  distillation,  65,  469. 


680 


INDEX. 


Wood,  for  gunpowder-charcoal,  418. 

-naphtha,  CH.O,  471. 

preservation  of,  633. 

-smoke,  639. 

-spirit,  471. 

-tar,  471. 
Woody  fibre,  469. 
Wool,  622. 

Wool  and  cotton,  separation,  622. 
Worm,  51. 
Wormwood,  479. 
Wort,  495. 
Wrought  iron,  308. 

Xylenes,  459. 

Xylene-sulphonic  acid,  464. 
Xylidine,  464. 
Xyloidine,  514. 
Xylole,  454. 

Yeast,  496. 

dried,  496. 
Yellow,  chrome,  332. 

dyes,  603. 

fire,  composition  for,  266. 

flowers,  603. 

ochre,  300. 

orpiment,  245. 

Paris,  377. 
Ytterbium,  297. 
Yttrium,  Y,  297. 
Yttrotantcdite,  352. 

Zaffre,  325. 
Zinc,  Zn,  284. 
Zinc-aoetimide,  553. 

action  of  air  on,  284. 

hydrochloric  acid  on,  159. 
sulphuric  acid  on,  288. 
on  water,  13. 


Zinc-alcohol,  535. 

-amalgam,  387. 

amalgamated,  386. 

amide,  553. 

amyle,  536. 

and  oxygen,  28. 

arsenide,  242. 

arsenite,  240. 

Ijoiling-point,  285. 

carbonate,  285. 

chloride,  289. 

dissolved  by  potash,  288. 

distilled,  285. 

ethyle,  Zn(C2H5)2,  536, 

extraction,  285. 

Belgian  method,  286. 
English  method,  285. 
Silesian  method,  287. 

granulated,  14. 

hydrosulphite,  214. 

hyposulphite,  214. 

identified,  288. 

impurities  in,  288. 

metallurgy  of,  285. 

-methyle,  535. 

nitride,  553. 

ores,  284. 

oxide,  ZnO,  288. 

in  glass,  408. 

oximide,  553. 

pheuylimide,  553. 

removal  of  lead  from,  287. 

sulphate,  ZnS04,  288. 

sulphide,  285. 

valerianate,  571. 
Zinc-white,  288. 
Zircon,  297. 
!  Zirconia,  297. 

Zirconium,  Zr,  297. 
I  ZnS,  zinc  sulphide,  283. 


ERRATUM. 

On  page  123,  line  32, /or  "  1872"  read  "1772." 


NF.ILL  AXD  COMPANT,  EDISBCROH, 
GOVJiR]{}IENT  BOOK  AHD  LAW   PRINTEBS  FOR  SCOTLAND 


CATALOGUE  NO.  1.  SEPTEMBER,  1884. 

CATALOGUE 


OF 


MEDICAL,  Dental,  Pharmaceutical 


AND 


SCIENTIFIC  PUBLICATIONS, 

PUBLISHED    BY 


P.BLAKISTON,  SON  4  C  0. 
IPUBllSHeRS.BOOKSEllURSairMPOhTCRSi 


P.  BLAKISTON,  SON  &  CO.. 

(SUCCESSORS    TO    LINDSAY   &    BLAKISTON) 

1012  WALNUT    STREET, 

PHILADELPHIA.. 


These  publications  may  be  had  through  Booksellers  in  all  the  principal  cities  of  the  Unite<J 
States  and  Canada,  or  any  book  will  be  seat,  postpaid,  by  the  publisher,  upon  receipt  of  price,  oi 
will  be  forwarded  by  express  C.  O.  D.  upon  receiving  a  remittance  of  25  per  cent,  of  the  amount 
ordered  to  cover  express  charges. 


MEDICAL    JOURNALS 

Published  by  P.  BLAKISTON,  SON  &  CO. 


THE  LONDON  MEDICAL  TIMES 

AND  GAZETTE. 

3Q  Pag^eai  "Weelcly  Ibr  ^S.OO  per  A^nnum,  Post-TVee. 

Commencing  with  the  number  for  January  5th,  1884,  the  London,"  ^^edical  Times 
and  Gazette  "  underwent  an  alteration  in  the  size  of  page,  that  makes  it  much  more  con- 
venient for  handling  and  binding.  A  clearer  type,  better  accommodated  to  the  eye,  has  been 
employed,  and  an  increase  in  the  number  of  pages  made,  thus  increasing  the  amount  of  reading 
matter.  The  contents  will  be  printed  on  the  first  page  of  reading  matter,  enabling  them  to 
be  bound  up  with  the  volume,  and  a  reduction  in  the  price,  of  one-half,  makes  it  at  once  one 
of  the  cheapest  and  best  Weekly  Medical  Papers  now  published. 

CON  TENTS. — The  coiuentsof  each  number  consist  of  several  original  Lectures  or  Contributions,  Reports  of 
Cases  from  the  large  London  or  British  Government  Hospitals,  Editorial  Notes  on  current  topics.  New  ^iethods 
of  Treatment  and  Research,  New  Discoveries,  Remedies,  Etc.  Leading  Articles,  Reviews  and  Book  Notices, 
.•Vbstracts  and  Selections,  Reports  of  the  London  and  Foreign  Medical  Societies,  Medical  Notes  and  News,  Etc. 
As  A  KEPRESK.\T.\T1VE  London  Journal  the  "  Medical  Times"  is  among  the  first,  and  its 
low  price,  compared  with  other  foreign  journals  of  the  same  size,  brings  it  within  the  reach  of 
every  physician  who  wishes  to  keep  acquainted  with  the  progress  of  Medical  Science  abroad  as 
well  as  at  home. 

THE  POLYCLINIC. 

A  monthly  Journal  of  Medicine  and  Surgery,  conducted  by  the  Faculty    of  the  Philadel- 
phia Polyclinic  and  College  for  Graduates  in  Medicine.     HENRY  LEFFMANN,  M.  D., 
Editor  in  Chief.     Published  on  the   15th  day  of  each  month.    Now  in  its  second  volume. 
Subscription,  per  annum,  ^i.oo. 

Partial  List  of  Contributors  to  Vol.  i. —  Dr.  J.  Solis-Cohen,  on  the  Throat,  Etc.; 
G.  C.  Harlan,  M.  D.,  Ophthalmolog)' ;  Prof.  Roberts  Bartholow,  Nervous  Prostration;  S.  Weir 
Mitchell  and  C.  K.  Mills,  M.  D.,  Nervous  Diseases;  Dr.  Arthur  Van  Harlingen,  Vice-Presi- 
dent of  the  American  Dermatological  Society,  on  Skin  Diseases;  Prof.  Jas.  Tyson,  The  Albu- 
min Test  Etc.;  Jas.  C.  W^ilson,  M.  D.;  Prof.  Theophilus  Parvin,  Obstetrical  Reports;  Drs.  John 
B.  Roberts  and  Thos.  G.  Morton,  General  Surgery  and  Hospital  Reports;  Dr.  J.  Henry  C. 
Simes,  Syphilis,  Chancre,  Urethritis,  Etc.;  Prof.  Henry  Leffmann,  Alcoholism,  Chemical  Notes, 
Poisoning,  Tests,  Hypnotism,  Etc.;  Charles  H.  Burnett,  M.  D.,  Otology;  Dr.  E.  O.  Shakespeare, 
and  others. 

contents. — Original  Clinical  Lectures,  or  Articles,  Editorials,  Book   Reviews,   Medical  Notes,   Selec- 
tions, Translations,  Hospital  and  Society  Reports. 

THE  OPHTHALMIC  REVIEW. 

A  monthly  record  of  Ophthalmic  Science,  now  in  its  third  volume. 

Subscription,  per  annum,  53-oo. 
The  Ophthalmic  Review  is  the  only  journal  devoted  to  this  special  branch  of  medicine 
that  is  published  in  England,  and  therefore  represents  the  advances  made  in  that  country,  as  no 
other  periodical  can. 

CONTENTS. — The  principal  contents  of  each  number  are  original  articles  with  some  illustrations,  transla- 
tions of  German  or  French  articles.  Bibliography,  Etc. 

ANNALES    DES   MALADIES    DE 

L'OREILLE    DES    LARYNX 

ET    DES   ORGANES   CONNEXES. 

Bt-MoNTHLY.      Subscription  $3.00. 

The  publishers  beg  to  announce  that  Dr.  J.  Solis-Cohen,  of  Philadelphia,  has  accepted  the 
American  Editorship  of  this  periodical,  and  Dr.  Morell  ^Iacke^zie  the  English  Editorship, 
and  that  hereafter  it  will  endeavor  to  be  international  in  character,  one-half  of  the  articles  be- 
ing in  French  and  one-half  in  English.  Any  articles  can  now  be  published  in  either  language, 
at  the  wish  of  the  author.     English  contributions  will  be  preceded  by  short  abstracts  in  French. 

B^^SPECIAL  NOTICE. — When  two  or  more  of  these  journals  are  taken,  club  rates  will 
be  allowed.  Correspondence  solicited.  Subscriptions  received  for  all  Medical  and  Scientific 
periodicals. 

P-  BLAKISTON,  SON  &  CO.,  Medical  Publishers  and  Booksellers, 
1012  Walnut  Street,  Philadelphia. 


Mr.    Presley  Blakiston  having  on   January  ist,  1882,  purchased  all  the 
interest  of  the  late  firm  of  Lindsay  &  Blakiston,  continues  the  publication 
and  sale  of  Medical  and  Scientific  Books  at  No.  1012  Walnut  Street,  Phil- 
adelphia, having  associated  with  him  his  son,  Kenneth  M.  Blakiston,  and 
Frank  W.  Robinson,  under  the  firm-name  of 

P.  BLAKISTON,  SON  &  CO. 


MEDICAL,  DENTAL,  SCIENTIFIC 


AND 


PHARMACEUTICAL  BOOKS 


PUBLISHED    BY 


P.  BLAKISTON,  SON  &  CO.    PHILADELPHIA. 

it^Any  book  in  this  catalogue  can  be  had  from  or  through  booksellers  in  the  principal  cities  in 
the  United  States,  or  will  be  forwarded  free,  by  mail  or  express,  upon  receipt  of  the  price  by  tho 
publisher. 


AMERICAN  HEALTH  PRIMERS. 

Edited  by  W.  W.  Keen,  m.d.     Complete  in  12  volumes,  handsomely  bound. 
Price,  in  cloth  binding,  50  cents  ;  paper  covers,  30  cents. 


I.  Hearing  and  How  to  Keep  It.     With  illus- 
trations.     By  ChAS    H.  Bl'RNETT,  M.D. 

II.  Long  Life,  and  How  to  Reach  It.     By  J.  G. 

Richardson,  m.d. 


VII.  The  Mouth  and  the  Teeth.     With  illustra- 
tions.    By  J.  W.  White,  m.d.,  d.d.s. 
VIII.  Brain   Work  and  Overwork.      By  H.  C 

Wood,  Jr.,  m.d. 


III.  The  Summer  and  Its  Diseases.     By  Jas.  C.    [      IX.  Our  Homes.     With  illustrations.    By  Henr? 


WiLSO.N,    M.D. 

IV.  Eyesight,  and  How  to  Care  for  It.  With  il- 
lustrations. By  George  C.  Harlan,  m.d. 

V.  The  Throat  and  the  Voice.  With  illustrations. 
By  J.  SoLis  Cohen,  m.d. 

VI.  The  Winter  and  Its  Dangers.  By  Hamilton 
Osgood,  m.d. 


Hartshorne,  m.d. 
X.  The  Skin  in  Healthand  Disease.    By  L.  D. 

BtiLKLEY,  M.D. 

XI.  Sea  Air  and   Sea  Bathing.     By  John  H. 
Packard,  m.d. 
XII.  School  and  Industrial  Hygiene.     By  D.  I« 

Lincoln,  m.d. 


LIBRARY  EDITION,  IN  4  VOLS.,  CLOTH,  EACH  $1.95. 

"  In  their  practical  teachings,  learning,  and  sound  j        "  These  handbooks  of  practical  suggestion  deserve 

sense,  these  volumes  are  worthy   of  all  the  compli-  hearty  commendation.     They  are  prepared  by  men 

ments  they  have  received.     They  teach  what  every  whose  professional  competence  is   beyond  question, 

n.an  and  woman  should  know,  and   yet  what  nine-  I    and  for  the  most  part,  by  those  who  have  made  the 


subject  treated   the  specific  study  of  their  lives. "^ 
Nezv  York  Sun. 


tenths  of  the  intelligent  class  are  ignorant  of,  or  at 
best,  have  but  a  smattering  knowledge  of" — Chicago 
Inter-Ocean. 

AMERICAN  PSYCHOLOGICAL  JOURNAL. 

Issued  bv  the  National  Association  for  the  Protection  of  the  Insane  and  Pre- 
rention  of  Insanity.     Edited  by  Joseph  Parrish,  m.d. 

Single  numbers  50  cents ;  per  annum,  S2.0G 


p.  BLAKISTON,  SON  6-  CO:S 


ACTON,  THE  REPRODUCTIVE  ORGANS. 

The  Functions  and  Disorders  of  the  Reproductive  Organs  in  Childhood, 
Youth,  Adult  Age  and  Advanced  Life,  considered  in  their  Physiological,  Social 
and  Moral  Relations.    By  William  Acton,  m.d.,  m.r.c.s.     Sixth  Edition.    8vo. 

Cloth,  %2.oo 

"  In  the  work  now  before  us,  all  essential  detail  upon  its  subject  matter  is  clearly  and  scientifically  given.  We 
recommend  it  accordingly,  as  meeting  a  necessary  requisition  of  the  day,  refusing  to  join  in  that  opinion  which 
regards  the  consideration  of  the  topics  in  question  as  beyond  the  duties  of  the  medical  practitioner." — Thi 
London  Lancet. 

"  On  the  subjects  of  Impotence  and  Spermatorrhoea,  those  bugbears  of  so  many  weak  and  foolish  persons,  and 
sources  of  inexhaustible  wealth  to  the  quack  fraternity,  Mr.  Acton  discourses  with  good  sense,  and  indignantly 
exposes  the  nefarious  tricks  of  the  scoundrels  who,  on  tlie  pretence  of  curing  a  disease  which  often  exists  only  in 
imagination,  extract  enormous  sums  from  their  unwary  victims.  He  seems  to  regard  the  spermatorrhoea-phobia, 
.IS  we  may  term  it,  to  be  a  species  of  monomania  ;  but  he  judiciously  advises  that  to  a  patiept  laboring  tinder  tliis 
form  of  mental  malady,  the  tone  adopted  should  be  one  of  sympathy  and  attention  ;  and  that  by  tne  employment 
of  appropriate  moral  and  therapeutical  means,  a  healthy  and  hopeful  tone  of  mind  be  restored. —  7'Ae  Medical 
Times. 

AGNEW,  ON  THE  PERINEUM  AND  FISTULA. 

Lacerations  of  the  Female  Perineum  and  Vesico-vaginal  Fistula.  Their  His- 
tory and  Treatment.  With  many  Illustrations.  By  D.  Hayes  Agnew,  M.d., 
Professor  of  Surgery,  University  of  Pennsylvania.     8vo.  Cloth,  Price  g;i.25 

So  many  applications  having  been  made  for  these  papers,  as  originally  issued, 
the  author  has  thought  best,  after  a  thorough  revision,  to  place  them  before  the 
profession  in  book  form. 

ALLBUTT.     VISCERAL  NEUROSES. 

The  Gulstonian  Lectures  for  March,  1884,  on  Neuralgia  of  the  Stomach  and 
Allied  Disorders.  By  T.  Clifford  Allbutt,  m.d.,  f.r.s.,  Consulting  Physician 
to  the  Leeds  General  Infirmary  and  the  Leeds  Hospital  for  Women  and  Children. 
Octavo.  Cloth,  ;? 1. 50 

ARMATAGE.    VETERINARY  REMEMBRANCER. 

The  Veterinarian's  Pocket  Remembrancer.  Containing  concise  directions  for 
the  Treatment  of  Urgent  or  Rare  Cases,  embracing  Semeiology,  Diagnosis,  Prog- 
nosis, Surgery,  Therapeutics,  Detection  of  Poisons,  Hygiene,  etc.  New  Revised 
Edition.     i8mo.-  .  Cloth,  1 1.2 5 

ALLAN,  FEVER  NURSING. 

Notes  on  Fever  Nursing.     Addressed  to  nurses  in  hospital  and  private  life. 

By  James  W.  Allan,  M.D.     i2mo.     Illustrated.  Price  .75 

ALLINGHAM,  DISEASES  OF  THE  RECTUM.       Illustrated. 

Fistula,  Haemorrhoids,  Painful  Ulcer,  Stricture,  Prolapsus,  and  other  Diseases 
of  the  Recturn,  their  Diagnosis  and  Treatment.  By  William  Allingham, 
F.R.c.s.     Fourth  Edition,  enlarged.  Price,  Paper  covers,  .75  ;  Cloth,  Ji. 25 

London  Edition,  thick  paper  and  larger  type,  $2.00. 
"  He  is  in  charge  of  the  only  hospital  in  the  world    1        "  This  book  has  always  been  a  great  favorite,  and 
i."^!.   Marks)  devoted    exclusively   to  diseases   of  the    j    deservedly  so.     It  is  practical  in  tone  and  character. 


'.:ctuni,  and  he  is  recognized,  both  in  this  country  and 
;ri  Europe,  as  the  highest  authority  upon  diseases  of 
.his  class." — Louisville  Medical  Herald. 


magisterial  in  its  teaching,  and  valuable  in  showing 
operative  results.  It  is  by  an  author  who,  as  an 
authority,  has  no  superior." — Gaillard' s  Medical 
yournal. 

"  No  book  oil  this  special  subject  can  at  all  approach    I  "  It  is,  as   indeed  the  verdict  of  the  profession  has 

Mr.  AUingham's  in  precision,  clearness  and   practical  already  pronounced  it,  one  of  the  very   best  works  on 

g'jodf.KKitt."— London  Medical  Times  and  Gazette.  Disease.^  of  the    Rectum." — Atiterican    yournal   of 

I  Medical  Science. 

ALTHAUS,  MEDICAL  ELECTRICITY. 

A  Treatise  on  Medical  Electricity,  Theoretical  and  Practical,  and  its  Use  in 
the  Treatment  of  Paralysis,  Neuralgia,  and  other  Diseases.  By  Julius  Althaus, 
M.D.     Third  Edition,  Enlarged.     246  Illustrations.     8vo.  Pi  ice  |6.oc 

In  revising  this  new  edition  the  author  has  carefully  brought  each  section  up 
with  the  latest  knowledge  of  the  subject. 


PUBLIC  A  TIONS. 


ANSTIE,  STIMULANTS  AND  NARCOTICS. 

With  special  researches  on  the  Action  of  Alcohol,  Ether  and  Chloroform  on 
the  Vital  Organism.     By  Francis  E.  Anstie,  m.d.      8vo.  Price  $3.00 

"  He  is  an  original  worker  and  independent  thinker.     His  opinions  and  conclusions  are  valuable,  and  cannot 

be  neglected.    — American  Medical  yournal. 

ATTHILL,  DISEASES  OF  WOMEN. 

Clinical  Lectures  on  Diseases  Peculiar  to  Women.  By  Lombe  Atthill,  m.d. 
5th  edition,  revised  and  enlarged,  with  numerous  illustrations.     i2mo.     Cloth. 

Price  t>i.i^ 

"  It  is  the  concentrated  essence  of  the  knowledge  of  one  who  has  become  wise  bj  reason  of  long  and  well- 
digested  experience  in  the  subjects  treated."— A>nerica>t  ^ourna/  o/ Medical  Science. 
"  The  work  is  one  of  great  value  to  the  general  x>^ct\t\oner."— American  yournal  of  Obstetrics. 

AITKEN'S  PRACTICE  OF  MEDICINE.     New  Edition. 

The  Science  and  Practice  of  Medicine.  By  William  Aitken,  m.d.,  f.r.s. 
London,  Professor  of  Pathology  in  the  Army  Medical  School,  etc.  Seventh 
Edition,  To  a  large  extent  rewritten  ;  enlarged,  remodeled  and  carefully  revised 
throughout.  In  Two  \'olumes.  196  Engravings  on  Wood,  and  a  Map  showing 
the  Geographical  Distribution  of  Diseases,  and  Copious  Index.     Octavo. 

Cloth,  $12.00;  Leather,  $14.00 

BALFOUR,  ON  THE  HEART  AND  AORTA. 

Clinical  Lectures  on  Diseases  of  the  Heart  and  Aorta.  By  G.  W.  Balfour, 
M.D.     Illustrated.     2d  Edition.  Price  $5.00 

"  The  whole  work  reflects  much  credit  on  its  author,  and  firmly  establishes  his  reputation  as  an  authority  on  the 
important  diseases  of  which  he  treats." — Lond<m  Fractitioner. 

BARTH    AND    ROGER,    AUSCULTATION    AND    PERCUS- 
SION. 

A  Manual  for  the  Student.  By  M.  Barth  and  M.  Henri  Roger.  Trans- 
lated from  the  6th  French  Edition.     i2mo.  Price  $1.00 

BIBLE  HYGIENE; 

Or,  Health  Hints.  By  a  Physician.  This  book  has  been  written,  first,  to  im- 
part in  a  popular  and  condensed  form  the  elements  of  Hygiene  ;  second,  to  show 
how  varied  and  important  are  the  Health  Hints  contained  in  the  Bible,  and  third, 
to  prove  that  the  secondary  tendency  of  modern  Philosophy  runs  in  a  parallel 
direction  with  the  primary  light  of  the  Bible.    i2mo.       Paper,  .50;  Cloth,  $1.00 

■'  The  scientific  treatment  of  the  subject  is  quite  abreast  of  the  present  day,  and  is  so  clear  and  free  from  unne- 
cessary technicalities  that  readers  of  all  classes  may  peruse  it  with  satis&ction  and  advantage." — Edinburgh 
Medical  yournal. 

BIDDLE,  MATERIA  MEDICA.      Ninth    Edition. 

{Contains  all  the  changes  in  the  Si.xth  Revision  of  the  New  Pharmacopoeia.') 
Materia  Medica.  For  the  L'^se  of  Students  and  Physicians.  By  the  late 
Prof.  John  B.  Biddle,  m.d..  Professor  of  Materia  Medica  in  Jefferson  Medi- 
cal College,  Philadelphia.  The  Ninth  Edition,  thoroughly  revised,  and  in 
many  parts  rewritten,  by  his  son,  Cle.ment  Biddle,  m.d.,  Assistant  Surgeon, 
U.  S.  Navy,  assisted  by  Henry  Morris,  m.d.  Containing  all  the  additions 
and  changes  made  in  the  last  revision  of  the  United  States  Pharmacopoeia. 
The  Botanical  portions  have  been  curtailed  or  left  out,  and  the  other  sections, 
on  the  Physiological  action  of  Drugs,  greatly  enlarged.     Octavo. 

Cloth,  S4.00;  Leather,  $4.75 

"  The  additions  are  valuable,  and  we  must  congrat-  !    ,    "  One  thing  that  particularly  recommends  this  work 

ulate    the  author  upon   having   improved   what   was  to  the  student  is,  that  the  book  is  not  so  large  as  to  dis- 

already  so  useful  a  work,  both  to  the  student  and  phy-  courage  and  cause  him  to  feel  that  it  is  impossible  for 

sician." — Phila.  Medical  and  Surgical  Reporter.  \    him  to  get  over  it  and  so  much  else  in  the  short  time 

■'  It  has  been  the  design  of  the  author  to  present  in  before  him."-5/'.  Louis  Medical  and  Surgical  your- 

his  work  a  text-book  for  the  student.     It  is  brief,  and  "'*'■ 

yet  sufficiently  comprehensive.     His  style  is  clear  and  ,        "  It  contains,  in  a  condensed  form,  all  that  is  valu- 

yet  succinct.     He  covers   the  ground — covers  it  well,  able    in   materia   medica,   and   furnishes   the   medical 

and  cumbers  his   work  with  nothing  superfluous." —  student   with  a  complete  manual  on  this  subject." — 

Atlanta  Medical  and  Surgical  yournal.  Canada  Lancet. 


p.  BLAKISTON,  SON  5-  CO:S 


BRE^VING,  DISTILLING,  ETC. 

The  Brewer,  Distiller  and  Wine  Manufacturer ;  a  Handbook  for  all  interested 
in  the  Manufacture  and  Trade  of  Alcohol  and  its  Compounds.  Edited  by  John 
Gardner,  Fellow  of  the  Chemical  Society  of  London.    Illustrated.  Cloth,  $1.75 

Synopsis  of  Contents. — Alcohol,  its  Preparations,  etc.;  Alcoholometry ; 
Brewing  and  Beers;  Varieties  of  Malt  Liquors;  Malt;  Raw  Grain;  Sugar; 
Hops ;  Arrangement  of  a  Brewery ;  Different  Processes ;  Chemical  Changes 
during  Washing,  Boiling,  Cooling,  Fermentation,  etc.,  etc. ;  Storing  and  Clari- 
fying, Porters,  Ales  ;  Analysis  of  Beers,  Ciders,  Perry,  Mum  ;  Liquors  and  Cor- 
dials, giving  over  80  preparations.  Other  sources  of  Spirituous  Liquors ;  Dis- 
tillation of  Alcoholic  Liquors,  including  Rums,  Brandies,  Whiskies,  Gins,  etc; 
Wine  and  Wine  Making  ;  Tests  for  Adulterations  ;  Remarks  on  the  Cultivation 
of  Grapes,  etc.;  Imitation  of  Wines. 
BLOXAM.CHEMISTRY,Inorganic  and  Organic.      Fifth  Edition. 

With  Experiments.  By  Charles  L.  Bloxam,  Professor  of  Chemistry  in 
King's  College,  London,  and  in  the  Department  for  Artillery  Studies,  Wool- 
wich.    Fifth  edition.     With  nearly  300  iingravings.     Cloth,  $3-75;  Leather,  $4-75 

A  most  complete  Text-Book  for  Schools  and  Colleges. 

"  Professor  Bloxam  has  given  us  a  most  excellent  and  useful  practical  treatise.     His  666  pages  (now  700)  are 
crowded  with  facts  and  experiments,  nearly  all  well  chosen,  and  many  quite  new,  even  to  scientific  men 
It  is  astonishing  how  much  information  he  often  conveys  in  a  few  paragraphs.     We  might  quote  fifty  instances  of 
this," — Chemical  News. 

BLOXAM.     LABORATORY  TEACHING.     Fourth  Edition. 

Progressive  Exercises  in  Practical  Chemistry.  By  Charles  L.  Bloxa.m, 
Professor  of  Chemistry  in  King's  College,  London,  etc.  Fourth  edition.  With 
89  engravings.     i2mo.  Price  $1.75 

This  work  is  intended  for  use  in  the  Chemical  Laboratory,  by  those  who  are 
commencing  the  study  of  Practical  Chemistry.     It  contains : — 

I.  A  series  of  simple  Tables  for  the  analysis  of  unknown  substances  of  all 
kinds.  2.  A  brief  description  of  all  the  practically  important  single  substances 
likely  to  be  met  with  in  ordinary  analysis.  3.  Simple  directions  and  illustra- 
tions relating  to  Chemical  Manipulation.  4.  A  system  of  Tables  for  the  detec- 
tion of  unknown  substances  with  the  aid  of  the  Blowpipe.  5.  Short  instructions 
upon  the  purchase  and  preparation  of  the  tests  intended  for  those  who  have  not 
access  to  a  Laboratory. 

•'  a  great  amount  of  valuable  practical  information  is  here  condensed  into  a  book  of  260  pages,  such  as  only  a 
()r:ictic:>l  teacher  could  prepare." — New  England  Journal  of  Education. 

BRUEN.     PHYSICAL  DIAGNOSIS.     Second  Edition. 

A  Pocket-Book  of  Physical  Diagnosis,  for  Physicians  and  Students.  By 
Edward  T.  Bruen,  m.d..  Demonstrator  of  Clinical  Medicine,  University  of 
Penn'a.     Illustrated  by  Original  Wood  Engravings.   i2mo.    2d  Ed.     Cloth,  $1.50 

■•  We  consider  the  description  of  the  manner  and  rules  governing  the  art  of  percussion  well  given.  The 
subject  is  always  a  difficult  one  for  beginners,  and  requires  to  be  well  handled  in  order  to  be  properly  under- 
siootl." — American  jfournal  of  Medical  Sciences. 

"  Tlie  volume  before  us  is  intended  as  a  guide  to  the  student  and  practitioner  in  making  a  diagnosis  of  Diseases 
of  the  Lungs  and  Heart,  and  as  such  is  an  excellent  book,  full  of  practical  hints  and  valuable  points." — 
rhiiadelphia  Medical  limes. 

BENNETT.     NUTRITION  IN  HEALTH  AND  DISEASE. 

A  Contribution  to  Hygiene  and  Clinical  Medicine.  By  J.  Henry  Ben- 
nett, M.D.     Third  Edition,  Revised  and  Enlarged.     Cloth.  Price  #2.50 


PUBLICA  riONS. 


BEALE  ON  SLIGHT  AILMENTS.     New  Edition.     Just  Ready. 

Slight  Ailments,  Their  Nature  and  Treatment.  By  Lionel,  S.  Beale,  m.d., 
F.R.S.,  Professor  of  Practice,  King's  Medical  College.  London.  Second  Edition, 
Enlarged  and  Illustrated.  Price,  Cloth,  $1.25  ;  Paper  covers,  .75  cents. 

Fine  Edition,  Heavy  Paper.  Extra  Cloth,  Price  31.75 

OUTLINE   OF   CONTENTS. 

Introductorj'.    The  Tongue  in  Health  and  Slight  Ailments.    Appetite.    Nausea.    Thirst.    Hunger.    Indigestion, 

its  Nature  and  Treatment.     Constipation,  its  Treatment.     DiarrhcEa.     Vertigo.     Giddiness.     Biliousness.     Sick 

Headache.     Neuralgia.     Rheumatism.     The  Feverish  and  Inflammatory  State.     Of  the  Actual  Changes  in  Fever 

and  Inflammation.     Common  Forms  of  Slight  Inflammation,  etc.,  etc. 

"We  venture  to  say  that  among  the  numerous  medical  publications  Issued  during  1880,  there  has  been  none 
which  will  prove  more  useful  to  the  young  general  practitioner,  for  whom  it  is  really  intended,  than  this  volume, 
while  the  time  of  the  older  physician  might  be  much  more  unprofitably  spent." — American  jfournal  0/ Medical 
Science. 

BY   SAME  AUTHOR. 

ON  LIFE  AND  VITAL  ACTION  IN  HEALTH  AND  DISEASE. 
I2mo.  Price  $2.00 

THE  USE  OF  THE  MICROSCOPE  IN  PRACTICAL  MEDI- 
CINE. 

For  Students  "and  Practitioners,  with  full  directions  for  examining  the  various 
secretions,  etc.,  in  the  Microscope.  Fourth  Edition.  500  Illustrations.  Much 
enlarged.     8vo.  Price  $7.50 

"  We  have  before  us  Prof  Beale's  work,  The  Micro-  '  "  As  a   microscopical    observer,  and  a  histological 
scope  in  Medicine,  a  book  which  it  gives  us  pleasure  to  j  manipulator,  his  (Dr.  Beale)  skill  and  eminence   are 
recommend  to  every  student  of  microscopy,  whether  he  j  generally  conceded." — Popular  Science  Monthly. 
be  a  physician  or  naturalist." — jFournal  o/ the  Frank- 
lin Institute,  Philadelphia.  \ 

HOW  TO  WORK  WITH  THE  MICROSCOPE. 

A  Complete  Manual  of  Microscopical  Manipulation,  containing  a  full  descrip- 
tion of  many  new  processes  of  investigation,  with  directions  for  examining  ob- 
jects under  the  highest  powers,  and  for  taking  photographs  of  microscopic 
objects.  Fifth  Edition.  Containing  over  400  Illustrations,  many  of  them  colored. 
Octavo.  Price  $7.50 

"The  Encyclopaedic  character  of  this  last  edition  of  Dr.  Beale's  well  known  work  on  the  Microscope  renders 
it  impossible  to  present  an  abstract  of  its  contents  ;  suffice  it  to  say,  that  anything  in  his  department  upon  which 
the  physican  can  desire  such  information  will  be  found  here,  and  much  more  in  addition.  It  is,  moreover,  a  store- 
house of  facts,  most  valuable  to  the  physician,  and  is  indispensable  to  eveiy  one  who  uses  the  microscope." — 
American  Journal  of  Medical  Science. 

BIOPLASM. 

A  Contribution  to  the  Physiology  of  Life,  or  an  Introduction  to  the  Study  of 
Physiology  and  Medicine,  for  Students.     With  numerous  Illustrations. 

Price  J2.25 
PROTOPLASM;  or  MATTER  AND  LIFE. 

Third  Edition,   very  much  enlarged.     Nearly  350  pages.     Sixteen  Colored 

Plates.    Part  i.  Dissentient.  Part  11.    Demonstrative.    Part  iii.  Suggestive. 

One  volume. 

LIFE    THEORIES ;    Their  Influence   upon  Religious    Thought. 

Six  Colored  Plates.  Price  $2.00 

ONE  HUNDRED  URINARY  DEPOSITS, 

On  eight  sheets,  for  the  Hospital,  Laboratory,  or  Surgery.  New  Edition. 
4to,  paper.  Price  g2.oo 

BERNAY,  CHEMISTRY. 

Notes  for  Students  in  Chemistry.  Compiled  from  Fowne's  and  other  manuals. 
By  Albert  J.  Bernav,  ph.d.     Sixth  Edition.     i2mo.  Price  $1.25 

BENTLEY'S  STUDENTS'   BOTANY. 

The  Students'  Guide  to  Structural  and  Physiological  Botany.  By  Professor 
Robert  Bentley.     Illustrated  by  nearly  500  Wood  Engravings. 

In  Preparation. 


p.  BLAKISTON,  SON  <S-  CO:S 


BEASLEY.  THE  BOOK  OF  PRESCRIPTIONS. 

Containing  over  3100  Prescriptions,  collected  from  the  Practice  of  the  most 
Eminent  Physicians  and  Surgeons — English,  French  and  American ;  a  Com- 
pendious History  of  the  Materia  Medica,  Lists  of  the  Doses  of  all  Officinal  and 
Established  Preparations,  and  an  Index  of  Diseases  and  their  Remedies.  By 
Henrv  Beasley.     Sixth  Edition,  Revised  and  Enlarged.  Price  $2.25 

BY    SAME   AUTHOR. 

THE  DRUGGIST'S  GENERAL  RECEIPT-BOOK. 

Comprising  a  copious  Veterinary  Formulary;  numerous  Recipes  in  Patent 
and  Proprietary  Medicines,  Druggists'  Nostrums,  etc.;  Perfumery  and  Cos- 
metics; Beverages,  Dietetic  Articles  and  Condiments;  Trade  Chemicals,  Scien- 
tific Processes,  and  an  Appendix  of  Useful  Tables.    Eighth  Edition.    Price  $2.25 

THE  POCKET  FORMULARY  and  Synopsis  of  the  British  and 
Foreign  Pharmacopoeias. 

Comprising  Standard  and  Approved  Formulae  for  the  Preparations  and  Com- 
pounds  Employed   in    Medical   Practice.      Tenth   Edition.     511    pp.      i8mo. 

Price  $2.25 
BENTLEY  AND  TRIMEN'S  MEDICINAL  PLANTS. 

A  New  Illustrated  Work,  containing  full  botanical  descriptions,  with  an  account 
of  the  properties  and  usesof  the  principal  plants  employed  in  medicine,  especial 
attention  being  paid  to  those  which  are  officinal  in  the  British  and  United  States 
Pharmacopoeias.  The  plants  which  supply  food  and  substances  required  by  the 
sick  and  convalescent  are  also  included.  By  R.  Bentley,  f.r.s.,  Professor  of 
Botany,  King's  College,  London,  and  H.  Trimen,  m.b.,  f.h.s..  Department  of 
Botany,  British  Museum.  Each  species  illustrated  by  a  colored  plate  drawn 
from  nature.     In  Forty-two  parts.     Eight  colored  plates  in  each  part. 

Price  %2  each,  or  handsomely  bound  in  4  volumes,  Half  Morocco,  $90.00 

"  It  would  be  impossible  to  enumerate  all  the  new 
plants  that  are  here  delineated.     The  result  is  a  work 


"  This  work  may  be  recommended  as  a  most  useful 
one  to  druggists,  and  all  who  desire  to  be  familiar 
with  the  Botany  of  Medicinal  Plants." — Druggists' 
Circular. 

"  The  work  when  complete  (it  is  now  complete) 
will  be  the  most  valuable  compend  of  Medical  Botany 
ever  published." — Boston  your nal  nf  Chemistry. 


which,  from  all  points  ofview,isa  credit  to  the  scientific 
literature  of  the  day." — London  Lancet. 

"It  is  an  indispensable  work  of  reference  to  every  one 
interested  in  pharmaceutical  Botany." — London  I'har- 
/iiaceutical  yourntil. 

BRUBAKER,  PHYSIOLOGY. 

A  Compend  of  Physiology  specially  adapted  for  the  use  of  Students  and  Phy- 
sicians.    "  No.  4,  ?  Quiz-Compend  Series  ?"     i2mo.  Cloth.  Price  Si .oo 

"  Dr.  Rrubaker  deserves  the  hearty  thanks  of  medical  students  for  his  Compend  of  Physiology'.  He  has 
arrani^ed  the  fundamental  and  practical  principles  of  the  science  in  a  particularly  inviting  and  accessible 
manner.     I  have  already  introduced  the  work  to  my  class." — Maurice  N.  Miller,  M.D.,  Demonstrator  of 

I'hysiology,  Medical  Department  University  0/ the  City  0/ New  York. 

BYFORD.     DISEASES  OF  WOMEN.     New  Revised  Edition. 

The  Practice  of  Medicine  and  Surgery,  as  applied  to  the  Diseases  of  Women. 
By  W.  H.  Byford,  a.m.,m.d..  Professor  of  Obstetrics  and  The  Diseases  of  Wo- 
men and  Children,  in  the  Chicago  Medical  College.  Third  Edition.  Revised 
and  Enlarged,  much  of  it  rewritten,   with  numerous  additional  illustrations. 

Price,  in  Cloth  $5.00;  Leather,  $6.00 

"  The  treatise  is  as  complete  a  one  as  the  present  "The  author  is  an  experienced  writer,  an  able  teach- 

state  of  our  science  will  admit  of  being  written.     We  1    er  in  his  department,  and  has  embodied  in  the  present 

commend  it  to  the  diligent  study  of  every  practitioner  work  the  results  of  a  wide  field  of  practical  observa- 

and  student,  as  a  work  calculated  to  inculcate  sound  tion.    We  have  not  had  time  to  read  its  pages  critically, 

I  riiiciplcs    and    lead    to    enlightened   practice. — Neiv  but  freely  commend  it  to  all  our  readers,  as  one  of  the 

Vi'rk  .Medical  Record.  most  valuable  practical  works  issued  from  the  Ameri- 

I    can  press." — Chicago  Medical  Examiner. 

BY    SAME   AUTHOR. 

ON  THE  UTERUS.     The  Chronic  Inflammation  and  Displace- 
ment of  the  Unimpregnated  Uterus. 

An  Enlarged  Edition,  with  Illustrations.     8vo.  Price  $2.50 

"A  good  book  from  a  good  man." — American  Journal  Medical  Science. 

"  It  is   a  sensible,  practical  work,  and  cannot  fail  to  be  read  with  interest  and  profit  " — Boston  Medical  anii 


PUB  Lie  A  TIONS. 


BRAUNE,  TOPOGRAPHICAL  ANATOMY. 

An  Atlas  of  Topographical  Anatomy.  Thirty-four  Full-page  Plates,  Photo- 
graphed on  Stone,  from  Plane  Sections  of  Frozen  Bodies,  with  many  other  illus- 
trations. By  WiLHELM  Braune,  Professor  of  Anatomy  at  Leipzig.  Translated 
and  Edited  by  Edward  Bellamy,  f.r.c.s..  Lecturer  on  Anatomy,  Charing 
Cross  Hospital,  London.     Quarto.     Price,  Cloth,    ;g8.oo  ;  Half  Morocco,  <;io.oo 

"  As  a  whole  the  work  cannot  fail  to  meet  with  a  hearty  reception  by  every  progressive  student  of  the  human 
body.  To  the  surgeon  it  is  a  contribution  to  the  study  of  topographical  anatomy  which  needs  to  be  known  to  be 
properly  appreciated  To  such  practitioners  who  reside  in  large  cities,  where  anatomy  can  be  studied  upon  the 
cadaver,  it  will  aflford  a  valuable  aid,  while  to  those  who  are  without  such  means  of  study  it  is  an  almost  indis- 
pensable addition  to  a  working  library." — Ne-w  York  Medical  Record. 

"  We  commend  the  book  most  heartily  to  the  Profession." — American  yournal  of  Medical  Science . 

BUCKNILL  AND  TUKE  ON  INSANITY. 

A  Manual  of  Pyschological  Medicine:  containing  the  Lunacy  Laws,  the 
Nosology,  (Etiology,  Statistics,  Description,  Diagnosis,  Pathology  (including 
morbid  Histology),  and  Treatment  of  Insanity.  By  John  Charles  Bucknill, 
M.D.,  F.R.S.,  and  Daniel  Hack  Tuke,  m.d.,  f.r.c.p.  Fourth  Edition,  much 
enlarged,  with  twelve  lithographic  plates,  and  numerous  illustrations.     Octavo. 

Price  $8.00 

•'  We  have  read  no  book  in  any  language,  and  certainly  none  in  English,  which   ought  to  be  preferred  to    this 
for  a  text  book,  by  those  who  wish  to  make  a  thorough  study  of  the  subject. — Edinburgh  Medical  yournal. 
"  We  can  heartily  commend  the  work. — American  yournal  of  Insanity. 

BURDETT,  HOSPITALS. 

Pay  Hospitals  and  Paying  Wards  throughout  the  World.  Facts  in  support 
of  a  rearrangement  of  the  system  of  Medical  Relief.  By  Henry  C.  Burdett. 
8vo.  Price  $2.25 

"  Mr.  Burdett  displays  and  discusses  the  whole  scheme  of  Hospital  accommodation  with  a  comprehensive 
understanding  of  its  nature  and  extent. — American  Practitioner. 

BY  SAME  AUTHOR. 

COTTAGE  HOSPITALS. 

General,  Fever,  and  Convalescent :  their  Progress,  Management,  and  Work. 
Second  Edition,  rewritten  and  much  Enlarged,  with  many  Plans  and  Illustra- 
tions.    Crown  8vo.  Price  $4.50 

Contents. — Chap. — i.  Origin  and  Growth  of  the  Cottage  Hospital  System.  2.  Comparative  Success  of 
Treatment  in  large  and  small  Hospitals.  3.  Finance.  4.  Cottage  Hospital  Construction  and  Sanitary  Arrange- 
ments. 5.  The  Medical  and  Nursing  Departments.  6.  Domestic  Supervision  and  General  Management.  7. 
Cottage  Hospital  Appliances  and  Fittings.  8.  Cottage  Fever  Hospitals.  9.  Midwifery  in  Cottage  Hospitals.  10. 
Remunerative  Paying  Patients.  11.  Convalescent  Cottages .  12.  Cottage  Hospitals  in  .\merica.  13.  Mortu- 
aries. 14.  A  more  Detailed  Account  of  certain  Cottage  Hospitals,  with  Plans  and  Elevations.  15.  Selected  and 
Model  Plans  criticised  and  compared,  with  a  detailed  description  of  various  Hospitals.  16.  Peculiarities  and 
Special  Features  in  the  Working  of  Cottage  Hospitals.  With  an  Appendix  containing  much  statistical  and  useful 
information. 

"  Mr.  Burdett's  book  contains  a  mass  of  information,  statistical,  financial,  architectural,  and  hygienic,  which  ha« 
already  proved  of  great  practical  utility  to  those  interested  in  cottage  hospitals,  and  we  can  confidently  recom- 
mend this  second  edition  to  all  who  are  in  search  of  the  kind  of  information  which  it  contains." — lancet. 

BUZZARD,  NERVOUS  DISEASES. 

Clinical  Lectures  on  Diseases  of  the  Nervous  System.  By  Thos.  Buzzard, 
M.D.     Illustrated.     Octavo.  Price  #5.00 

CARPENTER,  THE  MICROSCOPE.     Sixth  Edition. 

The  Microscope  and  its  Revelations.  By  W.  B.  Carpenter,  m.d.,  f.r.s. 
Sixth  Edition.     Revised  and  Enlarged,  with  over  500  Illustrations.     Price  S5.50 

"  Not  only  the  student  of  medicine,  but  amateurs,  |        "As  a  text  book  of  Microscopy  in  its  special  relation 

and  others  interested  in  the  study  of  natural  history,  to  natural  history  and  general  science,  the  work  before 

will  find  this  volume  one  of  great  practical  value." —  us  stands  confessedly  first,  and  is  alone  sufficient   to 

N  w  York  .\fedical  yournal .  I  supply  the  wants  of  the  ordinary  student." — Anurican 

"It  is  by  far  the  most  complete  and   useful  treatise  j  yournal  o/ Microscopy. 

now  accessible  to  the  student." — The  Technologist.  I 


lo  p.  BLAKISTON,  SON  &-  CO.'S 


CARTER,  EYESIGHT.     New  Edition  now  ready. 

Eyesight,  Good  and  Bad.  A  Treatise  on  the  ExercisiS  and  Preservation  of 
Vision.  By  Robert  Brudenell  Carter,  f.r.c.s.  Second  Edition,  with  50 
Illustrations,  Test  Types,  etc.     i2mo.  Price,  Cloth,  $1.25 

"  It  is  written  in  a  lucid  and  agreeable  style,  conveying  an  easily  comprehensible  account  of  the  structure  of 
the  eye  and  the  function  of  vision,  and  gives  a  description  of  the  principal  anomalies  of  the  latter,  at  the  same 
time  inculcating  such  salutary  advice  as  may  be  beneficial  for  the  preservation  of  sight.  —London  Medical 
Times  and  Gazette. 

"  There  is  much  wholesome  advice  given  on  the  '  Care  of  the  Eyes  in  Infancy  and  Childhood,'  and  on  this 
account,  if  no  other,  the  book  should  be  in  the  hands  of  every  parent  and  teacher."— 5^.  Louis  Courier  of 
Medicine. 

CARTER,  PRACTICE  OF  MEDICINE. 

Elements  of  Practical  Medicine.  By  Alfred  H.  Carter,  m.d.,  LondoK. 
Member  of  the  Royal  College  of  Physicians ;  Physician  to  the  Queen's  Hos- 
pital, Birmingham,  etc.     Crown  8vo.  Price  $3.00 

CULLINGWORTH,  ON  NURSING.     Illustrated. 

A  Manual  of  Nursing,  Medical  and  Surgical.  By  Charles  J.  Culling- 
woRTH,  M.D.,  Physician  to  St  Mary's  Hospital,  Manchester,  England.  With 
eighteen  Illustrations.     i2mo.  Cloth,  $i.oo 

BY   THE  SAME   AUTHOR. 

ON  MONTHLY  NURSING. 

A  Manual  for  Monthly  Nurses.     32mo.  Price,  Cloth,  »75 

CAZEAUX  AND  TARNIER'S  MIDWIFERY.  New  Revised 
Edition.     Twelve  Full-page  Plates. 

The  Theory  and  Practice  of  Obstetrics ;  including  the  Diseases  of  Pregnancy 
and  Parturition,  Obstetrical  Operations,  etc.  By  P.  Cazeaux,  Member  of  the 
Imperial  Academy  of  Medicine,  Adjunct  Professor  in  the  Faculty  of  Medicine  in 
Paris.  Remodeled  and  rearranged,  with  revisions  and  additions,  by  S.  Tarnier, 
M.D.,  Professor  of  Obstetrics  and  Diseases  of  Women  and  Children  in  the  Faculty 
of  Medicine  of  Paris.  A  New  American,  from  the  Eighth  French  and  First 
Itahan  Edition.  Edited  and  Enlarged  by  Robert  J.  Hess,  m.d..  Physician  to  the 
Northern  Dispensary,  Phila.,  etc.  About  iioo  pages  quarto,  with  12  Full-page 
Plates  ( five  of  which  are  beautifully  colored)  and  over  175  Wood  Engravings. 

Sold  by  subscription  only.  Circulars  and  information  will  be  sent,  upon  appli- 
cation to  the  Publishers. 

For  many  years  "  Cazeaux's  Obstetrics"  has  been  one  of  the  leading  text-books  in  America  and  Engl.ind,  as 
well  as  in  France,  and  the  recent  decision  of  four  of  the  foremost  Professors  of  Italy,  Drs.  Chiara,  Morisani,  Porro, 
uikI  Tibone,  to  translate  it  into  their  own  language,  is  a  further  proof  of  its  usefulness,  and  that  it  still  stands 
highest  as  a  practical  guii.te  to  the  general  practitioner.  Another  and  perhaps  a  stronger  proof  of  the  value  cf 
this  great  work,  is  the  fact  that  by  comparing  many  of  the  text-books  issued  since  the  first  edition  of  Cazeaux 
was  published,  it  will  be  found  that  the  later  authors  have,  to  more  or  less  extent,  used  it  as  a  foundation  for 
ihcir  work  ;  drawing  cases,  conclusions  and  illustrations  from  its  mass  of  facts  and  the  experience  of  its  author 
With  these  important  proofs  in  their  mind,  the  publishers  determined  to  issue  a  new  edition;  which  would 
represent  the  advances  made  in  the  science  of  midwifery.  Written  expressly  for  the  use  of  practitioners  and  ■ 
students  of  medicine,  and  those  of  midwifery  especially,  its  teachings  are  plain  and  explicit,  presenting  a 
cuiuleused  summary  of  the  leading  principles  established  by  the  masters  of  the  obstetric  art,  and  such  cbar, 
practical  directions  for  the  management  of  the  pregnant,  parturient  and  puerperal  states,  as  have  been  sanctioned 
by  the  most  authoritative  practitioners,  and  confirmed  by  the  author's  own  experience.  The  publishers  selected 
for  editor  a  gentleman  who  has  had  an  extended  experience  in  private  practice  and  through  his  connection  with 
one  of  the  largest  public  dispensaries  in  the  country.  The  revision  has  to  some  extent  been  based  on  the  last 
French  edition,  and  on  the  revisions  and  additions  made  by  the  Italian  translators.  The  writings  of  other  well- 
known  men  have  also  been  drawn  from,  as  well  as  the  experience  of  the  editor,  an  experience  gained  in  every- 
day work.  New  chapters  or  sections  have  been  written,  new  illustrations  inserted,  old  ones  recut,  and  twelve 
full-page  plates  added,  five  of  which  are  colored. 


PUB  Lie  A  TIONS. 


CHARTERIS,  PRACTICE  OF  MEDICINE. 

Hand-Book  of  the  Practice  of  Medicine.  By  M.  Charteris,  m.d.,  Member 
of  Hospital  Staff  and  Professor  in  University  of  Glasgow.  With  Microscopic  and 
other  illustrations.  Price  $1.25 

"  \Je.  have  not  often  met  with  a  book  which  can  be  so  confidently  recommended  to  physicians  or  men  in  general 
practice." — Lancet. 

"  The  style  in  which  it  is  written  is  clear  and  attraative.     The  illustrations  are  a  marked  feature  in  it.     It  can 
be  recommended  as  a  very  reliable,  handy  book,  well  adapted  for  ready  reference." — A'eiv  Remedies. 

CHAVASSE  ON  CHILDREN. 

The  Mental  Culture  and  Training  of  Children.     By  Pye  Henry  Chavasse. 

i2mo.  Price,  Paper  covers,  .50;  Cloth,  Si. 00 

The  mental  culture  and  training  of  children  is  of  immense  importance.     Many 

children  are  so  wretchedly  trained,  or  rather  not  trained  at  all,  and  so  mismanaged, 

that  a  few  thoughts  on  this  subject  cannot  be  thrown  away,  even  upon  the  most 

careful. 

CLAY  ON  OBSTETRIC  SURGERY.     Third  Edition. 

A  complete  Hand-Book  of  Obstetric  Surgery,  with  Rules  for  every  Emergency 
and  Descriptisns  of  the  more  difficult  as  well  as  the  every  day  operations.  By 
Charles  Clay,  m.d.,  with  numerous  Illustrations.  From  the  Third  London 
Edition.     l2mo.  Paper  Covers,  .75  ;  Cloth,  Si-5 

"  It  is  a  useful  and  convenient  book  of  reference ;  the  illustrations  are  good,  and  the  book  will  be  found  of  value 
to  the  student  and  young  practitioner,  as  well  as  to  the  skilled  Obstetrician." — American  yournal  of  Obstetrics. 

CLEVELAND,  POCKET  DICTIONARY. 

A  Pronouncing  Medical  Lexicon,  containing  correct  Pronunciation  and  Defi- 
nition of  terms  used  in  medicine  and  the  collateral  sciences.  By  C.  H.  Cleve- 
land, M.D.         Thirty-first  Edition.     i6mo. 

Price,  Cloth,  75  cents  ;  Tucks  with  Pocket,  $1.00 
This  is  a  most  convenient  size  for  the  pocket,  and  contains  all  the  principal  words 
in  use,  together  with  rules  for  pronunciation,  abbreviations  used  in  prescriptions,  list 
of  poisons,  their  antidotes,  etc. 

COHEN,  INHALATION.     Enlarged  Edition. 

Inhalation,  its  Therapeutics  and  Practice,  including  a  Description  of  tHe  Ap- 
paratus Employed,  etc.  By  J.  Solis  Cohen,  m.d.  With  cases  and  Illustrations. 
A  New  Enlarged  Edition.     8vo.  Price  $2.50 

"  The  book  has  the  merit  of  containing  much  information  that  cannot  be  found  elsewhere."— A^.  }'.  Medical 
yournal. 
"  One  of  the  best  treatises  we  have  seen  on  this  subject." — Medical  Times  and  Gazette. 

COOPER  ON  SYPHILIS. 

Syphilis  and  Pseudo-Syphilis.  By  Alfred  Cooper,  f.r.c.s..  Surgeon  to  the 
Lock  Hospital,  to  St.  Marks  and  to  the  West  London  Hospitals.     Octavo. 

Cloth,  53.50 

COBBOLD,  PARASITES. 

A  Treatise  on  the  Entozoa  of  Man  and  Animals,  including  some  account  of 
the  Ectozoa.  By  T.  Spencer  Cobbold,  m.d.,  f.r.s.  With  85  illustrations. 
8vo.  Price  $5.00 


12  P.  BLAKISTON,  SON  &-  CO.'S 

COLES,  THE  MOUTH.     Third  Edition,  just  ready. 

Deformities  of  the  Mouth,  Congenital  and  Acquired,  with  Their  Mechanical 
Treatment.  By  Oakley  Coles,  d.d.s.  Third  Edition.  83  Wood  Engravings 
and  96  Drawings  on  Stone.     8vo.  Price  I4.50 

'"  Altogether  we  must  heartily  congratulate  Mr.  Coles  on  this  creditable  completion  of  a  work  which  cannot 
lilt  redound  to  his  credit  wherever  it  is  known." — British  yournal  of  Dental  Science. 
■■  We  recommend  this  book  to  the  study  of  both  surgeons  and  dentists." — London  Lancet. 

BY   SAME  AUTHOR. 

CHAPMAN.     THE  CIRCULATION  OF  THE  BLOOD. 

A  History  of  the  Discovery  of  the  Circulation  of  the  Blood.  By  Hexrv 
C.  Chapman,  m.d.,  Professor  oflnstitutes  of  Medicine  and  Medical  Jurisprudence 
in  Jefferson  Medical  College,  Philadelphia.     Octavo.  Cloth,  31.00 

THE  DENTAL  STUDENT'S  NOTE-BOOK. 

A  new  Edition.     i6mo.  Price  $1.00 

CORMACK,  CLINICAL  STUDIES. 

Illustrated  by  Cases  Observed  in  Hospital  and  Private  Practice.  By  Sir 
John  Rose  CoRMACK,  v.D.,K.B.,  etc.  Illustrated.  2  vols.   1,127  pp.  Price  ^5.00 

COURTY,  THE  UTERUS,  OVARIES,   ETC.    Subscription  only. 

A  Practical  Treatise  on  Diseases  of  the  Uterus,  Ovaries,  and  Fallopian 
Tubes.  By  Prof.  A.  Courty,  of  Montpellier,  France.  Translated  from  the 
Third  Edition  by  his  pupil  and  assistant,  Agnes  McLaren,  m.d.,  m.k.q.c.p.i. 
With  a  Preface  by  J.  Matthews  Duncan,  m.d.,  ll.d.,  f.r.s.,  Obstetric  Physi- 
cian to  Saint  Bartholomew's  Hospital,  London.  With  431  Illustrations.  One 
Vol.,  8vo.    Price,  in  Handsome  Cloth,  $6.00 ;  Full  Sheep,  Raised  Bands,  J7.00 

OUTLINE  OF   CONTENTS. 
TPODucTioN. — On  the   Anatomy,   Physiology,  and  Teratology  of  the  Organs  of  Generation.     Part  i. — 
General  Survey  of  Uterine  Diseases.      Diagnosis  of  tfterine  Diseases  in  General;   Treatment  of 
Uterine  Disea.ses  in  General ;  General  Characteristics  of  Uterine  Diseases.    Part  ii. — Uterine  Diseases 
IN  Detail.     Functional  Disorders;  Changes  of  Position;    Morbid   States  without  Neoplasm;    Organic 
Alterations;  Diseases  of  the  Uterine  Appendages;  Pelvic  Hemorrhages  and  Peri-uterine  Haematocele; 
Cy.'t  of  the  Ovary  and  Genito-pelvic  Tumor;  Sterility,  etc.,  etc.     Index 
"  Courty's  work  has,  since  its  first  publication,  been  recognized  everywhere.     In  France,  its  position  is 
attested  by  the  sale  of  two  editions,  numbering,  I  am  told,  ten  thousand  copies,  and  by  the  appearance  of 
another,  the  third  edition.     I  recommend  to  the  careful  study  of  my  professional  brethren  a  book  which  has 
already  been  crowned  by  the  Institute  of  France." — J.  Matthews  Duncan. 

CURLING,  ON  THE  TESTIS. 

A  Practical  Treatise  on  the  Diseases  of  the  Testis,  Spermatic  Cord,  and 
Scrotum.  By  T.  B.  Curling,  m.d.,  f.r.s.  Fourth  Edition,  Enlarged  and  Il- 
lustrated.    8vo.  Price  $5.50 

"  We  believe  this  work  to  be  the  most  trustworthy  that  can  be  consulted  in  this  Department  of  Surgery, 

his  pages  abound  with  valuable  suggestions  and  cautions   that  mark  his  intimate  knowledge  of  the 

<iiibject." — London  Practitioner. 

COOPER'S  SURGICAL  DICTIONARY. 

A  Dictionary  of  Practical  Surgery  and  Encyclopaedia  of  Surgical  Science. 

By  Samuel  Cooper.     New  Edition,  brought  down  to  the  present  time.     By 

Samuel  A.   Lane,  f.r.c.s.,  assisted   by  various  eminent  Surgeons.     In  two 
vols.  Price  $12.00 

COTTLE,   ON  THE  HAIR. 

The  Hair  in  Health  and  Disease.  By  E.  W.  Cottle,  m.d.  Partly  from  the 
notes  of  the  late  George  Nayler.     i8mo. 

CORFIELD,    DWELLING  HOUSES. 

The  Sanitary  Construction  and  Arrangement  of  Dwelling  Houses.  By  W. 
H.  CoRFiEuD,  M.A.,  m.d.  Enlarged  Edition,  with  Plans  and  Illustrations. 
l2mo.  Price  gi.25 


PUBLICATIONS.  13 


COULSON,  THE  BLADDER.     Sixth  Edition. 

Diseases  of  the  Bladder  and  Prostate  Gland.  By  Walter  J.  Coulson,  f.r.c.S. 
Sixth  Edition.     Revised  and  Enlarged,  with  22  Engravings.     8vo.      Price  $6.40 

CRIPPS,  THE  RECTUM. 

Cancer  of  the  Rectum.  Its  Pathology,  Diagnosis  and  Treatment.  By.  W. 
Harrison  Ckipps,  f.r.c.s.     Illustrated  by  Plates.     8vo.  Price  $2.40 

DAY  ON  CHILDREN.     Second  Edition.     Just  Ready. 

The  Diseases  of  Children.  A  Practical  and  Systematic  Treatise  for  Practi- 
tioners and  Students.  By  Wm.  H.  Day,  m.d.  Second  Edition.  Rev/ritten  and 
very  much  Enlarged.     8vo.     752  pp.     '  Price,  Cloth,  $5.00;  Sheep,  $6.00 


"  Dr.  Day  brings  to  his  task  a  large  experience,  and 
evidences  a  very  thorough  knowledge  of  the  literature, 
native  and  foreign,  pertaining  to  this  special  branch  of 
medicine.  The  book  has  been  written  with  great  care, 
and  the  author  is  a  good  writer.  The  publisher's  part 
of  the  task  has  also  been  excellently  performed." — 
Boston  Medical  and  Surgical  journal. 


"  Believing  the  work  well  adapted  to  meet  the  wants 
of  the  Student  as  well  as  the  Practitioner,  I  will  recom- 
mend it  to  the  classes  of  Rush  Medical  College." — 
DeLeskie  Miller,  m.d.,  Chicago. 

"  On  the  whole,  we  must  confess  we  are  pleased  with 
this  book  and  can  heartily  recommend  it — a  recommen- 
dation which  it  does  not  appear  Ho  need,  as  it  has 
already  reached  its  second  edition." — American  jour- 
nal of  Medical  Science. 

DAY  ON  HEADACHES.     Fourth  Edition. 

The  Nature,'  Causes,  and  Treatment  of  Headaches.  Fourth  Edition,  Illus- 
trated.    By  Wm.  Henry  Day,  m.d.     Octavo. 

Paper  Covers,  75  cents;     Cloth,  $1.25 

Si;mmary  of  Contents. — Headache  from  Cerebral  Anaemia,  Cerebral  Hyperemia,  Sympathetic,  Congestive, 
Dyspeptic  or  Bilious  Headaches,  Headache  from  Plethora,  from  Exhaustion,  from  Change  in  Cerebral  Tissue, 
from  Affections  of  the  Periosteum,  Nervous  and  Nervo-Hyperaemic  Headache,  Toxaemic,  Rheumatic,  Arthritic 
or  Gouty  Headache,  Neuralgic  Headache,  and  Headaches  of  Childhood,  Early  and  Advanced  Life. 

"  Well  worth  reading.     The  remarks  on  treatment  are  very  sensible." — Boston  Medical  and  Surg,  yournal. 

DALBY,  ON  THE  EAR. 

The  Diseases  and  Injuries  of  the  Ear.  By  W.  B.  Daley,  m.d.,  Surgeon  and 
Lecturer  on  Aural  Surgery,  St.  George's  Hospital.     With  Illustrations.     i2mo. 

Price  $1.50 

'A  safe  and  readable  introduction  to  aural  surgery."  j  "The  lectures   occupy  226  pages,  are  clearly  and 

Medical  Press  and  Circular.  1  consisely  written,  contain  a  number  of  good  illustrations, 

"  Dr.  Dalby  has  presented  us  with  a  very  readable  t  ^"d  are  well  worth  the  careful  study  of  both  student 

little  book,  which  is  destined  to  render  much  service  in  j  and  practitioner.     To  aurists  the  work  will  be  most- 

lh.cs3.ymsol^r^:--N.  y.  Medical  yournal.  I  welcome  and  valuable.    -SJ>eciahst. 

DILLINGBERGER,     WOMEN     AND     CHILDREN'S     DIS- 
EASES. 

A  Hand-Book  of  the  Treatment  of  the  Diseases  Peculiar  to  Women  and  Chil- 
dren.    By  Dr.  Emil  DILLINGBERGER.     i2mo.  Price  $1.50 

"  It  is  a  magnum  in  parvo.  The  style  is  simple,  clear,  lucid,  and  free  from  theoretical  discussion.  No  one  will 
regret  the  small  outlay  for  this  volume. — Richmond  and  Louisville  Medical  Journal. 

DUNCAN  ON  STERILITY. 

Sterility  in  Women  ;  being  the  Gulstonian  Lectures  delivered  in  the  Royal 
College  of  Physicians,  February,  1883.  By  J.  Mathews  Duncan,  m.d.,  ll.u., 
Obstetric  Physician  to  St.  Bartholomew's  Hospital,  etc.    Octavo.         Cloth,  $2.00 

DURKEE,  VENEREAL  DISEASES.     Sixth  Edition. 

Gonorrhoea  and  Syphilis.  By  Silas  Durkee,  m.d.  Sixth  Edition.  Revised 
and  Enlarged,  with  Portrait  and  Eight  Colored  Illustrations.     8vo.     Price  ;SS3.5o 

"  We  may,  finally,  recommend  Dr.  Durkee's  book  as  eminently  practical,  well  written,  full  of  excellent  counsel, 
and  worthy  of  being  cors  ilted  by  every  member  of  the  profession.  A  late  number  of  the  London  Medical  Times 
and  Gazette  also  speaks  of  the  book  in  terms  of  the  highest  approval." — Boston  Medical  and  Surgical  Journal 


14  P.  BLAKISTOX,  SON  <S-   CO:S 

DAGUENET,  OPHTHALMOSCOPY. 

A  Manual  of  Ophthalmoscopy,  for  the  Use  of  Students.  By  Dr.  Daguenet. 
Translated  from  the  French,  by  Dr.  C.  S.  Jeaffreson,  f.r.c.s.e.  Illustrated. 
i2mo.  Price  $1.50 

"  Its  portable  size,  the  condensed  nature  of  its  text,  and  the  admirably  systematic  arrangement  of  its  contents, 
render  it  extremely  useful  as  a  pocket  manual  for  Students. —  Translator' s  Pre/ace. 

DOBELL,  WINTER  COUGH  AND  CATARRH. 

On  Winter  Cough,  Catarrh,  Bronchitis,  Emphysema,  Asthma,  etc.  By 
Horace  Dobell,  m.d..  Lecturer  at  the  Royal  Hospital  for  Diseases  of  the 
Chest.     Third  Edition.     With  Colored  Plates.     8vo.  Price  S3  50 

BY    same   author. 

ON  LOSS  OF  WEIGHT.     Revised  Edition. 

Blood  Spitting  and  Lung  Disease.  Colored  Frontispiece  of  Lung.  Tabular 
Map,  etc.     Second  Edition  Enlarged.     8vo.  Price  $4.00 

DOMVILLE,  ON  NURSING. 

A  Manual  for  Hospital  Nurses  and  others  engaged  in  attending  to  the  sick. 
4th  Edition.     With  Recipes  for  Sick  Room  Cookery,  etc.  Price  .75 

DRUITT'S  MODERN  SURGERY.     Eleventh  Edition. 

The  Surgeon's  Vade  Mecum ;  a  Manual  of  Modern  Surgery.  By  Robert 
Druitt,  f.r.c.s.  Eleventh  Enlarged  Edition,  with  369  Illustrations.  864  pp. 
1878.  Price  $5.00 

This  is  a  most  complete,  accurate,  and  trustworthy  Hand,  or  Text-Book  of  Sur- 
gery. Unrivaled  as  a  book  for  the  Student.  Fully  illpstrated,  and  brought  up  to 
the  present  state  of  the  science.     In  use  in  many  Medical  Colleges. 

DULLES,  ACCIDENTS. 

What  to  Do  First,  In  Accidents  and  Poisoning.  By  C.  W.  Dulles,  m.d. 
Second  Edition,  Enlarged,  with  new  Illustrations.  Cloth,  .75 

"  Its  usefulness  entitles  it  to  a  wide  and  permanent  I  "  So  plain  and  sensible  that  it  ought  to  be  introduced 

circulation." — Boston  Gazette.  into    every    female     seminary. — Evening    Chronicle, 

" -A.  complete  guide  for  sudden  emergencies. — Phila-  \  Pittsburgh. 

delj'hia  Ledger.  \ 

EDWARDS,  BRIGHT'S  DISEASE.     New  Edition. 

How  a  Person  Affected  with  Bright' s  Disease  Ought  to  Live.  By  Jos.  F.  Ed- 
wards, M.D.     Second  Edition.     i2mo.  Price  .75 

"  Physicians,  as  well  as  laymen,  will  find  the  work  interesting,  and  will  obtain  many  valuable  hints  as  to  the 
proper  hygiene  to  be  observed  in  this  disease." — Cincinnati  Medical  News. 

BY  SAME   AUTHOR. 

CONSTIPATION.     New  Edition. 

Plainly  Treated  and  Relieved  Without  the  Use  of  Drugs.  Second  Edition. 
i2mo.  Price  .75 

MALARIA. 

Malaria  :  What  It  Means ;  How  to  Escape  It ;  Its  Symptoms ;  \Vhen  and 
Where  to  Look  for  It.     i2mo.  Price  .75 

VACCINATION  AND  SMALL-POX. 

Showing  the  Reasons  in  favor  of  Vaccination,  and  the  Fallacy  of  the  Argu- 
ments .Advanced  against  it,  with  Hints  on  the  Management  and  Care  of  SmaH- 
Pox  patients.     i6mo.  Price  .50 

These  are  invaluable  little  treatises  upon  subjects  that  enter  painfully  into  the 
life  experiences  of  a  large  majority  of  the  human  family.  Dr.  Edwards  shows  not 
only  how  they  may  be  avoided,  but  in  plain  and  simple  language  he  tells  those 
already  afflicted  with  them  how  they  may  find  relief. 


PUB  Lie  A  TIONS.  \  5 


ELLIS,  DISEASES  OF  CHILDREN. 

A  Practical  Manual  of  the  Diseases  of  Children,  with  a  Formulary.  By  Ed- 
WARD  Ellis,  m.d.  Late  Physician  to  the  Victoria  Hospital  for  Children 
London.     Fourth  Edition  Enlarged.     Now  Ready.  Price  %-},.oc 

BY   SAME  AUTHOR. 

WHAT  EVERY  MOTHER  SHOULD  KNOW. 

i2mo.  Price  .75 

"  It  is  only  too  true  that  our  children  have  to  dodge  through  the  early  part  of  life  as  through  a  labyrinth.  Wc 
must  be  thankful  to  meet  with  such  a  sensible  guide  for  them  as  Dr.  Ellis."— /'a//  Mall  Gazette. 

FLUCKIGER,  THE  CINCHONA  BARKS. 

The  Cinchona  Barks  Pharmacognostically  Considered.  By  Professor  Fried- 
rich  Fluckiger,  of  Strasburg.  Translated  by  Frederick  B.  Power,  ph.d., 
formerly  Professor  of  Chemistry,  Philadelphia  College  of  Pharmacy,  now  Prc- 
fossor  of  Materia  Medica  and  Pharmacy,  University  of  Wisconsin.  With  8 
Lithographic  Plates.     Royal  Octavo.  Cloth,  $1.50 

FENNER,  ON  VISION,   Second  Edition,  Enlarged. 

Vision ;  Its  Optical  Defects,  the  Adaptation  of  Spectacles,  Defects  of  Accommo- 
dation, etc.  By  C.  S.  Fenner,  m.d.  With  Test  Types  and  74  Illustrations. 
Second  Edition,  Revised  and  Enlarged.     8vo.  Price  $3.50 

FENWICK,  THE  PRACTICE  OF  MEDICINE. 

Outlines  of  the  Practice  of  Medicine.  With  Appropriate  Formulas  and  Illus- 
trations.    By  Samuel  Fenwick,  m.d.,  Physician  to  the  London  Hospital.    i2mo. 

"  This  little  work  displays  a  sound  judgment  in  the  arrangement  of  its  subject  matter,  and  an  intimate  acquaint- 
ance with  the  practice  of  medicine  possessed  by  but  few  writers,  and  should  have  been  elaborated  into  a  more 
comprehensive  work.     Of  all  the  hand-books  we  have  seen,  this  is  certainly  one  of  the  best." — Medical  Herald. 

"  It  is  an  eminently  practieal  little  treatise,  pervaded  with  much  common  sense,  and  will  doubtless  be  found 
useful,.particularly  by  advanced  students." — Boston  Medical  and  Surgical  Journal. 

« 

BY   SAME   AUTHOR. 

ON  THE  STOMACH. 

Atrophy  of  the  Stomach  and  Its  Effect  on  the  Nervous  Affections  of  the  Digest- 
ive Organs.     8vo.  Price  $3.20 

FOTHERGILL,  ON  THE  HEART.     Second  Edition. 

The  Heart  and  Its  Diseases.  With  Their  Treatment.  Including  the  Gouty 
Heart.  By  J.  Miln'er  Fothergill,  m.d.,  Associate  Fellow  of  the  College  of 
Physicians  of  Philadelphia.      Second  Edition,   Entirely   Re-written.     Octavo. 

Price  53.50 

"  It  is  the  best,  as  well  as  the  most  recent  work  on  ;       "  To  many  an  earnest  student  it  will  prove  a  Kght  in 

the  subject  in  the  English  language."— A/i-rf/ca/  Press  darkness  ;    to  many  a  practitioner  cast  down  with  a 

and  Circular.  sense  of  his  powerlessness  to  cope  with  the  rout  and 

,,  rw.,               '.                      V      .       •         J     t..  ji     .v..  demoralization   of  Nature's   forces,  a   present  help  in 

••  The  most  interesting  chapter  is  undoubtedly  that  ,    °«    °«  ^^^Mit." -Philadelphia  Medical  Times. 

on  the  gouty  heart,  a  subject  which  Dr.  Fothergill  has  j    "■■■<="■"""■•                       r                  ■          e          \.- 

specially  studied,  and  on  which   he  entertains  views  "The  work  throughout  is  a  masterpiece  of  graphic. 

«;uch  as  are  likely,  we  think,  to  be  generally  accepted  lucid  writing,  full  of  good,  sound  teaching,  which  will 

by  clinical  physicians,  although  they  have  not  before  be  appreciated  alike  by   the  practitioner  and  the  stu- 

been  stated,  so  far  as   we  are   aware,  with  the  same  \    A^ta." —Students'  Journal. 

breadth  of  view  and  extended  illustration." — British  j 

Medical  yournal.  ' 

FULTON,  ON  PHYSIOLOGY. 

A  Text-Book  of  Physiology.  By  J.  Fulton,  m.d..  Professor  at  Trinity 
Medical   College,   Toronto.     Second   Edition,  Illustrated  and   Revised.     8vo. 

Price  %\.oo 


i6  P.  BLAKISTON,  SON  &-  CO.'S 


FLOWER,  DIAGRAMS  OF  THE  NERVES. 

Diagrams  of  the  Nerves  of  the  Human  Body.  Exhibiting  their  Origin, 
Divisions,  and  Connections,  with  their  Distribution  to  the  various  Regions  of  the 
Cutaneous  Surface,  and  to  all  the  Muscles.  By  William  H.  Flower,  f.r.c.s., 
F.R.S.,  Hunterian  Professor  of  Comparative  Anatomy,  and  Conservator  of  the 
Museum  of  the  Royal  College  of  Surgeons.  Third  Edition,  thoroughly  revised. 
With  six  Large  Folio  Maps,  or  Diagrams.     Royal  Quarto.  Price  $3.50 

"  Admirably  arranged,  and  will  be  of  incalculable  aid  to  the  student  of  anatomy.  Each  of  the  large  and 
beautiful  plates  is  accompanied  with  explanatory  text." — A^  K  Medical  Record. 

"  The  nerves  and  ganglia  are  clearly  represented.  The  impressions  are  well  made,  and  no  doubt  the  diagrams 
will  prove  \i%f^i\3\."— Medical  and  Surgical  Reporter. 

FLAGG,  PLASTIC  FILLING. 

Plastics  and  Plastic  Filling ;  As  Pertaining  to  the  Filling  of  all  Cavities  of  De- 
cay in  Teeth  below  Medium  in  Structure,  and  to  Difficult  and  Inaccessible 
Cavities  in  Teeth  of  all  Grades  of  Structure.  With  some  beautifully  executed 
Illustrations.  By  J.  Foster  Flagg,  d.d.s..  Professor  of  Dental  Pathology  and 
Therapeutics  in  Philadelphia  Dental  College.     Octavo.  2d  Edition.     Price  $400 

FOX,  WATER,  AIR  AND  FOOD. 

Sanitary  Examinations  of  Water,  Air  and  Food.  By  Cornelius  B.  Fox, 
M.D.    94  Engravings.     8vo.  Price  $4.00 

FOSTER,  CLINICAL  MEDICINE. 

Lectures  and  Essays  on  Clinical  Medicine.  By  Balthazar  Foster,  m.d. 
Illustrated.     8vo.  Price  S'l.oo 


"No  one  can  peruse  the  thoughtful  comments  of  our 
author  upon  every  subject  he  considers,  without  feeling 
himself  a  wiser  man  for  his  pains." — N.  Y.  Medical 
yourttal. 


"  It  is  the  record  of  honest  work,  such  as  Dr.  Foster 
may  be  proud  of ;  we  can  recommend  itto  the  profession; 
it  may  be  read  with  profit  and  advantage  by  both  prac- 
titioner and  student. — Edinburgh  Medical  journal. 


FOX,  ATLAS  OF  SKIN  DISEASES. 

Complete  in  Eighteen  Parts,  each  containing  Four  Chromo- Lithographic  Plates, 
with  Descriptive  Text  and  Notes  upon  Treatment.  In  all  72  large  colored  Plates. 
By  Tilbury  Fox,  m.d.,  f.r.c.p.,  Physician  to  the  Department  for  Skin  Diseases 
in  University  College  Hospital.     Folio  Size. 

Price  $1.00  each,  or  complete,  bound  in  cloth,  $20.00 

No  Atlas  of  Skin  Diseases  has  been  issued  in  this  country  for  many  years,  and  no 
complete  work  of  the  kind  is  now  procurable  by  the  Profession.  This  one,  brought 
out  under  the  editorial  supervision  and  care  of  Dr.  Tilbury  Fox  (the  most  distin- 
guished writer  on  Cutaneous  Medicine  now  in  the  English  language),  is  partly  based 
upon  the  classical  work  of  Willan  and  Bateman  (now  entirely  out  of  print),  but  com- 
pletely remodeled,  so  as  to  represent  fully  the  Dermatology  of  the  present  day. 

"  Preference  will  be  given  to  this  work  over  Hebra;  not  simply,  however,  because  it  is  a  home  production,  but 
by  reason  of  the  manner  of  its  execution,  the  excellent  delineation  of  disease,  and  the  natural  coloring  of  the  plates. 
.  .  .  The  letter-press  is  entirely  new.  In  the  accuracy  of  the  latter  the  subscriber  may  have  the  fullest  confi- 
dence, since  it  is  from  the  pen  of  Dr.  Tilbury  Fo.x." — British  and  Foreign  Medico- Chirurgical  Review. 

FRANKLAND,  WATER  ANALYSIS. 

Water  Analysis,  For  Sanitary  Purposes,  with  Hints  for  the  Interpretation  of 
Results.     By  E.  Frankland,  m.d.,  f.r.S.     Illustrated.     i2mo.  Price  51.00 

"The  work  is  one  which  physicians  practicing  is 
the  country  and  in  villages  and  towns  remote  from 
medical  centres  cannot  afford  to  be  without." — Medical 
and  Surgical  Reporter. 


"  The  author's  world-wide  reputation  will  commend 
this  manual  to  all  sanitarians,  and  they  will  not  be  dis- 
appointed in  finding  all  the  essentials  of  the  important 
subject  of  which  it  ireMs."— The  Sanitarian. 


GRANVILLE.    NERVE  VIBRATION  AND  EXCITATION. 

Nerve  Vibration  and  Excitation  as  Agents  in  the  Treatment  of  Functional 
Disorder  and  Organic  Disease.  By  J.  Mortimer  Granville,  m.d.  Illustrated. 
8vo.  Price  $2.00 


PUBLICA  TIONS.  17 


GALLABJN.     DISEASES  OF  WOMEN. 

The  Student's  Guide  to  the  Diseases  of  Women.  By  A.  Lewis  Gallabin, 
M.A.,  M.D.,  F.R.c.P.     Illustrated  with  63  Engravings.     i2mo.  Price  $1.25 

15V  SAME  AUTHOR. 

A  MANUAL  OF  MIDWIFERY. 

For  Students  and  Practitioners.     Illustrated.  In  Press. 

%*  Prof.  Gallabin  is  Obstetric  Physician  to  Guy's  Hospital,  London,  and  occupies 
the  chair  of  Midwifery  in  that  Institution.  His  work  in  this  department  has  been 
noted  for  its  perfection  and  practical  character. 

GAMGEE.     WOUNDS  AND  FRACTURES. 

The  Treatment  of  Wounds  and  Fractures.  Clinical  Lectures  by  Sampson 
Gamgee,  F.R.S.E.,  Consuhing  Surgeon  to  Queen's  Hospital,  Birmingham.  34 
Engravings.     Second  Edition.     Octavo.  Price  $3.50 

GARDNER.     BRE^VING,  DISTILLING,  ETC. 

The  Brewer,  Distiller  and  Wine  Manufacturer ;  a  handbook  for  all  interested 
in  the  Manufacture  and  Trade  of  Alcohol  and  Its  Compounds.  Edited  by  John 
Gardner,  Fellow  of  the  Chemical  Society  of  London,  Editor  of  "  Cooley's 
Cyclopaedia,"  etc.     Illustrated.  Price  $1.75 

BV  THE  SAME  AUTHOR. 

THE  DYER  AND  BLEACHER, 

The  Dyer  and  Bleacher  ;  being  the  second  volume  of  the  Technological  Hand- 
books.    Octavo.  Price  $1.75 

GIBBES.     STUDENT'S  PATHOLOGY. 

Practical  Histology  and  Pathology.  By  Heneage  Gibbes,  m.b.  i2mo. 
Cloth.     Second  Edition.  Price  $1.50 

GILL.     ON   INDIGESTION.     Third  Edition. 

Indigestion  :  What  It  Is;  What  It  Leads  To  ;  and  a  New  Method  of  Treating 
it.     By  John  Beadnell  Gill,  m.d.     Third  Edition.     i2mo.  Price  $1.25 

GILLIAM'S  PATHOLOGY.     Illustrated. 

The  Essentials  of  Pathology ;  a  Handbook  for  Students.  By  D.  Tod  Gilliam, 
M.D.,  Professor  of  Physiology,  formerly  Professor  of  Pathology,  Starling  IVtedical 
College,  Columbus,  O.     With  47  Illustrations.     i2mo.  Cloth,  ;^2.oo 

GLISAN.     TEXT-BOOK  OF   MODERN   MIDWIFERY. 

A  Text-Book  of  Modern  Midwifery.  By  Rodney  Glisan,  m.d..  Emeritus 
Professor  of  Midwifery  and  Diseases  of  Women  and  Children,  in  the  Medical 
Department  of  Willamette  University,  Portland,  Oregon,  and  Late  President 
of  the  Oregon  State  Medical  Society.  With  129  Illustrations.  One  Volume. 
Octavo.     624  pp.  Price,  in  Cloth,  54.00  ;  in  Leather,  S5.00 

GOODHART.     THE   DISEASES  OF  CHILDREN. 

The  Student's  Guide  to  the  Diseases  of  Children.  By  J.  F.  Goodhart,  m.d., 
F.R.c.P.,  Physician  to  Evelina  Hospital  for  Children,  Demonstrator  of  Morbid 
Anatomy  at  Guy's  Hospital.  In  Press. 

GORGAS.     DENTAL  MEDICINE. 

A  Manual  of  Dental  Medicine,  Materia  Medica  and  Therapeutics.  By 
Ferdin.\nd  J.  S.  GoRG.^S,  M.D.,  D.D.S.,  Professor  of  the  Principles  of  Dental 
Science,  Dental  Surgery  and  Dental  Mechanism,  in  the  Dental  Department  of 
the  University  of  Maryland.     Octavo.  Price  S3.00 

GROSS.     BIOGRAPHY  OF  JOHN    HUNTER. 

John  Hunter  and  His  Pupils.  By  S.  D.  Gross,  m.d.,  Professor  of  Surger)'  In 
Jefferson  Medical  College,  Philadelphia.  With  a  beautifully  executed  full  length 
Portrait  of  the  Author  in  his  Study.  A  Handsome  Octavo  volume.  Bound  in 
Beveled.  Cloth.  Paper,  .75  ;  Cloth,  $1.25 


i8  P.  BLAKISTON,  SON  &'  CO:S 

GODLEE'S  ATLAS  OF  HUMAN  ANATOMY. 

Illustrating  most  of  the  Ordinary  Dissections  and  many  not  usually  practiced 
by  the  Student.  Accompanied  by  References  and  an  Explanatory  Text.  Com- 
plete. Folio  Size.  48  Colored  Plates.  By  Rickman  John  Godlee,  m.d., 
F.R.C.s.  Forming  a  large  Folio  Volume,  with  References,  and  an  Octavo 
Volume  of  Letter-press. 

Price  of  the  two  Volumes,  Atlas  and  Letter-press,  Cloth,  $20.00 

"  It  is  likely  to  prove  as  useful  to  the  physician  and  I  "  The  explanatory  text  is  concise,  well  written,  and 
surgeon  as  to  the  anatomist." — Medical  Times  and  contains  many  valuable  suggestions  for  the  surgeon." 
Gazette.  I    — London  Lancet. 

GOWERS,  SPINAL  CORD. 

Diagnosis  of  Diseases  of  the  Spinal  Cord.  With  Colored  Plates  and  Engrav- 
ings. A  Second  Edition,  Revised  and  Enlarged.  By  William  R.  Cowers, 
M.D.,  Assistant  Professor  Clinical  Medicine,  University  College,  London.  8vo. 
Third    Edition.  Price  $1.50 

BY  SAME  AUTHOR. 

OPHTHALMOSCOPY. 

A  Manual  and  Atlas  of  Medical  Ophthalmoscopy.  With  16  Colored  Auto" 
type  and  Lithographic  Plates  and  26  Wood  Cuts,  comprising  112  Original  Illus- 
trations of  the  Changes  in  the  Eye  in  Diseases  of  the  Brain,  Kidneys,  etc.   8vo. 

Price  $6.00 

EPILEPSY  AND  ITS  TREATMENT. 

Epilepsy  and  other  Chronic  Convulsive  Diseases  :  Their  Causes,  Symptoms, 
and  Treatment.     Octavo.  Price,  Cloth,  $4.00 

NERVOUS  DISEASES. 

A  Manual  of  Diseases  of  the  Nervous  System,  for  Practitioners  and  Students. 

In  Press. 

"  Dr.  Gowers,  while  profoundly  conversant  with  the  literature  of  his  subject,  has  not  allowed  himself  to  be 
influenced  to  an  undue  extent  by  the  writings  of  others,  but  while  fairly  stating  their  views,  where  this  is  neces- 
sary, he  at  the  same  time  brings  to  bear  upon  them  the  experience  derived  from  his  own  extensive  observations, 
and  when,  consequently,  they  receive  confirmrition  or  not  at  his  hands,  they  are  all  the  more  valuable  as  being  the 
outcome  of  the  most  searching  and  unbiased  criticism.  It  would  be  impossible,  within  the  limits  of  a  shot:  re- 
view, to  convey  an  adequate  idea  of  the  extent  of  Dr.  Gowers'  work." — Ediniurgk  Medical  yournal. 

GREENHOW,  BRONCHITIS. 

On  Chronic  Bronchitis,  especially  as  connected  with  Gout,  Emphysema,  and 
Diseases  of  the  Heart.     By  E.  Headlam  Greenhow,  m.d.  i2mo.      Price  $1.50 

BY    SAME  AUTHOR. 

ADDISON'S  DISEASE. 

Being  the  Croonian  Lectures,  delivered  before  the  Royal  College  of  Physi- 
cians, London.     Revised  and  Illustrated  by  Plates  and  Reports  of  Cases.     8vo. 

Price  I3.00 

"  The  book  forms  a  most  interesting  and  valuable  monograph,  comprehensive  and  exhaustive." — British 
.Medical  yournal. 

HUGHES,  COMPEND  OF  THE  PRACTICE  OF  MEDICINE. 

A  Compend  of  Practice.  By  Daniel  E.  Hughes,  m.d.,  Demonstrator  of 
Clinical  Medicine  at  Jefferson  Medical  College,  Philadelphia.     In  two  parts — 

Part  I. — Continued,  Eruptive,  and  Periodical  Fevers,  Diseases  of  the  Stom- 
ach Intestines,  Peritoneum,  Biliary  Passages,  Liver,  Kidneys,  etc.,  and  General 
Diseases,  etc. 

Part   II. — Diseases   of  the   Respiratory   System,    Circulatory   System,   and 
Nervous  System  ;  Diseases  of  the  Blood,  etc. 
Price  of  each  Part,  in  Cloth,  $1.00;  interleaved  for  the  addition  of  Notes,  51-25 

*^.*  These  little  books  can  be  regarded  as  a  full  set  of  notes  upon  the  Practice 
of  Medicine,  containing  the  Synonyms,  Definitions,  Causes,  Symptoms,  Prog- 
nosis, Diagnosis,  Treatment,  etc.,  of  each  disease,  and  including  a  number  of 
new  prescriptions.  They  have  been  compiled  from  the  lectures  of  prominent 
Professors,  and  reference  has  been  made  to  the  latest  writings  of  Professors 
Flint,  Da  Costa,  Reynolds,  Bartholow,  Roberts  and  others. 


PUBLICA  riONS. 


»9 


HABERSHON,  ON  THE   STOMACH. 

On  Diseases  of  the  Stomach — The  Varieties  of  Dyspepsia — Their  Diagnosis 
and  Treatment.  By  S.  O.  Habershon,  m.d.,  f.r.c.p.,  Senior  Physician  to,  and 
Late  Lecturer  on,  the  Principles  and  Practice  of  Medicine  at  Guy's  Hospital. 
Third  Edition,  Revised.     Crown  8vo. 

"  As  an  expression  of  the  results  of  long  personal  experience  in  both  hospital  and  private  practice,  conveyed 
in  agreeable  though  not  always  perspicuous  diction,  this  contribution  of  Dr.  Habershon's  has  special  value  of  its 
own,  and  is  so  far  entitled  to  the  favorable  consideration  of  the  practitioner,  as  is  already  testified  by  a  demand 
for  a  third  edition." — American  yournal  of  Medical  Sciences. 

HALE,  ON  CHILDREN. 

The  Management  of  Children  in  Health  and  Disease.  A  Book  for  Mothers. 
By  Mrs.  Amie  M.  Hale,  m.d.  Abounding  in  valuable  information  and  com- 
mon sense  advice.     New  Enlarged  Edition.     i2mo.  Price  .75 

"  We  shall  use  our  influence  in  the  introduction  of  this  work  to  families  under  our  care,  and  we  urge  the  pro- 
fession generally  to  follow  our  example." — Buffalo  Medical  and  Surgical  yournal. 

HORWITZ,  COMPEND  OF  SURGERY. 

A  Compend  of  Surgery,  including  Minor  Surgery,  Amputations,  Fractures, 
Ligatures,  Dislocations,  Surgical  Diseases,  etc.,  with  Differential  Diagnosis  and 
Treatment.     By  Orville  Horwitz,  b.s.,  m.d.,  with  Illustrations.  i2mo. 

Cloth,  ;^i.oo 

HARDWICKE,  MEDICAL  EDUCATION. 

Medical  Education  and  Practice  in  All  Parts  of  the  World.  Containing 
Regulations  for  Graduation  at  the  Various  Universities  throughout  the  World. 
By  Herbert  Junius  Hardwicke,  m.d.,  m.r.c.p, 


8vo. 


Price 


„  00 

"  Dr.  Hardwicke's  book  will  prove  a  valuable  source  of  information  to  those  who  may  desire  to  know  the 
conditions  upon  which  medical  practice  is  or  may  be  pursued  in  any  or  every  country  of  the  world,  even  to  the 
lemotest  corners  of  the  earth.  The  work  has  been  compiled  with  great  care,  and  must  have  required  a  vast 
amount  of  labor  and  perseverance  on  the  part  of  its  author." — Dublin  Medical  yournal. 

HARLEY,  ON  THE  LIVER.     Illustrated. 

On  Diseases  of  the  Liver,  with  or  without  Jaundice.  Diagnosis  and  Treat- 
ment. By  George  Harley,  M.D.  Author  of  the  Urine  and  Its  Derangements. 
With  Colored  Plates  and  Numerous  Illustrations.     Royal  Octavo. 

Price,  Cloth,  $5.00  ;  Leather,  $6.00. 

"  The  whole  subject-matter  is  treated  in  a  masterly 
manner,  and  the  work  is  destined  to  find  a  place 
among  the  classics." — Medical  Herald,  Louisville, 
Ky. 

"It  Is  the  outcome  of  a  mind  that  went  to  its  task 
amply  equipped  therefor.  It  is  the  product  of  long 
thinking  and  ripe  judgment.  .  .  .  We  must  con- 
tent ourselves  with  this  bare  statement,  hoping  that 
those  who  read  the  b:iok  will  derive  as  much  benefit  as 
ourselves." — New  Orleans  Medical  and  Surgical 
yournal. 


"  It  is  one  o{x.\\e  yreshest,  mast  readable,  and  most 
instructive  medical  books  that  have  been  laid  upon  our 
table  during  the  present  decade.  .  .  In  conclusion, 
we  commend  again  most  heartily  Dr.  Harley's 
extremely  valuable  book." — Philadelphia  Medical 
Times. 

"  The  work  is  far  in  advance,  in  original  and  prac- 
tical information,  of  any  treatise  on  the  subject  with 
which  we  are  acquainted,  and  is  worth  many  times  its 
cost  to  any  physician  treating  hepatic  troubles." — 
Chicago  Medical  Times. 

HOLDEN,  HUMAN  OSTEOLOGY.     Sixth  Edition. 

Comprising  a  Description  of  the  Bones,  with  Colored  Delineations  of  the  At- 
tachments of  the  Muscles.  The  General  and  Microscopical  Structure  of  Bone 
and  its  Development.  By  the  Author  and  A.  Doran,  f.r.c.s.,  with  Lithographic 
Plates,  etc.  By  Luther  Holden,  f.r.c.s.  Numerous  Illustrations.  Sixth 
Edition,  carefully  Revised.  Price  $6.00 

BY   same   author. 

ANATOMY. 

Manual  of  Dissections  of  the  Human  Body. 
200  Illustrations. 


Fifth  London  Edition.    With 
In  Press. 


LANDMARKS. 

Landmarks,  Medical  and  Surgical.     Third  London  Edition.      Revised  and 
Enlarged.  Price  ji.. 00 

"  Mr  Holden  is  the  happy  possessor  of  the  faculty  of  writing  interesting  works  on  Anatomy.  A  part  of  the 
charm  consists  in  the  frequent  references  to  practical  points,  and  in  the  explanation  of  the  advantages  a-x  object* 
of  details  of  structures."— .fft'rff'w  Medical  and  Surgical  yournal. 


p.  BLAKISTON,  SON  &-  CO:s 


HEATH'S  OPERATIVE  SURGERY. 

A  Course  of  Operative  Surgery,  consisting  of  a  Series  of  Plates,  each  plate 
containing  Numerous  f'igures.  Drawn  from  Nature  by  the  Celebrated  Anatomi- 
cal Artist,  M.  Leveille,  of  Paris,  Engraved  on  Steel  and  Colored  by  Hand, 
under  his  immediate  superintendence,  with  Descriptive  Text  of  Each  Operation'. 
By  Christopher  Heath,  f.r.c.s..  Surgeon  to  University  College  Hospital,  and 
Holme  Professor  of  Clinical  Surgery  in  University  College,  London.  One  Large 
Quarto  Volume.      Second  Edition,  Revised  and  Enlarged.     Subscription. 

The  author  has  embodied  in  this  work  the  experience  gained  by  him  during 
twenty  years  of  surgical  teaching.  It  comprises  all  the  operations  that  are  required 
in  ordinary  surgical  practice.  He  has  selected  for  illustration  and  description  those 
methods  which  appear  to  give  the  best  results  in  practice,  referring  to  the  errors 
likely  to  occur  and  the  best  methods  of  avoiding  them. 

BY   SAME   author. 

THE   STUDENT'S  GUIDE  TO  SURGICAL   DIAGNOSIS. 

i3mo.  Price  ^1.25 

"Mr.  Heath  is  so  well  known,  both  as  a  practical  surgeon,  teacher  and  writer,  that  anything  from  his  pen  re- 
quires no  introduction  from  the  hands  of  reviewers,  and  scarcely  any  notice  but  the  announcement  of  the  fact  that 
he  has  written  a  book." — Medical  Record. 

A  MANUAL  OF   MINOR    SURGERY   AND   BANDAGING. 

Sixth    Edition,   Revised    and   Enlarged.      With    115    Illustrations.       i2mo. 

Price  $2.00 

"This  excellent  work  should  not  be  termed  a  '  Minor'  Surgery,  but  it  really  consists  of  the  sum  and  substance 
of  Practical  surgery.     We  would  not  exchange  it  for  any  book  in  our  possession." — Southern  Clinic. 

HEATH'S  PRACTICAL  ANATOMY.     Fifth  London  Edition. 

Practical  Anatomy.  A  Manual  of  Dissections.  Fifth  London  Edition.  24 
Colored  Plates,  and  nearly  300  other  Illustrations.  Price  I5.00 

INJURIES  AND  DISEASES  OF  THE  JAWS. 

The  Jacksonian  Prize  Essay  of  the  Royal  College  of  Surgeons  of  England, 
1867.      Third  Edition.    Revised,  with   over   150  Illustrations.     Octavo. 

HOOD,  ON  GOUT  AND  RHEUMATISM. 

A  Treatise  on  Gout,  Rheumatism,  and  the  Allied  Affections.  Their  Treat- 
ment, Complications,  and  Prevention.  By  Peter  Hood,  m.d.  Second  Edi- 
tion, Revised  and  Enlarged.     With  some  Considerations  on  Longevity.  Octavo. 

Price  ^53. 50 

"  The  Observations  on  Treatment  are  specially  to  be  commended." — London  Lancet. 

HOLDEN,  THE  SPHYGMOGRAPH. 

The  Sphygmograph.  Its  Physiological  and  Pathological  Indications.  By 
Edgar  Holden,  m.d.  .  Illustrated  by  Three  Hundred  Engravings  on  Wood. 
8vo.  Price  $2.00 

HOLMES,  THE  LARYNGOSCOPE. 

A  Guide  to  the  Use  of  the  Laryngoscope  in  General  Practice.  By  Gordon 
Holmes,  m.d.,  Physician  to  the  Throat  and  Ear  Infirmary.     i2mo.     Price  Si.oo 

BY   SAME   author. 

VOCAL  PHYSIOLOGY. 

Vocal  Physiology  and  Hygiene.  With  reference  to  the  Cultivation  and 
Preservation  of  the  Voice.     Illustrated.     i2mo. 

HOFF,  ON  HEMATURIA. 

Haematuria  as  a  Symptom  of  the  Diseases  of  the  Genito-Urinary  Organs.  By 
O.  Hoff,  m.d.     Illustrated.     i2mo.  Price  .75 


PUB  Lie  A  TIONS.  21 


HUNTER,  MECHANICAL  DENTISTRY. 

A  Practical  Treatise  on  the  Construction  of  the  Various  kinds  of  Artificial 
Dentures,  with  Formulae,  Receipts,  etc.  By  Charles  Hunter,  d.d.s.  100 
Illustrations.     i2mo.  Price  $1.50 

"  It  is  the  outcome  of  his  own  experience  of  some  twenty  years  as  a  Mechanical  Dentist,  and  contains,  moreover, 
much  derived  from  practical  knowledge  of  other  dentists.  The  value  of  the  book  is  also  much  added  to  by  illus- 
Jrations.  It  will  be  very  useful  to  the  Dental  Student,  and  to  all  Mechanical  Dentists." — London  Medical  Times 
*nd  Gazette. 

HUTCHINSON'S    ILLUSTRATIONS    OF    CLINICAL   SUR- 
GERY.    First  Volume  Complete. 

Consisting  of  Plates,  Photographs,  Woodcuts,  Diagrams,  etc.  Illustrating 
Surgical  Diseases,  Symptoms,  and  Accidents;  also  Operations  and  other 
Methods  of  Treatment.  With  Descriptive  Letter-press.  By  Jonathan  Hutch- 
inson, F.R.C.S.,  Senior  Surgeon  to  the  London  Hospital,  Surgeon  to  the  Moor- 
fields  Ophthalmic  Hospital,  and  to  the  Hospital  for  Diseases  of  the  Skin,  Black- 
friars.  In  Quarterly  Fasciculi.  Imperial  4to.  Volume  i.  (Ten  Fasciculi)  bound 
complete  in  itself.  Price  $25.00.  Parts  Eleven  to  Sixteen  of  Volume  2,  Now 
Ready.  Each,  $2.50 

HEWITT,  DISEASES  OF  WOMEN.     Fourth  Edition. 

The  Diagnosis,  Pathology,  and  Treatment  of  Diseases  of  Women,  Including 
the  Diagnosis  of  Pregnancy.  Founded  on  a  Course  of  Lectures  Delivered  at  St. 
Mary's  Hospital  Medical  School.  By  Graily  Hewitt,  m.d.,  Lond.,  m.r.c.p.. 
Physician  to  the  British  Lying-in  Hospital ;  Lecturer  on  Midwifery  and  Diseases 
of  Women  and  Children  at  St.  Mary's  Hospital  Medical  School;  Honorary 
Secretary  to  the  Obstetrical  Society  of  London,  etc.  The  Fourth  American 
Edition.     Revised  and  Enlarged,  with  New  Illustrations.     Octavo. 

Price,  Paper,  $1.50;  Cloth,  $2.50 


"  Readers  of  the  former  editions  will  not  require  to 
be  told  that  the  additions  now  made  are  of  the  highest 
possible  excellence." — Times  and  Gazette. 

"  It  is  one  of  the  most  useful,  practical,  and  compre- 
hensive works  upon  the  subject  in  the  English  language, 
a  true  guide  to  the  student,  and  an  invaluable  means  of 
reference  for  the  teacher." — ^V.  Y.  Medical  Record. 


"  The  excellent  work  of  Dr.  Hewitt  presents — in  a 
form  well  adapted  to  conduct  the  student  to  a  knowledge 
of  the  Diseases  of  Women,  and  to  assist  the  young 
practitioner  in  his  study  of  these  diseases  at  the  bedside 
of  the  patient — a  very  full  and  clear  exposition  of  the 
views  entertained  by  the  most  authoritative  teachers  as 
to  their  pathological  treatment  and  their  correct  Diag- 
nosis."— A>ner.  Med.  yournal. 

HAY,  SARCOMATOUS  TUMOR. 

History  of  a  Case  of  Recurring  Sarcomatous  Tumor  of  the  Orbit  in  a  Child. 
By  Tho.mas  Hay,  m.d.     Illustrated.     Paper.  Price  .50 

HEWSON,  EARTH  IN  SURGERY. 

Earth  as  a  Topical  Application  in  Surgery,  Being  a  Full  Exposition  of  its  Use 
in  Cases  Requiring  Topical  Applications.  By  Addinell  Hewsox,  m.d.  Illus- 
trated.   8vo.  Price  $2.50 

HODGE,  ON  ABORTION. 

On  Foeticide  or  Criminal  Abortion.     By  Hugh  L.  Hodge,  m.d. 

Price,  Paper,  .30;  Cloth,  .50 
HODGE,  CASE-BOOK. 

Note-Book  for  Cases  of  Ovarian  Tumors.  By  H.  Lennox  Hodge,  m.d.  With 
Diagrams.  Price,  Paper,  .50 

HIGGINS,  DISEASES  OF  THE  EYE.     Now  Ready. 

A  Hand-Book  of  Ophthalmic  Practice.  By  Charles  Higgins,  f.r.c.s. 
Ophthalmic  Assistant  Surgeon    at  Guy's   Hospital.      Second  Edition.      i6mo. 

Price  .50 

Contents.— Section  i.  Discharge  from  the  Eyes.  ii.  Intolerance  of  Light,  in.  Iritis  and  Glaucoma,  iv. 
Diseases  of  the  Eyelids,  v.  Watering  of  the  Eye.  vi.  Acuteness  of  Vision,  Field  of  Vision,  Anomalies  of  Re- 
fraction, Astigmatism,  Accommodation,  Presbyopia,  vii.  Disturbance  of  Vision,  Use  of  the  Ophthalmoscope; 
Normal  and  Morbid  Appearances,     viii.  Injuries. 

'■We  have  rarely  seen  so  much  important  information  condensed  in  so  short  a  space." — American  Medical 
Vaurnal, 


22  P.  BLAKISTON,  SON  &-  CO.'S 


HARRIS,  THE  PRACTICE  OF  DENTISTRY.     Tenth  Edition. 

The  Principles  and  Practice  of  Dentistry.  Tenth  Revised  Edition.  In  great 
part  Rewritten,  Rearranged,  and  with  many  new  and  important  Illustrations. 
By  Chapin  a.  Harris,  m.d.,  d.d.s.  Edited  by  P.  H.  Austen,  m.d..  Professor 
of  Dental  Science  and  Mechanism  in  the  Baltimore  College  of  Dental  Surgery. 
With  nearly  400  Illustrations.     Royal  Octavo.    Price,  Cloth,  1:6.50 ;  Leather,  $7.^0 

This  new  edition  of  Dr.  Harris'  work  has  been  thoroughly  revised  in  all  its  parts, 
more  so  than  any  previous  edition.  So  great  have  been  the  advances  in  many 
branches  of  dentistry  that  it  was  found  necessary  to  rewrite  the  articles  or  subjects, 
and  this  has  been  done  in  the  most  efificient  manner  by  Professor  Austen,  for  many 
years  an  associate  and  friend  of  Dr.  Harris,  assisted  by  Professor  Gorgas  and  Thomas 
S.  Latimer,  m.d.  The  publishers  feel  assured  that  it  will  now  be  found  the  most 
complete  text-book  for  the  student,  and  guide  for  the  practitioner  in  the  English 
language. 

BY    SAME  AUTHOR. 

MEDICAL  AND  DENTAL  DICTIONARY.     Fourth  Edition. 

A  Dictionary  of  Medical  Terminology,  Dental  Surgery,  and  the  Collateral 

Sciences.     Fourth  Edition,  Carefully  Revised  and  Enlarged.     By  Ferdinand 

J.  S.  Gorgas,  M.D.,  d.d.s.,  Professor  of  Dental  Surgery  in  the  Baltimore  College, 

etc.     Royal  Octavo.  Price,  Cloth,  $6.50;  Leather,  ^357. 50 

This  Dictionary,  having  passed  through  three  editions,  and  been  for  some  time 
out  of  print,  has  been  again  carefully  revised  by  F.  J.  S.  Gorgas,  m.d.,  Dr.  Harris' 
successor  as  Professor  of  Dental  Surgery  in  the  Baltimore  College  of  Dental  Surgery. 
In  his  preface  to  this  new  edition,  the  editor  says  : — 

"  The  object  of  the  reviser  has  been  to  bring  the  book  thoroughly  up  to  the  pres- 
ent requirements  of  the  profession,  the  Medical  portion  having  been  as  carefully  re- 
vised and  added  to  as  that  devoted  more  especially  to  Dental  Science,  while  a 
number  of  obsolete  terms  and  methods  have  been  omitted.  In  nearly  every  one  of 
the  seven  hundred  and  forty-three  pages  of  the  former  edition  corrections  and  addi- 
tions have  been  made,  and  many  new  processes,  terms  and  appliances  described, 
some  of  which  are  not  found  in  any  other  work  published." 

HANDY,  ANATOMY. 

Text-Book  of  Anatomy  and  Guide  to  Dissections.  For  the  Use  of  Students. 
By  W.  R.  Handy,  m.d.     312  Illustrations.  Price  J53.00 

HILLIER,  DISEASES  OF  CHILDREN. 

A  Clinical  Treatise  on  the  Diseases  of  Children.  By  Thomas  Hillier,  m.d, 
8vo.  Price  $2.oc 

HUFELAND,  LONG  LIFE. 

The  Art  of  Prolonging  Life.  By  C.  W.  Hufeland.  Edited  by  Erasmus 
Wilson,  m.d.     i2mo.  Price  $i.oa 

"We  wish  all  doctors  and  all  their  intelligent  clients  would  read  it,  for  surely  its  perusal  would  be  attended 
-vith  pleasure  and  benefit." — American  Practitioner. 

"  It  certainly  should  be  in  the  library  of  every  physician." — Medical  Brief. 

HUNTER,  PORTRAIT  OF. 

Portrait  of  John  Hunter.  From  Sharp's  well  known  Engraving;  a  copy  of 
Sir  Joshua  Reynold's  Portrait.  For  Framing.  Large  size,  9x11;  sheet  16  x  20. 
Price,  in  the  Sheet,    sent  free  by  mail,   50   cents ;    or,   Handsomely    Framed^ 

Price  |(2.oo 


PUBLICA  TIONS.  23 


HEADLAND,  THE  ACTION  OF  MEDICINES.       Ninth  Edition. 

On  the  Action  of  Medicines  in  the  System.  By  F.  W.  Headland,  m.d. 
Ninth   American  Edition,  Revised  and  Enlarged.    8vo.  Price  $3.00 

"  It  displays  in  every  page  the  evidence  of  extensive  knowledge  and  of  sound  reasoning  ;  it  will  be  useful  alike 
to  those  who  are  just  commencing  their  studies,  and  to  those  who  are  engaged  iu  the  active  pursuits  of  pro- 
fessional life." — Medical  Times. 

"  The  very  favorable  opinion  which  we  were  amongst  the  first  to  pronounce  upon  this  essay  has  been  fully 
C'jnfirmed  by  the  general  voice  of  the  profession,  and  Dr.  Headland  may  now  be  congratulated  on  having  pro- 
duced a  treatise  which  has  been  weighed  in  the  balance,  and  found  worthy  of  being  ranked  with  our  standard 
medical  works." — London  Lancet. 

JAMES,  SORE  THROAT. 

On  Sore  Throat,  Its  Nature,  Varieties  and  Treatment,  Including  its  Con- 
nection with  other  Diseases.  By  Prosser  James,  m.r.c.p.  Fourth  Edition, 
Revised  and  Enlarged.     With  Colored  Plates  and  Numerous  Wood-cuts.     i2mo. 

Price  $1.25 

"  We  can  confidently  recommend  his  therapeutic  teachings  as  well  worthy  of  the  careful  consideration  of  the 
Profession,  for  they  set  forth  the  practice  of  an  enthusiastic  worker,  whose  special  experience  has  been  large  and 
lengthened." — British  Medical  yournal. 

"  The  practitioner  who  buys  Dr.  James'  unpretending  little  book  will  provide  himself  with  a  wise  and  practical 
clinical  commentary',  and  with  a  well  arranged  digest  of  long  and  varied  experience." — Westminster  Revievj. 

JONES,  AURAL  ATLAS. 

An  Atlas  of  Diseases  of  the  Membrana  Tympani.  Being  a  Series  of  Colored 
Plates,  containing  62  Figures.  With  appropriate  Letter-press  and  Explanatory 
Text.  By  H.  Macnaughton  Jones,  m.d.,  Surgeon  to  the  Cork  Ophthalmic  and 
Aural  Hospital.     4to.  Price  $4.00. 

"  The  cases  are  well  selected,  the  drawings  executed  from  life,  highly  artistic  and  very  conscientious,  and  the 
commentaries  indicate  familiarity  with  the  subject  and  good  judgment  in  dealing  with  it."^British  Medical 
yournal. 

BY   SAME    AUTHOR. 

AURAL  SURGERY. 

A  Practical  Hand-book  on  Aural  Surgery.  Illustrated.  Second  Edition,  Re- 
vised and  Enlarged,  with  new  Wood  Engravings.     i2mo.     Cloth.       Price  $2. 75 

JONES,  SIEVEKING  AND  PAYNE,  PATHOLOGICAL  AN- 
ATOMY. 

A  Manual  of  Pathological  Anatomy.  By  C.  Handfield  Jones,  m.d.,  and 
Edward  H.  Sieveking.  m.d..  Physician  to  St.  Mary's  Hospital..  A  New  En- 
larged Edition.  Edited  by  J.  F.  Payne,  m.d..  Lecturer  on  Morbid  Anatomy  at 
St.  Thomas'  Hospital.     With  Numerous  Illustrations.     Demi  8vo.     Price  $5.50. 

JONES,  ON  SIGHT  AND  HEARING. 

The  Defects  of  Sight  and  Hearing,  their  Nature,  Causes,  and  Prevention.  By 
T.  Wharton  Jones,  m.d.     Second  Edition.     i6mo.  Price  .50. 

KIRBY,  ON  PHOSPHORUS.     Fifth  Edition. 

Phosphorus  as  a  Remedy  for  Functional  Diseases  of  the  Nervous  System. 
By  E.  A.  KiRBY,  m.d.     Fifth  Edition.     8vo.  Price  $1.00 

BY   the  same   AUTHOR. 

SELECTED  REMEDIES. 

A  Pnarmacopceia  of  Selected  Remedies,  with  Therapeutic  Annotations,  Notes 
on  Alimentation  in  Disease,  Air,  Massage,  Electricity,  and  other  Supplementary 
Remedial  Agents,  and  a  Clinical  Index  ;  arranged  as  a  Handbook  for  Prescribers. 
By  Edmund  A.  Kirby,  m.d.,  m.r.c.s.,  late  Physician  to  the  London  City  Dis- 
pensary.    Sixth  Edition,  Enlarged  and  Revised.     4to.  Price  §2.25 

KOLLMEYER,  KEY  TO  CHEMISTRY. 

Chemia  Coartata,  or  Key  to  Modern  Chemistry.  By  A.  H.  Kollmeyer,  m.d. 
With  Numerous  Tables,  Tests,  etc.  Price  $2.25 

KIRKE,  PHYSIOLOGY.     Revised  and  Enlarged. 

A  Hand  book  of  Physiology.  By  Kirke.  Eleventh  London  Edition.  By 
W.  MoRRANT  Baker,  m.d.     420  Illustrations.     A'ow  Ready.  Price  $5.00 

"  This  is  undoubtedly  the  best  work  for  students,  on  Physiology,  extant." — Cincinnati  Med.  News. 


24  p.  BLAKISTON,  SON  &-  CO.'S 


KANE,  THE  OPIUM,  MORPHINE  AND  SIMILAR  HABITS. 

Drugs  that  Enslave.  The  Opium,  Morphine,  Chloral,  Hashisch  and  Similar 
Habits.    By  H.  H.  Kane,  m.d.,  of  New  York.     With  Illustrations.     Price  ?i.25. 

"  It  contains  a  large  amount  of  information  collected  with  much  labor  and  presented  in  a  systematic  manner. 
The  subject  of  the  chloral  habit  has  not  been  investigated  by  any  one,  we  believe,  so  thoroughly  as  Dy  Dr.  Kane." 
— Medical  Record. 

"  It  deserves  to  be  read  by  those  who  feel  an  interest  in  discouraging  .he  use  of  these  dangerous  drugs.  The 
book  is  embellished  by  an  excellent  phototype  frontispiece  of  Laocoon." — American  your nal  o/ Pharmacy. 

"  A  work  of  more  than  ordinary  ability  and  careful  research.  .  .  .  For  the  first  time,  reliable  statistics  on 
the  use  of  chloral  are  classified  and  published,  .  .  .  and  it  is  shown  that  the  use  of  c\\\ora\  cause.'i  a  mort 
complete  and  rapid  ruin  of  mind  and  body  than  either  opium  or  xaorphxat."— Druggists'  Circular  and  Gazette. 

KIDD,  THERAPEUTICS. 

The  Laws  of  Therapeutics ;  or,  the  Science  and  Art  of  Medicine.  By  Joseph 
KiDD.  M.D.     i2mo.     Cloth.  Price  $1.25. 

"  Dr.  Kidd  acknowledges  two  laws — that  oi contraria  contrariis  Z-nAsimilia  similibtis :  but  the  cases  he  gives 
in  his  chapter  on  ars  niedica  show  that,  like  a  sensible  practitioner,  he  does  not  allow  himself  Mindly  to  follow 
either  the  one  or  the  other,  but  seeks  out  the  cause  of  disease,  and  tries  by  rational  measures  to  remove  it.  The 
cases  are  the  most  valuable  part  of  the  book." — London  Practitioner . 

LANDIS,  A  COMPEND  OF  OBSTETRICS.     Illustrated. 

A  Compend  of  Obstetrics;  especially  adapted  to  the  Use  of  Students  and 
Physicians.  By  Hen'ry  G.  Landis,  m.d..  Professor  of  Obstetrics  and  Diseases 
of  Women  in  Starling  Medical  College,  Columbus,  Ohio.  Illustrated.  12  mo. 
Cloth.  Price  gi.oo:  interleaved  for  the  addition  of  Notes,  $1.25 

"  The  questions  are  well  chosen,  the  answers  clear,  "  It   is  complete,  accurate  and  scientific  ;  the  very 

concise,  and  well  up  to  the  present  state  of  obstetrical  i    best  book  of  its   kind." — Prof.   jf.   S.    Knox,   Rush 

science.      It  will  be  a  handy  book    for  reference  for  Medical  College,  Chicago. 

practitioner   as   well   as    student." — Prof.    E.    O.   P-  \        "I  have  been  teaching  in  this  department  for  many 

Roler,  Chicago  Afedical  College.  years,  and  am  free  to  say  that   this  will   be  the  best 

"  I  have  observed  no  statement  to  the  correctness  assistant  I  ever  had.     It  is  accurate  and  comprehen- 

of  which  I  could  take  exception.     There  are  very  few  |    sive,  but  brief  and  pointed." — Prof.  P.  D.    Yost,  St. 

practitioners  who  cannot  be  instructed  by  its  perusal."  Louis. 

—David  IVark,  M.D.,   U.  S.  Medical  College,  New  \ 

York.  ! 

LEGG,  ON  THE  URINE. 

Practical  Guide  to  the  Examination  of  the  Urine,  for  Practitioner  and  Student. 
By  J.  WiCKHAM  Legg,  m.d.     Fifth  Edition,  Enlarged.     Illustrated.     i2mo. 

Price  .75 

This  little  work  is  intended  to  supply  the  Physician  or  Student  with  a  concise  guide 

to  the  recognition  of  the  different  characteristics  of  the  urine,  and  though  small  and 

well  adapted  to  the  pocket,  contains,  probably,  everything  that  could  be  gleaned 

from  a  larger  work. 

LEARED,  IMPERFECT  DIGESTION. 

The  Causes  and  Treatment  of  Imperfect  Digestion.  By  Arthur  Leared,  m.d. 
The    7th    Edition.     Revised  and  Enlarged.     i2mo.  Price  >2.oo 

LIEBREICH,  ATLAS  OF  OPHTHALMOSCOPY. 

An  Atlas  of  Ophthalmoscopy,  containing  12  Full-page  Chromo-Lithographic 
Plates,  with  59  Figures.  By  R.  Liebreich,  m.d.  Second  Edition,  Enlarged. 
Large  Quarto. 

LIVEING,  ON  SICK  HEADACHE. 

Megrim,  or  Sick  Headache  and  Some  Allied  Disorders.  By  Edward  Live- 
ING,  M.D.     With  Plates,  Tables,  etc.     8vo.  Price  $5. 50 

LEBER  AND  ROTTENSTEIN,  DENTAL  CARIES. 

Dental  Caries  and  Its  Causes.  An  Investigation  into  the  Influence  of  Fungi 
in  the  Destruction  of  the  Teeth.  By  Drs.  Leber  and  Rottenstein.  Illustrated. 
8vo.  Paper  Cover  75  cents  ;    Cloth,  Si. 25 

'■  The  work  gives  the  result  of  patient  observation,  presents  the  deductions  of  its  authors  with  a  perspicuity  ami 
111  Hi<_!,ty  calculated  to  secure  for  its  positions  a  thoughtful  consideration.  We  heartily  commend  it  as  an  eduCA 
tional  work." — Dental  Cosmos. 


PUBLIC  A  TIONS.  s; 


I.EWIN,  ON  SYPHILIS. 

The  Treatment  of  Syphilis.  By  Dr.  George  Lewin,  of  Berlin.  Translated 
by  Carl  Proegler,  m.d.,  and  E.  H.  Gale,  m.d.,  Surgeons  U.  S.  Army.  Illus- 
trated.    l2mo.  Price  $1.25 

"  When  such  authorities  as  Dr.  Drj-sdale  (as  we  quoted  a  few  weeks  ago)  condemn  theuseof  mercury  in  syphilis 
as  "  too  dangerous,"  while,  on  the  other  hand,  eminent  surgeons,  such  as  Professor  Gross,  will  not  treat's  case 
without  that  drug,  general  practitioners  will  gladly  welcome  any  media  via  which  gives  us  all  the  good  effects  oi 
mercurials  without  any  danger  of  their  ill  results  appearing.  This  is  what  is  accomplished  by  Dr.  Lewin." — 
Philadilphia  Medical  and  Surgical  Reporter. 

LIZARS,  ON  TOBACCO. 

The  Use  and  Abuse  of  Tobacco.     By  John  Lizars,  m.d.  i2mo.         Price  .50 

LONGLEY,   POCKET  MEDICAL  LEXICON. 

Students'  Pocket  Medical  Dictionary,  Giving  the  Correct  Definition  and  Pro- 
nunciation of  all  Words  and  Terms  in  General  Use  in  Medicine  and  the  Collate- 
ral Sciences,  with  an  Appendix,  containing  Poisons  and  their  Antidotes,  Abbre- 
viations Used  in  Prescriptions,  and  a  Metric  Scale  of  Doses.  By  Ell^vs  Longley. 
24mo.  Price,  Cloth,  $1.00;  Tucks  and  Pocket  $1.25 

This  is  an  entirely  new  Medical  Dictionary,  containing  some  300  compactly 
printed  24mo  pages,  very  carefully  prepared  by  the  author,  who  has  had  much  ex- 
perience in  the  preparation  of  similar  works,  assisted  by  the  Professors  of  Chemistry 
and  of  Botany  in  one  of  our  leading  medical  colleges. 

"  This  little  book  will  be  welcomed  by  students  in  |  "  It  is,  we  believe,  also  the  only  lexicon  in  existence 

medicine  and  pharmacy  as  a  convenient  pocket  com-  ,  in  which  the  pronunciation  of  words  is  fully  and  dis- 

panion,    giving  the   pronunciation,    acceptation,   and  '  tinctly  marked." — Canada  Medical  Review. 

definition  of  medical,  pharmaceutical     chemical   and  \  "  This  is  a  very  compact  and  complete  little  diaion- 

botanical  terms.    —American  Jour  nal  of  Pharmacy.  ^ry.  We  commend  it  as  particularly  useful  to  students." 

"  It  would  seem  to  be  just   the  book  for  dental  and  I  — New  York  Medical  yournal. 

medical  students." — Dental  Advertiser .  I 

LEFFMANN.     ORGANICAND  MEDICAL  CHEMISTRY. 

A  Compend  of  Organic  Chemistry,  including  Medical  Chemistry,  Urine  Ana- 
lysis and  the  Analysis  of  Water  and  Food.  By  Henry  Leffmann,  m.d., 
Professor  of  Clinical  Chemistry  and  Hygiene  at  the  Philadelphia  Polyclinic  and 
College  for  Graduates  in  Medicine.     i2mo. 

Cloth,  Price,  $1.00;  Interleaved  for  the  addition  of  Notes,  $1.25 

THE  POLYCLINIC. 

A  Monthly  Journal  of  Medicine  and  Surgery,  conducted  by  the  Faculty  of 
the  Philadelphia  Polyclinic  and  School  for  Graduates  in  Medicine.  Sample- 
copies  free.  Terms,  per  Annum,  Jlco 

MACDONALD,      MICROSCOPICAL       EXAMINATION      OF 
WATER  AND  AIR. 

A  Guide  to  the  Microscopical  Examination  of  Drinking  Water,  with  an  Appen- 
dix on  the  Microscopical  Examination  of  Air.  By  J.  D.  Macdoxald,  m.d. 
With  Twenty-five  Full-page  Lithographic  Plates,  Reference  Tables,  etc.  Second 
Edition,  Revised.     8vo.  Price  $2.75 

"The  volume  is  an  excellent  Aand-book  and  will  greatly  facilitate  the  study  of  the  subject." — Popular  Scicnct 
Monthly. 

UPCiS,  THE  THERAPEUTIC  FORCES; 

Or,  The  Action  of  Medicine  in  the  Light  of  the  Doctrine  of  Conservation  of 
Force.     By  Tho.mas  J.  Mays,  m.d.     i2mo.  Price  $1.25 


p.  BLAKISTON,  SON  6-   CO:S 


MACKENZIE,  ON  THE  THROAT  AND  NOSE.      Ready. 

Including  the  Pharynx,  Larynx,  Trachea,  CEsophagus,  Nasal  Cavities,  and 
Neck.  By  Morell  Mackenzie,  m.d.,  London,  Senior  Physician  to  the  Hos- 
pital tor  Diseases  of  the  Chest  and  Throat,  Lecturer  on  Diseases  of  the  Throat 
at  London  Hospital  Medical  College,  etc.,  etc. 

Vol.  I.     Including  the   Pharynx,  Larynx,  Trachea,  etc.     112  Illustrations. 

Price,  Cloth,  ^^4.00  ;  Leather,  ^S-oo 
Vol.  11.     Including  the  CEsophagus,  Nasal  Cavities,  Neck,  etc.     Illustrated. 

Price,  Cloth,  $3.00;  Leather,  $4.0x3 

THE  TWO  VOLUMES  TAKEN  TOGETHER,  CLOTH,  $6.00;  LEATHER,  $7.50. 
Author's  Edition,  issued-  under  his  supervision,  containing  all  the  original  Wood 
Engravings,  and  the  essay  on  "  Diphtheria,  Its  Causes,  Nature,  and  Treatment,"  for- 
merly published  separately.     Each  volume  sold  separately. 

"We  have  long  felt  the  want  of  a  thoroughly  practical  and  systematic  treatise  on  diseases  of  the  throat 
and  nasal  passages.  Admirable  essays  have  from  time  to  time  appeared  ;  no  standard  work  has  been  written. 
Any  one  familiar  with  laryngoscopic  work  must  appreciate  the  valuable  addition  now  made  to  this  spcc>al 
department  in  the  work  before  us.  The  entire  work  will  include  the  consideration  of  affections  of  the  pharynx, 
larynx,  trachea,  oesophagus,  nasal  cavities,  and  neck.  The  matter  now  presented  complete  for  the  first  time  is 
the  result  of  the  author's  large  and  unrivaled  experience,  both  in  hospital  and  private  practice,  extending  over 
a  period  of  twenty  years.  There  can  be  but  one  verdict  of  the  profession  on  this  manual — it  stands  without  any 
competitor  in  medical  literature,  as  a  standard  work  on  the  organs  it  professes  to  treat  of." — Dublin  yournal. 

"  It  is  both  practical  and  learned  ;  abimdantly  and  well  illustrated  ;  its  descriptions  of  disease  are  graphic,  and 
the  diagnoses  the  best  we  have  anywhere  seen.  To  give  examples  of  the  thoroughness  of  Dr.  Mackenzie's  book, 
we  may  cite  the  chapter  on  diphtheria,  which  embraces  47  pages.  The  chapter  on  non-malignant  tumors  of  the 
larynx  would  appear  to  be  absolutely  exhaustive.  Nowhere  else  have  we  seen  so  elaborate  a  statement  of  the  sub- 
ject. We  can  predict  for  this  work  a  high  position,  and  congratulate  its  distinguished  author  upon  its  appear- 
ance."— Philadelphia  Medical  Times. 

BY   SAME  AUTHOR. 

THE  PHARMACOPCEIA  of  the   Hospital  for  Diseases   of  the 
Throat  and  Nose. 

The  Fourth  Edition,  much  enlarged,  containing  250  Formulae,  with  Directions 
for  their  Preparation  and  Use.     i6mo.  Price  $1.25 

GROWTHS  IN  THE  LARYNX. 

Their  History,  Causes,  Symptoms,  etc.  With  Reports  and  Analysis  of  one 
Hundred  Cases.     With  Colored  and  Other  Illustrations.     8vo.  Price  $2.00 

HAY  FEVER:  ITS  ETIOLOGY  AND  TREATMENT. 

A  Lecture  delivered  at  the  London  Hospital  Medical  College      Octavo. 

Price,  Paper  covers,  .50 

MACNAMARA,  DISEASES  OF  THE  EYE. 

A  Manual  of  the  Diseases  of  the  Eye.  By  C.  Macnamara,  m.d.  Fourth 
Edition,  Carefully  Revised ;  with  Additions  and  Numerous  Colored  Plates,  Dia- 
grams of  Eye,  Wood-cuts,  and  Test  Types.     Demi  8vo.  Price  $4.00 

"As  a  book  of  ready  reference  on  diseases  of  the  eye  it  has  no  superior,  and  we  may  safely  say,  no  equal  in  our 
l^^nguage." — Cincinnati  Lancet  and  Obseruer. 

MADDEN,  HEALTH    RESORTS. 

Health  Resorts  for  the  Treatment  of  Chronic  Diseases.  A  Hand-Book,  the 
result  of  the  author's  own  observations  during  several  years  of  health  travel  in 
many  lands,  containing  also  remarks  on  climatology  and  the  use  of  mineral 
waters.     By  T.  M.  Madden,  m.d.     8vo.  Price  $2.50 

'■  Rarely  have  we  encountered  a  book  containing  so  much  information  for  both  invalids  and  pleasure  secl;ers." 

•-The  Sanitarian. 

MEDICAL  DIRECTORY  OF  PHILADELPHIA. 

A  Directory  of  the  Physicians,  Pharmacists,  Dentists,  Nurses,  Veterinary  Sur- 
geons, etc.,  of  Philadelphia.  Compiled  from  the  Registrar's  Records  in  the  Court 
of  Common  Pleas.  Containing  information  concerning  Medical  Colleges,  Hospi- 
tals, Asylums,  Charities,  etc.,  etc.     By  S.  B.  Hoppin,  m.d.     i2mo. 

Price,  Cloth,  $1.50 


PUBLICA  TIONS.  27 

MARSHALL  &  SMITH,  ON  THE  URINE. 

The  Chemical  Analysis  of  the  Urine.  By  John  Marshall,  m.d.,  and  Edgar 
F.  Smith,  m.d.,  of  the  Chemical  Laboratory,  Medical  Department,  University  of 
Pennsylvania.     Illustrated  by  Phototype  Plates.  i2mo.  Price  $1.00 

MARSHALL,  ANATOMICAL  PLATES; 

Or  Physiological  Diagrams.     Life  Size  (7  by  4  feet)  and  Beautifully  Colored. 
By  JOHX  Marshall,  f.r.s.     An  Entirely  New  Edition,  Revised  and  Improved, 
Illustrating  the  Whole  Human  Body. 
The  Set,  Eleven  Maps,  in  Sheets,  Price  $50.00 

"  "  handsomely  Mounted  on  Canvas,  with 

Rollers,  and  Varnished,  Price  $80.00 
An  E.xplanatory  Key  to  the  Diagrams,  Price  .50 

No.  I.  The  Skeleton  and  Ligaments.  No.  2.  The  Muscles,  Joints,  and  Animal  Mechanics.  No.  3.  The  Vis- 
cera in  Position^The  Structure  of  the  Lungs.  No.  4.  The  Organs  of  Circulation.  No.  5.  The  Lymphatics  or 
Absorbents.  No.  6.  The  Digestive  Organs.  No.  7.  The  Brain  and  Nerves.  No.  8.  The  Organs  of  the  Senses 
and  Organs  of  the  Voice,  Plate  i.  No.  g.  The  Organs  of  the  Senses,  Plate  2.  No.  10.  The  Microscopic 
Structure  of  the  Textures,  Plate  1.     No.  11.  The  Microscopic  Structure  of  the  Textures,  Plates. 

MARSDEN,  ON  CANCER. 

A  New  and  Successful  Mode  of  Treating  Certain  Forms  of  Cancer.  By  Alex- 
ander Marsden,  m.d.     Second  Edition.     Colored  Plates.     8vo.        Price  $3.00 

MARTIN,  MICROSCOPIC  MOUNTING. 

A  Manual  of  Microscopic  Mounting.  With  Notes  on  the  Collection  and  Ex- 
amination of  Objects,  and  upwards  of  150  Illustrations.  By  John  H.  Martin. 
Second  Edition,  Enlarged.     Svo.  Price  $2.75 

MORRIS,  ON  THE  JOINTS. 

The  Anatomy  of  the  Joints  of  Man.     Comprising  a  Description  of  the  Liga 
ments,  Cartilages,  and  Synovial  Membranes;  of  the  Articular  Parts  of  Bones, 
etc.     By  Henry  Morris,  f.r.c.s.     Illustrated  by  44  Large  Plates  and  Numerous 
Figures,  many  of  which  are  Colored.     Svo.  Price  §5.50 

MUTER,    MEDICAL   AND    PHARMACEUTICAL   CHEMIS- 
TRY. 

An  Introduction  to  Pharmaceutical  and  Medical  Chemistry.  Part  One. — 
Theoretical  and  Descriptive.  Part  Two. — Practical  and  Analytical.  Arranged 
on  the  principle  of  the  Course  of  Lectures  on  Chemistry  as  delivered  at,  and  the 
Instruction  given  in  the  Laboratories  of,  the  South  London  School  of  Pharmacy. 
By  John  Muter,  m.d.,  President  of  the  Society  of  Public  Analysts.  A  Second 
Edition,  Enlarged  and  Rearranged.  The  Two  Parts  bound  in  one  large  octavo 
volume.  Price  $6.00 

Part  Two. — Practical  and  Analytical.  Bound  Separately,  for  the  Special  Con- 
venience of  Students.     Large  8ro.     Cloth.  Price  $2.50 

MAC  MUNN,  THE  SPECTROSCOPE. 

The  Spectroscope  in  Medicine.  By  Chas.  A.  Mac  Munn,  m.d.  With  3 
Chromo-lithographic  Plates  of  Physiological  and  Pathological  Spectra,  and  13 
Wood  Cuts.     8vo.  Price  S3.0G 

"  This  book  is,  without  qiiestion,  the  best  that  has  yet  been  published  on  the  subject ;  to  those  not  familiar  with 
Physiological  Spectroscopy  it  will  prove  interesting,  while  to  those  who  are  working  in  this  field  it  is  a  neces' 
irfty." — AVzt/  York  Medical  yournul. 

MERRELL'S  DIGEST  OF  MATERIA  MEDICA. 

A  Digest  of  Materia  Medica  and  Pharmacy ;  forming  a  complete  Pharmaco- 
poeia for  the  use  of  Physicians,  Pharmacists  and  Students.  By  Albert  Mer- 
rell,  m.d.     Octavo.  Price,  Half  dark  Calf,  J400 


28  p.  BLAKISTON,  SON  6^»  CO:S 

MANN,  PSYCHOLOGICAL  MEDICINE. 

A  Manual  of  Psychological  Medicine  and  Allied  Nervous  Diseases.  Their 
Diagnosis,  Pathology,  Prognosis  and  Treatment,  including  their  Medico-Legal 
Aspects ;  with  chapter  on  Expert  Testimony,  and  an  abstract  of  the  laws  relating 
to  the  Insane  in  all  the  States  of  the  Union.  By  Edward  C.  AIann,  m.d.,  of 
New  York.  With  Illustrations  of  Typical  Faces  of  the  Insane,  Handwriting  of 
the  Insane,  and  Micro-Photographic  Sections  of  the  Brain  and  Spinal  Cord. 
Octavo.  Cloth,  $5.00 ;  Full  Leather,  s6.oo 

Fkom  The  London  Lancet,  April  iqth,  1884. 

'■  A  perusal  of  this  volume  reveals  the  (act  that  an  enormous  amount  of  research  has  been  carried  out  by  the 
author  in  order  to  present  to  the  proiesiion  a  digest  of  most  of  what  is  known  of  insanity  in  its  medical,  legal 
and  social  aspects.  The  lengthy  preface,  which  is  written  in  admirable  style,  shows  the  thorough  grasp  and 
liberal  spirit  with  which  thp  writer  has  prosecuted  his  work.  At  the  outset  an  energetic  protest  is  entered  against 
the  pernicious  system  of  forcing  the  intellect  at  the  expense  of  the  natural  development  of  the  nervous  systtm. 
This  comes  as  a  timely  warning  when  the  tendency  is  strong,  b6th  in  America  and  this  country,  to  educate  child- 
ren irrespective  of  their  physical  powers  and  mental  receptivity.  The  opening  chapter  is  devoted  10  a  consideia- 
tion  of  the  history  and  classification  of  insanity.  Others  follow  on  jeliology,  diagnosis  and  treatment,  civil  in- 
capacity, general  paralysis,  idiocy  and  dementia;  criminal  responsibility;  morbid  anatomy  and  pathology; 
treatment;  expert  testimony;  codification  of  the  criminal  common  law;  evolution  of  insanity  and  neuroses; 
and,  lastly,  the  psychology  of  crime.  Of  the  four  appendices,  the  first,  which  occupies  forty  pages  of  closely 
printed  matter,  consists  of  a  resume  of  the  legal  enactments  and  procedure  as  adopted  in  the  several  States  in 
the  Union ;  whilst  the  last  is  a  copious  index  of  the  literature  of  diseases  of  the  mind.  As  a  matter  of  course, 
the  author  condemns  the  practice  of  restraint  in  the  treatment  of  lunatics.  He  argues  strongly  in  favor  of  the 
appointment  of  expert  commissioners,  who  shall  exercise  a  supervision  of  asylums,  and  determine  the  medical 
questions  in  cases  of  alleged  criminal  irresponsibility.  The  letter-press  is  good,  and  the  phototypes  ol  the  phy- 
siognomy of  some  of  the  more  pronounced  of  mental  disorders  well  executed." 
Fkom  Thb  Alienist  and  NEfROLOGisT. 

"It  will  in  no  way  detract  from  the  merits  of  other  contemporary  works  to  say  that  Dr.  Mann's  book  will 
supply  a  want  which  no  other  has  yet  filled,  viz.:  a  manual  of  plain  rules  for  guidance  in  the  practical  considera- 
tion of  insanity  and  the  treatment  of  the  various  alhed  nervous  affections." 

MEADOWS,  OBSTETRICS,     Revised  Edition. 

A  Text-Book  of  Midwifery.  Including  the  Signs  and  Symptoms  of  Preg- 
nancy, Obstetric  Operations,  Diseases  of  the  Puerperal  State,  etc.  By  Alfred 
Meadows,  m.d.  Third  American,  from  Fourth  London  Edition.  Revised  and 
Enlarged.     With  145  Illustrations.     8vo.  Price  $2.00 


"  It  is  with  great  gratification  that  we  are  enabled 
to  class  Dr.  Meadows'  Manual  as  a  rare  exception, 
and  to  pronounce  it  an  accurate,  practical,  and  cred- 
itable work,  and  to  unhesitatingly  recommend  it  to 
both  student  and  practitioner." — American  yournal 
0/  Obstetrics. 

"  We  cannot  but  feel  that  every  teacher  of  Obstet- 
rics has  good  cause  to  congratulate  himself  on  being 
able  to  put  in  the  hands  of  the  student  a  book  which 
contains  so  much  valuable  and  reliable  information." 
— PhiUuielphia  Medical  Times. 


"  On  all  questions  of  treatment,  whether  by  medi- 
cines, by  hygienic  regimen,  or  by  mech.inical  or  oper- 
ative appliances,  this  treatise  is  as  satisfactory  as  a 
work  of  manual  size  could  be  :  students  and  practi- 
tioners can  liardlv  do  better  than  adopt  it  as  their 
vade  mecum." — The  Practitioner. 

"  The  systematic  arrangement  of  subjects,  and  the 
concise,  praetical  style  in  which  it  is  written,  make 
the  work  especially  valuable  as  a  student's  manual." 
Cliicago  Medical  Examiner. 


MEARS,  PRACTICAL   SURGERY. 

Practical  Surgery.  Including  :  Part  i. — Surgical  Dressings  ;  Part  it. — Band- 
aging; Part  III. — Ligations;  Part  iv. — Amputations.  With  227  Illustrations. 
By  J.  EvviNG  Mears,  m.d.,  Demonstrator  of  Surgery  in  Jefferson  Medical  Col- 
lege, and  Professor  of  Anatomy  and  Clinical  Surgery  in  the  Pennsylvania  Col- 
lege of  Dental  Surgery.     i2mo.  Price  $2.00 

"  Professor  Mears  has  written  a  convenient  and  use-  [  "  It  contains  a  great  deal  of  information  upon  the 
fill  book  for  students.  We  can  most  cordially  endorse  |  subjects  of  which  it  treats,  in  a  convenient  and  con- 
it  as  fulfilling  well  the  promise  made  in  its  modest  densed  form.  Each  division  is  well  illustrated,  thereby 
preface  " — Cincinnati  Lancet  and  Clinic.  I  rendering  the  text  doubly  clear." — Neiu  York  Meaical 

I  Record. 

MILLER,  ON  ALCOHOL. 

Alcohol.    Its  Place  and  Power.    By  Ja.mes  Miller,  f.r.c.s.   i2mo.    Price  .50 

MILLER  &  LIZARS,  ALCOHOL  AND  TOBACCO. 

Alcohol.  Its  Place  and  Power.  By  James  Miller,  f.r.c.s.  ;  and,  Tobacco, 
Its  Use  and  Abuse.  By  John  Lizars,  m.a.  The  two  essays  in  one  volume. 
i2mo.  Price  Si.cxa 


FUBLICA  TIONS.  29 


MENDENHALL,  VADE  MECUM. 

The  Medical  Student's  Vade  Mecum.  A  Compend  of  Anatomy,  Physiology, 
Chemistry,  The  Practice  of  Medicine,  Surgery,  Obstetrics,  etc.  By  George 
Mendenhall,  m.d.     Eleventh  Edition.     224  Illustrations.     8vo.        Price  $2.00 

MEIGS  AND  PEPPER,  DISEASES  OF  CHILDREN. 

A  Practical  Treatise  on  the  Diseases  of  Children.  By  J.  Forsyth  Meigs,  m.d., 
Fellow  of  the  College  of  Physicians  of  Philadelphia,  etc.,  etc.,  and  William 
Pepper,  m.d.,  Physician  to  the  Philadelphia  Hospital,  Provost  University  of 
Pennsylvania.  Seventh  Edition,  thoroughly  Revised  and  Enlarged.  A  Royal 
Octavo  Volume  of  over  1000  pages.  Price,  Cloth,  0.oo;  Leather,  $7.00 

"  With  the  recent  additions  it  may  safely  be  pronounced  one  of  the  best  and  most  comprehensive  worlcs  on  Dis- 
eases of  Children." — Nezu  York  Medical  yournal. 

"  Must  be  regarded  as  the  most  complete  work  on  Diseases  of  Children  in  our  IsinguOLge/'—Edindur^h  Medical 
yournal. 

"  We  have  seldom  met  with  a  text-book  so  complete,  so  just  and  so  readable  as  the  one  before  us." — American 
yournal  of  Obstetrics. 

MATHIAS,  LEGISLATIVE  MANUAL. 

A  Rule  for  Conducting  Business  in  Meetings  of  Societies,  Legislative  Bodies, 
Town  and  Ward  Meetings,  etc.  By  Benj.  Mathias,  a.m.  Sixteenth  Edition. 
i6mo.  Price  .50 

MORTON,  REFRACTION  OF  EYE. 

The  Refraction  of  the  Eye.  Its  Diagnosis  and  the  Correction  of  its  En  ors. 
With  Chapter  on  Keratoscopy.  By  A.  Stanford  Morton,  m.b.,  f.r.c.s.  i2mo. 
Second  Edition.  Price  $1.00 

"  The  author  has  not  only  given  very  thorough  rules  for  the  objective  and  subjective  examinations  of  the  eye  in 
the  various  conditions  of  refraction  which  present  themselves,  but  has  entered  into  an  explanation  of  the  phenom- 
ena observed,  which  is  at  once  scientific  and  elementary." — Edinburgh  Medical  yournal. 

MEDICAL  TIMES  AND  GAZETTE  (LONDON). 

A  Weekly  Journal  of  32  pages,  containing  Clinical  Lectures,  Hospital  Reports. 
Leading  Articles,  News,  Notes,  Book  Reviews,  Correspondence,  etc.,  etc. 

Subscription,  per  Annum,  $5.00 
OPHTHALMIC  REVIEW. 

A  Monthly  Record  of  Ophthalmic  Science.  Edited  by  Karl  Grossmann, 
m.d.,  of  Liverpool,  Priestley  Smith,  m.d.,  of  Birmingham,  and  John  B.  Story, 
M.D.,  of  Dublin.  The  only  periodical  representing  the  advancement  of  this 
science  in  England.     Now  in  its  third  year.         Subscription,  per  Annum,  $3.00 

OVERMAN,  MINERALOGY. 

Practical  Mineralogy,  Assaying,  and  Mining,  with  a  Description  of  the  Useful 
Minerals,  etc.  By  Frederick  Overman,  Mining  Engineer,  nth  Edition, 
l2mo.     Cloth.  Price  $1.00 

OGSTON,  MEDICAL  JURISPRUDENCE. 

Lectures  on  Medical  Jurisprudence.  By  Drs.  Francis  and  Francis  Ogston, 
Jr.     With  Copper-plate  Illustrations.     8vo.  Price  $6.00 

"  We  have  a  high  appreciation  of  Dr.  Ogston's  lectures,  and  can  cordially  recommend  the  work  as  accomplish- 
ing all  that  the  distinguished  author  promised  for  it." — American  yournal  o/ Medical  Science. 

OLDBERG,  PRESCRIPTION  BOOK.     300  New  Prescriptions. 

Three  Hundred  Prescriptions,  Selected  Chiefly  from  the  Best  Collections  of 
Formulae  used  in  Hospital  and  Out-patient-practice,  with  a  Dose  Table,  and  a 
Complete  Account  of  the  Metric  System.  By  Oscar  Oldberg,  phar.  d..  Late 
Medical  Purveyor,  United  States  Marine  Hospital  Service;  Professor  of  Materia 
Medica,  National  College  of  Pharmacy,  Washington,  D.  C. ;  Member  of  the 
American  Pharmaceutical  Association,  and  of  the  Sixth  Decennial  Committee 
of  Revision  and  Publication  of  the  Pharmacopoeia  of  the  United  States. 
i2mo.    Price,  Paper  Covers,  .75;  Cloth,  $1.25 


30  P-  BLAKISTON,  SON  &^  CO.'S 


BY   SAME   AUTHOR. 

THE  UNOFFICIAL  PHARMACOPCEIA.    Subscription  only. 

Comprising  over  700  Popular  and  Useful  Preparations,  not  Official  in  the 
United  States,  of  the  various  Elixirs,  Fluid  Extracts,  Mixtures,  Syrups,  Tinct- 
ures, Ointments,  Wines,  etc.,  etc.,  in  constant  demand  throughout  the  country. 
Thick  i2mo.     503  pp.     Half  Morocco.  Price  $3. 50 

"This  volume  is  one  of  the  most  practical  and  valuable  contributions  to  Pharmaceutical  work  of  recent  publica- 
tion, it  has  received  high  commendation  from  many  of  our  best  pharmacists  " — Lazell,  Marsh  &'  Gardiney, 
Wholesale  Druggists,  New  York  City. 

OTT,  ACTION  OF  MEDICINES. 

The  Action  of  Medicines.  By  Isaac  Ott,  m.d.,  late  Demonstrator  of  Experi- 
mental Physiology  in  the  University  of  Pennsylvania.  With  22  Illustrations. 
8vo.  Price  $2.00 

PAGE,  INJURIES  OF  THE  SPINE. 

Injuries  of  the  Spine  and  Spinal  Cord,  without  apparent  Lesion  and  Nervous 
Shock.  In  their  Surgical  and  Medico-Legal  Aspects.  By  Herbert  W.  Page, 
M.D.,  M.c. CANTAB.,  F.R.C.S.,  Surgeon  to,  and  Lecturer  on  Surgery  at,  St.  Mary's 
Hospital,  London.     Octavo,  Cloth.  Price  $4-oo 

PAGET,  SURGICAL  PATHOLOGY. 

Lectures  on  Surgical  Pathology,  Delivered  at  the  Royal  College  of  Surgeons. 
By  James  Paget,  f.r.s.  Third  Edition.  Edited  by  William  Turner,  m.d. 
With  Numerous  Illustrations.     8vo.  Price,  Cloth,  $7.00;  Leather,  $8.00 

PARKES,  PRACTICAL  HYGIENE.     Sixth  Edition. 

A  Manual  of  Practical  Hygiene.  By  Edward  A.  Parkes,  m.d.  The  Sixth 
Revised  and  Enlarged  Edition.     With  Many  Illustrations.     8vo.        Price  $3-oo 

"  Altogether  it  is  the  most  complete  work  on  Hygiene  which  we  have  seen." — Nevj  York  Medical  Record. 

"  We  find  that  it  never  fails  to  throw  light  on  any  hygienic  question  which  may  be  proposed." — Boston  Medi- 
cal and  Surgical  Journal. 

"  We  commend  the  book  heartily  to  all  needing  instruction  (and  who  does  not),  in  Hygiene  " — Chicago  Medi- 
cal Journal.  • 

PIESSE,  THE  MANUFACTURE  OF  PERFUMERY.    Fourth 
Edition. 

The  Art  of  Perfumery ;  or  the  Methods  of  Obtaining  the  Odors  of  Plants,  and 
Instruction  for  the  Manufacture  of  Perfumery,  Dentifrices,  Soap,  Scented  Pow- 
ders, Odorous  Vinegars  and  Salts,  Snuff,  Cosmetics,  etc.,  etc.  By  G.  W.  Septi- 
mus  PiESSE.      Fourth   Edition.      Enlarged.     366   Illustrations.      8vo.     Cloth. 

Price  $5.50 

"An  excellent  book." — Commercial  Advertiser. 
"  It  is  the  best  book  on  Perfumery  yet  published." — 
Scientific  American. 


"  Exceedingly  useful  to  druggists  and  perfumers." — 
Journal  of  Chemistry . 

"  Is  in  the  fullest  sense,  comprehensive." — Medical 
Record. 


PROCTER'S  PRACTICAL  PHARMACY. 

Lectures  on  Practical  Pharmacy.  With  43  Engravings  and  32  Lithographic 
P'ac-simile  Prescriptions.    By  Barnard  S.  Procter.    Second  Edition.    Octavo. 

Cloth,  ^4.50. 

PARRISH,  ALCOHOLIC  INEBRIETY. 

Alcoholic  Inebriety  from  a  Medical  Standpoint,  with  Illustrative  Cases  from 
the  Clinical  Records  of  the  Author.  By  Joseph  Parrish,  m.d.,  President  of 
the  American  Association  for  the  Cure  of  Inebriates.     i2mo.  Cloth,  $1.25 


POTTER'S     COMPENDS,    FOR    PHYSICIANS    AND    "STU- 
DENTS. 

These  Compends  are  based  on  the  lectures  of  prominent  Professors  and  the 
most  popular  Text-books.     They  ^^  ill  be  found  very  serviceable  to  physicians, 
as  remembrancers,  and  invaluable  to  students  in  the  Quiz  Class  and  Examina- 
tion Room.    By  Samuel  O.  L.  Potter,  m.d. 
ANATOMY,  with  63  Illustrations.     Revised  Edition. 
VISCERAL  ANATOMY,  with  Illustrations. 

MATERIA  MEDICA,  arranged  in  accordance  with  the  Sixth  Revision  U.  S.  Phar- 
macopoeia.    i2mo.     Cloth.     Revised  Edition,  with  Index. 

Price  for  each,  Interleaved  for  taking  Notes,  $1.25  ;  plain,  $1.00 

BY   THE   SAME   AUTHOR. 

SPEECH,  AND  ITS  DEFECTS. 

Considered  Physiologically,  Pathologically,  Historically,  and  Remedially;  being 
the  Lea  Prize  Thesis  of  Jefferson  Medical  College,  1882.  Revised  and  Corrected 
for  Publication.     i2mo.     Cloth.  Price  $1.00 

PENNSYLVANIA  HOSPITAL  REPORTS, 

Edited  by  a  Committee  of  the  Hospital  Staff.  J.  M.  DaCosta,  m.d.,  and 
William  Hunt,  m.d.  Vols,  i  and  2,  containing  Original  Articles  by  former 
and  present  Members  of  the  Staff.  With  Li«;hographic  and  other  Illustrations. 
8vo.  Price,  per  volume,  152.00 

PEREIRA,  PRESCRIPTION  BOOK.     Sixteenth  Edition. 

Physician's    Prescription    Book.     Containing   Lists  of  Terms,   Phrases,  Con- 
tractions and  Abbreviations  used  in  Prescriptions,  Explanatory  Notes,  Gram- 
matical Construction  of  Prescriptions,  Rules  for  the  Pronunciation  of  Pharma- 
ceutical   Terms.      By  Jonathan    Pereira,    m.d.,   f.r.s.      Sixteenth    Edition. 
Price,  Cloth,  $1.00;  Leather,  with  tucks  and  pockets,  $1.25 

PHYSICIAN'S  VISITING  LIST.     PUBLISHED  ANNUALLY. 

THIRTY-THIRD  YEAR  OF  ITS  PUBLICATION. 
SIZES   AND    PRICES. 

For  25  Patients  weekly.  Tucks,  pockets,  and  pencil,       -         -                  -  $1.00 

50         "             "  ....                      •>....  1.25 

75         "             "  ....                     "           .        .        .        .  1.50 

100         "             "  ....                     "            .        .        .        _  2.00 

5°  "     ■■-<"-  &yZ'D::.}     "    -  -  -  ■  ..50 

-         ■•  "-°>-      ljSryS&e"c'}  •■  -        ■        -         ■       3- 

INTERLEAVED   EDITION. 

For  25  Patients  weekly,  interleaved,  tucks,  pockets,  etc.,         -        -        -        -       1.25 
5°       "  ■■-<"-     {feJo&c}  "  ;       -       ;       -      3- 

PERPETUAL    EDITION,   WITHOUT    DATES    AND    WITH    SPECIAL    ME.MORANDUM    PAGES. 
SAME  SIZE  AS  THE  2$  PATIENTS,  INTERLEAVED.  Price,  $1.25 

The  Visiting  List  contains  a  List  of  New  Remedies,  a  Diagram  of  the  Chest, 
Upper  Abdomen  ;  a  New  Table  of  Poisons  and  their  Antidotes.  The  Metric  or 
French  Decimal  System  of  Weights  and  Measures.  Posological  Tables,  showing 
the  relation  of  our  present  system  of  Apothecaries'  Weights  and  Measures  to  that  of 
the  Metric  System,  giving  the  Doses  in  both. 

This  last  is  a  most  valuable  addition,  and  will  materially  aid  the  Physician.  So 
many  writers  now  use  the  metric  system,  especially  in  foreign  books  and  journals, 
that  one  not  familiar  with  it  is  constantly  confused,  and  in  many  cases  unable  to 
■understand  the  measurements  or  doses. 


"  It  is  certainly  the  most  popular  Visiting  List  ex- 
tant."— New  York  Medical  yotirnal. 

"  Its  compact  size,  convenience  of  arrangement,  dur- 
ability, and  neatness  of  manufacture  have  everywhere 


"The  book  is  convenient  in  form,  not  too  bulky,  and 
in  every  respect  the  very  best  Visiting  List  published." 
—  Canada  Medical  and  Surgical  yjurnal. 

"This  standard  Visiting  List,  for  completeness,  corn- 
obtained  for  it  a  preference." — Canada  Lancet.  \    pactness,  and  simplicity  of  arrangement,  is  excelled  hor 

none  in  the  market." — New  York  Medical  Record- 


p.  BLAKISTON,  SON  &-  CO:S 


POWER,  HOLMES,  ANSTIE  AND  BARNES  {^Drs.~). 

Reports  on  the  Progress  of  Medicine,  Surgery,  Pliysiology,  Midwifery,  Dis- 
eases of  Women  and  Children,  Materia  Medica,  Medical  Jurisprudence,  Ophthal- 
mology, etc.,  etc.     Reported  for  the  New  Sydenham  Society.     8vo.     Price  $2.00 

PURCELL,  ON  CANCER. 

Cancer.  Its  Allies  and  other  Tumors,  with  Specia  Reference  to  their  Medi- 
cal and  Surgical  Treatment.  By  F.  Albert  Purcell,  m.d  ,  m.r.c.s.  Surgeon 
to  the  Cancer  Hospital,  Brompton,  England.     8vo.  Price  $3.75 

PIGGOTT,  ON  COPPER. 

Copper  Mining  and  Copper  Ore.  With  a  full  Description  of  the  Principal 
Copper  Mines  of  the  United  States,  the  Art  of  Mining,  etc.  By  A.  Snowden 
PiGGOTT.     i2mo.  Price  $1.00 

PRINCE,  ORTHOPEDIC  SURGERY. 

Plastic  and  Orthopedic  Surgery.  By  David  Prince,  m.d.  Containing  a 
Report  on  the  Condition  of,  and  Advance  made  in.  Plastic  and  Orthopedic  Sur- 
gery, etc.,  etc.,  and  Numerous  Illustrations..    8vo.  Price  $4.50 

RADCLIFFE,  ON  "EPILEPSY. 

On  Epilepsy,  Pain,  Paralysis,  and  other  Disorders  of  the  Nervous  System. 
By  Charles  Bl.\nd  RADCLypE,  M.D.     Illustrated.     i2mo.  Price  $1.50 

"To  no  authority  can  the  medical  inquirer  turn  for  an  analysis  of  the  phenomena  of  epilepsy  with  more  satisfac- 
tion than  to  the  admirable  essay  of  Dr.  Radcliffe." — American  Journal  Medical  Sciences. 

RECORD   FOR  THE   SICK-ROOM. 

Designed  for  the  Use  of  Nurses  and  others  engaged  in  Caring  for  the  Sick. 
It  consists  of  Blanks,  in  which  may  be  recorded  the  Hour,  State  of  Pulse. 
Temperature,  Respiration,  Medicines  to  be  Given,  Food  Taken,  etc.,  etc.; 
together  with  a  List  of  Directions  for  the  Nurse  to  pursue  in  Emergencies.  By 
the  use  of  this  form  the  Nurse  can  at  a  glance  recall  the  Physician's  directions, 
instead  of  trusting  to  memory;  and  the  Physician  can,  by  consulting  it,  obtain 
correct  information  regarding  the  patient  during  his  absence.  Sample  Pages 
Free.  One  Copy,  25  cents  ;  Per  Dozen,  $2.50 

REYNOLDS,  ELECTRICITY. 

Lectures  on  the  Clinical  Uses  of  Electricity,  By  J.  Russell  Reynolds,  m.d., 
f.r.s.     Second  Edition.     i2mo.  Price  $1.00 

"  It  is  thoroughly  reliable  as  a  guide,  very  concise,  and  will  be  found  exceedingly  useful  to  the  general  practi- 
tioner."—  Canada  Lancet. 

RICHARDSON,    MECHANICAL    DENTISTRY.      Third   Edi- 
tion. 

A  Practical  Treatise  on  Mechanical  Dentistry.  By  Joseph  Richardson,  d.d.s. 
Third  Edition.     With  185  Illustrations.    8vo.    Price,  Cloth,  $4.00;  Leather,  $4.75 

"  Taken  as  a  whole.  Professor  Richardson's  work  is  a  valuable  contribution  to  the  dental  art,  and  is  beyond  all 
4iiestion  the  best  treatise  extant  upon  the  general  subject  of  Mechanical  Dentistry." — Dental  Cosmos. 

RIGBY  AND  MEADOWS,  OBSTETRIC  MEMORANDA. 

Dr.  Rigby's  Obstetric  Memoranda.  Fourth  Edition.  Revised.  By  Alfred 
Meadows,  m.d.     32mo.  Price  .qo 

RYAN,  ON  MARRIAGE. 

The  Philosophy  of  Marriage.  In  its  Social,  Moral  and  Physical  Relations, 
and  Diseases  of  the  Urinary  Organs.  By  Michael  Ryan,  m.d.  Member  of 
the  Royal  College  of  Physicians,  London.     i2mo.  Price  Ji.oo 


PUBLICA  TIONS.  33 


ROBERTS.     PRACTICE  OF   MEDICINE.     Fifth  Edition. 

The   Theory   and    Practice   of   Medicine.     By   Frederick    Roberts,   m.d. 
Fifth  Edition,  thoroughly  revised  and  enlarged,  with  New  Illustrations,     8vo. 

Price,  Cloth,  $5.00;  Leather,  f6.oo 

Recommended  at  the  University  of  Pennsylvania,  Yale  and  Dartmouth  Colleges, 
University  of  Michigan,  and  many  other  Medical  Schools. 

The  unexceptional  large  and  rapid  sale  of  this  book,  and  the  universal  commen- 
dation it  has  received  from  the  profession,  seems  to  be  a  sufficient  guarantee  of  its 
merits  as  a  Text-book.  The  publishers  are  in  receipt  of  numerous  letters  from 
Professors  in  the  medical  schools,  speaking  favorably  of  it,  and  below  they  give 
extracts  from  the  medical  press,  American  and  English,  attesting  its  superiority  and 
value  to  both  student  and  practitioner.  The  present  edition  has  been  thoroughly 
revised  and  much  of  it  re-written. 

"The  best  Text-book  for  Students  in  the  English  \  "To  the  student  it  will  be  a  gift  of  priceless  value." 
language.     We  know  of  no  work  in  the  English  Ian-  ;  — Detroit  Revieiu  of  Medicine. 

guage,   or  in  any   other,   which  competes  with   this  .      •<  \Ve  heartily  recommend  it  to  students,  teachers, 
one." — Edinburgh  Medical  fournal.  |  and  practitioners."— .Soj/ow   Medical  and    Surgical 

"  It  is  a  remarkable  evidence  oi  industry,  experi-  J  journal. 
ence,  and  research." — Practitioner.  "  it  is  of  a  much  higher  order  than  the  usual  compi- 

"  Dr.  Roberts'  book  is  admirably  fitted  to  supply]   ations  and  abstracts  placed  in  the  hands  of  students." 
the  want  of  a  good  hand-book,  so  much  felt  by  every    1 — Medical  and  Surgical  Ke/orter. 
medical  student." — Student's  journal  and  Hospital        ••  ][  jg  unsurpassed  by  any  work  that  has  fallen  into 
Gazette.  I  our    hands    as   a   compendium    for    students."  —  Tlie 

"  It  contains  a  vast  deal  of  capital  instruction  for  :  Clinic. 
the  student." — Medical  Times  and  Gazette.  \      "  We  particularly  commend  it  to  students  about  to 

"  There  are  great  excellencies  in  this  book,  which    enter  upon  thepracticeof  their  profession." — St.  Louis 
will  make  it  agreat  favorite  with  the  student. "—i^/cA-  i  Medical  and  Surgical  Journal, 
wond  and  Louisville  fournal.  I 

BY  THE  SAME  AUTHOR. 

MATERIA  MEDICA  AND    PHARMACY. 

A  Compend  for  Students.     i2mo.  Ready. 

RINDFLEISCH,  GENERAL  PATHOLOGY. 

General  Pathology;  a  Handbook  for  Students  and  Physicians.  By  Prof. 
Edward  Rindfleisch,  of  Wurzburg.  Translated  by  Wm.  H.  Mercur,  m.d., 
Edited  and  Revised  by  James  Tyson,  m.d..  Professor  of  Morbid  Anatomy  and 
Pathology,  University  of  Pennsylvania,  Cloth,  |2.co 

RINDFLEISCH,  PATHOLOGICAL  HISTOLOGY. 

A  Text-Book  of  Pathological  Histology.     By  Dr.  Edward  Rindfleisch. 
Translated  by  Drs.  Wm.  C.  Kolman  and  F.  T.  Miller.     208  Illustrations. 
Svo. 
ROYLE  AND  HARLEY,  MATERIA  MEDICA.    Sixth  Edition. 

A  Manual  of  Materia  Medica  and  Therapeutics.  By  Dr.  J.  Forbes  Royle. 
Sixth  Edition.  Edited  by  John  Harley,  m.d.  840  pages  and  numerous  Illus- 
trations.    Demi  Svo.  P"^^  ^5-00 

RICHTER'S    INORGANIC    CHEMISTRY. 

Inorganic  Chemistry,  a  Text-Book  for  Students.  By  Prof.  Victor  von 
Richter,  University  of  Breslau.  Authorized  Translation  from  the  Third  German 
Edition,  bv  Edgar  F.  Smith,  m.a.,  Ph.D.,  Prof,  of  Chemistry,  Wittenberg 
College,  formerly  in  the  Laboratories  of  the  University  of  Pennsylvania, 
Member  of  the  Chemical  Societies  of  Berlin  and  Paris,  with  89  Illustrations  and 
a  Colored  Plate  of  Spectra.     i2mo.     424  pages.  Cloth,  Price  $2.00 

by  same  author  and  translator. 
ORGANIC    CHEMISTRY. 

Organic  Chemistry,  a  Text-Book  for  Students,  authorized  translation  from  the 
Fourth  German  Edition.     Illustrated.  Preparing- 


54  P.  BLAKISTON,  SON  &-  CO.'S 

REESE.       MEDICAL      JURISPRUDENCE     AND     TOXI- 
COLOGY. 

A  Text-Book  of  Medical  Jurisprudence  and  Toxicology,  for  Medical  and 
Legal  Practitioners  and  Students.  By  John  J.  Reese,  m.d.,  Editor  of  Taylor's 
Jurisprudence,  Professor  of  the  Principles  and  Practice  of  Medical  Jurisprudence, 
including  Toxicology,  in  the  University  of  Pennsylvania  Medical  and  Law 
Schools.     Crown  Octavo.  Cloth,  $4.00;  Leather,  $5.00 

SANDERSON  AND  FOSTER,  THE   PHYSIOLOGICAL  LA- 
BORATORY. 

A  Hand-book  of  the  Physiological  Laboratory.  Being  Practical  Exercises  for 
Students  in  Physiology  and  Histology.  By  J.  Burdon  Sanderson,  m.d.,  E. 
Klein,  m.d.,  Michael  Foster,  m.d.,  f.r.s.,  and  T.  Lauder  Brunton,  m.d. 
With  over  350  Illustrations  and  Appropriate  Letter-press  Explanations  and  Ref- 
erences. 

Price,  Two  Volumes,  Text  and  Plates,  separate,       ...    J56.00 

'*      One  "  "  "  bound  together,  Cloth,        5,00 

"        "  "  "  "  "  "  Leather,    6.00 

Adopted  as  a  Text-book  at  Yale  College,  and  used  at  other  Medical  Schools  in 

America  and  England. 

"  Recognizing  the  fact  that  Physiology  is  emphatic-  I  "  We  confidently  recommend  it  to  the  attention  of  all 

ally  an  experimental  science,  it  furnishes  minute  in-  I  who  are  interested  in  the  wide  and  fertile  field  of  Phy- 

structions    for   performing  a  great  variety  of  exper-  I  siological  research." — Neiv  York  Medical  yournal. 
iments.  A  student  could  scarcely  desire  a  better  guide  "' 


— Boston  Medical  and  Surgical  journal. 


his  is  a  most  sup>erb  book,  and  fills  a  hiatus  which 
every  physiological  student  has  lamented." — Chicago 
Medical  yournal. 


SANDERSON,  PHYSIOLOGY.     Second  Edition. 

A  Syllabus  of  a  Course  of  Lectures  on  Physiology.  By  J.  Burdon  Sander- 
son, m.d.     For  the  Use  of  Students.     Second  Edition.     8vo.  Price  $1.50 

SANDERSON,  PRACTICAL  EXERCISES  IN  PHYSIOLOGY. 

8vo.     Illustrated. 

SANSOM,  PHYSICAL  DIAGNOSIS.     Third  Edition  just  ready. 

The  Physical  Diagnosis  of  Diseases  of  the  Heart.  Including  the  Use  of  the 
Sphygmograph  and  Cardiograph.  By  Arthur  Ernest  Sansom,  m.d.  Third 
Edition.     Revised  and  Enlarged.     With  Illustrations.     i2mo.  Price  ,52.00 

BY  SAME  author. 

DISEASES  OF  THE  HEART. 

The  Lettsomian  Lectures  on  the  Treatment  of  some  of  the  Forms  of  Valvular 
Disease  of  the  Heart.     Illustrated.     i2mo.  Cloth,  $1.25 

BY   SAME   author. 

ON   CHLOROFORM. 

Chloroform.     Its  Action  and  Administration.     i2mo.  Price  $1.50 

SMITH.     DYSMENORRHCEA. 

Its  Pathology  and  Treatment.  By  Heywood  Smith,  m.d..  Physician  to  the 
Hospital  for  Women  and  to  the  British  Lying-in  Hospital.     i2mo.       Price  $1.75 

SMITH,  RINGWORM. 

The  Diagnosis  and  Treatment  of  Ringworm.  By  Alder  Smith,  f.r.c.s. 
With  Illustrations.     i2mo.  Price  $1.00 

SMITH,  ON  NURSING. 

The  Efficient  Training  of  Nurses  for  Hospital  and  Private  Practice.  By  Wil- 
liam Robert  Smith.     Illustrated.    Third  Edition.  Price 


PUBLICA  TIONS.  35 


SMITH,  ON  CHILDREN. 

Clinical  Studies  of  Diseases  in  Children.     By  Eustace  Smith,  m.d.  Second 
Revised  Edition.  Price  §2.50 

MEDICAL  HERESIES,  HISTORICALLY  CONSIDERED. 

A  Series  of  Critical  Essays  on  the  Origin  and  Evolution  of  Sectarian  Medi- 
cine, embracing  a  Special  Sketch  aad  Review  of  Homoeopathy,  Past  and  Pres- 
ent. By  GoNZALVO  C.  Smythe,  a.m.,  m.d.  Professor  of  the  Principles  and 
Practice  of  Medicine,  College  of  Physicians  and  Surgeons,  Indianapolis,  Indi- 
ana.    i2mo.     Cloth.  Price  $1.25 

"  This  book  gives,  in  a  small  compjiss,  an  excellent  I  "  Students  and  others  interested   in   the  subject  of 

history  of  medicine,  from  its  earliest  day  to  the  present  ;  medicine  will  find  a  digest  of  the  entire  controversy 

time." — Buffalo  Medical  and  Surgical  Journal .  (between  the  various  schools  of  medi«-.ine)  presented  in 

"  Cannot  fail  to  be  of  interest,  not  only  to  the  medi-  I  '"i'*  \o\Mxa^." —Jjurnal  of  Education. 

cal  profession,  but  ;o  the  general  reader." — Baltimore  I  "  Professor  Smythe  has  succeeded  in  writing  a  brief, 

Gazette.  I  clfar,  and  interesting  sketch  of  the  evolution  of  medical 

•'  The  work  is  pleasantly  written,  in  an  easy,  familiar  \  f^entricities  and  of  modern  homoeopathy,  iu  facts  and 

«yle,  and  has  cost  the  writer  much  literary  research."  fallacies.   —Philadelphia  Medical  rimes. 

~Neiu  York  Medical  yournal.  \ 

SAVAGE,  FEMALE  PELVIC  ORGANS.     Author's  Edition. 

The  Surgery,  Surgical  Pathology  and  Surgical  Anatomy  of  the  Female  Pelvic 
Organs.  In  a  Series  of  Colored  Plates  taken  from  Nature,  with  Commentaries, 
Notes  and  Cases.  By  Henry  Savage,  m.d.,  f.r.c.s.  New  Edition.  Issued  by 
arrangement  with  the  Author,  from  the  original  Plates.     Quarto.       Price  $12.00 

SMITH.     WASTING    DISEASES  OF  CHILDREN. 

The  Wasting  Diseases  of  Infants  and  Children.  By  Eu.stace  Smith,  m.d  , 
F.R.C.P.,  Physician  to  the  East  London  Children's  Hospital.  Fourth  London 
Edition,  Enlarged.     Octavo.  Price  $3.00 

SCHULTZE,  OBSTETRICAL  PLATES. 

Obstetrical  Diagrams.  Life  Size.  By  Prof.  B.  S.  Schultze,  m.d.,  of  Berlin. 
Twenty  in  the  Set.     Colored. 

Price,  in  Sheets,  $15.00;  Mounted  on  Rollers  $25.00 

SCANZONI,  DISEASES  OF  WOMEN. 

A  Practical  Treatise  on  the  Diseases  of  the  Sexual  Organs  of  Women.  By 
Dr.  F.  W.  Von  Scanzoxi.     Translated  by  A.  K.  Gardiner,  m.d.     8vo. 

Price  $5.00 

SIEVEKING,  LIFE  ASSURANCE. 

The  Medical  Adviser  in  Life  Assurance.  By  E.  H.  Sieveking,  m.d.  i2mo. 
Second  Edition,  Revised.  Price  $2.00 

SHEPPARD,  ON  MADNESS. 

Madness,  in  its  Medical,  Social  and  Legal  Aspects.  A  series  of  Lectures  de- 
livered at  King's  Medical  College,  London.     By  Edgar  Sheppard,  m.d.     8vo. 

Price  $2.25 

STOCKEN,  DENTAL  MATERIA  MEDICA.     Third  Edition. 

The  Elements  of  Dental  Materia  Medica  and  Therapeutics  with  Pharmacopceia- 
By  James  Stocken,  d.d.s.     Third  Edition.     i2mo.  I2.50 

The  first  edition  of  this  book  was  disposed  of  in  a  little  less  than  four  months.  In 
making  this  revision  the  author  has  endeavored  to  make  it  still  more  useful  by  the 
addition  of  considerable  new  matter. 

SUTTON,  VOLUMETRIC  ANALYSIS.     Fourth  Edition. 

A  Systematic  Handbook  of  Volumetric  Analysis,  or  the  Quantitative  Estima- 
tion of  Chemical  Substances  by  Measure,  Applied  to  Liquids,  Solids,  and  Gases, 
By  Francis  Sutton,  f.cs.  Fourth  Edition.  Revised  and  Enlarged,  with  Illus- 
trations.    8vo.  Price  #5.00 


36  P.  B LA  K IS  TON,  SON  &-  CO.'S 


SEWELL,  DENTAL  ANATOMY  AND  SURGERY. 

A  Manual  of  Dental  Anatomy  and  Surgery,  Including  the  Extraction  of  Teeth. 
By  H.  E.  Sewell,  d.d.s.,  m.d.     With  77  Illustrations.     i2mo.  Price  $1.25 

"*  A  valuable  book  for  the  general  Practitioner  who    I  "  It  will  be  found  useful  to  the  general  Practitioner  in 

fe  in  want  of  a  practical  manual  relating  especially  to  the  management  of  many  incidental  affections  connected 

Jiseases  of  the  teeth." — Medical  Brief.  with  the  teeth  and   moulh,  which  cannot  always  be 

j  handed  over  to  the  specialist." — Pacific  Mtd.  Journal 

STILLE,  ON  MENINGITIS. 

Epidemic  Meningitis,  or  Cerebro-spinal  Meningitis.  By  Alfred  Stille,  m.d.. 
Professor  of  Practice  at  the  University  of  Pennsylvania.     8vo.  Price  $2.00 

"  The  name  of  the  author  is  a  sufficient  guarantee  that  this  monograph  is  elegant  in  style,  exhaustive  of  its  sub- 
ject and  rich  with  practical  suggestions."— /'A/V<xrf«'//A/a  Medical  and  Surgical  Reporter. 

STOKES,  DISEASES  OF  THE  HEART. 

The  Diseases  of  the  Heart  and  Aorta.  By  William  Stokes,  m.d.  Thick 
8vo.  Price  $3.00 

SWERINGEN,  REFERENCE  BOOK. 

A  Pharmaceutical  Lexicon  or  Dictionary  of  Pharmaceutical  Science.  Contain- 
ing explanations  of  the  various  subjects  and  terms  of  Pharmacy,  with  appropriate 
selections  from  the  Collateral  Sciences.  Formulae  for  Officinal,  Empirical,  and 
Dietetic  Preparations,  etc.,  etc.     By  Hiram.  V.  Sweringen,  m.d.     8vo. 

Price,  Cloth,  $3.00 ;  Leather,  %^.oo 

"  It  is  worthy  of  a  welcome,  and  sure  of  a  ready  recognition  of  its  merits." — London  Pharntaceutical  yournal. 
"  It  will  prove  of  great  service  to  the  pharmaceutical  student,  apprentice,  pharmacist,  druggist  and  physician,  as 
a  book  of  ready  reference  and  as  an  aid  to  the  study  of  scientific  works." — American  yournal  of  Pharmacy. 

SOLLY.     COLORADO  SPRINGS  FOR  HEALTH. 

Colorado  Springs  and  Manitou  as  Health  Resorts.  By  S.  Edwix  Solly,  m.d., 
M.R.C.S.,  Eng.,  including  an  article  descriptive  of  the  scenery  and  resources  of 
the  State.     i2mo.  Paper  covers,  25  cents. 

TEMPERATURE  CHARTS. 

Charts  for  Recording  Temperature,  Respiration,  Pulse,  Day  of  Disease,  Date, 
Age,  Sex,  Occupation,  Name,  etc.  Put  up  in  pads,  each  50  cents. 

THOMPSON.     MANUAL  OF  PHYSICS. 

A  Student's  Manual  of  Physics.  By  Silvanus  P.  Thompson,  b.a.,  d.Sc. 
F.R.A.S.,  Professor  of  Experimental  Physics  in  University  College,  Bristol,  England. 

Preparing. 

THOMPSON,  LITHOTOMY  AND  LITHOTRITY. 

Practical  Lithotomy  and  Lithotrity ;  or,  an  Inquiry  into  the  best  Modes  of 
Removing  Stone  from  the  Bladder.  By  Sir  Henry  Thompson,  f.r.c.s.,  Emer- 
itus Professor  of  Clinical  Surgery  in  University  College.  Third  Edition.  8vo. 
With  87  Engravings.  Price  $3.50 

"  The  chapters  of  most  interest  are  those  in  which  Bigelow's  operation  is  discussed,  and  the  final  one,  in 
which  is  a  record  of  500  operations  for  stone  in  cases  of  male  adults  under  the  author's  care.  Such  a  table  hai 
never  belore  been  compiled  by  any  surgeon." — LMncet. 

BY  SAME   AUTHOR. 

URINARY  ORGANS.     Seventh  Edition. 

Diseases  of  the  Urinary  Organs.  CUnical  Lectures.  Seventh  London  Edition. 
Enlarged,  with  73  Illustrations.  Price,  Cloth,  $1.25  ;  Paper,  .75 

ON  THE  PROSTATE. 

Diseases  of  the  Prostate.  Their  Pathology  and  Treatment.  Fifth  London 
Edition.     8vo.     With  Numerous  Plates.     Price,  Cloth,  ^1,25  ;  Paper,  .75. 

CALCULOUS  DISEASES. 

The  Preventive  Treatment  of  Calculous  Disease,  and  the  Use  of  Solvent 
Remedies.     Second  Edition.     i6mo.  Price  $1.00 

"  Catholic  in  his  investigation  of  the  fruit  of  the  labor  of  others,  cautious  in  all  his  deductions,  nyecting  all  spe- 
ciou.s  theories  in  the  effort  to  obtain  practically  useful  results,  as  clever  with  his  pen  as  he  is  with  the  sound  or 
lithotrite,  one  can  scarcely  wonder  that  he  is  esteemsd  the  master  that  he  \»."^AtKirican   yournal  q/'  Medical 

Science. 


PUB  Lie  A  TIONS.  37 


THOMPSON,  COUGHS  AND  COLDS. 

The' Causes,  Nature,  and  Treatment  of  Coughs  and  Colds.  By  E.  S.  Thomp- 
son, M.D.     i6mo.  Price  .60 

THOROWGOOD,  MATERIA  MEDICA. 

The  Student's  Guide  to  Materia  Medica.  By  John  C.  Thorowgood,  m.d. 
Illustrated.     318  pages.     i2mo.        ,  Price  $2.00 

BY   SAME   author. 

ON  ASTHMA. 

The  Forms,  Nature,  and  Treatment  of  Asthma.       2d  Edition.     Cloth,  $1.75 

TUSON,  VETERINARY  PHARMACOPCEIA. 

A  Pharmacopceia,  Including  the  Outlines  of  Materia  Medica  and  Therapeu- 
tics. For  the  Use  of  Students  and  Practitioners  of  Veterinary  Medicine.  By 
Richard  V.  Tuson,  f.c.s.     Third  Edition.     i2mo.  Price  $2.50 

"  Not  only  practitioners  and  students  of  veterinary  medicine,  but  chemists  and  druggists  will  find  that  this 
book  supplies  a  want  in  veterinary  literature." — Druggist  and  Chemist. 

THUDICHUM  ON  THE  URINE.     Second  Edition. 

The  Pathology  of  the  Urine  and  Complete  Guide  to  Analysis.  By  John  L. 
W.   Thudichum,    m.d.      Second    Edition.     Enlarged  and    Illustrated.      8vo. 

Price  $5.00 

"The  treatise  of  Dr.  Thudichum  is  well  known  as  one  of  the  medical  classics  of  the  language,  and  in  com- 
pleteness, thoroughness,  and  originality,  the  volume  before  us  has  few  rivals  in  any  branch  of  our  science.  For 
the  specialist,  for  the  physiological  chemist,  for  the  physiologist,  the  volume  of  Dr.  Thudichum  is  a  sine  gua 
Hon,  and  to  such  the  new  edition  must  be  a  most  welcome  guest." — Philadelphia  Medical  Times. 

TROUSSEAU,  CLINICAL  MEDICINE. 

Lectures  on  Clinical  Medicine,  Delivered  at  the  Hotel  Dieu,  Paris,  by  A. 
Trousseau,  Professor  of  Clinical  Medicine  to  the  Faculty  of  Medicine,  Paris, 
etc.,  etc.  Translated  from  the  Third  Revised  and  Enlarged  Edition  by  P.  Vic- 
tor Bazire,  m.d  ,  London  and  Paris  ;  and  John  Rose  Cormack,  m.d.,  Edin- 
burgh, F.R.S.,  etc.  With  a  full  Index,  Table  of  Contents,  etc.  2  vols.  8vo. 
Sold  by  Subscription  only. 

Trousseau's  Lectures  have  attained  a  reputation,  both  in  England  and  in  this 
country,  far  greater  than  any  work  of  a  similar  character  heretofore  written.  In 
order  to  bring  the  work  within  the  reach  of  all  the  profession,  the  publishers  now 
issue  an  American  edition,  containing  all  the  lectures  as  contained  in  the  five-vol- 
ume Sydenham  edition,  at  a  much  lower  price.  Below  are  a  few  only  of  the  many 
favorable  opinions  expressed  of  the  work: — 

"  A  clever  translation  of  Prof.  Trousseau's  admirable  !  "We  scarcely  know  of  any  book  better  fitted  for 

»od  exhaustive  work  ;   the  best  book  of  reference  upon  i  presentation   to  a  young  man  when  entering  upon  the 

the  Practice  of  Medicine." — Indiana  Medical  Gazette,  j  practical  work  of  his  life." — London  Medical  Times 

I  and  Gazette. 

TEST  TYPES. 

Selections  from  Snellen's  Test  Types  mounted  upon  heavy  card  board  ;  suit- 
able for  hanging  in  the  office.  Price  50  cents 

TIDY,  MODERN  CHEMISTRY. 

A  Hand-Book  of  Modern  Chemistry.  Organic  and  Inorganic.  By  C.  Mev- 
mott  Tidy,  m.d.     8vo.  Price  $5.00 

"We  doubt  if  any  other  chemical  work  containing  so  large  an  amount  of  information  could  be  procured." — 
Dublin  Medical  Tournal. 


38  P.  BLAKISTON,  SON  &-  CO.'S 


TILT,  THE  CHANGE  OF  LIFE  IN  WOMEN. 

The  Change  of  Life  in  Health  and  Disease.  A  Practical  Treatise  on  the 
Diseases  incidental  to  Women  at  the  Decline  of  Life.  By  Edward  John  Tilt, 
M.D.     Fourth  London  Edition.     8vo.  Price,  Cloth,  $1.25;  Paper  cover,  .75 

"  We  believe  Dr.  Tilt  brings  much  more  than  ordinary  merit  to  bear  on  his  subject,  and  handles  it  accord- 
ingly.    Few  books  are  issued  that  are  more  indispensable  to  the  general  practitioner." — Phila.  Med.  Times. 

"  Dr.  Tilt's  clear  and  concise  style  makes  the.  book  at  once  a  pleasant  one  to  read  and  an  easy  guide  to  follow, 
and  we  are  quite  sure  it  is  the  most  valuable  one  we  have  on  the  subject." — Boston  Med.  •Sr'  Surg,  yournal. 

"  The  best  work  on  the  subject."— Z.o«<fo«  Lancet. 

TOMES,  DENTAL  ANATOMY.     Second  Edition. 

A  Manual  of  Dental  Anatomy,  Human  and  Comparative.  By  C.  S.  Tomes, 
D.D.s.     With  179  Illustrations.     Second  Edition.     i2mo.  Price  $4.25 

TOMES,  DENTAL  SURGERY. 

A  System  of  Dental  Surgery.  By  John  Tomes,  f.r.s.  The  Second  Edition, 
Revised  and  Enlarged.     By  C.  S.  Tomes,  D.D.s.     With  263  Illustrations.     i2mo. 

Price  % 

"  We  rejoice  that  such  books  as  these  (Dr.  Tomes'  Works)  are  demanded  by  the  profession,  and  that  the  men 
to  write  them  are  furnished  by  the  profession." — Dental  Cosmos. 

TAFT,  OPERATIVE  DENTISTRY.     Fourth  Edition. 

A  Practical  Treatise  on  Operative  Dentistry.  By  Jonathan  Taft,  D.D.s. 
Fourth  Revised  and  Enlarged  Edition.     Over  100  Illustrations.     8vo. 

Price,  Cloth,  ^4.25;  Leather,  5.00 

"  It  is  a  thorough  and  complete  treatise  on  the  Art 
of  Practical  Dentistry." — London  Medical  Times  and 
Gazette. 


"All  the  important  operations,  in  all  their  modifica- 
tions, are  clearly  discussed  by  the  author,  and  the 
work  is  highly  practical  throughout." — Dental  Regis- 


TANNER,  INDEX  OF  DISEASES.     Second  Edition. 

An  Index  of  Diseases  and  their  Treatment.    By  Thos.  Hawkes  Tanner,  m.d., 

F.R.c.p.    Second  Edition.    Revised  and  Enlarged.    By  W.  H.  Broadbent,  m.d. 

With  Additions.     Appendix  of  Formulae,  etc.     8vo.  Price  $3.00 

By  this  useful  hand-book  the  character  of  any  disease  may  be  determined  in  a 

moment,  and  the  general  outline  of  treatment  pursued  by  the  best  authorities  made 

apparent. 

"  This  work,  like  others  from  the  gifted  author,  has  |  "  Finally,  a  chapter  on  the  climates,  countries,  mine- 
already  won  for  itself  a  reputation."  .  .  .  "  It  is  ral  springs,  etc.,  best  adapted  to  the  various  classes  of 
in  truth  what  its  title  indicates." — New  York  Medical  invalids,  makes  this  work  the  most  complete  practi- 
Record.  t'oner's  manual  that  we  have  yet  seen. — Chicago  Medi- 

\  cal  Times. 

BY  same  author. 

THE  DISEASES  OF  INFANCY. 

A  Practical  Treatise  on  the  Diseases  of  Infancy  and  Childhood.     Third  Edi- 
tion.    Carefully  Revised  and  much  Enlarged.      By  Alfred  Meadows,  m.d. 
8vo. 
Recommended  as  a  Text-book  at  Jefferson  Medical  College  and  other  schools  of 
Medicine. 

"One  of  the  most  careful,  ornate,  and  accessible  I  "  We  consider  the  views  of  the  author  on  the  subject 
manuals  on  the  subject." — London  Lancet.  of  therapeutics  as   rational   in  the  highest  degree." — 

I    Boston  Medical  and  Surgical  yournal. 

MEMORANDA  OF  POISONS. 

A  Memoranda  of  Poisons  and  their  Antidotes  and  Tests.       Fifth  American, 
from  the  Last  London  Edition.     Revised  and  Enlarged.  Price  .75 

This  most  complete  Toxicological  Manual  should  be  within  reach  of  all  physi- 
cians and  pharmacists,  and  as  an  addition  to  every  family  library,  would  be  thi; 
means  of  saving  life  and  allaying  pain  when  the  delay  of  sending  for  a  physician 
would  prove  fatal. 


PUB  Lie  A  TIONS. 


TRANSACTIONS  OF  THE  AMERICAN    SURGICAL  ASSO- 
CIATION. 

Volume  I.  Illustrated.  Edited  by  J.  Ewing  Mears,  m.d.,  Recorder  of  the 
Association.     Royal  8vo.  Cloth,  $3.50 

TRANSACTIONS  OF  THE  COLLEGE  OF  PHYSICIANS. 

The  Transactions  of  the  College  of  Physicians  of  Philadelphia.  New  Series. 
Vols.  I,  11,  III,  IV,  V.     8vo.  Price,  per  volume,  $2.50 

Vol.  VI.  Containing  Articles  and  Discourses  by  Drs.  Atlee,  Da  Costa,  Mills, 
A.  V.  Meigs,  H.  C.  Wood,  Cohen  ;  Profs.  Tyson,  Gross,  Bartholow,  Allen,  Leeds 
and  others.  Cloth,  Gilt  Top,  ^3.50 

TYSON,  BRIGHT'S  DISEASE  AND  DIABETES. 

A  Treatise  on  Diabetes  and  Bright's  Disease.  With  Especial  Reference  to 
Pathology  and  Therapeutics.  By  James  Tyson,  m.d..  Professor  of  Pathology 
and  Morbid  Anatomy  in  the  University  of  Pennsylvania.  With  Colored  Plates 
and  many  Wood  Engravings.     8vo.  Price  $3.50 

"This  volume  is  the  outcome  of  some  fifteen  years*  \  "The  symptoms  are  clearly  defined,  and  the  treat- 
special  study  and  observation,  and  will  be  foimd  to  be  1  ment  is  exceedingly  well  described,  so  that  every  one 

a  very  well  prepared  monograph His  direc-  reading  the  book  must  be  prohced  " — Cincinnati  Lan- 

tions  are  clear  and  minute. — Med.  and  Suyg.  Reporter.  \  cet  and  Clinic. 

BY   SAME   AUTHOR. 

GUIDE  TO  THE  EXAMINATION  OF   URINE. 

A  Practical  Guide  to  tlie  Examination  of  Urine.  For  the  use  of  Physicians  and 

Students.    With  Colored  Plates  and  Numerous  Illustrations  Engraved  on  Wood. 

Fourth  Edition.     i2mo.  Price  $\.^o 

Advantage  has  been  taken,  in  bringing  out  a  new  edition  of  this  work,  not  only  to 

correct  the  previous  one,  but  to  make  such  additions  of  new  Facts  and  Processes  as 

would  add  to  its  value  without  materially  increasing  its  size. 

"Dr.  Tyson  commences  with  a  short  account  of  the  theory  of  renal  secretion,  the  physical  and  chemical  fharac- 
ters  of  the  urine,  and  the  reagents  and  apparatus  used  in  its  analysis.  Excellent  rules  are  then  given  for  detecting 
the  presence  of  albumen,  sugar,  coloring-matters,  bile,  urea,  uric  acid,  chlorides,  phosphates  and  sulphates  ;  an« 
minute  instructions  for  approximative  and  quantitative  determination  of  most  of  those  ingredients  by  volumetric 
analysis  are  supplied." — Philadelphia  Medical  Times. 

"  We  have  experienced  both  pleasure  and  profit  ftom  the  perusal  of  this  book.  It  is  agreeably  written,  contains 
much  practical  information,  and  is,  we  believe,  a  reliable  and  satisfactory  guide  to  the  clinical  examination  of 
arine.  We  can  recommend  Dr.  Tyson's  book  as  one  that  amply  supplies  the  clinical  needs  of  the  physician." — 
Duilin  Journal  of  Medical  Science. 

THE  CEI^L  DOCTRINE.     Second  Edition. 

The  Cell  Doctrine.  Its  History  and  Present  State.  With  a  Copious  Biblio- 
graphy of  the  subject.  Illustrated  by  a  Colored  Plate  and  Wood  Cuts.  Second 
Edition.     8vo.  Price  $2.00 

TURNBULL,  ARTIFICIAL  ANAESTHESIA. 

The  Advantages  and  Accidents  of  Artificial  Anaesthesia ;  Its  Employment  in 
the  Treatment  of  Disease ;  Modes  of  Administration  ;  Considering  their  Rela- 
tive Risks;  Tests  of  Purity;  Treatment  of  Asphyxia;  Spasms  of  the  Glottis; 
Syncope,  etc.  By  Laurence  Turnbull.  m.d.,  ph.g.,  Aural  Surgeon  to  Jeffer- 
son College  Hospital,  etc.  Second  Edition.  Revised  and  Enlarged.  With  27 
Illustrations  of  Various  Forms  of  Inhalers,  etc.     i2mo.  Price  $1.50 

"  Anaesthesia  is  a  subject  of  %re.2X  interest  and  importance  to  physicians  and  dentists,  and  everything  that  will 
aid  them  in  better  understanding  the  subject  is  sought  with  great  avidity.  This  work  we  regard  as  the  best  aid  in 
the  study  of  the  subject,  and  it  presents  the  subject  up  to  the  present  hour." — Dental  Register. 

TUKE.     SLEEP-\A/^ALKING. 

Sleep-Walking  and  Hypnotism.  By  D.  Hack  Tuke.  M.D.,  LL.D.,  F.R.C.P.,  Co- 
Editor  of  the  Journal  of  Mental  Diseases.     8vo.  Cloth,  $1.75 


^o  p.  BLAKISTON,  SON  &*  CO:S 


VAN  HARLINGEN,  ON  SKIN  DISEASES. 

A  Practical  Manual  on  Diseases  of  the  Skin,  with  Diagnosis  and  Treatment 
For  Students  and  Practitioners.  By  Arthur  Van  Harlingen,  m.d.,  Vice- 
President  of  the  American  Dermatological  Association.  Including  Formulae. 
Illustrated  by  two  Colored  Plates.     i2mo.     Cloth.  In  Press. 

VALENTIN.     QUALITATIVE  ANALYSIS. 

A  Course  of  Qualitative  Chemical  Analysis.  By  Wm.  G.  Valentin,  f.c.s. 
Sixth  Edition,  Enlarged.    With  over  260  Illustrations.    OcUvo.    Cloth.    In  Press. 

VACHER,  CHEMISTRY. 

A  Primer  of  Chemistry,     Including  Analysis.     By  Arthur  Vacher.     i8mo. 

Price  .50 

VIRCHOW,  POST-MORTEM  EXAMINATIONS.  Second  Edi- 
tion. 

Post  mortem  Examinations.  A  Description  and  Explanation  of  the  Method 
of  Performing  them  in  the  Dead  House  of  the  Berlin  Charite  Hospital,  wiih 
especial  reference  to  Medico-legal  Practice.  By  Prof.  Virchow.  Translated 
by  Dr.  T.  P.  Smith.     Second  Edition.     i2mo.     With  4  Plates.  Price  $1.25 

•    "  A  most  useful  manual  from    the  pen  of  a  master.  I        "  Its  low  price  and  portability  make  it  accessible  and 
.     .     .     For  thorough  and   systematic  method  in        convenient  to  every  surgical  registrar  and  practitioner." 
the  performance  of  post-mortem  examinations,  there  is        — British  Medical  jfournal. 

no  guide  like  it." — Lancet.  \ 

WAGSTAFFE,   HUMAN  OSTEOLOGY. 

The  Student's  Guide  to  Human  Osteology.  By  William  Warwick  Wag- 
STAFFE,  F.R.c.s.  With  23  Lithographic  Plates  of  the  Bones,  Showing  Muscle 
Attachments,  and  60  Wood  Engravings.     i2mo.  Price  $3.00 

WICKES.     SEPULTURE. 

Sepulture :  Its  History,  Methods  and  Sanitary  Requisites.  By  Stephen 
WiCKES,  a.m.,  M.D.,  Author  of  a  History  of  Medicine  and  Medical  Men  of  New 
Jersey,  etc.     Octavo.  Pricejji.50 

WEST.     ON  THE  CHEST. 

How  To  Examine  the  Chest.  A  Practical  Guide  for  the  use  of  Students.  By 
Samuel  West,  m.d.  Oxon.,  m.r.c.p.,  Physician  to  the  City  of  London  Hospital 
for  Diseases  of 'the  Chest.     Illustrated.     32mo.  Cloth,  Si.75 

WOOD.     BRAIN  WORK. 

Brain  Work  and  Overwork.     By  Prof.  H,  C.  Wood,  Jr.     32mo. 

Price,  Paper  cover,  .30;  Cloth,  .50 

WATTS.     CHEMISTRY. 

A  Manual  of  Chemistry,  Physical  and  Inorganic.  By  Henry  Watts,  b.a., 
F.R.S.,  Editor  of  the  Journal  of  the  Chemical  Society;  Author  of  "A  Dictionary 
of  Chemistry,"  etc.  With  Colored  Plate  of  Spectra  and  other  Illustrations. 
121T10.     595  pages.  Price,  Cloth,  5I52.25 

This  volume  commences  with  a  short  sketch  of  the  more  important  Elementary  Bodies,  the  principal  Laws  of 
Chemical  Combination,  and  the  representation  of  the  constitution  and  reactions  of  bodies  by  Symbolic  Notation, 
followed  by  a  section  on  Chemical  Physics,  including  the  determination  of  Densities,  the  mechanical  proper- 
ties of  Gases,  and  the  chief  phenomena  of  Heat,  Light,  Electricity  and  Magnetism.  The  next  section  contains 
:i  description  of  the  Non-metallic  Elements,  and  the  more  important  Compounds  which  they  form  with  one 
•mother  :  followed  by  a  discussion  of  the  general  principles  of  Chemical  Philosophy.  In  this  part  of  the  work 
[he  Laws  of  Chemical  Combination  and  Decomposition  and  the  principles  of  the  Atomic  Theorj-,  briefly  noticed 
in  the  introduction,  are  more  fully  developed.  The  last  section  is  devoted  to  the  Chemistry  of  the  Metals.  A 
comparison  of  the  Centigrade  and  Fahrenheit  Scales  of  temperature  is  given  at  the  end  of  the  volume. 


PUB  Lie  A  TIONS.  41 


WEST,  THE  DISEASES  OF  WOMEN.     Fourth  Edition. 

Lectures  on   the   Diseases   of  Women.     By  Charles  West,  m.d.     Fourth 
London  Edition.     Revised  and  in  part  re-written  by  the  Author.     With  Numer- 
ous Additions  by  J.  Mathews  Duncan,  m.d.,  Obstetric  Physician  to  St.  Bar- 
tholomew's Hospital     8vo.  Price  $5.00 
Drs.  West  and  Duncan   are,  perhaps,  the  most  celebrated    London  physicians 
giving  attention  to  the  Diseases  of  Women,  and  together  have  made  a  most  com- 
plete work,  either  for  the  physician  or  student. 

WILKS,  PATHOLOGICAL  ANATOMY. 

Lectures  on  Pathological  Anatomy.  By  Samuel  Wilkes,  f.r.s.  Second 
Edition.  Revised  and  Enlarged  by  Walter  Moxon,  m.d.,  f.r.s.,  Physician  to 
and  Lecturer  at  Guy's  Hospital,  London.     8vo.  Price  ;j6.oo 

BY   SAME   author. 

DISEASES  OF  THE  NERVOUS  SYSTEM. 

Lectures  on  Diseases  of  the  Nervous  System,  Delivered  at  Guy's  Hospital, 
London.    New  Edition,  with  Additions,  Numerous  Illustrative  Cases,  etc.     8vo. 

Cloth,  $6.00 

"  A  book  of  great  value,  embodying  as  It  does  the  results  of  the  experience  and  observation  of  one  of  the  most 
accomplished  of  the  London  Hospital  Physicians." — American  yournal  of  Medical  ScieHce. 

WRIGHT,  ON  HEADACHES.     Ninth  Thousand. 

Headaches,  their  Causes,  Nature  and  Treatment.  By  Henry  G.  Wright, 
M.D     izmo.  Price  .50 

WILSON,  ON  DRAINAGE. 

Drainage  for  Health ;  or.  Easy  Lessons  in  Sanitary  Science,  with  Numerous 
Illustrations.  By  Joseph  Wilson,  m.d.,  ]\Iedical  Director  United  States  Navy. 
One  Vol.     Octavo.  Price  $1.00 

"  Dr.  Wilson  is  favorably  known  as  one  of  the  lead-  "  Easily  understood,  and  briefly  and  concisely  pre- 

ing  American   writers  on  hygiene  and  public  health.  sented." — Providence  yournal. 

The  book  deserves  popularity." — Medical  and  Surgi-  "Will  be  found  of  value." — Boston  Transcript, 

cal  Reporter.  "Worthy  of  praise  as  a  popular  statement  of  the 

"  Well  written  and  well  illustrated.     Attention  to  its  subject." — Boston  jfournal  of  Chemistry. 

teachings  may  save  much  disease  and  perhaps  many  "  Will  be  sure  to  be  a  harbinger  of  good  in  every  fam- 

lives." — Cincinnati  Gazette.  '    ily  whose  good  fortune  it  may  be  to  possess  a  copy." — 

"  Interesting  as  well  as  useful." — Philadelphia  Led-  \    Builder  and  Wood  Worker, 
ger. 

BY   SAME   AUTHOR. 

NAVAL  HYGIENE. 

Naval  Hygiene,  or,  Human  Health  and  Means  for  Preventing  Disease.  Witi» 
Illustrative  Incidents  derived  from  Naval  Experience.  Illustrated.  Second 
Edition.     Svo.  Price  ^3.00 

W^ILSON,    HOW  TO  LIVE. 

Health  and  Healthy  Homes.  A  Guide  to  Personal  and  Domestic  Hygiene. 
By  George  Wilson,  m.d.,  Medical  Officer  of  Health.  Edited  by  Jos.  G. 
Richardson,  m.d.,  Professor  of  Hygiene  at  the  University  of  Pennsylvania. 
314  pages.     i2mo.  Price  $i.oc 

Chapter  i. — Introductorj-,  page  17.  11.  The  Human  Body,  33.  in.  Causes  of  Disease,  66.  IV.  Food  and 
Diet,  119.  V.  Cleanliness  and  Clothing,  169.  VI.  Exercise,  Recreation  and  Training,  187.  Vll.  Home  and  Its 
Surroundings,  Drainage,  Warming,  etc.,  221.     viii.   Infectious  Diseases  and  their  Prevention,  269. 

"  A  most  useful,  and  in  every  way,  acceptable  \iOoV."—Ne'w  York  Herald. 

"  Marked  throughout  by  a  sound,  scientific  spirit,  and  an  absence  of  all  hasty  generalizations,  sweeping  asser- 
tions, and  abuse  of  statistics  in  support  of  th«  writer's  particular  views.  .  .  .  We  cannot  speak  too  highly  of 
a  work  which  we  have  read  with  entire  satisfaction." — Medical  Timet  and  Gazette. 

BY    SAME    AUTHOR. 

A  HAND-BOOK  OF  HYGIENE 

And  Sanitary  bcience.  With  Illustrations.  Fifth  Edition.  Revised  and 
Enlarged.     Svo.  Price  J2.75 


42  p.  BLAKISTON,  SON  6-  CO.'S 


WILSON,  HUMAN  ANATOMY.     Tenth  Edition. 

The  Anatomist's  Vade-Mecum.  General  and  Special.  By  Prof.  Erasmus  Wil- 
son. Edited  by  George  Buchanan,  Professor  of  Clinical  Surgery  in  the  Uni- 
versity of  Glasgow;  and  Henry  E.  Clark,  Lecturer  on  Anatomy  at  the  Royal 
Infirmary  School  of  Medicine,  Glasgow.  Tenth  Edition.  With  450  Engravings 
(including  26  Colored  Plates).     Crown  8vo.  Price  $6.00 

Recommended  as  a  Text-book  at  Rush  Medical  College,  Chicago  ;  Bellevue  Hos- 
pital, New  York ;  St.  Louis  Medical  College ;  Yale  and  Dartmouth  Schools ,  aiid 
many  other  Colleges. 

BY   same   author. 

HEALTHY  SKIN.     Eighth  Edition. 

A  Practical  Treatise  on  the  Skin  and  Hair ;  their  Preservation  and  Manage- 
ment.    Eighth  Edition.     i2mo.     Paper.  Price  jSi.oo 

WILSON,  SEA  VOYAGES  FOR  HEALTH. 

The  Ocean  as  a  Health  Resort.  A  Hand-book  of  Practical  Information  as  to 
Sea  Voyages,  for  the  Use  of  Tourists  and  Invalids.  By  Wm.  S.  Wilson,  l.r.c.p. 
Lond.,  m.r.c.s.e.  With  a  Chart  showing  the  Ocean  Routes,  and  Illustrating  the 
Physical  Geography  of  the  Sea.     Crown  8vo.  Price  $2.50 

WELCH.     ENTERIC  FEVER. 

Enteric  Fever:  Its  Prevalence  and  Modifications;  Etiology,  Pathology  and 
Treatment,  as  illustrated  by  army  data  at  home  and  abroad.  By  Francis  H. 
Welch,  f.r.c.s.,  Surgeon  and  Major  a.m.d.  Being  the  Alexander  Prize  Essay, 
Modified  and  Revised.     8vo.  Price,  Cloth,  ;$2.oo 

WELLS,  OVARIAN  AND  UTERINE  TUMORS. 

The  Diagnosis  and  Surgical  Treatment  of  Ovarian  and  Uterine  Tumors,  By 
T.  Spencer  Wells,  m.d.     Illustrated.     Svo.  Price,  Cloth,  $7.00 

So  long  a  time  having  elapsed  since  Dr.  Wells  has  collected  the  results  of  his 
large  experience  in  book  form,  the  present  volume  will  be  eagerly  looked  for  by  all 
interested  in  this  very  important  subject. 

WOLFE,  ON  DISEASES  OF  THE  EYE. 

A  Practical  Treatise  on  Diseases  and  Injuries  of  the  Eye.  Being  a  Course  of 
Systematic  and  Clinical  Lectures  to  Students  and  Medical  Practitioners.  By  M. 
Wolfe,  f.r.c.p.e.,  Senior  Surgeon  to  the  Glasgow  Ophthalmic  Institution,  etc. 
With  10  Colored  Plates,  and  numerous  other  iftustrations.  Octavo.      Price  $7.00 

WALKER,  INTERMARRIAGE. 

Intermarriage,  or.  The  Mode  in  which,  and  the  Causes  why,  Beauty,  Health 
and  Intellect  result  from  certain  Unions ;  and  Deformity,  Disease  and  Insanity 
from  others.     Illustrated.     i2mo.  Price  $1.00 

WARD'S  COMPEND  OF  CHEMISTRY.  Revised  Edition. 

A  Compend  of  Chemistry  for  Chemical  and  Medical  Students.  By  G.  Mason 
Ward,  m.d..  Demonstrator  of  Chemistry  in  Jefferson  Medical  College.  Phila- 
delphia. Containing  a  Table  of  Elements  and  Tables  for  the  Detection  of 
Metals  in  Solutions  of  Mixed  Substances,  etc.     i2nio.     Cloth. 

Interleaved  for  the  addition  of  Notes,  $1.25  ;  plain,  $i.oc 


PUB  Lie  A  TIONS.  43 


WOODMAN  and  TIDY,  MEDICAL  JURISPRUDENCE. 

Forensic  Medicine  and  Toxicology.  By  W.  Bathurst  Woodman,  m.d., 
Physician  to  the  London  Hospital,  and  Charles  Meymott  Tidy,  f.c.s.,  Pro- 
fessor of  Chemistry  and  Medical  Jurisprudence  at  the  London  Hospital.  With 
Chromo-Lithographic  Plates,  representing  the  Appearance  of  the  Stomach  in 
Poisoning  by  Arsenic,  Corrosive  Sublimate,  Nitric  Acid,  Oxalic  Acid ;  the  Spectra 
of  Blood  and  the  Microscopic  Appearance  of  Human  and  other  Hairs ;  and 
116  other  Illustrations.     Large  octavo.    Sold  only  by  Subscription. 

Price,  Cloth,  $7.50;  Medical  Sheep,  $8.50;  Law  Leather,  $8.50 

WOAKES,  ON  DEAFNESS  AND  GIDDINESS. 

On  Deafness,  Giddiness  and  Noises  in  the  Head ;  or,  The  Naso-Pharyngeal 
Aspect  of  Ear  Disease.  By  Edward  Woakes,  m.d  ,  Senior  Aural  Surgeon  to 
the  Hospital  for  Diseases  of  the  Throat  and  Chest.  Third  Edition.  Revised  and 
Enlarged,  with  Additional  Illustrations,     izmo. 

"  Xo  brief  summary  of  his  views  could  do  full  justice  to  the  cogency  and  subtlety  of  his  reasons.  We  prefer 
to  commend  the  whole  work  to'  the  thoughtful  perusal  of  all  intelligent  medical  practitioners  who  desire  to  rise 
above  the  level  of  mere  routine  empiricism." — Lancet. 

BY   THE  SAME   AUTHOR. 

W^OAKES,  ON    NASAL  CATARRH. 

Catarrh  and  Diseases  of  the  Nose,  Causing  Deafness.     i2mo.     Illustrated. 

Cloth,  $1.50 

WYTHE,  ON  THE  MICROSCOPE. 

The  Microscopist.  A  Manual  of  Microscopy  and  Compendium  of  the  Micro- 
scopic Sciences,  Micro-Mineralogy,  Micro-Chemistry,  Biology,  Histology,  and 
Practical  Medicine.  By  Joseph  H.  Wythe,  a.m.,  m.d.  Fourth  Edition.  252 
Illustrations.     8vo.  Price,  Cloth,  ^3.00;  Leather,  $4.00 

An  Index  and  Glossary  have  been  combined  in  this  edition,  so  as  to  be  a  source 
of  valuable  information.  Notices  of  recent  additions  to  the  microscope,  together 
with  the  genera  of  microscopic  plants,  have  been  given  in  an  Appendix. 

"  From  what  we  knew  of  the  author  of  this  work,  as  |  "  This  is  one  of  the  most  valuable  text-books  on  mi- 
a  skilled  practical  Microscopist,  a  successful  teacher  of  i  croscopy  ever  offered  to  students  or  practitioners  of 
the  science,  and  a  practitioner  of  medicine  and  surgery  '  medicine.  This  edition  has  been  greatly  enhanced  in 
of  long  and  varied  experience,  we  had  a  right  to  expect  value  by  the  addition  of  chapters  on  the  use  of  the 
a  good  book  from  his  hands.  Our  expectations  are  hilly  \  microscope  in  pathology,  diagnosis,  and  etiology,  and 
realized  in  the  volume  before  us.  The  style  is  clear  numerous  new  illustrations,  some  of  which  are  from 
and  distinct,  and  one  reads  the  book  with  the  utmost    I    Rindfleisch. 

facility  of  comprehension.  It  is  the  more  valuable  to  '  "The  author  very  carefiiUy  brings  out  every  neces- 
the  physician  and  medical  student  on  account  of  its  sary  fact  and  principle  relating  to  the  use  of  the  micro- 
closer  application  of  the  microscope  to  medical  subjects  scope,  and  now  that  this  instrument  has  become  an  es- 
than  we  find  elsewhere.     The  numerous  plates,  many       sential  part  of  every  practitioner's  armajncntarium,  a 

practical  guide  and  reference  book  is  also  a  necessity, 
and  we  are  fully  warranted  in  reiterating  the  statement 
that  this  is  one  of  the  most  valuable  text-books  ever 
offered  to  students  and  practitioners  of  medicine." — 
The  Cincinnati  LMncet  and  Clinic. 


of  which  are  beautifully  colored,  are  not  to  be  excelled. 
We  feel   proud  of  it   as  an  American  production 
Pacific  Medical  and  Surgical  Journal. 


BY   SAME  AXJTHOR. 

DOSE  AND  SYMPTOM  BOOK.     Eleventh  Edition. 

The  Physician's  Pocket  Dose  and  Symptom  Book.  Containing  the  Doses  and 
Uses  of  all  the  Principal  Articles  of  the  Materia  Medica,  and  Original  Prepara- 
tions. •  Eleventh  Revised  Edition. 

Price,  Cloth,  $1.00;  Leather,  with  Tucks  and  Pocket,  $1.23 

"  The  chapter  on  Dietetic  Preparations  will  be  found  useful  to  all  practicing  physicians,  most  of  whom  have  but 
little  acquaintance  with  the  mode  of  preparing  the  various  articles  of  diet  for  the  sick." — Boston  Medical  and 
Surgical  yournal. 

"  Many  a  hard-worked  practitioner  will  find  it  a  useful  little  work  to  have  on  his  study  table." — Canada  Medical 
and  Surgical  Journal. 


44  p.  BLAKISTON,  SON  &-  CO:S  PUBLICATIONS. 


YEO.     A  MANUAL  OF  PHYSIOLOGY. 

A  Manual  of  Physiology ;  being  a  Text-book  for  Students  of  Medicine.  By 
Gerald  F.  Yeo,  m.d.,  f.r.c.s.,  Professor  of  Physiology  in  King's  College,  Lon- 
don. With  over  300  carefully  printed  Illustrations.  A  Glossary  and  Complete 
Index.     Crown  Octavo.  '  Price,  Cloth,  ;J4.oo;  Leather,  $5.00 

"  This  work  *  •  •  is  the  legitimate  successor  of  the  similar  treatise  by  Dr.  Carpenter,  which,  excellent  as 
that  was  at  the  time  it  was  written,  has,  we  suppose,  been  found  so  defective  as  to  require  more  time  and  trouble 
to  renovate  than  would  be  demanded  to  write  a  new  worlc.  We  thinic  the  publishers  have  done  well  in  selecting 
Dr.  Gerald  Yeo  for  the  author  of  their  new  manual.  This  gentleman  occupies  the  physiological  chair  at  King's 
College,  has  a  good  reputation  as  a  teacher,  and  is  known  as  having  ably  assisted  Dr.  Ferrier  in  the  interesting 
researches  made  by  tliat  physician  in  the  localization  of  function  in  the  brain. 

"  The  plan  followed  in  the  work  is,  to  give,  in  the  first  place,  a  general  view  of  the  animal  structures,  then  to 
describe  the  chemical  basis  of  the  body  and  tl^e  vital  characteristics  of  animal  organisms,  and  next  to  consider, 
in  succession,  and  in  the  following  order,  the  functions  of  digestion,  absorption,  circulation,  respiration,  secre- 
tion, animal  heat,  muscle,  voice  and  speech,  the  nervous  system,  special  senses,  reproduction  and  developement. 
In  dealing  with  his  subject,  Dr.  Yeo  has  introduced  in  many  places  a  brief  account  of  the  histological  features  of 
llie  parts  of  which  he  is  about  to  show  the  uses.  *  *  *  The  mode  in  which  Dr.  Yeo  deals  with  disputed 
points  has,  in  every  instance  we  have  met,  been  remarkably  sensible  and  straightforward.  •  »  •  Upon  the 
whole,  although  we  have  taken  exception  to  one  or  two  points,  we  consider  Dr.  Yeo's  book  to  be  a  very 
god  one,  it  is  most  worthy,  and  clearly  and  intelligently  written.  We  cannot  conclude  our  notice  of  this  work 
without  referring  to  the  excellence  of  the  wood-cuts.  These  are  not  only  very  numerous  and  generally  well 
executed,  but  to  a  large  extent  novel." — Londnn  l.an:ei.  May  Zfth,  1SS4.. 


ILLUSTRATED    BOOKS. 

MEDICINAL  PLANTS. 

Being  Descriptions,  with  original  Figures,  of  the  Principal  Plants  employed  in 
Medicine,  and  an  account  of  their  Properties  and  Uses.  By  Robert  Bentley, 
F.L.S.,  Professor  of  Botany  in  the  King's  College,  and  to  the  Pharmaceutical 
Society,  and  Henry  Trimens,  m.b.,  f.l.s.,  late  Lecturer  on  Botany  at  St. 
Mary's  Hospital  Medical  School.  In  42  Parts,  each,  $2.co,  or  in  4  vols.,  large 
8vo,  with   306  Colored  Plates,  bound  in  half  morocco,  gilt  edged.  ;j;90.cx3 

AN  ATLAS  OF  TOPOGRAPHICAL  ANATOMY. 

After  Plane  Sections  of  Frozen  Bodies.  By  William  Braune,  Professor  of  Anatomy 
in  the  University  of  Leipzig.  Translated  by  Edward  Bellamy,  f.r.c.s..  Sur- 
geon to  and  Lecturer  on  Anatomy  at  Charing  Cross  Hospital.  With  34  Photo- 
lithographic Plates  and  46  Wood  cuts.     Large  imp.  8vo.  $  8.00 

ATLAS  OF  SKIN  DISEASES. 

Consisting  of  a  Series  of  Illustrations,  with  Descriptive  Text  and  Notes  upon 
Treatment.  By  Tilbury  Fox,  m.d.,  f.r.c.p.,  late  Physician  to  the  Department 
for  Skin  Diseases  in  University  College  Hospital.  With  72  Colored  Plates. 
In  18  Parts,  each,  $1.00  or,  i  Vol.,  Royal  4to,  Cloth.  $20.00 

AN  ATLAS  OF  HUMAN  ANATOMY. 

Illustrating  most  of  the  ordinary  Dissections,  and  many  not  usually  practiced  by 
the  Student.  By  Rickman  J.  Godlee,  m.s.,  f.r.c.s.,  Assistant  Surgeon  to 
University  College  Hospital,  and  Senior  Demonstrator  of  Anatomy  in  Universi- 
ty College.  With  48  imp.  4to  Colored  Plates  (112  Figures),  and  a  volume  of  Ex- 
planatory Text.  ;f2o.oo 

A  COURSE  OF  OPERATIVE  SURGERY. 

By  Christopher  Heath,  f.r.c.s..  Home  Professor  of  Clinical  Surgery  in  Uni- 
versity College,  and  Surgeon  to  the  Hospital.  With  20  Plates  drawn  from 
Nature  by  M.  Leveille,  and  colored  by  hand  under  his  direction.  Second 
Edition,  Enlarged.     4to.        Sold  oniy  by  Subscription.  514.00 

ILLUSTRATIONS  OF  CLINICAL  SURGERY. 

Consisting  of  Plates,  Photographs,  Wood  cuts,  Diagrams,  etc.,  etc.,  illustrat- 
ing Surgical  Diseases,  Symptoms,  and  Accidents  ;  also  Operative  and  other 
Methods  of  Treatment,  with  Descriptive  Letterpress.  By  Jonathan  Hutchin- 
son, F.R.C.S.,  Senior  Surgeon  to  the  London  Hospital.  Vol.  I,  containing  fas- 
ciculi I  to  X,  bound,  with  Appendix  and  Index.  ^^25.00 
Fasciculi  XI  to  XVI.    Ready.                                                              Each,  $2.50 


NOW  READY,  THE  SEVENTH  REVISED  EDITION. 

MEIGS  AND  PEPPER,  ON  CHILDREN 

THE  MOST  THOROUGH,  COMPLETE  AND  PRACTICAL  WORK 
ON  THE  SUBJECT  NOW  BEFORE  THE  PROFESSION. 

A  PRACTICAL  TREATISE  ON  THE  DISEASES  OF  CHILD- 
REN. By  J.  Forsyth  Meigs,  m.d.,  one  of  the  Physicians  to  the  Pennsylvania 
Hospital,  Consulting  Physician  to  the  Children's  Hospital,  etc.,  and  William 
Pepper,  m.d..  Professor  of  Clinical  Medicine,  University  of  Pennsylvania,  Provost 
and  ex-officio  President  of  the  Faculty,  Physician  to  the  Philadelphia  Hospital, 

Fellow  of  the  College  of  Physicians,  etc.,  etc.     The  Seventh  Revised  and  Improved 

Edition.     In  one  volume  of  over  iioo  royal  octavo  pages. 

Price,  handsomely  bound  in  Cloth,  $6.00;  Leather,  $7.00. 

The  rapid  sale  of  six  large  editions  of  Drs.  Meigs  and  Pepper's  work  on  Children, 
and  the  demand  for  the  new  edition  now  ready,  is  sufficient  evidence  of  its  great 
popularity.  The  large  practice,  of  many  years'  standing,  of  the  authors,  imparts  to  it  a 
value  unequaled,  probably,  by  any  other  on  the  su^ject  now  before  the  profession. 

The  entire  work  has  been  now  again  subjected  to  an  entire  and  thorough  revision, 
some  articles  have  been  rewritten,  many  additions  made,  and  great  care  observed  by 
the  authors,  that  it  should  be  most  effectually  brought  up  to  the  light,  pathological 
and  therapeutical,  of  the  present  day. 

The  publishers  have  very  many  favorable  notices  of  the  previous  editions,  re- 
ceived from  numerous  sources,  foreign  and  domestic.  They  appen  J  a  few  from  lead- 
ing journals,  which  will  give  a  general  .dea  of  the  value  placed  upon  it,  both  as  a 
Text- Book  for  the  Student  and  a  work  of  reference  for  the  General  Praditioner. 

"  It  is  the  most  complete  work  upon  the  subject  in  our  language  ;  it  contains  at  once  the  results  of  pei"%onal  and 
the  experience  of  others ;  its  quotations  from  the  most  recent  authorities,  both  at  home  and  abroad,  are  ampto  and 
we  think  the  authors  deserve  congratulations  for  having  produced  a  book  unequaled  for  the  use  of  the  stuaent, 
and  iitdispensable  as  a  work  of  reference  for  the  practitioner." — American  Medical  youmal. 


"  But  as  a  scientific  guide  in  the  diagnosis  and  treatment  of  the  diseases  of  children,  we  do  not  hesitate  to  say 
that  we  have  seldom  met  with  a  text-book  so  corolete,  so  just,  and  so  readable,  as  the  one  before  us,  which  in  its 
new  torm  cannot  fail  to  make  friends  wherever  -t  saall  go,  and  wherever  great  erudition,  practical  tact,  and  fluent 
and  Agreeable  diction  are  appreciated." — American  youmal  of  Obstetrics. 


"  It  is  only  three  years  since  we  had  the  pleasure  of  recommending  the  Fifth  Edition  of  this  excellent  work. 
With  the  recent  additions  it  may  safely  be  pronounced  one  of  the  best  and  most  comprehensive  works  on  diseases 
of  children  of  which  the  American  Practitioner  can  avail  himself,  for  study  or  referaice.'' — iV.  K.  Mrd.  yournal. 


"  It  is  not  necessary  to  say  much,  in  the  way  of  criticism,  of  a  work  so  well  known.  But  it  is  clinical.  Like  so 
many  other  good  American  medical  books,  it  marvelously  combines  a  risumt  of  all  the  best  European  literature 
and  practice,  with  evidence  throughout  of  good  personal  judgment,  knowledge,  and  experience.  The  book  also 
abounds  in  exposition  of  American  experience  and  observation  in  all  that  relates  to  the  diseases  of  children.  We 
are  glad  to  add  it  to  our  library.  There  are  few  diseases  of  children  which  it  does  not  treat  of  fully  and  wisely,  in 
the  light  of  the  latest  physiological,  pathological,  and  therapeutical  science." — London  Lancet. 

P.  BLAKISTON,  SON  &  CO.,  Publishers, 

Successors  to  LINDSAY  &  BLAKISTON, 

1012  WALNUT  STREET,  PHILADELPHIA. 


NOW  READY. 

Diseases  of  the  Liver. 

BY  GEORGE  HARLEY,  M.D.,  F.R.S.,  Etc., 

Author  of  "  The  Urine  and  Its  Derangements, "  and  "  Diabetes,  Its  Various  Form*  and  Treatment." 

Oh  Fine  Paper,  from  Good  Type,  with   Colored  Plates  and  Thirty-six    Wood-cuts. 
Bound  in  Heavy  Cloth,  Beveled  Edges,  $5.00;  Leather,  with  Raised  Bands,  $6.00. 

THE  Publishers  call  special  attention  to  this  work,  the  only  thorough  book  now 
before  the  profession.     The  reputation  of  its  distinguished  author  is  a  guar- 
jintee  of  its  merits. 

THE  AUTHORj  IN  HIS  PREFACE,  SA^S,; 

THIS  NEWTREA  TISE,  which  I  have  thought  fit  to  entitle  Diseases  of  the  Liver,  with 
and  without  Jaundice,  with  special  application  to  Diagnosis  and  Treatment, 
embodies  within  it  the  whole  substance  of  my  original  monograph  on  Jaundice  and 
Diseases  of  the  Liver ;  though  greater  than  it,  both  as  regards  its  scope  and 
materials,  and  the  large  amount  of  clinical  and  scientific  data  that  has  nevei 
before  been  collected  together  into  one  volume ;  while  in  a  great  many  instances 
it  gives  a  new  rendering  to  old  clinical  facts,  by  presenting  them  to  the  reader  in 
the  light  of  modern  pathological  science. 

As  I  think  time  is  quite  of  as  much  value  to  the  professional  as  it  is  to  the  mercantile  man, 
I  have  endeavored  to  condense  my  materials  to  the  utmost,  without  running  the 
risk  of  endangering  their  perspicuity.  Added  to  which,  as  this  treatise  has  not 
been  penned  either  for  the  use  of  the  tyro  or  the  dilettante  in  medicine,  but  for 
that  of  my  qualified  brethren,  I  shall  neither  waste  time  by  entering  into  detailed 
accounts  of  the  literature,  nor  give  tedious,  and  probably  at  the  same  time  profit- 
less, discussions  of  the  theories  of  the  mechanism  of  jaundice  in  hepatic  derange- 
ments. Taking  care,  however,  in  order  that  it  may  carry  more  weight  with  it 
in  the  eyes  of  the  reader,  to  illustrate  it  freely  with  cases  reported  by  indepen- 
dent observers,  both  at  home  and  abroad.  While,  in  order,  again,  that  the  reader 
maybe  able  to  see  for  himself,  at  a  glance,  how  many,  of  the  old-fashioned  theories 
of  the  pathology  of  jaundice  have  been  abandoned,  as  well  as  how  many  new  ones 
have  been  espoused,  I  have  put  my  views,  in  accordance  with  the  facts  and 
arguments  expressed  throughout  the  body  of  the  volume,  into  a  concise  and 
diagrammatic  tabular  form. 

[  WOULD  DIRECT  \he  special  attention  of  my  readers  to  the  chapter  devoted  to 
•treatment,  as  well  as  that  at  the  end  of  the  book,  entitled  Hints  on  Diagnosis. 

SYNOPSIS   OF  THE   CONTENTS. 

Introduction,  ^ving  a  general  view  of  the  scope  of  the 
volume,  and  the  application  of  Physiological  Chemistry 
to  the  diagnosis  and  treatment  of  Hepatic  affections. 

Chemistry,  Physics  and  Physiology  of  the  Liver  and 
its  secretions. 

Etiology  of  Jaundice — different  kinds — causes  pro- 
ducing th  .m — treatment. 

Signs  and  Symptoms  of  Liver  Diseases. 

General  remarl<s  on  all  kinds  of  Hepatic  Remedies. 

Special  Hepatic  Medicines;  their  modes  of  action 
«nd  uses. 

llineral  Waters,  Wines  and  Foods;  treatment  of 
Pyrexia,  Cerebral  complications,  etc. 

Congenital  and  Hereditary  Liver  Diseases,  Bilious- 
ness;   Its  Varieties  and  Treatment. 

Jaundice  from  Enervation,  all  its  forms  explained  and 
their  different  Treatments 

Different  forms  of  Inflammation  of  the  Uvcr  and  their 
Treatments. 

Jaundice  caused  by  Di8ea.se  Germs,  Ye\;<»w  Fevers, 
Cont;igious  and  Epidemic  Jaundice,  diflferent  kinds  and 
■Jieir  Treatments. 

Jaundice  of  Pregnancy. 

biffere...  forms  of  Hepatic  Atrophy  and  Ascites. 

This  work  is  now  ready,  and  will  be  sent  by  mail,  postpaid,  upon  receipt  of  price. 
(Cloth,  $5.00.     Leather,  Jt6.oo  - 

P.  BLAKISTON,  SON  &  CO.,  Publishers,  Philadelphia 


Biliary  Concretions,  Inspissated  Bile.  Gall-Stones  of 
every  kind  and  form,  direct  and  indirect  effects  of, 
their  Symptoms  and  Treatment,  very  fully  gone  into. 

Different  kinds  of  Colics,  etc. 

Catarrhal  Jaundice. 

Jaundice  from  Poisons. 

Different  kinds  of  Jaundice  from  Permanent  Obstruc- 
tions. 

Physiological  Chemistry  of  the  Excretions,  Ufine 
and  Stools,  as  a  Guide  to  Diagnosis  and  Treatment. 

AH  kinds  of  Abscess,  Tropical,  Pysemic,  Metastatic, 
etc. 

Different  kinds  of  Cancers  of  the  Liver  and  its  Appen- 
dages. 

Hydatid  and  Cystic  Diseases  of  the  Liver;  Syphilitic 
and  Fibroid  Diseases  of  the  Liver. 

Embolisms,  Fatty,  Amyloid  and  other  Degenerations 
of  the  Liver. 

Traumatic  Diseases  of  the  Liver. 

Diseases  of  the  Gall  Bladder. 

A  concluding  chapter,  entitled  Hints  on  Differentia] 
Diagnosis. 

Index. 


PRESS  NOTICES  AND  RECOMMENDATIONS 

OF 

Dr.  George  Harley's  New  Book  on 

Diseases  of  the  Liver. 


"  The  Medical  Profession,  bot)  n  Englam  and  Amer- 
ica, has  for  some  time  been  on  W.i  qui  7'ive  :'^r  ihis  new 
work  on  the  Liver,  both  because  hepatic  literature  is  mea- 
gre in  the  extreme,  and  because  it  was  well  known  that 
Prof.  Harley  was  specially  qualified  to  write  an  authorita- 
tive work  on  the  subject.  .  .  .  The  author  has  unques- 
tionably written  the  most  valuable  work  on  hepatic  dis- 
eases that  has  yet  appeared.  We  must  confess  that  we 
have  tried,  and  tried  hard,  to  find  some  error  in  the  work, 
to  preclude  the  charge  of  partiality  being  made." — yir- 
ginia  Medical  Monthly. 

"  It  is  one  of  the  /resftesi ,  tuosi  readable,  and  ntost 
instructive  medical  books  that  have  been  laid  upon  our 
table  during  the  present  decade.  ...  In  conclusion,  we 
commend  again  most  heartily  Dr.  Harley's  extremely 
valuable  book." — Philadelphia  Medical  Times, 

"The  work  is  far  in  advance,  in  original  and  practical 
information,  of  any  treati.se  on  the  subject  with  which  we 
are  acquainted,  and  is  worth  many  times  its  cost  to  any 
physician  treating  hep.-vtic  troubles." — Chicago  Medical 
Times. 

"The  urnole  subject-matter  is  treated  in  a  masterly 
maimer,  and  the  work  is  destined  to  find  a  place  among 
the  classics." — Medical  Herald,  Louisville ,  Ky. 

"  It  is  the  outcome  of  a  mind  that  went  to  its  task 
amply  equipped  thertfor.  It  is  the  product  of  long  think- 
ing and  ripe  judgment.  .  .  .  We  must  content  ourselves 
with  this  bare  statement  hoping  that  those  who  read  the 
book  win  derive  as  much  benefit  as  ourselves." — NeH> 
Orleans  Medical  and  Surgical  journal. 

"  The  work  before  us  is  one  of  the  most  thoroughly 
scientific  ever  offered  to  the  medical  profession  upon  the 
diagnosis  and  treatment  of  diseases  of  the  liver.  This 
book  will  prove  especially  valuable  to  the  Southern  prac- 
titioner, who,  on  account  of  climatic  influences,  is  daily 
forced  to  combat  these  ailments.  In  this  section  of 
countrj'  hepatic  disorders  are  not  only  common  as  inde- 
pendent conditions — diseases  per  se — but  they  form  im- 
portant factors  in  the  production  of,  and  are  ordinary 
concomitants  of,  most  of  our  malarial  diseases." — 7%e 
Mississippi  Valley  Medical  Monthly,  Memphis,  Tenn. 

"The  work  of  Dr.  Harley  is  the  most  complete  work 
upon  diseases  of  the  liver  now  before  the  profession.  It 
embodies  not  only  the  results  of  his  own  large  experience 
and  observations,  but  also  exhibits  the  researches  of  oth- 
ers in  the  same  class  of  diseases.  As  a  scientific  treatise 
of  hepatic  affections  and  their  treatment,  it  will  certainly 
hold  a  first  position  among  the  standard  works." — Cin- 
iinnati  Medical  News. 

"  We  regard  it  as  one  of  the  most  valuable  of  the  recent 
additions  to  medical  literature." — Southern  Practitioner, 
Nashville,  Tenn. 


"  His  especial  point,  as  mdicated  in  the  titje,  is  to 
bring  prominently  forward  the  relations  of  physiulog)-  to 
the  forms  of  disease.  Too  exclusive  attention,  he  thinks, 
has  been  paid  to  pathology.  It  has  been  regr.rded  us  a 
science  ajiart.  The  great  truth  has  been  overlooked  that 
the  same  fimdameni.-\l  laws  regulate  the  phenomena  both 
of  health  and  disea.se. 

"  With  this  a-s  his  gtiiding  principle,  he  approaches  the 
complicated  problem  of  '  liver  complaints'  and  '  bilious 
ness'  with  a  much  stronger  hand  than  his  predecessors  in 
that  field.  Afflicted  as  many  districts  of  our  country  are, 
with  many  and  pUz/ling  forms  of  these  maladies,  we  be- 
lieve Dr.  Harley's  volume  will  be  a  welcome  addition  to 
many  a  library." — Philadelphia  Meidcal  and  Surgical 
Reporter. 

"  We  have  read  the  volume  before  us  with  peculiar  in. 
terest,  and  it  will  be  read  especially  by  Southern  doctors, 
who,  although  they  do  not  nave  a  monopoly  of  disexses 
of  the  liver,  by  reason  of  semi-tropical  malarial  climate 
encounter  a  large  proportion  of  such  diseases.  .  .  .  We 
most  heartily  commend  this  book  to  our  readers  as  a  val- 
uable addition  to  the  working  volumes  of  their  libraries  . 
for  without  any  exception  it  is  the  most  entertaining  and 
instructive  volume  we  had  the  pleasure  of  reading  for 
many  years." — North  Carolina  Medical  journal. 

"  The  author  has  succeeded  admirably  in  the  work  he 
has  undertaken,  and  has  placed  before  the  profession  a 
work  that  will  be  of  inestimable  value  to  the  practi- 
tioner."— Nashville  youmal  of  Medicine  and  Surgery. 

"  His  chapter  on  '  Hints  to  Aid  in  the  Diagnosis  of 
Liver  Disease,'  is  one  of  the  best  in  the  book,  and  will 
amply  repay  any  one  for  its  perusal." — Indiana  Medical 
yournal. 

"  With  unusual  gratification  we  have  receiveo  this 
most  excellent  work,  and  present  it  to  the  medical  profes- 
sion with  an  unqualified  endorsement.  We  know  of  no 
work  of  the  kind,  as  this,  based  upon  the  unvar>-ing  rela- 
tion between  physiology  and  pathology,  the  only  avenue 
of  approach  to  the  cause  of  disea.se  and  proper  treat- 
ment."— Missouri  Valley  Medical  yournal. 

"  Those  features  which  are  the  most  noteworthy  from 
their  novelty,  or  as  showing  individuality  in  treatment, 
are  to  be  found  in  the  chapter  on  '  The  General  Treat- 
ment of  Hepatic  Disease,'  and  in  that  on  the  '  Chemistry 
of  the  Excretions.'  In  the  former  the  author  takes  up 
the  most  prominent  articles  in  the  materia  medica  having 
a  reputation  in  this  class  of  diseases,  and  considers  their 
chemistry,  their  mode  of  action,  and  the  conditions  which 
seem  to  indicate  their  employment,  after  adding  brief 
cases  in  illustration." — N'eiv  York  Herald. 

"  We  commend  the  book  to  the  profession  as  eminently 
worthy  of  study,  and  one  that  should  be  in  the  library  of 
every  physician." — Southern  Medical  Record. 


O^    ,;  PRICES: 

Heavy  Cloth,  Beveled  Edges #5  00 

Full  Leather,  Raised  Boards 6  c« 

Will  be  sent,  prepaid,  by  mail  or  express,  upon  receipt  of  either  of  the  above  prices. 

P.  BLAKISTON,  SON  &  CO., 

(SUCCKSSORS  TO    UNDSAT   *   BLAKISTON) 

N"o.    1013    -WA.I..NUT    STREET.    PHILADELPHIA.. 


1 

Date  Due 

1 

1 

PRINTED   IN 

U.S.A.            CAT.   NO.   24    161               SS 

sJCfT^  •<^ 


A     000  502  859 


^ 

QD31 

b65Tc 

1883 

Bloxam,  Chsurles  L 

Chemistry,  inorganic  and 

organic. 

QD31 
b65Tc 
1883 
31oxam,  Charles  L 

Chemistry,  inorganic  and  organic. 

MEDICAL  SCIENCES  LIBRARY 

UNIVERSITY  OF  CALIFORNIA,  IRVINE 

IRVINE.  CALIFORNIA  92664 


